Animal Kingdom Body and Function

THE ANIMAL BODY INTRODUCTION TOSTRUCTURE AND FUNCTION The size of cells is limited by the ratio of surface area plasma membrane to its volume The plasma membrane needs to be large enough relative to the cell's volume to permit passage of materials into and our to the cell The large size of animals is due to the greater number cells they have Multicellularity allows the organisms to be more diverse and the cells to become specialized A tissue is made of a group of closely associated similar cells adapted to carry out specific functions An organ consists of a group of tissues associated into a differentiated structure to perform a specific function or functions in the body Organs are associated together into organ systems Organ systems perform together a specialized and vital function in the body Organs and organ systems work together to maintain appropriate conditions in the body a constant internal environment called homeostasis Homeostatic mechanisms that maintain homeostasis may involve several organ systems that work together TISSUES Animal tissues are classified as epithelial connective muscle and nervous tissue Epithelial tissue epithelium consists of fitted tightly together to form a continuous layer or sheet It covers body surfaces and lines cavities It functions in protection absorption secretion and sensation The outer surface of this tissue is typically exposed because it lines cavities The cell layer is attached to the underlying tissue by a noncellular membrane the basement membrane made polysaccharides and fibers Epithelial cells may be organized or differentiated into epidermis skin membranes glands and sensory receptors Epithelial cells are cuboidal columnar or squamous Epithelial tissue may be simple stratified or pseudostratified The lining of the blood vessels is of endodermal origin and it is called endothelium Structurally endothelial cells are typical epithelial Glands are made of epithelial cells specialized to secrete a substance e g sweat hormones saliva milk enzymes Glands may be endocrine or exocrine Exocrine glands secrete their products through a duct to an organ surface e g sweat glands Endocrine glands secrete their products hormones into the blood stream or interstitial fluid e g thyroid Goblet cells secrete mucus and are found in epithelial tissue lining body cavities and passageways Mucus lubricates the surface and facilitates movement of materials Epithelial membranes consist of a layer of epithelial cells and a layer of underlying connective tissue Mucosas or mucous membranes line body cavities that open to the outside e g digestive and respiratory track The epithelial layer secretes mucus Serous membranes line body cavities that do not open to the outside of the body It consists of a simple squamous epithelium over a thin loose underlying connective tissue The epithelial layer secretes a fluid that fills the cavity E g pleural and pericardial membranes Connective tissue joins other tissues of the body supports the body and its organs and protects underlying organs It consists of relatively few cells separated by an intercellular substance Typically the intercellular substance consists of fibers made of proteins scattered through a matrix a thin gel made of polysaccharides Different kinds of connective tissue will have different kinds of fibers and matrices The nature and function of each kind of connective tissue is determined in part by the structure and properties of the intercellular substance Intercellular substance contains Collagen fibers made of the protein collagen the most abundant protein in the body Collagen fibers are wavy flexible and resistant to stretching Elastic fibers are made of the protein elastin and branch and fuse to form a network They return to their original form after the stretching force is removed Reticular fibers are very small-branched fibers that form delicate networks They are made of collagen and glycoprotein Specialized cells Each major class of connective tissue has a fundamental cell type that exists in immature and mature forms The undifferentiated cells are indicated by the suffix blast forming These undifferentiated blast' cells are actively dividing and secrete the ground substance and the fibers characteristic of their particular matrix Fibroblasts are specialized cells that secrete proteins to make fibers and carbohydrates for the matrix Macrophages are scavenger cells that wander through the tissue engulfing and digesting bacteria molecules and dead cells Mast cells detect foreign substances and initiate inflammatory responses they secrete histamines during allergic reactions Plasma cells secrete antibodies Adipose cells or adipocytes secrete fats Chondroblast cells secrete cartilage Osteoblast cells secrete bone matrix Hemocytoblast or hematopoietic stem cells secrete blood components TYPES OF CONNECTIVE TISSUES Loose areolar connective tissue is found everywhere in the body It supports organs and is a reservoir of salts and fluid Together with adipose tissue it forms the subcutaneous layer that attaches the skin to muscles and other structures beneath The matrix is gel-like and contains all three fiber types mast cells fibroblasts and macrophages Dense connective tissue is found in the tendons ligaments and dermis of the skin It supports and transmits mechanical forces Dense connective tissue may be regular or irregular depending on the arrangement of the collagen fibers The matrix is made primarily of collagen fibers and a few elastin fibers Fibroblasts are the major cellular component Elastic connective tissue is found in structures that must expand like lungs and large arteries It consists of bundles of parallel elastic fibers Fibroblasts present Reticular connective tissue makes the framework of organs like the liver lymph nodes bone marrow and spleen Fibers form a soft internal skeleton stroma that provides support for other cell types Adipose tissue is found in the subcutaneous layer and in patches around some internal organs It stores food insulates the body and provides additional support to organs like kidneys and mammary glands Adipocytes store fat Cartilage makes the skeleton of chondrichthyes it is found at the end of bones of other vertebrates and provides flexible support to organs like the trachea ears and nose It resists compression Chondrocytes mature cells found in lacunae This tissue lacks nerves lymph and blood vessels Chondrocytes are nourished by diffusion through the matrix Chondrocytes remain alive and lie in lacunae Bone makes the skeleton most vertebrates It supports and protects internal organs acts as a reservoir of calcium and place for muscle attachment Osteocytes mature cells are found in lacunae In compact bone the lacunae are arranged in concentric circles around the Haversian canal through which capillaries and nerves pass Compact bone consists of units called osteons This tissue is rich in blood vessels Blood is found within the heart and blood vessels In its liquid matrix transports cells RBC WBC platelets wastes nutrients and other materials Muscle tissue is specialized to contract Each cell is an elongated fiber containing many myofibrils Myofibrils are made of the protein actin and myosin Skeletal muscles are striated and under voluntary control Striations or bands reflect the alignment of the filaments responsible for contraction of the muscle cells The cells are multinucleated Smooth muscles contract involuntarily lack striations and cells are uninucleate Cardiac muscles are striated and act involuntarily Cardiac muscle cells branch and the fibers are joined end to end at the intercalated disc They are found only in the heart Nervous tissue is composed of neurons which are cells specialized for conducting nerve impulses and glial cells which are supporting cells A typical neuron consists of a cell body dendrites and an axon Neurons communicate at junctions called synapses A nerve consists of many neurons bound together by connective tissue The nervous tissue also contains various types of supporting cells that insulate and protect the delicate neurons ORGAN SYSTEMS There are ten organ systems in complex animals The systems work together to maintain homeostasis Homeostasis is the maintenance of a constant internal environment and physiological conditions in a changing external environment It is maintained mostly by negative feedback mechanisms In the negative feedback mechanism the output of a system shuts off the stimulus and reduces the its intensity It works like a thermostat Regulation of blood sugar in the blood There are few positive feedback mechanisms The response to the stimulus enhances the original stimulus and the output is accelerated Blood clotting contraction of the uterus during birth and contraction of the urinary bladder during urination are examples of positive feedback mechanisms Many animals are capable of thermoregulation the ability to maintain a constant temperature independent of environmental temperature The body temperature depends to a large extent on environmental temperature in ectotherms Ectotherms use structural and behavioral strategies to control their body temperature Endotherms derive heat from metabolic processes Chapter SKIN SKELETON AND MUSCLE SKIN In invertebrates the external epithelium protects the internal organs The integumentary system consists of the skin and the structures derived from it FUNCTIONS OF THE VERTEBRATE SKIN Protection against infection dehydration mechanical and chemical damage Temperature regulation Detects touch temperature changes pressure and pain Excretes water salts and wastes Synthesize vitamin D Stores some nutrients Gas exchange in some species It may be specialized for Secretion of cuticle scales lubricants adhesives marking trails poisons communication chemicals and net construction Gas exchange Receptors of stimuli e g light touch chemicals In vertebrates the skin protects internal organs prevents dehydration secretes substances receives stimuli and regulates body temperature The skin of vertebrates varies birds have feathers reptiles have scales amphibians have a naked moist skin and placoid and horny scales in fishes Human skin includes nails hair sweat glands oil glands mammary glands and sensory receptors Oil glands in humans empty via short ducts into hair follicles Oil glands secrete sebum a complex mixture of hydrocarbons fats and waxes that keep hair and skin pliable and prevent cracking Sebum prevents the growth of harmful bacteria Structure of the human skin The human skin consists of several layers or strata Epidermis the outer layer Stratum basale cell division production of keratin melanin Stratum corneum cells eventually die and wear off Dermis the inner layer Made of dense fibrous connective tissue Contains hair follicles capillaries and sensory receptors Subcutaneous tissue is made of adipose tissue a good insulator SKELETON Main functions of the human skeleton are Transmit mechanical forces created by muscles levers Support internal organs and tissues Protect internal organs Storage of calcium salts Blood cell production hematopoiesis Coelomates have a hydrostatic skeleton used to transmit forces created by muscles Exoskeleton of invertebrates is a non-living deposit on top of the epidermis Arthropod exoskeleton is made of chitin jointed need to molt Chitin is nitrogen containing polysaccharide Mollusks produce a calcium containing shell It varies in thickness and flexibility throughout the body Need to molt in order to grow Endoskeleton of echinoderms and chordates is composed of living tissue and capable of growth Echinoderm endoskeleton is made calcium plates and spines GENERAL STRUCTURE OF THE SKELETON Vertebrate endoskeleton consists of two portions Axial skeleton skull vertebrae ribs and sternum Appendicular skeleton bones of arms legs pectoral girdle and pelvic girdle Skull consists of cranial bones and facial bones Vertebral column is made of vertebrae and two fused bones the sacrum and coccyx Cervical region vertebrae Atlas is the first cervical vertebra and supports the skull Axis is the second cervical vertebra and allows the head to rotate Thoracic region vertebrae Lumbar region vertebrae Sacral region fused vertebrae Coccygeal region fused rudimentary vertebrae Vertebrae differ in size and shape Centrum bears the weight of the body Neural arch surrounds and protects the spinal cord Processes project out to provide articulation and attachment The mammalian rib cage consists of the sternum and pairs of ribs Five pairs are attached directly to the sternum Three pairs are attached indirectly by means of cartilage Two pairs have no attachment the floating ribs Pectoral girdle consists of the scapulas shoulder blades and clavicles collarbones Pelvic girdle is made of two large bones made in turn by three fused bones Arms and legs of humans are made of bones and end in five digits Pigs have four digits rhinoceros have three two in camel and one in horses Apes and humans have an opposable thumb useful in grasping and manipulating objects Apes also have an opposable big toe STRUCTURE OF BONES Typical long bones consist of compact and spongy bone Compact bone is very dense and hard It is found primarily near the surfaces of a bone Spongy bone consists of a network of thin strands of bone The spaces between the strands are filled with bone marrow The periosteum is the double-layered membrane that surrounds the bones and produces fresh layers that increase the diameter of the bone The inner layer against the bone is made mostly of osteoblasts and osteoclasts The outer layer is made of connective tissue The periosteum is richly supplied with nerves blood vessels and lymphatic vessels Parts of a long bone Expanded epiphysis at each end Diaphysis or shaft Metaphysis made of cartilage in children The central cavity is filled with the bone marrow Red marrow produces red blood cells Yellow marrow produces fatty connective tissue Osteons or Haversian systems form the compact bone Each osteon is an elongated cylinder oriented parallel to the long axis of the bone Osteoblasts bone forming and osteoclasts bone reabsorbing Haversian canals through which nerves and blood vessels pass Lacunae are the spaces that contain osteocytes the trapped osteoblasts in the bone matrix Bones are remodeled through life Stress and exercise cause thickening of the bone Osteoblasts and osteoclasts work together In humans bone tissue is replaced as many as ten times in a lifetime Long bones develop from cartilage endochondral development Flat bones develop from noncartilage connective tissue intramembranous development Osteoblasts secrete collagen Calcium phosphate hydroxyapatite is the main component of bone matrix It is found in solution in the interstitial fluid Calcium phosphate crystallizes around the fibers and forms bone matrix Osteoblasts become isolated in the lacunae and are called osteocytes Osteoclasts digest bone to prevent excessive thickening Joints are junctions between bones Their outer surfaces are covered with articular cartilages Ligaments are bands of fibrous connective tissue that connect bones Synovial fluid acts as a lubricant MUSCLE Prefixes myo or mys muscle the prefix sarco flesh A muscle is an organ made of contractile cells that allow movement FUNCTIONS OF MUSCLES Produce movement of body parts circulation of blood passing of food through the digestive system and manipulation of objects Maintain posture Stabilize joints of the skeleton that do not have complementary articular surfaces Generate heat There are three types of muscles striated smooth and cardiac MUSCLE STRUCTURE In vertebrates muscles are organs Muscle cells are called fibers Muscle fibers are huge cells ranging between and m - m up to x that of an average body cell their length could reach cm inches Muscle fibers are multinucleate Muscle fibers originate from the fusion of hundreds of embryonic cells Actin is a contractile protein found in all eukaryotic cells In most cells myosin is associated with actin Fibers are grouped into bundles called fascicles Fascicles are wrapped by connective tissue making the muscle Plasma membrane or sarcolemma has many inward extensions called T tubules transverse tubules Cytoplasm or sarcoplasm ER of sarcoplasmic reticulum Myofibrils run the length of the muscle fiber Myofibrils are made of two kinds of myofilaments Thick myofilaments made of myosin Thin myofilaments made of actin The proteins tropomyosin and troponin complex are also present Myofilaments are organized into repeating and contractile units called sarcomeres Sarcomeres are joined end to end at the Z line The Z line is made of a protein that anchors the thin filaments and connects each myofibril to the next Hundreds of sarcomeres connected end-to-end make up the myofibril Contraction occurs when actin and myosin filaments slide past each other MUSCLE CONTRACTION During muscle contraction the thin actin filaments are pulled between the myosin filaments toward the center of the sarcomere Sequence of events Motor neuron releases acetylcholine into the cleft between the neuron and muscle fiber Acetylcholine causes the depolarization of the sarcolemma and the transmission of an action potential The impulse spreads through the T tubules and stimulates Ca ion release from the sarcoplasmic reticulum Ca ions initiate a process that uncovers the active sites of the actin filaments Ca bind to troponin causing a change in shape Troponin pushes tropomyosin away exposing the active sites on actin filaments Myosin molecules is made of a folded into two globular structures called heads and a long tail ATP is bound to myosin when the fiber is at rest Myosin heads have the ability to breakdown ATP in the presence of Ca Cross bridges form linking the myosin and actin filaments ADP and Pi are released Cross bridges flex utilizing the energy released by ATP and the filaments are pulled past one another The muscle shortens The actin-myosin complex binds to ATP again and myosin separates from actin This series of events takes milliseconds ENERGY SOURCE ATP provides energy for the first few seconds of strenuous activity Creatine phosphate is an energy storing compound found in the sarcoplasm The energy stored in the creatine phosphate is passed on to ATP as needed Glycogen a glucose polymer releases glucose and restores the supply of creatine phosphate and ATP as they become depleted MUSCLE ACTION Muscle tone is the state of partial contraction characteristic of muscles Skeletal muscles produce movements by pulling on tendon cords of connective tissue that attach muscles to bones Smooth muscles are not attached to bone They form tubes and squeeze the contents of the tube e g blood and food Muscles can only pull they cannot push Muscles act antagonistically to one another Agonist the contracting muscle Antagonist muscle causes the opposite movement Not all muscular activity is the same White fibers are specialized for quick response and red fibers for slower longer response White fibers obtain most of its energy from glycolysis White fibers use glycogen quickly and fatigue rapidly Red fibers are rich in myoglobin a red pigment similar to hemoglobin There are two types of red fibers fast-twitching fibers specialized for quick response and slow-twitching fibers specialized for slow response Myoglobin is a protein that stores oxygen within the muscle fiber it is similar to hemoglobin Chapter NEURAL CONTROL NEURONS The ability of an organism to survive and maintain homeostasis depends largely on how it responds to internal and external stimuli A stimulus is an agent or a change within the body that can be detected by an organism Nerve cells are called neurons These cells are specialized for transmitting electrical and chemical signals through a network The nervous system consists of this network of neurons and supporting cells Neurotransmitters are chemical messengers used by neurons to signal other neurons and that allows the nerve impulse to be transmitted across a synapse or connection between neurons and or receptors FUNCTION OF THE NERVOUS SYSTEM The nervous system has four overlapping functions related to stimuli from within and without the body It is the master controlling and communicating system of the body It is responsible for behavior thought actions emotions and maintaining homeostasis together with the endocrine system Reactions to stimulus depends on four processes Reception afferent or sensory neurons and sense organs detect the stimulus Transmission messages are transmitted from neuron to neuron to organs and to the Central Nervous System CNS Integration involves sorting and interpreting information and determining proper response Response efferent neurons bring the proper message to muscles and glands Neurons that transmit messages to the CNS are called afferent or sensory neurons Neural messages are transmitted from the CNS by efferent neurons or motor neurons to effectors muscles or glands The action by effectors is the response to the stimulus CELL TYPES A Glial cells are supporting cells There are several types Envelop the neuron to form and insulating sheath around them Phagocytes that remove microorganisms and debris Lines the cavities of the brain and spinal cord Anchor neurons to blood vessels Glial cells are sometimes called collectively neuroglia Vertebrates have six types of glial cells Four types are found in the Central Nervous System CNS Microglia cells are found near blood vessels in the nervous system They remove cellular debris produced by injury or infection Monitor the overall health of neurons Astrocytes are star-shaped cells that anchor neurons to capillaries which are the nutrient supply line Some are phagocytic Some regulate the concentration of K in the extracellular fluid of the nervous tissue Others recapture or regulate the concentration of released neurotransmitters Oligodendrocytes envelop neurons in the CNS with myelin and insulate them Ependymal cells are either squamous or columnar and many are ciliated Line the central cavity of the brain and spinal cord The beating of the cilia help circulate the cerebrospinal fluid found in these cavities that helps cushion the brain and spinal cord These two types are found outside the CNS in the peripheral nervous system PNS Schwann cells are found outside the CNS and form an outer cellular sheath around the axon called neurilemma and an inner myelin sheath The plasma membrane of the Schwann cell is rich in myelin a white fatty substance that acts as an insulator Gaps in the myelin sheath are called nodes of Ranvier Satellite cells surround neurons within ganglia outside the CNS and have protective function Help to control the chemical environment of the neurons to which they are associated Multiple sclerosis occurs when the myelin sheath around the axons deteriorates and is replaced by scar tissue The damage interferes with the conduction of the nerve impulse The cause of MS is a mystery but there is some evidence that indicates that it is an autoimmune disease B Nerve cells are called neurons A typical neuron has cell body dendrites and an axon Dendrites are short highly branched cytoplasmic extensions specialized to receive stimuli and send nerve impulses to the cell body In many brain areas the finer dendrites have thorny projections called dendrite spines The axon is a long extension sometime more than meter long and conducts impulses away from the cell body The axon ends in many terminal branches called axon terminals with a synaptic terminal or knob at the very end that releases neurotransmitters Axons may branch forming axon collaterals Axons outside the CNS and more than m in diameter are myelinated The junction between a synaptic terminal and another neuron is called a synapse A nerve consists of hundreds or thousands of axons wrapped together in connective tissue Within the CNS bundles of axons are called tracts or pathways Outside the CNS cells bodies form masses called ganglia Inside the CNS groups of cell bodies are referred to as nuclei rather than ganglia THE RESTING POTENTIAL Most animal cells have a difference in electrical charge across the plasma membrane more negative on the inside and more positive on the outside of the cell in the fluid The plasma membrane is said to be polarized when one side or pole has a different charge from the other side When this occurs a potential energy difference exists across the membrane If the charges are allowed to come together they have the potential to do work Neurons use electrical signals to transmit information A resting neuron is the one not transmitting an impulse For an impulse to be fired the plasma membrane of the neuron must maintain a resting potential It must be polarized The resting potential is the difference in electrical charge across the plasma membrane The inner surface of the membrane is negative The interstitial fluid surrounding the neuron is positive An electrical potential difference exists across the membrane It is called the resting or membrane potential The resting potential of a neuron is mV millivolts By convention it is expressed as - mV because the inner side is negatively charged relative to the interstitial fluid The resting potential develops by transporting Na out of the neuron and K into the neuron using sodium-potassium pumps The concentration of K is about three times greater inside the cell than outside The concentration of Na is about ten times greater outside the cell than inside the cell Pumps work against concentration gradient and require ATP For every three Na pumped out of the cell two K are pumped in More positive ions are pumped out than in Proteins in the plasma membrane form specific passive ion channels Ions also flow through these channels down the concentration gradient passive transport Neurons have three types of ion channels Passive ion channels which are generally open E g Na K Cl- and Ca Voltage activated ion channels are kept closed and respond only to voltage changes Chemically activated ion channels found on the dendrites and cell body K channels are the most common and they make the membrane more permeable to potassium than to sodium K leak out more rapidly than Na can leak into the cell The membrane is about times more permeable to K than to Na Na pumped out of the neuron cannot easily pass back into the cell but the potassium ions pumped into the neuron can diffuse out The flow of K ions in and out of the cell eventually reaches a flow equilibrium called equilibrium potential at - mV resting potential Some Cl- ions also diffuse into the cell and contribute to the inner negative charge Negatively charged proteins and organic phosphates contribute to the negative charge inside the membrane An electrical imbalance is created mostly due to Negative protein anions inside the cell Outward diffusion of K Inward diffusion of Cl- THE NERVE IMPULSE The nerve impulse is an action potential Electrical chemical or mechanical stimulus may alter the membrane's permeability to Na The axon contains specific voltage-activated ion channels that open when they detect a change in the resting potential When the change reaches threshold levels the protein changes shape the channels open and Na flows into the cell The membrane of a neuron can depolarize by about mV without initiating an impulse The threshold to open the voltage-activated sodium-ion channels is - mV The inside of the cells becomes positive These causes a momentary reversal of polarity as the membrane depolarizes and overshoots to mV creating a spike After a certain time the sodium-ion channels close The closing depends on time rather than on voltage K channels also open but more slowly and remain open until the resting potential has been restored Once depolarization occurred in one portion of the membrane the adjacent areas also become depolarize and the ion gates open This is done by a positive feedback mechanism This process is repeated creating a wave of depolarization until the depolarization reaches the end of the axon Repolarization occurs in less than one millisecond later when the channels close and the membrane becomes impermeable to Na Leakage of K out of the cell also occurs and restores the interior of the membrane to its negative state Sodium-potassium pumps begin to function again When the membrane is depolarized it cannot transmit another impulse no matter how great stimulus is applied This is called the absolute refractory period When the resting potential is being restored the membrane can send impulses only when the stimulus is greater than normal This is the relative refractory period Continuous conduction occurs in unmyelinated axons In unmyelinated neurons the speed of transmission is proportional to the diameter of the axon Axons with larger diameter transmit more rapidly Squids and other invertebrates have large unmyelinated axons In myelinated axons depolarization action potential jumps from one node of Ranvier to the next The voltage-activated ion channels are concentrated at the nodes where the membrane is in contact with the interstitial fluid This mode of conduction is called saltatory conduction It is fifty times faster than continuous conduction There is no variation in the strength of a single impulse The all-or-none law Differences in the level of intensity of a sensation e g severe pain vs mild pain depend on the number of neurons stimulated and their frequency of discharge The threshold level for different stimuli depends on the neuron type Some neurons have lower threshold for certain type of stimulus Substances that increase the permeability of a neuron to sodium ions cause the neuron to become more excitable than normal Calcium balance is essential to normal neural function Calcium ions bind to sodium channel proteins and increase the threshold voltage needed to open the channels When there are many calcium ions the neuron is less excitable and more difficult to fire If calcium concentration is low the sodium channels fail to close and the threshold lowers making the neuron closer to firing This results in muscle spasms or tetany Many narcotics and anesthetics block conduction of nerve impulses by affecting the sodium channels SYNAPTIC TRANSMISSION A synapse is the junction between two neurons or between a neuron and an effector Neuromuscular junction or motor end plate is the synapse between a muscle and a neuron Presynaptic neuron and postsynaptic neuron Signals across the synapse can electrical or chemical Electrical synapses occur when the neurons are very close together synaptic cleft less than nm It allows the passage of ions from one neuron to the next and the impulse is directly transmitted Between axons and cell body cell body to cell body dendrites and axons dendrites and dendrites For quick communication and coordination between many neurons Chemical synapses are separated by the synaptic cleft about nm wide Most synapses are chemical Chemical messengers or neurotransmitters conduct the message When depolarization reaches the end of the axon it cannot jump across the cleft The electrical signal is converted to a chemical one Neurotransmitters are the chemicals that conduct the signal across the synapse and bind to chemically activated ion channels in the membrane of the postsynaptic neuron TYPES OF NEUROTRANSMITTERS More than different chemicals are known or suspected to function as neurotransmitters Each type of neuron is thought to release one type of neurotransmitter A postsynaptic neuron may have more than one type of receptors for neurotransmitters Acetylcholine is important in muscle contraction and in the autonomic nervous system It is released from motor neurons called cholinergic neurons Norepinephrine serotonin and dopamine are biogenic amine or catecholamine It affects mood and it has been linked to depression attention deficit disorder and schizophrenia Adrenergic neurons release it Other biogenic amines serotonin and dopamine GABA is an amino acid that inhibits neurons in the brain and spinal cord Some neurotransmitters are small molecules that act rapidly Others are neuropeptides larger molecules that modulate the effects of the small-molecule neurotransmitters Neurotransmitters are stored in the synaptic terminals within membrane-bound sacs called synaptic vesicles Neurotransmitters are produced in the terminal knobs of the presynaptic axon Action potential upon reaching the synaptic terminal activates voltage-sensitive Ca channels Ca from the surrounding interstitial fluid pass into the synaptic terminal Ca cause the synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitters into the synaptic cleft by exocytosis Diffuse across the synaptic cleft and combines with specific receptors on the postsynaptic neuron Receptors are proteins that control chemically activated ion channels They are called ligand-gated ion channels The neurotransmitter the ligand binds to the receptor and the ion channel opens Opening of the channels may cause a depolarization of the postsynaptic membrane Neurotransmitter must be removed enzymatically for repolarization to occur Some neurotransmitters like serotonin operate through the production of a second messenger Through a series of reactions an enzyme is activated that causes the closure of K channels Neurotransmitters may bring the neuron closer to firing producing an excitatory postsynaptic potential or EPSP Some neurotransmitters make the membrane more negative hyperpolarize thus requiring a stronger stimulus to fire This potential change is called inhibitory postsynaptic potential or IPSP EPSP may be added together in a process called summation to produce an action potential Temporal summation happens when the new EPSP occurs before the previous decayed Spatial summation occurs when several neurons release their neurotransmitters at once bringing the postsynaptic neuron close to firing NEURAL INTEGRATION It is the process of adding and subtracting signals and determining whether or not to fire an impulse Each neuron may synapse with hundreds of other neurons Presynaptic knobs may cover as much as of the postsynaptic neurons' dendrites and cell body Neural circuits may be organized in several ways Convergence a single neuron receives signals from several presynaptic neurons Divergence a single presynaptic neuron stimulates many postsynaptic neurons The mechanism of facilitation slightly depolarizes a neuron so another presynaptic neuron may stimulate it to the threshold level In a reverberating circuit a neuron may fire many times The postsynaptic neuron synapses with an interneuron which in turn synapses with the presynaptic neuron Chapter NERVOUS SYSTEMS INVERTEBRATE NERVOUS SYSTEMS Nerve nets and radial nervous systems are characteristic of radially symmetrical animals Nerve nets consist of scattered neurons impulses may flow in both directions of the synapse and the impulse weakens as it spreads from the point of stimulation There is no CNS Found in cnidarians Some cnidarians have two nerve nets one for slow for tentacle movement and another for faster to coordinate swimming Echinoderms have a nerve ring and nerves that extend into various parts of the body Bilateral nervous systems are found in bilateral animals Neurons aggregate to form ganglia nerves nerve cords and a brain Trends in the evolution of the nervous system An increase number of neurons Concentration of neurons to form ganglia and brain and thick cords of tissue that become nerves and nerve cords A specialization of function e g afferent and efferent neurons transmit different type of impulse parts of the brain perform different functions Increase number of association neurons and complex synaptic contacts that allow better integration of incoming messages provide a greater range and precision of responses Cephalization with a concentration of sense organs toward the anterior end Planaria has a ladder-type of nervous system The two anterior ganglia control to some extent the rest of the system Annelids and arthropods have one or two ventral nerve cords that extend the length of the body An anterior pair of ganglia dorsally located is needed to respond adequately to stimuli and to coordinate input Mollusks have three pairs of ganglia Each ganglion controls a different region of the body Pedal ganglia control the movement of the foot Visceral ganglia control the opening and closing of the shell Cerebral ganglion that controls complex reflexes and motor functions Pedal and visceral ganglia are connected to the cerebral ganglia by nerve cords In cephalopods the three ganglia are clustered in a ring surrounding the esophagus in a sort of circular brain DIVISIONS OF THE VERTEBRATE NERVOUS SYSTEM brain Central spinal cord Vertebrate Nervous receptors System Somatic afferent nerves receptors to CNS efferent nerves CNS to skeletal muscles Peripheral Receptors Autonomic afferent n receptors to CNS efferent n CNS to organs sympathetic parasympathetic THE VERTEBRATE BRAIN The embryonic neural tube differentiates into three regions Presencephalon or forebrain Mesencephalon or midbrain Rhombencephalon or hindbrain These primary divisions in turn differentiate to give rise to specific structures of the adult brain The hindbrain develops into the medulla pons and cerebellum The midbrain is prominent in amphibians and fishes It receives sensory information integrates it and distributes to appropriate motor nerves It is the center of vision In reptiles birds and mammals it consists of The superior colliculi centers for visual reflexes e g pupil constriction The inferior colliculi center of certain auditory reflexes The forebrain gives rise to the thalamus hypothalamus and cerebrum Telencephalum develops into the cerebrum Diencephalum gives rise to the thalamus and hypothalamus In vertebrates the thalamus receives sensory messages except olfactory messages and distributes them to the sensory areas of the brain The hypothalamus forms the floor of the third ventricle and receives olfactory messages and regulates the function of internal organs maintains homeostasis temperature respiration regulation of pituitary gland appetite etc The cerebrum of fish and amphibians is almost entirely concerned with the integration of olfactory information In other vertebrates it integrates olfactory and other information In most vertebrates the cerebrum is divided into right and left hemispheres White matter is made of myelinated axons Gray matter cerebral cortex is made of cell bodies and dendrites Folds of the cerebrum are called convolutions or gyri gyrus Furrows are called sulci sulcus is shallow or fissures if deep In birds the corpus striatum controls behavior and another part controls learning In reptiles and mammals the neopallium in the cortex integrates sensory and motor functions and is responsible for higher functions like learning Neopallium makes the bulk of the mammalian cerebrum of the cortex in humans is the neopallium Made of six distinct layers HUMAN CENTRAL NERVOUS SYSTEM The CNS is protected by bone skull and vertebrae and three membranes the meninges dura mater arachnoid and pia mater The subarachnoid space is found between the arachnoid and the pia mater and it contains the cerebrospinal fluid The choroid plexus is a network of capillaries that secretes the cerebrospinal fluid CSF The plexus and the arachnoid act as a barrier between the blood and the CSF Exchanges nutrients and waste between the blood and the CNS Prevent harmful substances in the blood to enter the CNS Shock absorbing fluid The CSF travels through the sinuses and the cerebral ventricles The spinal cord Function so the spinal cord Transmits impulses to the from the brain Controls many reflex activities The spinal cord extends from the base of the brain to the second lumbar vertebrae The spinal cord consists of gray matter and white matter It has a small central canal The white matter surrounds the gray matter The gray matter has the shape of an H The gray matter consists of cell bodies dendrites and unmyelinated axons The white matter is made of myelinated axons arranged into tracts or pathways A reflex action or withdrawal reflex is a fixed response to a simple stimulus A message is also send to the cerebrum and pain touch etc is felt Many activities such as breathing are controlled by reflex action The cerebrum The cerebrum is the largest and most prominent part of the human brain Cerebral cortex is made of gray matter arranged into sulci Sensory areas receive information from senses and receptors Motor areas control the movement of voluntary muscles Association areas are the site of intellect learning memory language and emotion interprets sensory information The cortex has been mapped into areas responsible for certain functions Occipital lobe visual centers Temporal lobes auditory centers Parietal lobes receive information about heat touch and pressure Other areas are involved in complex integrative activities The size of the motor area in the brain for any given part of the body is proportional to the complexity of movement involved and not to the amount of muscle White matter lies beneath the cerebral cortex Corpus callosum connects right and left hemispheres Axons are arranged into bundles tracts The basal ganglia a cluster of nuclei within the white matter are important centers of motor function The basal ganglia send information to the substantia nigra and receive input from it Other neurons found in the substantia nigra relay information to the motor cortex BRAIN ACTIVITY EEG or electroencephalogram is a recording of the brain's electrical activity Activity follows a wake-sleep pattern Alpha waves are produced during relaxed periods when the eyes are closed Beta waves are produced during heightened activity e g reading a book Delta waves are produced when the person is asleep during non-REM sleep Theta waves are produced in children and in frustrated adults Reticular activating system RAS is a complex pathway within the brain stem and thalamus Maintains consciousness and determines the degree of alertness Receives messages from the spinal cord and communicates with the cerebral cortex Sleep is a state of unconsciousness with decrease brain activity During REM rapid eye movement state the eyes move rapidly with the eyelids closed delta waves become erratic and dreams occur REM caused by a release of norepinephrine in the brain stem During REM blood flow in the frontal lobes was reduced and blood flow increased in areas that produce visual scenes and emotions During Non-REM sleep metabolic rate and breathing slows down blood pressure decreases and delta waves are produced Neurons in the RAS fatigue after many hours of activity and the sleep centers secrete serotonin a neurotransmitter involved in sleep Neurophysiologists do not know why sleep is necessary Both non-REM and REM are necessary The limbic system controls emotions sexual behavior motivation pain pleasure rhythms and autonomic responses It consists of the hypothalamus hippocampus and amygdala The substantia nigra is also involved in motivation and release dopamine when stimulated Dopamine may be involved in concentration and attention Its role is controversial at present Other areas of the brain are involved in emotions like the frontal area of the cerebral cortex Learning is a change in behavior that results from experience Memory is the storage of knowledge and the ability to retrieve it Information is transferred from sensory memory to short-term memory to long-term memory Short term memory allows recalling information for a few minutes and it may be based on reverberating circuits Information may be transferred to long term memory Long-term memory may require gene activation and formation of new synaptic connections Memories are stored throughout the sensory and association areas of the cerebrum Wernicke's area in the temporal lobe is an association area involved in language function Short term memory involves brief changes in neurotransmitter receptors and second messengers are linked to ion channels in postsynaptic neurons Specific protein kinases are activated by the secondary messenger cyclic AMP These kinases phosphorilate and affect specific ion channels In long term memory the changes in the postsynaptic neuron are slower but longer lasting Cyclic AMP activate protein kinases which enter the nucleus and leading to gene activation The kinases phosphorylate a regulatory protein known as CREB CREB turns on the transcription of certain genes Some types of learning are related to permanent changes in presynaptic terminals and postsynaptic neurons Neurotransmitter release may be enhanced or inhibited Calcium ions accumulate inside the presynaptic terminal Synaptic facilitation occurs after a single action potential Potentiation is a longer form of enhancement that lasts for several minutes Habituation is a decrease response due to repeated exposure to a harmless stimulus Calcium channels are inactivated in presynaptic neurons It results in a decrease in neurotransmitter release Sensitization results in an increase response after experiencing an unpleasant stimulus The presynaptic terminals release more neurotransmitters Sensitization usually lasts for a few minutes Classical conditioning is an association between an unconditioned stimulus and a conditioned stimulus The conditioned stimulus provokes a conditioned response This reaction may involved a second messenger protein kinases gene activation and protein synthesis Neurons have the ability to change in response to environmental stimuli this is known as neural plasticity Early environmental stimulation can enhance the development of motor areas PERIPHERAL NERVOUS SYSTEM PNS It consists of sensory receptors and nerves The somatic system allows the body to adjust to external environment cranial nerves emerge from the brain Involved with the head region sensory and motor pairs of spinal nerves Originate from the spinal cord Each has a dorsal and a ventral root Dorsal root forms a ganglion of sensory neurons before entering the spinal cord Ventral root contains motor neurons whose body is in the gray matter of the spinal cord The autonomic nervous system regulates the internal activities of the body The efferent portion of the autonomic nervous system is divided into Sympathetic NS permits the body to respond to stressful situations Preganglionic neurons paravertebral sympathetic ganglion chain and postganglionic neurons transmit the message to the effector Parasympathetic NS restores the body to resting state and actively maintains normal body functions Parasympathetic preganglionic neurons synapse with postganglionic neurons in ganglia near or within the walls of the effector organs The autonomic nervous system uses a relay of two neurons between the CNS and the effector Preganglionic neuron has the cell body and dendrite within the CNS Its axon is part of a peripheral nerve and synapses with the postganglionic neuron Postganglionic neuron is entirely outside the CNS and its axon ends near the effector The paravertebral sympathetic ganglion chain is found on each side of the spinal cord from the neck to the abdomen Some sympathetic preganglionic neurons end in ganglia of the abdomen close to the aorta and its major branches known collateral ganglia Celiac ganglion superior mesenteric ganglion and inferior mesenteric ganglion Parasympathetic preganglionic neurons synapse with the postganglionic neurons in terminal ganglia near or within the wall of the organs they innervate DRUGS Many drugs alter mood by increasing or decreasing the concentrations of specific neurotransmitters within the brain Habitual use of almost any mood-altering drug can cause psychological dependence Physical addiction occurs when the drug has components similar to substances manufactured by cells Drug addition involves a mechanism of neurons that release dopamine These neurons are located in the midbrain and through dopamine affect behavioral control centers in the limbic system Norepinephrine serotonin and dopamine influence mood Alcohol metabolism occurs at a fixed rate in the liver and it is not affected by coffee Inhibits water reabsorption in the kidneys and more water is excreted as urine than consumed It results in dehydration and low blood sugar level that may cause stupor Depresses the CNS impairs coordination and judgment lengthens reaction time Damage to pancreas liver and brain physical dependence Many drugs induce tolerance in which the body response to the drug decreases so that greater amounts are needed to obtain the desired effect Tolerance occurs when response to the drug decreases The liver increase of enzyme concentration that metabolize the drug Addiction is the result of psychological changes or a lowered production of a needed substance due to drug use Chapter SENSORY RECEPTORS Sensory receptors are structures specialized to respond to stimuli and changes in the external environment Sensory receptors consists of Neuron endings Specialized cells in close contact with neurons These receptors transduce convert the energy of the stimulus into electrical signals that are then transmitted by the neurons Sensory receptors and other types of cells make the sense organs eyes ears nose taste buds There are six senses recognized by biologists sight hearing smell taste touch and balance CLASSIFICATION OF RECEPTORS Receptors are classified according to the source or type of stimulus According to location Exteroceptors receive stimuli from outside the body Proprioceptors are located within muscles tendons and joints and enable the animal to perceive the position of arms legs etc and the orientation of the body as a whole Interoceptors are located within body organs and detect physiological changes e g pH temperature chemicals in blood According to types of stimuli to which they respond Mechanoreceptors respond to mechanical energy e g pressure touch and gravity Chemoreceptors respond to chemicals e g odors Thermoreceptors detect changes in temperature Photoreceptors respond to light Electroreceptors detect electrical energy RECEPTOR POTENTIAL Sensory receptors maintain a resting potential a difference in charge between the inside and the outside of the cell membrane Receptor cells absorb energy converts transduce that energy into electrical energy and produce a receptor potential that may result in an action potential Each receptor is sensitive to a particular type of energy A stimulus causes changes in the permeability of the membrane and specific ion channels open or close If the difference in charge is increased the receptor becomes hyperpolarized If the potential decreases the receptor becomes depolarized Stimulus transduction into electrical energy receptor potential action potential Sensory receptors perform three important functions Detect the stimulus in the environment by absorbing energy Converts the energy of the stimulus into electrical energy transduction Produces a receptor potential that may become an action potential The receptor response to a stimulus is a graded response The intensity of the stimulus is coded by the frequency of action potentials fires by sensory neurons during the stimulus A strong stimulus causes greater depolarization of the receptor membrane which in turn causes the neuron to fire action potentials with greater frequency The size of each action potential does not change however law of all-or-none The ability to differentiate stimuli seeing light from tasting sugar depends on the receptor and the brain Sensation takes place in the brain Interpretation of the sensation depends on the type of association neurons that receive the message Some sensory messages never give rise to sensation e g those that sense internal changes in blood pH Impulses from the sensory receptors may differ in Total number of fibers transmitting The specific fiber carrying the action potential The total number of action potentials passing over a given fiber The frequency of the action potentials passing over a given fiber Many receptors adapt to the stimulus and do not continue to respond at the initial rate even if the stimulus continues at the same intensity This is called sensory adaptation Receptors that adapt slowly or not at all are called tonic receptors Those that adapt rapidly are phasic receptors Sensory adaptation enables the animal to discriminate between important and unimportant stimuli that requires attention MECHANORECEPTORS Mechanoreceptors respond to touch pressure gravity stretch and movement Mechanoreceptors are activated when they change shape as a result of being activated by being pushed or pulled They provide information about shape texture weight and topographical relations of object in the external environment Some provide information about internal organs food in stomach urine in bladder fetus in uterus Others enable the organism to maintain body position with respect to gravity Some maintain postural relation of part of the body with another Touch receptors are located in the skin The simplest receptors are nerve endings Meissner's corpuscles perceive light touch for about one second and adapt quickly Merkel's discs adapt slowly and perceive continuos touch Pacinian corpuscles are sensitive to deep pressure especially pulsing and vibrating stimuli Phasic receptors stimulated only when there is movement of the tissues It consists of a nerve ending surrounded by concentric layers of connective tissue with fluid in between Ruffini corpuscles adapt very slowly and detect stretching and distortion of the dermis and provides information about heavy and continuous touch and pressure In many invertebrates and vertebrates tactile receptors are located at the base of a hair or bristle that are stimulated when the hair is distorted Many invertebrates have gravity receptors called statocysts Infolding of the skin lined with cells that have hairs Statoliths are tiny granules of sand or CaCO located in the infolding of the skin Lateral line organs are found in fish and aquatic in aquatic amphibians Long canal running the length of the body and head Line with sensory cells with hairs Tips of hairs have a cupula a mass of gelatinous material Respond to waves and currents in the water Complement vision PROPRIORECEPTORS They contribute to muscle coordination and body balance Muscle spindles Golgi tendon organs and joint receptors are proprioreceptors Respond to tension position and movement in the muscles and joints Muscle spindles are specialized muscle fibers in the center of which there is an area with sensory nerve endings Muscle spindles respond to muscle stretching Skillful use of muscles will be impossible without proprioreceptors SENSE OF HEARING AND BALANCE Functions in hearing and maintaining equilibrium or balance Three regions External ear ear and ear canal in some vertebrates Middle ear tympanic membrane and auditory bones Inner ear semicircular canals vestibule and cochlea All vertebrates have inner ears Outer and middle ears may be absent in some groups Auditory bones are the malleus incus and stapes The vestibule consists of two chambers the saccule and the utricle The vestibule and semicircular canals are also known as the labyrinth The inner ear is made of a membrane that fits inside the skull bone EQUILIBRIUM Equilibrium in humans depends on the proper functioning of the labyrinth and proprioceptors the sense of vision and stimulus coming from the soles of the feet The saccule and utricle of vertebrates contain otoliths CaCO that change position when the head is tilted or when the body is moving in straight line Hair cells are located in the saccule and utricle Hair cells surrounded at their tips by a gelatinous cupula Hair cells send information to the brain about the direction of gravity Each cell has a cilium and several small stereocilia The semicircular canals inform the brain about turning movements linear acceleration Each canal is hollow connected to the utricle and at right angle to the other two Filled with endolymph At one of the openings of each semicircular canal there is a bulb-like enlargement the ampulla Each ampulla contains a cluster of hair cells called the crista Each hair cell has a cilium and stereocilia Endolymph movement stimulates the cristae No otoliths are present in the ampulla AUDITORY RECEPTION Auditory receptors are located in the cochlea A spiral tube consisting of three canals separated by membranes Canals are filled with the perilymph Vestibular canal and tympanic canal are connected at the apex of the cochlea The middle canal is filled with endolymph and contains the organ of Corti Basilar membrane separates the tympanic canal from the medial canal Above the organ of Corti is the tectorial membrane Distortion of the basilar membrane causes the organ of Corti to rub against the tectorial membrane Loud sounds cause waves of greater amplitude resulting in greater stimulation of hair cells and transmission of greater number of impulses per second Pitch depends on the frequency of the sound waves e g high frequency results in high pitch CHEMORECEPTORS The senses of smell and taste use chemoreceptors TASTE gustation Taste receptors are specialized epithelial cells in the taste buds located in the mouth In humans taste buds are located on the tongue in tiny elevations or papillae There are about papillae on the human tongue Each taste bud is an epithelial capsule containing about taste receptor cells interspersed with supporting cells Tips of the taste receptor cells have microvilli that extend into the taste pore on the tongue's surface These receptors detect food molecules dissolved in saliva There are four basic tastes salty sweet sour and bitter Flavor depends on the four tastes in combination with smell texture and temperature The ability to taste certain chemicals is inherited SMELL olfaction In humans the olfactory epithelium is found on the roof of the nasal cavity It contains about million specialized olfactory cells with ciliated tips The cilia extend into the layer of mucus on the epithelial surface of the nasal passageway Receptor molecules on the cilia bind to compounds that dissolve in the mucus The other end of each olfactory cell is an axon that extends directly into the brain These axons make the first cranial nerve Messages travel to the olfactory bulb in the brain then to the olfactory cortex to the limbic system and finally to other areas of the cortex by way of the thalamus The number of odorous molecules determines the intensity of the receptor potential Humans can detect seven main groups of odors Each odor is made of several components and each component may bind with a particular type of receptor The combination of receptors activated determines the odor we perceive Olfactory organs react to a very small amount of stimulant ionone odor of violet can be detected at in billion parts Olfactory sense adapts very quickly THERMORECEPTORS Many invertebrates are sensitive to changes in temperature Mosquitoes ticks and other blood-sucking arthropods use thermoreceptors to find an endothermic animal They are important in endothermic animals Free nerve endings in the skin and tongue detect temperature In some snakes and invertebrates they are used to locate prey or an endothermic host Some antennae are sensitive to a oC change Pit organs of snakes detect warm-blooded animals at far as -meter distance In humans three types of receptors detect temperature changes warm receptors cold receptors and pain receptors for extreme temperatures Thermoreceptors in the hypothalamus detect internal changes in temperature and initiates homeostatic mechanisms to maintain constant body temperature ELECTRORECEPTORS Electric organs are found in a few species of sharks rays and bony fishes These fishes can detect electrical fields generated by the muscles of their prey These animals have neurons that are linked to the neurons supplying the lateral line organs Sharks have an additional set of electroreceptors on their head called the ampullae of Lorenzini Some electroreceptors are sensitive enough to detect the Earth's magnetic field Electric organs found in some fishes are made specialized muscle or neuron cells that produce an electric current These electric currents help in orientation in muddy water stunning a prey or attacker and finding a mate since male and females produce different frequency discharges PHOTORECEPTORS Most animals have photoreceptors that use a group of the pigments called rhodopsins to absorb light Invertebrates have eyespots simple eyes and compound eyes Simplest are found in some cnidarians and flatworms Eyespots are called ocelli a bowl shaped cluster of light sensitive cells within the epidermis They detect light intensity and direction but no images Effective image formation requires a lens that concentrates light on photoreceptors The brain interprets the message of the photoreceptors - VISION It integrates information about brightness location position and shape of the stimulus THE COMPOUND EYE Compound eyes are found in crustaceans and insects They consist of ommatidia which collectively produce a mosaic image Some crustaceans have ommatidia and dragonflies have Each ommatidium has a convex lens and a crystalline cone These structures focus light on retinular cells Rhodopsin is located in microvilli found in the membranes of the retinular cells Adjacent cells fuse their membrane and form the rod-shaped rhabdome Compound eyes form a mosaic image based on the message sent by each ommatidium The eye is sensitive to flickers of high frequencies e g a fly can follow flickers of about flickers second Compound eyes are sensitive to wavelengths from red to UV THE VERTEBRATE EYE Position of the eye offers different advantages e g lateral eyes of grazers allow them to detect predators Humans have binocular vision useful in judging distance and depth Two layers of tissue protect the eye Choroid cells contain black pigment that absorbs extra light and prevents internally reflected light from blurring the image Sclera the outer coat of the eye is a tough layer of connective tissue that protects and helps maintain the rigidity of the eyeball The thin transparent cornea is the continuation of the sclera on the front of the eye Iris controls the amount of light entering the eye Ciliary muscles adjust the lens to focus for near or far vision The lens of the eye is a transparent elastic ball immediately behind the iris The anterior cavity between the cornea and the lens is filled with a watery substance the aqueous fluid The larger posterior cavity between the lens and the retina is filled with viscous fluid called the vitreous body The anterior margin of the choroid is thick and forms the ciliary processes glandlike structures that secrete the aqueous fluid The retina contains light-sensitive rods million in humans and cones million Rods are for dim-light vision and allow detecting shape and movement Rods are more numerous in the periphery of the retina Cones are responsible for color fine detail and bright-light vision Cones are concentrated in the fovea a small depressed area in the center of the retina Light must pass through several layers of connecting neurons in the retina to reach the rods and cones The retina has five main types of neurons Photoreceptors rods and cones Bipolar cells which make synaptic contact with Ganglion cells Their axons form the optic nerve Horizontal cells receive information from photoreceptors Amacrine cells receive messages from bipolar cells and send signals to ganglion cells Vision events Light passes through Cornea aqueous fluid lens vitreous body image forms on the retina rods cones impulses in bipolar cells impulses in ganglion cells optic nerve transmits nerve impulses to thalamus integration by visual areas of cerebral cortex Rhodopsin in the rod cells and other related pigments in the cones are responsible for the ability to see A chemical change in rhodopsin leads to the response of a rod to light Rhodopsin is made of opsin polypeptide and retinal pigment from vitamin A Two isomers of retinal exist cis and trans forms In the dark the photoreceptors have the Na channels open and are depolarized The photoreceptors are releasing glutamate an inhibitory neurotransmitters Retinal binds to opsin in the cis form to make rhodopsin Cyclic GMP guanosine monophosphate maintains the Na open The release of neurotransmitter is graded according to the degree of depolarization When light strikes rhodopsin rhodopsin breaks down into opsin and retinal Cis retinal changes to trans-retinal Opsin then becomes activated as an enzyme The opsin molecule activates a G protein called transducin In turn transducin activates and enzyme that converts cGMP to GMP Sodium channels must be bound to cGMP to remain open When cGMP decreases and GMP increases the Na channels begin to close and the cell becomes polarized The rate of neurotransmitters declines The release of glutamate hyperpolarizes the bipolar cells A decrease in glutamate thus results in depolarization Depolarized bipolar cells release neurotransmitters that stimulate the ganglion cell which sends its axon to the brain in the optic nerve COLOR VISION There are three types of cones blue red and green absorbing cones Each type has a different photopigment The retinal is the same as in rhodopsin but the opsin is slightly different in each type All three types respond to a wide range of wavelengths The three types are named according to the wavelength that its pigment responds more strongly Ganglion cells transmit specific types of visual stimuli such color brightness and motion The optic nerves cross the floor of the hypothalamus and form the optic chiasm Some axons crossover to the other side of the brain Axons end and transmit information to the lateral geniculate nuclei in the thalamus From there neurons bring information to the primary visual cortex in the occipital lobe of the cerebrum Information is then transmitted to other cortical areas for further integration The mechanism involved in the integration of visual information is not well understood Chapter Internal Transport Circulatory System FUNCTION To supply cells with all the necessary materials for metabolism and to remove wastes products The human circulatory system is also known as the cardiovascular system Circulatory systems consists of Blood a connective tissue made of cells cell fragments and a fluid known as plasma A pumping organ usually a heart A system of blood vessels or spaces through which the blood circulates INVERTEBRATE TRANSPORT SYSTEMS In all animals fluid between the cell called interstitial fluid or tissue fluid bathes the cells and provides a medium for diffusion of oxygen and nutrients Sponges cnidarians ctenophorans platyhelminthes etc depend on diffusion for internal transport Arthropods and mollusks have an open circulatory system Blood flows into a homocoel bathing the tissues directly The hemocoel is made of spaces or sinuses The hemocoel is not part of the coelom Hemolymph blood and interstitial fluid are indistinguishable Hemocyanin an oxygen-transporting pigment found in some mollusks and arthropods contains copper CLOSED CIRCULATORY SYSTEM Some invertebrates e g cephalopods echinoderms annelids and vertebrates have a closed circulatory system Nemerteans have a primitive circulatory system that is closed but does not have a pumping organ Blood moves depending on the movements of the animal and contractions in the wall of the large blood vessels Earthworms have hemoglobin dissolved in the blood plasma Functions of the vertebrate circulatory system Transports oxygen metabolic wastes nutrients and hormones Helps maintain fluid balance Defends the body against invading microorganisms Distributes metabolic heat to maintain normal body temperature Helps maintain appropriate pH Exchange of materials occurs through the thin wall of capillaries BLOOD Blood is a type of connective tissue containing different kinds of cells suspended in a liquid matrix the plasma Plasma makes about of the blood The remaining are made up of blood cells and platelets Plasma is about water proteins and the rest consists of nutrients organic wastes and electrolytes ions Blood makes up about of the body weight Humans have to liters of blood The plasma contains nutrients wastes hormones and respiratory gases The plasma and interstitial fluid are similar in composition except that the plasma contains a higher protein concentration than the interstitial fluid When proteins involved in blood clotting have been removed from the blood the remaining liquid is called serum Plasma proteins Globulins are of three kinds Alpha globulins include certain hormones and proteins involved in their transport HDL high-density lipoproteins transport fats and cholesterol Beta globulins are lipoproteins that bind to minerals vitamins lipids and cholesterol to dissolve and transport Gamma globulins are antibodies that provide immunity against certain diseases Globulins make up of the plasma proteins Albumins help to regulate the amount of fluid in the plasma and interstitial fluid and help maintain osmotic pressure and proper blood volume They constitute of plasma proteins Fibrinogen and prothrombin function in the clotting reaction Plasma proteins act as buffers in order to maintain a constant pH of The liver synthesizes more than of the blood proteins all of albumin and fibrinogen and most of the globulins Immunoglobulins are produced by plasma cells Protein hormones are produced in endocrine glands Red blood or erythrocytes cells RBC transport oxygen and carbon dioxide Made in the bone marrow ribs long bones vertebrae and skull bones million l mm in men and million l mm in women Lack nucleus and live for about days Liver and spleen remove old RBC from circulation Hemoglobin is the oxygen transporting protein contains Fe Fe deficiency causes anemia a decrease production of hemoglobin and RBCs Anemia is a deficiency in hemoglobin Hemolytic anemia is due to an increase rate of RBC destruction Hemorrhage decrease RBC production is other causes of anemia RBC production is regulated by the protein erythropoietin which is released by the kidneys in response to a decrease in oxygen Birds have large oval nucleated RBCs White blood cells or leukocytes WBC defend the body against disease-causing microorganisms Humans have five kinds of leukocytes that may be classified granular or agranular About cells l mm in human blood - cells on the average The number increases temporarily during infections Made in the bone marrow Travel in the blood stream for a short time and can migrate across the endothelial lining of the capillaries Their collective function is to fight infections Chemotactic attraction to invading pathogens Granular leukocytes are manufactured in the red bone marrow Their nuclei are lobed and large and the cytoplasms have distinct granules Neutrophils are the principal phagocytic cells in the blood Eosinophils play a role in allergic responses detoxification of foreign proteins and parasitic infestations Basophils contain histamine and are involved in allergic reactions Some have heparin and anticoagulant that prevents clotting in the blood vessels Agranular leukocytes are manufactured in the red bone marrow Their nuclei are round or kidney shaped and lacks granules Lymphocytes produce antibodies and attack foreign cells They become B cells and T cells which produce an immune response to foreign substance Monocytes develop into macrophages that destroy bacteria cell debris and dead cells Leukemia is a form of cancer in which one the of the leukocytes types multiplies rapidly do not mature and crowd out developing RBC and platelets leading to anemia and impaired clotting Platelets or thrombocytes function in blood clotting They are pinched off from very large cells called megakaryocytes in the red bone marrow Cell fragments containing enzymes Lack nucleus About platelets l Hemostasis clumping and sticking to collagen fibers along the walls of the cut blood vessel More than substances interact in the clotting process Coagulation Fibrinogen and prothrombin are proteins found in the plasma Platelets release several factors that combine with Ca in order to convert prothrombin to the active enzyme thrombin Thrombin then converts the soluble protein fibrinogen into the insoluble fibrin Fibrin polymerizes and sticks to the damaged surface forming a web RBC and platelets get trapped in the web and form the clot There are more than factors interacting during the clotting process The absence of one of these factors due to genetic mutation is the cause of hemophilia BLOOD VESSELS Arteries carry blood away from the heart Veins carry blood to the heart Capillaries are thin-walled vessels through which materials pass back and forth between blood and tissues Smaller secondary branches of arteries are called arterioles and of veins venules Notice that arteries and veins are distinguished by the direction in which they carry blood and not by the characteristics of the blood Veins and arteries have three layers of tissues Tunica intima consists of squamous epithelium endothelium Tunica media is made of connective tissue and smooth muscle Tunica adventitia consists of connective tissue rich in elastic and collagen fibers The smooth muscle in the wall of arteries can constrict vasoconstriction or dilate vasodilation The thick wall of the arteries and veins prevent gases from passing through Capillaries form a network between arterioles and venules Metarterioles connect directly an arteriole with a venule Capillaries branch off metarterioles Precapillary sphincters are located whenever a capillary branches off a metarteriole These sphincters open and close continuously to direct blood to needed sectors of the tissues Vasoconstriction and vasodilation help maintain the appropriate blood pressure and control the volume of blood passing to a particular tissue Changes in blood flow are regulated by the autonomic nervous system in response to metabolic needs of tissues HEART In vertebrates the heart consists of one or two atria which receive the blood and one or two ventricles which pump the blood In fish there is one atrium and one ventricle and blood flows in a single circuit Atrium ventricle conus arteriosus aorta gill capillaries organ capillaries sinus venosus atrium In amphibians there are two atria and one ventricle Systemic and pulmonary circulation a double circuit Ventricle aorta body capillaries veins sinus venosus right atrium ventricle pulmonary artery lung and skin capillaries veins left atrium ventricle Oxygen-poor blood is pumped out the ventricle before the oxygen-rich blood enters it Reptiles have a double circuit blood flow and the ventricle is partly divided Some mixing of blood occurs Ventricle sides contract at different times Crocodiles have two ventricles In birds and mammals the heart ventricles are separated There are two ventricles The conus arteriosus becomes the base of the aorta and pulmonary artery Body capillaries veins right atrium right ventricle pulmonary arteries lung capillaries pulmonary veins left atrium left ventricle aorta body organs veins right atrium A sac of connective tissue the pericardium protects human heart The inner surface of the pericardium and outer surface of the heart are covered by a smooth layer of endothelium The space in between the pericardial cavity is filled with a fluid which reduces friction during heartbeats The fossa ovalis is located on the interatrial septum It marks the location of the foramen ovalis in the fetus On the upper surface of each atria lie a small muscular pouch called the auricle The right atrio-ventricular valve AV or tricuspid valve controls the blood flow between the right atrium and right ventricle The left AV is called the mitral valve The cordae tendinae attach the valves to the papillary muscles of the heart The semilunar valves guard the exits from the heart aortic and pulmonary valves HEARTBEAT The heart is capable of beating independently of the nervous system At the end of cardiac muscle cells there are dense bands called intercalated discs gap junctions in which two cells are connected through pores The sinoatrial node SA or pacemaker initiates the heartbeat It is located near the point where the superior vena cava enters the right atrium Because cardiac muscle cells are coupled by the gap junctions of the intercalated discs the electrical impulse they produce spread rapidly through the wall of the atria making them contract in unison Atrial muscle fibers conduct the action potential to the atrioventricular node located in the right atrium on the lower part of the septum From the AV node the action potential travels into the AV bundle also known as the bundle of His made of the Purkinje fibers The AV bundle branches into sending branches into each ventricle From the AV bundle the action potential spreads through the ordinary cardiac muscle fibers The contraction of the heart is called systole and the relaxation of the heart is known as diastole When the semilunar valves do not close tightly during diastole the blood flows back with a hiss known as a heart murmur The electrical activity of the heart spreads through the body fluids to the body surface and can be recorded in a graph called the electrocardiogram ECG or EKG The oscilloscope and the electrocardiograph are the instruments used to record and monitor the heart activity P waves correspond to the contraction of the atria QRS complex reflects the contraction of the ventricles T wave shows the relaxation of the ventricles Abnormalities in the EKG indicate a disorder in the heart or its rhythm The SA sets the tempo for the entire heart and it is influenced by several factors Hormones like epinephrine secreted by the adrenal gland Body temperature An increase of body temperature by C increases the heart rate by beats min Exercise in order to bring enough oxygen to the muscles Cardiac output is the volume of blood pumped by the left ventricle into the aorta in one minute The stroke volume is the volume of blood pumped into the aorta during one beat ml stroke Heart rate is the number of contractions per minute strokes min Cardiac output stroke volume X heart rate ml min Stroke volume depends on the venous inflow that stretches the walls of the heart Starling's law of the heart The more blood is delivered into the heart by veins the more blood the heart pumps More blood stretches the walls of heart and the heart contracts with greater force The increase in stroke volume increases the cardiac output Mainly the nervous system hormones body temperature and other factors regulate heart rate The heart rate is a compromise between the opposing actions of two sets of nerves The Parasympathetic n s relaxes the heart Parasympathetic neuron releases acetylcholine Acetylcholine binds to receptors on the plasma membrane of the cardiac muscle The receptor activates G proteins Activated G proteins bind to K channels causing them to open K leave the cell and the cell becomes hiperpolarized The rate of the action potential drops The Sympathetic n s increases the rate and strength of the heart's contractions Sympathetic neuron releases norepinephrine Norepinephrine binds to -adrenergic receptors on the plasma membrane of the cardiac muscle -adrenergic receptors activate G proteins Activated G proteins in turn activate adenyl cyclase which convert ATP to cyclic AMP cAMP activates protein kinases which phosphorylate Ca channels Ca channels open and calcium ions enter the cell causing depolarization Action potential occurs more rapidly Although the heart is capable of beating independently its rate is highly regulated by the autonomic nervous system and the endocrine nervous system Blood pressure is the force exerted by the blood against the inner walls of the blood vessel It is determined by cardiac output blood volume and resistance to blood flow Resistance to flow is caused by the viscosity of the blood and by friction against the wall of blood vessels A change in the diameter of a blood vessel affects blood pressure significantly It is greatest in arteries and decreases as blood flows through the capillaries Blood pressure increases during systole and decrease during diastole Baroreceptors located on the walls of certain vessels and heart chambers are sensitive to blood pressure Baroreceptors send messages to the cardiac and vasomotor centers of the medulla when the pressure increases The cardiac center stimulates the parasympathetic NS that slows the heart rate and the vasomotor center inhibits the sympathetic NS that constricts the blood vessels All these reduce blood pressure Angiotensins are hormones that act as vasoconstrictors and increase blood pressure Blood pressure rises during systole and drops during diastole For a young adult male is mm Hg as measured by the sphygmomanometer BLOOD CIRCULATION Pulmonary circulation oxygenates the blood Systemic circulation delivers blood to the tissues Coronary arteries feed the heart Carotid arteries bring blood to the brain Subclavian arteries to the shoulder region and arms Mesenteric arteries to the intestines Renal arteries to the kidneys Iliac arteries to the legs Blood returns to the heart in veins The superior vena cava collects blood from jugular and subclavian veins drain the brain and arms Renal iliac and hepatic veins empty into the inferior vena cava Coronary capillaries empty in the coronary veins which in turn join to form a large vein the coronary sinus that empties directly into the right atrium The hepatic portal system delivers nutrients to the liver The hepatic portal system delivers blood rich in nutrients to the liver Blood flows from the liver to the small intestine through the superior mesenteric artery Blood flows through the capillaries of the intestine and collects glucose amino acids and other nutrients This blood passes to the mesenteric vein and then into the hepatic portal vein which delivers the nutrient rich blood to the liver Four arteries deliver blood to the brain two carotids and two vertebral arteries At the base of the brain these arteries branch and fuse again forming the circle of Willis LYMPHATIC SYSTEM The lymphatic system is an accessory circulatory system which Collects and returns interstitial fluid to the blood Defends against disease-causing organisms Absorb lipids from the small intestine The lymphatic system consists of Lymphatic vessels that conduct lymph Lymphatic tissue organized into lymph nodes and nodules Tonsils thymus gland and spleen Interstitial fluid enters the lymph capillaries and is called lymph Lymph capillaries are dead-end and extend into almost all tissues of the body Lymph capillaries join to form large lymphatics lymph veins Thoracic duct empties the lymph into the left subclavian vein Right lymphatic duct empties into the right subclavian vein Valves within the lymph veins prevent the lymph from flowing backwards Tonsils are lymphatic tissues that protect the respiratory system from infections They are found at the back of the nose and on the throat When enlarged the tonsils found at the back of the nose are called adenoids When blood enters the capillaries under pressure some plasma and proteins filters out into the tissues forming the interstitial fluid Only about one fourth of the blood proteins pass into the tissues Lymph capillaries are made of overlapping cells that separate under pressure allowing excess interstitial fluid and proteins in it to enter and drain the tissue Obstruction of the lymph vessels causes edema the swelling that occurs due to the accumulation of interstitial fluid Chapter INTERNAL DEFENSE - IMMUNE SYSTEM Disease-causing microorganisms are called pathogens They include bacteria viruses protozoans and fungi Internal defense depends on the ability of the organisms t distinguish between its own cells and those of foreign organisms - between self and nonself Cells have surface proteins different from those of other organisms Pathogens have macromolecules on their cell surfaces that the body recognizes as foreign These foreign substances stimulate an immune response They are called antigens An immune response involves the recognition of the foreign substance and a response aimed at eliminating it Antigenic molecules antigens include DNA RNA proteins and some carbohydrates Immunology is the study of specific defense mechanisms There are Specific defense mechanisms and Nonspecific defense mechanisms also known as innate immune response Specific defense responses are known as adaptive or acquired immune responses INVERTEBRATES They have mostly nonspecific internal defense mechanisms Prevent pathogens from entering the body Destroy pathogens that to enter the body e g phagocytosis Substances in the hemolymph kill bacteria Sponges and cnidarians exhibit immune response Annelids and some cnidarians have specific immune mechanisms Coelomates have phagocytes Arthropods echinoderms and simple chordates have immunological memory Echinoderms and tunicates are the simplest organisms that have differentiated WBC that perform immune function VERTEBRATES Nonspecific defense mechanisms include mechanical and chemical barriers Mechanical barriers include skin hair mucous Chemical barriers include sweat sebum tears and stomach acid Lysozymes are enzymes found in tears sebum and tissues that attack the cell wall of bacteria Cytokines are regulatory proteins interferons and interleukins secreted by cells of the immune system They are important signaling cells during immune responses Cytokines can influence nearby cells and modify their functions Interferons are proteins produced by virus infected cells Some produced by macrophages or fibroblasts inhibit viral replication and kill tumor cells Type I and stimulate macrophages Type II interferons They do not benefit the infected cell but signal other cells to produce chemicals that inhibit viral replication Interleukins are secreted mostly by macrophages and leukocytes They regulate the interaction between leukocytes and other cells and can cause fever kill tumor cells and cause other responses Tumor necrosis factors TNF are secreted by macrophages and lymphocytes T cells They kill tumor cells and initiate an inflammatory response Cytokines also regulate cell growth repair and cell activation Complement proteins complement system increase the inflammatory response and phagocytosis some complement proteins digest part of the pathogen cell others attract WBC to the infection site chemotaxis Complement the action of other defense mechanisms specific and non-specific defense More than proteins found in the plasma and other body fluids Inactive until the body is exposed to an antigen They act against any antigen Lyse the pathogen's cell wall coat the pathogen so it can be digested by macrophages attract WBC increase inflammation by dilating capillaries and increasing permeability Inflammation is a protective mechanism Damage to tissue by physical injury or by infection triggers the inflammatory response It is regulated by proteins in the plasma by cytokines and by substances called histamines released by platelets by basophils WBC and by mast cells Blood flow increases bringing phagocytic cells to the site of infection This is probably the most important element of inflammation Histamines cause vasodilation and make capillaries more permeable allowing antibodies to enter the tissues Leukocytes release prostaglandins that increase blood flow to the injured area Blood flow to the injured area brings clotting elements to initiate tissue repair makes the skin feel warm and may causes redness Edema swelling occurs Fever is a widespread inflammatory response Pathogens may trigger fever Some leukocytes release interleukins pyrogens reset the body thermostat in the hypothalamus Fever interferes with the growth and replication of microorganisms It may kill some microorganisms Causes lysosomes to break and destroy infected cells Promotes activity of lymphocytes T cells antibody production and phagocytosis Phagocytes destroy bacteria and other cells Neutrophils are the first phagocytes to arrive usually within an hour of injury Monocytes arrive next and become large macrophages Both phagocytize pathogens their products and dead and injured cells A neutrophil can phagocytize about cells and a macrophage cells before they become inactive and die Pus consists of dead phagocytic cell fluid and proteins leaked out of capillaries Acid secretions and enzymes in the stomach There are exceptions Hepatitis A virus survives stomach acids and penetrates the body via the digestive tract Specific defense mechanisms or immune responses Cells of the immune system include lymphocytes T lymphocytes or T cells B lymphocytes or B cells natural killer NK cells and phagocytes These cells circulate throughout the body in the blood and lymph and are concentrated in the spleen lymph nodes and other lymphatic tissues T lymphocytes and B lymphocytes target specific invaders T lymphocytes or T cells Responsible for cellular immunity Originate in the bone marrow In the thymus they become immunocompetent that is capable of immune response In the thymus they divide many times and some develop specific surface proteins with receptor sites These cells are selected to divide positive selection T cells that react to self-antigens undergo apoptosis In this way T cells can distinguish between foreign antigens and the body's own antigens They produce different kinds of cytokines that affect T cell development B cell development NK development and the action of macrophages There are several types and subtypes of T cells Cytotoxic T cells or CD T cells killer cells recognize and destroy cells with antigens on their surface like cancer cell virus-infected cells etc they release cytokines that lyse cells Helper T cells or CD T cells activate the immune system by secreting certain cytokines helper cells or Th promotes cell-mediated immune response helper cells or Th stimulate B cells to divide and produce specific antibodies B cells Responsible for antibody-mediated immunity Produced in the bone marrow daily by the millions They mature in the bone marrow Carry specific glycoprotein receptor to bind to a specific antigen When a B cell comes into contact with an antigen that binds to its receptors it clones identical cells and produces plasma cells that manufacture antibodies Also produce memory B cells that continue to produce small amounts of antibody after an infection Natural killer cells NK Large granular lymphocytes that originate in the bone marrow Attack cancer cells infected cells and pathogens including certain fungi Release antibodies and cytokines that destroy target cells by lysing the cells Do not have to be sensitized or stimulated by an antigen They are stimulated by interferons Macrophages ingest bacteria and digest most but not all of its antigens It displays the bacterial-antigens as well as its own proteins on its surface antigen-presenting cell or APC Secrete over compounds that kill and destroy bacteria Secrete interleukins that activate B cells and helper T cells Also cause other responses like fever THYMUS A gland with two functions Makes T cells capable of immunological response by developing surface proteins with receptor sites Produces the hormone thymosin that probably stimulates T cells after they leave the thymus causing them to become immunologically active MAJOR HISTOCOMPATIBILITY COMPLEX MHC The ability to distinguish self from nonself depends largely on a group of cell surface proteins known as MHC antigens Class I MHC molecules and Class II MHC molecules mark body cells as self It permits recognition of self a biochemical fingerprint The MHC antigens are a group of membrane glycoproteins that act as markers on the surface of the cells of the individual Glycoproteins are proteins with a sugar chain attached to it In humans it is known as the human leukocyte antigen group or HLA A group of closely linked polymorphic genes e g multiple alleles for each locus sometimes up to or even alleles for one gene determine these glycoproteins This family of genes is called the major histocompatibility complex or MHC There are three sets of MHC genes that code for proteins Class I Found on all nucleated cells Distinguish self from non-self Forms MHC-antigen complex on the surface of the cell surface These MHC-antigen complexes are recognized by cytotoxic T cells Class II Found on specialized cells including macrophages B cells activated T cells spleen cells lymph node cells and the cells in the interior of the thymus Forms complexes with antigens and stimulate helper T cells to form interleukins and activate B cell Class III These proteins are part of the complement system IMMUNE TOLERANCE FOR SELF Thymus cells have a high level of class I MHC molecules and class II MHC molecules Only T cells bearing receptors with affinity for self-MHC reach maturity Developing T cell with affinity for class I MHC molecules develop into cytotoxic T cells those with affinity for class II molecules become helper T cells Lymphocytes with receptors specific for molecules already present in the body are either rendered nonfunctional or destroyed by programmed cell death apoptosis This leaves only lymphocytes that react with foreign molecules Failure of self-tolerance leads to autoimmune diseases like multiple sclerosis ANTIBODY-MEDIATED IMMUNITY B cells are responsible for antibody-mediated immunity also called humoral immunity Antibody molecules serve as cell surface receptors that combine with antigens Only B cells bearing a matching receptor on its surface can bind a particular antigen B cell must be activated Macrophage engulfs bacterium Antigen forms complex with the class II MHC protein Macrophage displays MHC-antigen complex on its cell surface Helper T cells are activated when their receptors combine with the MHC-antigen complex Macrophage also secretes interleukins which activate T cells Activated helper T cells secrete interleukins cytokines that activate B cells Independently B cells bind with complementary antigen and forms MHC-antigen complex on its own surface Interleukin and MHC-antigen complex stimulate B cells to divide and differentiate IL- also stimulates cytotoxic T cells to become active killers Activated B cells form many clones some of which differentiate into plasma cells and some into memory B cells Plasma cells remain in the lymph nodes and secrete specific antibodies Antibodies are transported via lymph and blood to the infected region Antibodies form complexes with antigens on the surface of the pathogen Memory cells survive for a long time and continue to produce small amounts of antibody long after the infection has been overcome Memory cells when stimulated can produce clones of plasma cells ANTIBODIES Antibodies have two main functions Combine with antigen and labels it for destruction Activates processes that destroy the antigen that binds to it Antibodies do not destroy the antigen It labels the antigen for destruction Antibodies are globular proteins also known as immunoglobulins Ig An antigen that is a protein has a specific sequence of amino acids that makes up the epitope or antigenic determinant These antigen determinants vary in number from to more than on a single antigen The shape of the epitope can be recognized by the antibody or a T cell receptor An antibody interacts with a small accessible portion of the antigen the epitope Antibodies are grouped into five classes of immunoglobulins or Ig based on the constant region of the heavy chains IgG and IgM defend the body against pathogens in the blood and stimulate macrophages and the complement system IgA is present in the mucus saliva tears and milk It prevents pathogens from attaching to epithelial cells IgD found on B cells surface helps activate them following antigen binding They are needed to initiate the differentiation of B cells into plasma and memory B cells IgE when bound to an antigen releases histamines responsible for many allergic reactions It also prevents parasitic worms A typical antibody is an Y-shaped molecule consisting of four polypeptide chains Two identical heavy chains and two identical light chains joined by disulfide bridges to form the Y shaped molecule The part of the antibody that binds to the antigen is called the Fab region and the part that binds to the cell the Fc region The tips of the Y are the variable regions V regions of the heavy and light chains The tail of the Y shaped antibody is made of the constant or C regions of the heavy chains Antibodies combine with antigens to forms specific complexes that stimulate phagocytosis inactivate the pathogen or activate the complement system Antibodies may inactivate a pathogen e g when the antibody attaches to a virus the virus may lose its ability to attach to a host cell This is called neutralization The antigen-antibody complex may stimulate phagocytic cells to ingest the pathogen Antibodies enhance macrophage attachment to the microbes for phagocytosis This is called opsonization Clumping of bacteria and viruses neutralizes and opsonizes the microbes for phagocytosis This is called agglutination Antibodies can bind to soluble antigens and form immobile precipitates that can be disposed of by phagocytes This is called precipitation The antigen-antibody complex allows complement system proteins to penetrate the pathogen's membrane and open a pore that causes the lysis of the pathogenic cell This is called complement fixation Microbes coated with antibodies and complement proteins tend to adhere to the wall of blood vessels making them easy preys for phagocytes CELL-MEDIATED IMMUNITY Cytotoxic T lymphocytes and macrophages are responsible for cell-mediated immunity Cytotoxic T cells destroy infected cells and cells altered in some way like cancer cells Cytotoxic T cells recognized antigens only when they are presented forming the MHD-antigen complex Pathogen invades the body and infects cells Macrophage engulfs pathogen Antigen forms complex with the class I MHC protein Macrophage displays MHC-antigen complex on its cell surface Helper T cells recognize the foreign antigen-MHC complex and secrete IL- Competent T cells are in turn activated increase in size and divide mitotically Clones of competent T cells are produced Clones differentiate into memory T cells cytotoxic T cells and other types of cells Cytotoxic T cells leave the lymph nodes and migrate to the area of infection At the site of infection All nucleated cells have class I MHC proteins on its surface Some viral proteins are broken down and carried by newly made class I MHC proteins to the surface of the cell The infected cell displays class I MHD-antigen complex on its surface Cytotoxic T cells recognize the displayed complex and binds to the infected cell Cytotoxic T cells leave the lymph nodes and release proteins lymphotoxins perforins in the site of infection and destroy pathogens by lysing Macrophages are attracted to the site to ingest pathogens IMMUNITY Memory B and memory T cells may persist throughout the lifetime of the individual and responsible for long-term immunity The first exposure to an antigen stimulates a primary response IgM is the principal antibody synthesized during the primary response The secondary response is much faster than the first response due to the presence of memory cells A second exposure to an antigen causes a secondary response The predominant antibody produced is IgG Constant evolution of pathogens causes different antigens that are no longer recognizable by memory cells and thus cause the disease again e g cold flu Types of immunity Active immunity is developed by exposure to antigens Naturally induced by an infection Artificially induced through a vaccine Passive immunity is caused by the injection of antibodies produced by other organisms Naturally induced by the mother to the developing baby Artificially induced through injection of antibodies gamma globulin Babies who are breastfed continue to receive immunoglobulins IgA in the milk MONOCLONAL ANTIBODIES Cancer cells can live and divide in tissue culture indefinitely B lymphocytes live in tissue culture for only a few generations B cells of an infected mouse are collected and suspended in a culture medium with myeloma cells a type of cancer These cells B lymphocytes and myeloma cells fuse and form hybridomas Hybridoma cells have properties of both parent cells ability to produce antibodies and to live and divide indefinitely in a culture medium These cell can be cloned and culture for a long time and continue to produce antibodies Because of the high specificity of hybridomas they can be used to detect specific molecules even if they are present in very small amounts GRAFT REJECTION It is an immune response against transplanted tissue T cells are responsible for the destruction of the transplanted organ The transplanted tissue has MHC antigens that are different from those of the host that stimulate the immune response Certain part of the body accept any foreign tissue e g cornea Because of the difficulty of finding a good match to transplant tissues or organs biologists are investigating techniques to transplant animal tissues and organs to humans This procedure is called xenotransplantation Animals can be genetically engineered so that they do not produce antigens that stimulate the immune system of the host CANCER Cancer cells usually form abnormal proteins on their surface that are recognized by the immune system as antigens NK and cytotoxic cells are the most important in this process If cancer cells do not form different surface proteins they will not be recognized as defective and will continue to multiply Cancer cells may produce blocking antibodies so the T cells cannot adhere to their surfaces ALLERGIC RESPONSE Hypersensitivity is a damaging immunological response to an antigen that is harmless Mild antigens called allergens cause allergic reactions It involves sensitization activation of mast cells and allergic response It involves the production of IgE by plasma cells Hayfever reaction Exposure to pollen causes plasma cells to make pollen specific IgE IgE becomes attached to mast cells receptors When more pollen is inhaled allergen pollen molecules attach to the IgE on the mast cells surface Mast cells then release histamine and serotonin These chemicals cause vasodilation increase permeability and inflammation Allergic asthma occurs when the IgE becomes attached to mast cells in the bronchioles of the lungs Chemical released by mast cells cause smooth muscles to contract and airways narrow making breathing difficult When the allergen reaction takes place in the skin the person develops hives Systemic anaphylaxis is hypersensitivity to a drug like penicillin compounds in food insect sting or venom The reaction is widespread Massive amounts of histamine are released into the blood Extreme vasodilation and permeability follows causing shock and death Antihistamine drugs block the effect of histamines released by mast cells Autoimmune disease is a form of hypersensitivity when the body reacts against its own tissues E g Multiple sclerosis rheumatoid arthritis lupus and psoriasis During lymphocyte development complex mechanisms are developed so the WBC become self-tolerant and do not attack the tissues of their own body It is possible that some lymphocytes remain and launch an attack against its own tissues AIDS - ACQUIRED IMMUNE DEFICIENCY SYNDROME It is cause by the retrovirus HIV human immunodeficiency virus Retroviruses are RNA viruses that use RNA as a template to make DNA with the help of reverse transcriptase HIV destroys helper T cells and macrophages by attaching to the CD molecules on the surface of the T lymphocyte There are some evidences of destruction of the lymph nodes The ability of suppress infection is impaired and the patient falls victim to infectious diseases and cancer AZT acidothymidine blocks the action of reverse transcriptase HIV has a high rate of mutation Chapter GAS EXCHANGE - RESPIRATORY SYSTEM The exchange of gases between an organism and its environment is called respiration Organismic respiration brings oxygen from the environment to the cells Aerobic respiration occurs within the cell in the mitochondria Ventilation is the movement of air or water over the respiratory surfaces In order for oxygen and carbon dioxide to diffuse across a cell membrane they must dissolve in water Water is more viscous and dense than air and the aquatic animal must spend a lot of its energy moving water over the gills Aquatic animals spend of its energy while terrestrial animals spend - of its total energy Air contains much larger concentration of oxygen than water Terrestrial animals have to compensate for water loss during breathing Respiratory surfaces must be maintained moist and air has to pass through a long series of tubes to reach these surfaces TYPES OF RESPIRATORY SURFACES Body surface Used by small animals with low metabolic rate Tracheal tubes that deliver oxygen to all parts of the body It consists of a network of tracheal tubes that open on the body surface through up to tiny openings called spiracles Gills containing capillaries Echinoderms have dermal gills Chordates usually have internal gills In bony fish the gills are protected by a bony plate the operculum Counter current system is an efficient method of obtaining oxygen Lungs formed by in-growth of the body surface or from the wall of the body cavity Spiders have book lungs Located in an inpocketing of the abdominal wall Open to the outside by a spiracle A series of plates rich in hemolymph separated by air spaces Osteichthyes have a swim bladder It is used to control buoyancy Lungfishes use it breath air at certain times in their life cycle Amphibians and reptiles have simple lungs The lungs of toads and frogs are simple sacs with ridges that increase the respiratory surface Some amphibians do not have lungs and exchange gases through the skin Reptiles have sacs with folding of the wall to increase the respiratory surface Birds have the most efficient respiratory system of any living vertebrate Their lungs have air sac extensions that reach into many parts of the bird's body Hemoglobin increases the capacity to transport oxygen by about times There are several types of hemoglobin All contain iron as part of a heme group Heme group is bound to a protein called globin Protein portion varies in size and AA in different species It is present in some invertebrates like annelids nematodes mollusks and arthropods Hemocyanins are copper containing proteins found in arthropods and some mollusks Lack heme group Copper-containing proteins Dissolved in the blood rather than contained in cell Blue when combined with oxygen without oxygen is colorless It is found many species of mollusks and arthropods HUMAN RESPIRATORY SYSTEM The human respiratory system is typical of air-breathing vertebrates Nostrils are the opening of the nose Nasal cavities moisten warm and filter the air Pharynx or throat is used also by the digestive system Larynx also called voice box contains the vocal cords and is supported by a cartilage Epiglottis is a small flap of tissue that closes the larynx during swallowing Trachea or windpipe is supported by rings of cartilage Bronchi are branches of the trachea that lead to each lung Both trachea and bronchi are lined with a mucous membrane containing ciliated cells Bronchioles and alveoli make most the lungs Each lung is covered with a pleural membrane which also lines the thoracic cavity Pleural cavity is the space in between the pleural membranes and it's filled with a fluid The pleural fluid provides lubrication between the lungs and the body wall The alveoli are tiny air sacs at the end of the bronchioles and are lined with a very thin epithelium Capillaries surround the alveoli Gas exchange occurs in the alveoli of the lungs The lungs as such consist mostly of air tubes and elastic tissue with a very large internal surface Passage of air Nostrils nasal cavities pharynx larynx trachea bronchi bronchioles alveoli BREATHING Ventilation is accomplished by breathing Breathing is the mechanical processes of moving air from he environment into the lungs inspiration and expelling the air from the lungs expiration During inspiration the volume of the thoracic cavity is increased by contraction of the diaphragm Contraction moves the diaphragm downward increasing the volume of the thoracic cavity The pressure of the air in the lungs decreases by or mm Hg below the atmospheric pressure With the increase in volume in the thoracic cavity the pressure drops and air is forced in by the atmospheric pressure Expiration occurs when the diaphragm relaxes The normal amount of air inhaled at rest is called tidal volume ml The vital capacity is the maximum amount of air a person can exhale after filling the lungs to the maximum extent O and CO are exchanged between alveoli and blood by diffusion The difference in partial pressure of oxygen between the inhaled air and the blood allows the oxygen to diffuse Pox mm in air and Pox mm in venous blood Therefore oxygen diffuses into the blood Pox mm in arterial blood Pox - mm in tissues Therefore oxygen diffuses into the tissues Fick's law the greater the partial pressure difference and the larger the surface area the faster the gas will diffuse About of the oxygen is transported as oxyhemoglobin and dissolves in the plasma The maximum amount of oxygen that can be transported by hemoglobin is called the oxygen carrying capacity The actual amount of oxygen bound to hemoglobin is the oxygen content The ration of oxygen content to oxygen capacity is the percent oxygen saturation Oxyhemoglobin dissociates faster in an acid medium Lactic acid released during muscular activity lower the pH and therefore decreases the affinity of hemoglobin to oxygen and oxygen is released more easily in the muscles Bohr effect Changing the blood pH affects the of O saturation of blood CARBON DIOXIDE TRANSPORT Carbon dioxide is transported mainly as bicarbonate ions About of the CO dissolves in the plasma and forms HCO - and H lowering the pH About - dissolves in the plasma About - enter the red blood cells and combines with hemoglobin forming carbaminohemoglobin This reaction occurs in the RBC catalyzed by carbonic anhydrase Carbonic anhydrase CO H O ------- H CO H HCO - Most of the H released from carbonic acid combine with hemoglobin and do not change the pH of the blood Many of the bicarbonate ions leave the RBCs and diffuse into the plasma Chloride ions diffuse into the RBC to replace the bicarbonate ions This is known as the chloride shift As CO diffuses out of the alveolar capillaries the resulting lower CO concentration reverses the previous reaction BREATHING CONTROL CENTERS Breathing is regulated by respiratory centers in the pons medulla and in the walls of the carotid arteries and aorta Chemoreceptors sensitive to increases in CO and H and to low O concentrations regulate the respiratory centers Neurons originating in the medulla send messages to the diaphragm and external intercostal muscles causing them to contract and inspiration occurs Negative feedback mechanism prevents our lungs from overexpanding stretch sensors in the lung tissue send nerve impulses back to the medulla inhibiting its breathing control center After several seconds the neurons become inactive the muscles relax and expiration occurs The medulla control center maintains homeostasis by monitoring the amount of CO in the blood Slight drop in the pH of the blood and cerebrospinal fluid means an increase in CO in the tissues and blood The medulla registers these changes and increases the depth and rates of breathing so the excess of CO is eliminated in exhaled air Oxygen concentration generally does not play an important role in breathing regulation Only if the partial pressure of oxygen drops markedly the aortic and carotid centers become stimulated to send messages to the respiratory centers in the brain Hyperventilation reduces the concentration of CO in the blood Certain amount of CO is needed to maintain normal blood pressure CO stimulates vasoconstrictors in the brain in order to maintain muscle tone in the walls of blood vessels As altitude increases barometric pressure decreases and less oxygen enters the blood and leads to hypoxia A rapid drop of barometric pressure that produces gas bubbles in the blood causes decompression sickness or bends Dissolved gases and some liquids bubble out of solution when the barometric pressure drops below the total pressure of the gases in solution Diving mammals have high concentration of myoglobin an oxygen binding pigment found in muscles Myoglobin stores oxygen in diving mammals up to ten times more than in terrestrial mammals Weddell seal store about of its oxygen in muscle compared to only in humans Diving reflex reduces the heart rate blood is redistributed and other physiological changes occur that allow the diving mammal to conserve oxygen Polluted air results in bronchial constriction increase mucus secretion and damage to ciliated cells Chronic bronchitis causes the production of too much mucus and damaged ciliated cells cannot expel it The body resorts to coughing as the way of clearing respiratory passages Emphysema is caused the loss of elasticity in the alveoli and air cannot be expelled effectively Also gas exchanged is impaired The right ventricle compensates by pumping harder and becoming enlarged Heart failure is common among emphysema patients Lung cancer Chapter PROCESSING FOOD AND NUTRITION Processing food includes ingestion digestion absorption and elimination of wastes Nutrients are substances used as a source of energy in metabolic processes and as building blocks in the growth and repair of tissues Nutrition is processes of taking and assimilating food Autotrophs or producers are organisms that manufacture their own food to be used as a source of energy Heterotrophs are organisms that must eat molecules manufactured by other organisms Herbivores carnivores and omnivores Ingestion is the process of taking food into the mouth and swallowing it Digestion breaks down food into simpler components Simpler molecules pass through the lining of the small intestine into the blood by absorption Undigested food is passed out through the process of egestion in simple animals or elimination in more complex animals ANIMAL ADAPTATIONS TO NUTRITION Herbivores feed on plant material and are also known as primary consumers Carnivores feed on herbivores or other carnivores They are known as secondary or high-order consumers Omnivores have a very varied diet of plants and animals Suspension feeders are omnivores that remove small organisms like algae and minute crustaceans from the water They feed on plankton DIGESTIVE SYSTEMS OF INVERTEBRATES Porifera lack systems They digest the food they capture intracellularly Cnidarians and platyhelminthes have a gastrovascular cavity with only one opening Cnidarians have intracellular and extracellular digestion More complex invertebrates and all vertebrates have a complete digestive system with two openings mouth and anus Most invertebrates and all vertebrates have a tube-within-a-tube body plan Peristalsis is the waves of muscular contraction that move food through the digestive track HUMAN DIGESTIVE SYSTEM The wall of the digestive tract consists of four layers The mucosa or inner layer lines the lumen The submucosa is a layer of connective tissue rich in blood vessels lymphatic vessels and nerves Surrounding the submucosa is the muscularis or muscle layer The adventitia is the outermost layer and is made of connective tissue Below the level of the diaphragm the adventitia becomes the visceral peritoneum The visceral peritoneum is connected to the parietal peritoneum the connective tissue that lines the walls of the abdominal and pelvic cavities Peritonitis is an inflammation of the peritoneum due to an infection MOUTH Mechanical digestion and enzymatic digestion of food begins in the mouth Teeth are specialized to perform different functions in different animal groups Fish reptiles and amphibians do not have specialized teeth Mammals have incisors for biting canines for tearing and premolars and molars for grinding Each tooth consists of an outer coat of enamel the inner dentine and the pulp cavity where capillaries and nerves are located Three pairs of salivary glands in the mouth region secrete about a liter of saliva containing salivary amylase which begins starch digestion Salivary amylase breaks down polysaccharides into maltose and small polysaccharides PHARYNX AND ESOPHAGUS They conduct food to the stomach Peristaltic movements push the food bolus toward the stomach During swallowing the epiglottis closes the entrance to the larynx STOMACH Mechanical and chemical digestion continues in the stomach A sphincter or ring of muscles normally closes the entrance to the stomach Folds in the stomach wall are called rugae and are lined with a simple columnar epithelium Rugae smooth out when food enters the stomach to increase its capacity Tiny gastric glands in the stomach wall secrete chemicals Parietal cells secrete HCl and intrinsic factor for the absorption of vitamin B Chief cells secrete pepsinogen which is converted to pepsin when comes in contact with HCl The gastric mucosa secretes an alkaline mucous that protects the stomach Epithelial cells of the lining of the stomach fit tightly together preventing gastric juice from leaking between them When part of the stomach is digested a peptic ulcer develops These sores or ulcers can also occur in the esophagus or in the duodenum Chyme is partially digested food in the stomach When digestion is finished in the stomach peristaltic movements propel the chyme through the exit opening controlled by a sphincter the pylorus SMALL INTESTINE Most enzymatic digestion takes place in the small intestine The wall consists of folds plicae and tiny finger-like projections called villi Microvilli are elongations of the cell membrane of the villi There are about microvilli on each villus It consists of three regions Duodenum is the cm closest to the stomach It receives the chyme from the stomach and secretions from the pancreas and liver Jejunum begins at an abrupt bend of the small intestine m ft long Most absorption occurs here Plicae and villi are prominent but gradually decrease along its length Ileum is about m long and continues absorption The ileocecal valve controls the passage of the remnant of digestion into the large intestine LARGE INTESTINE or COLON The large intestine is about m long Most of the nutrients in the chyme have been absorbed by the time it reaches the large intestine Large intestine absorbs water and sodium ions and eliminates wastes defecation Bacteria act on the unabsorbed material and produce vitamins K and B which are also absorbed The caecum and vermiform appendix are located below the junction of the small and large intestine Their functions are unknown in humans Both are functional in some herbivores The parts of the large intestine are known as the caecum ascending colon transverse colon descending colon sigmoid colon rectum and anus Elimination is the term used for getting rid of digestive waste Excretion is the process of getting rid of metabolic waste In mammals it mostly happens in the kidneys and lungs DIGESTIVE GLANDS Liver It is the largest and most complex organ of the body A liver cell carries more than metabolic reactions Digestive functions Produces bile Helps in homeostasis by adding and removing nutrients from the blood Converts excess glucose to glycogen and store it Converts amino acids to fatty acids and urea Stores iron and certain vitamins Detoxifies drugs and poisons that enter the blood Bile consists of water salts pigments cholesterol and the phospholipid lethicin Bile is stored in the gall bladder which releases it into the duodenum as needed Bile emulsifies fats so they can be acted upon by lipase Pancreas Pancreas secretes digestive enzymes and hormones that regulate the level of glucose in the blood Trypsinogen is an inactive enzyme that is acted upon by enterokinase and forms trypsin Trypsin then activates chymotrypsin and carboxypeptidase Pepsin trypsin and chymotrypsin break the internal bonds of proteins and polypeptides resulting into dipeptides Carboxypeptidases remove amino acids from the carboxyl end of polypeptide chains Aminopeptidases and dipeptidases remove amino acids from the amino end of the chain or split small peptides to amino acids Lipases break down fats into monoglycerides diglycerides glycerol and fatty acids Undigested triacylglycerols triglycerides are absorbed in small amounts Pancreatic amylase converts undigested polysaccharides to maltose Maltase splits the disaccharide maltose into two glucose molecules Sucrase converts the disaccharide sucrose to glucose and fructose Lactase splits the milk sugar lactose a disaccharide into glucose and galactose Most digestive enzymes are produced only when food is present in the digestive tract Salivary secretion is controlled entirely by the nervous system The nervous system and hormones control secretion of other digestive enzymes The wall of the digestive tract has a network of neurons the enteric nervous system that regulates many motor and secretory activity of the digestive tract independently of the autonomic nervous systems At least four hormones regulate the digestive system gastrin secretin cholecystokinin CCK and gastric inhibitory peptide GIP The stomach releases gastrin and the duodenum releases secretin CCK and GIP Gastrin stimulates the secretion of pepsinogen in the stomach Secretin signals the release of sodium bicarbonate by the pancreas and bile secretion by the liver CCK stimulates the release of digestive enzymes by the pancreas and bile by the gallbladder GIP decreases stomach churning and slows emptying ABSORPTION Only a few substances like water simple sugars slats alcohol and certain drugs are small enough to be absorbed through the stomach wall Most absorption occurs in the small intestine To reach the blood a nutrient molecule must pass through an epithelial cell in the wall of the small intestine and through a cell of the blood or lymph vessel lining The absorption of glucose and amino acids is coupled with the active transport of sodium Fructose is absorbed by facilitated diffusion Micelles are soluble complexes of fatty acids and monoacylglycerols combined with bile salts Micelles transport the fatty acid to the epithelium Micelles are soluble in the phospholips of the plasma membrane Glycerol fatty acids and monoacylglycerols are absorbed into the epithelial cells by diffusion Micelles become free to pick up more fatty acids and glycerol In the epithelial cell glycerol and fatty acids resynthesize to form triacylglycerols which along with phospholipids and cholesterol form protein covered globules called chylomicrons Chylomicrons pass out of the cell into the lacteal by diffusion The lymph transports the chylomicrons to the blood NUTRITION Carbohydrates Carbohydrates are used mainly as a source of energy Most carbohydrates are ingested as polysaccharides in the form of starch and cellulose Cellulose is indigestible and is a major component of fiber Polysaccharides are called complex carbohydrates by nutritionists Lipids Lipids are used as a source of energy components of cell membranes and to synthesize steroid hormones There are three essential fatty acids linoleic linolenic and arachidonic acids that must included in the diet The body can synthesize all other lipids of the lipids in the diet are ingested as triacylglycerols triglycerides Fats are broken down into fatty acids and glycerols in the liver Fatty acids are broken down into acetyl-CoA molecules which are then used in the Krebs cycle and into ketone bodies which are converted to pyruvate and acetyl-CoA molecules The process is called -oxidation Glycerol is converted into glyceraldehyde- -phosphate G P and used in glycolysis Acetyl-CoA enters cellular respiration and is also converted to other needed lipids Pyruvate enters cellular respiration Proteins Proteins serve as enzymes cell structural components and other needed substances like hemoglobin and myosin The body can synthesize amino acids Amino acids that must be provided by the diet are called essential amino acids Amino acids are taken up by cells and converted to proteins Excess amino acids are deaminated in the liver and converted to keto acids and ammonia Ammonia converted to urea and excreted in urine Keto acids are converted to carbohydrates fats pyruvate acetyl-CoA and alpha ketoglutarate Vitamins Vitamins are organic compounds required in small amounts and serve mostly as components of coenzymes There are fat soluble A D E K and water soluble B C vitamins We do not understand all of the biochemical roles played by vitamins Overdoses of vitamins are harmful and fat soluble vitamins are difficult to excrete Minerals Minerals are inorganic ions needed to maintain body fluid balance components of proteins cytochromes hormones and other metabolites activators of enzymes involved in nerve impulse and other functions Essential minerals are required in amounts of mg day or more e g Na Cl K Ca P Mg and S Trace elements are required in amounts less than mg day e g Fe Cu F Zn Mn Se and I Phytochemicals Phytochemicals are plant products that play an important role in nutrition Carotenoids are converted to vitamin A The nutritional effects of other phytochemicals are poorly known and are being investigated Flavonoids function as antioxidants Indoles and isocyanate increase the production of enzymes that detoxify carcinogens ENERGY METABOLISM Basal metabolic rate BMR is the amount of energy needed to maintain the body functions Total metabolic rate is the BMR plus the energy needed to carry out daily activities When energy input equals energy output body weight remains constant Malnutrition is the lack of specific dietary requirement Essential amino acids are often the major cause of malnutrition Other commonly deficient nutrients are iron calcium and vitamin A Kwashiorkor is caused by protein deficiency Chapter EXCRETORY SYSTEM Water is the medium in which most metabolic reactions take place FUNCTIONS The functions of the excretory system are Regulation of body fluids by osmoregulation Excretion of metabolic waste The body maintains a constant osmotic pressure by actively regulating the concentration of solutes in the body fluids osmoregulation Excretion is the process of ridding the body of metabolic wastes including water It is different from elimination of feces or defecation Principal metabolic wastes are water carbon dioxide and nitrogenous wastes ammonia urea and uric acid Nitrogenous wastes are the products of deamination of amino acids Ammonia is highly