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chapter 8 of principles of animal physiology by Moyes and Schulte

Uploaded: 6 years ago
Contributor: bio_man
Category: Physiology
Type: Lecture Notes
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Filename:   chapter 8 2009.ppt (7.76 MB)
Page Count: 71
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Circulatory Systems Limits of Diffusion Unicellular organisms and some small metazoans lack circulatory systems Rely on diffusion to transport molecules Diffusion can be rapid over small distances, but is very slow over large distances Large animals move fluid through their bodies by bulk flow, or convective transport Transport can occur over greater distance Requires energy Overview Most metazoans larger than a few cells have circulatory systems Major function Transport oxygen, carbon dioxide, nutrients, waste products, immune cells, and signaling molecules throughout the body Circulatory systems move fluids by increasing the pressure of the fluid in one part of the body Fluid flows through the body, “down” the pressure gradient Three main components are needed Pump or propulsive structures For example, a heart System of tubes, channels, or spaces Fluid that circulates through the system For example, blood Types of Pumps Chambered hearts Contractile chambers Blood enters atrium Blood is pumped out by ventricle Skeletal muscle Squeeze on vessels to generate pressure Pulsating blood vessels Peristalsis Rhythmic contractions of vessel wall pumps blood One-way valves help to ensure unidirectional flow Closed and Open Circulatory Systems Open Circulatory fluid comes in direct contact with the tissues in spaces called sinuses Circulating fluid mixes with interstitial fluid Closed Circulatory fluid remains within vessels and does not come in direct contact with the tissues Circulating fluid is distinct from interstitial fluid Molecules must diffuse across vessel wall Types of Fluid Interstitial fluid Extracellular fluid that directly bathes the tissues Formed by ultrafiltration Blood Fluid that circulates within the vessels of a closed circulatory system Lymph Fluid that circulates in the secondary circulatory system of vertebrates; the lymphatic system Carries fluid (lymph) that has filtered out of the vessels Hemolymph Fluid that circulates in an open circulatory system Some Animals Lack Circulatory Systems Sponges, cnidarians, and flatworms Lack circulatory systems but have mechanisms for propelling fluids around their bodies Sponges and flatworms Flagella or ciliated cells move water within body cavity Cnidarians Muscular contractions of body wall pump water in and out of body cavity Bulk flow of fluid is part of a combined respiratory, digestive and circulatory system Annelids Three main classes of annelids Polychaeta (tube worms) Oligochaeta (earth worms) Hirudinea (leeches) Polychaetes and oligochaetes circulate interstitial fluid with cilia or muscular contractions of body wall Most have vessels that circulate fluid with oxygen carrier protein Circulatory system can be open (polychaetes) or closed (oligochaetes) Molluscs All have hearts and some blood vessels Most have open systems Only cephalopods have closed systems Very active mode of life ? metabolism Similar to birds and mammal system! Figure 8.5 Arthropods All have one or more hearts and some blood vessels All have open systems Insects Relatively simple open circulatory system But high metabolic rate? Insects use a tracheal system for most gas transport Multiple, contractile “hearts” along dorsal vessel Crustaceans Circulatory systems become more complex in larger animals Small sinuses function as vessels Some control over distribution of blood flow in body Structurally open Functionally closed Evolution of Circulatory Systems First evolved to transport nutrients to body cells Very early began to serve respiratory function Closed systems evolved independently in jawed vertebrates, cephalopods, and annelids Increased blood pressure and flow Increased control of blood distribution Closed systems evolved in combination with specialized oxygen carrier molecules High metabolic rates The Circulatory Plan of Vertebrates All have closed circulatory systems (except Agnathans) Muscular, chambered heart contracts to increase the pressure of the blood Blood flows away from the heart in arteries Arteries branch to form more numerous, but smaller diameter, arteries Small arteries branch into arterioles within tissues Blood flows from arterioles into capillaries Capillaries are the site of diffusion of molecules between blood and interstitial fluid Capillaries coalesce to form venules Venules coalesce to form veins Veins carry blood to the heart Vertebrate Blood Vessels A complex wall surrounding a central lumen Wall composed of up to three layers Tunica intima (internal lining) Smooth, epithelial cells (vascular endothelium) Tunica media (middle layer) Smooth muscle Elastic connective tissue Tunica externa (outermost layer) Collagen Thickness of the wall varies among vessels Vertebrate Blood Vessels Figure 8.10 Arterioles have the greatest influence on local blood flow and overall blood pressure Vein – thinner wall and larger lumen than artery of similar size Capillaries Lack tunica media and tunica externa Continuous Cells held together by tight junctions Skin and muscle Fenestrated Cells contain pores Specialized for exchange Kidneys, endocrine organs, and intestine Sinusoidal Few tight junctions Porous for exchange of large proteins Liver and bone marrow Figure 8.11 Jawed Vertebrates – Phylum Chordata Structure varies depending on respiratory strategy Water-breathing fish Single circuit Some fish have accessory hearts in the tail Air-breathing tetrapods Two circuits Pulmonary - right side Systemic circuit – left side Birds and Mammals Four-chambered heart Two atria and Two ventricles Systemic and pulmonary circuits are divided Pressure can be different in the two circuits High pressure systemic Low pressure pulmonary Oxygenated and deoxygenated blood are completely separate Amphibians and Reptiles Heart is only partially divided Three chambered heart Two atria and a single ventricle Blood from both atria flow into the ventricle Oxygenated and deoxygenated blood can mix But experiments show that are kept fairly separate Ventricle pumps blood into pulmonary and systemic circuits Blood can be diverted between pulmonary and systemic circuits Physics of Blood Flow Law of bulk flow: Q = ?P/R Q = flow ?P = pressure drop R = resistance (due to friction) R = 8L?/?r4 L = length of the tube ? = viscosity of the fluid r = radius of the tube (greatest effect) Think effects of vasoconstriction or vasodilation Poiseuille’s equation: Q = ?P ? r4 / 8L? More detailed version of law of bulk flow Modeling Circulatory Systems Like electrical resistors, blood vessels can be arranged in series or parallel Resistors in series RT = R1 + R2… RT increases Resistors in parallel 1/RT = 1/R1 + 1/R2… RT decreases Because of the law of conservation of mass, the flow through each segment of the system must be equal Figure 8.14 Allows fresh blood to tissues Blood Velocity Flow (Q) Volume of fluid transferred per unit time (a rate) Velocity Distance transferred per unit time Blood velocity = Q/A A = cross-sectional area of the vessels Therefore, V is inversely related to total X-sectional Area For example, total cross-sectional area of capillaries is very large ?velocity is slow ? long time for diffusion Analogy: River ? Swamp ? River Transmural Pressure Pressure exerts a force across vessel wall Law of LaPlace T(?) = Pr/w T = tension in vessel wall P = transmural pressure difference between internal and external pressure r = vessel radius w = vessel wall thickness Figure 8.15 Aorta ? Large r ? large T (large Stress) ? Thick Wall to Reduce Tension Compare to Vena Cava?? Hearts Cardiac cycle – pumping action of the heart Two phases Systole Contraction and emptying Spread of excitation Blood is forced out into the circulations Diastole Relaxation and filling Follows repolarization Blood enters the heart Arthropod Heart - Neurogenic Figure 8.16 Arthropod Cardiac Cycle Cardiomyocytes contract Volume of heart decreases; pressure increases Ostia valves close Blood leaves the heart via arteries Stretched ligaments pull apart walls of heart Volume of heart increases; pressure decreases Ostia valves open Blood is sucked into heart Cardiac ganglion neurons spontaneously and rhythmically depolarize Thus, arthropod hearts function as both pressure and suction pumps Vertebrate Hearts Complex walls with four main parts Pericardium Sac of connective tissue that surrounds heart Outer (parietal ) and inner (visceral) layers Space between layers filled with lubricating fluid Epicardium Outer layer of heart, continuous with visceral pericardium Contain nerves that regulate heart and coronary arteries Also extend into myocardium Myocardium Layer of heart muscle cells (cardiomyocytes) Endocardium Innermost layer of connective tissue covered by epithelial cells (called endothelium) Myocardium Two types of myocardium Compact Tightly packed cells Regular pattern Highly vascularized Spongy Loosely connected cells Some not vascularized Relative proportions vary among species Mammals Mostly compact Fish and amphibians Mostly spongy Arranged as trabeculae that extend into chambers Fish and Amphibian Hearts Fish Four chambers arranged in series 2 primary and 2 auxillary 1 atria / 1 ventricle Contract in sequence Figure 8.18a Amphibians Three-chambered heart Two atria, one ventricle How keep deoxygenated and oxygenated blood separate? Trabeculae in ventricle Spiral fold in conus arteriosus Reptile Hearts Five-chambered heart Two atria and three interconnected ventricular compartments Cavum venosum - leads to systemic aortas Cavum pulmonale - leads to pulmonary artery Cavum arteriosum – cavity at base of pulmonary vein Separation of oxygenated and deoxygenated blood in the ventricle is nearly complete Birds and Mammals Four chambers Two atria Two ventricles separated by intraventricular septum Figure 8.20 Valves Atrioventricular (AV) valves Between atria and ventricles Tricuspid (R) and Bicuspid (L) Semilunar valves Between ventricles and arteries Aortic and Pulmonary Cardiac Cycle – highly coordinated Fish hearts Serial contractions of chambers Valves are passive Open and close according to pressure differences Assure unidirectional flow of blood In teleosts, noncontractile bulbus arteriosus serves as volume and pressure reservoir Figure 8.18a Mammalian Cardiac Cycle Atria and ventricles alternate systole and diastole The two atria contract simultaneously, Slight pause Two ventricles contract simultaneously Atria and ventricles relax while the heart fills with blood EDV ESV Animation Ventricular Filling In birds and mammals ventricles fill passively during diastole Atrial contraction adds little blood to ventricles In fish and some amphibians ventricle filled by contraction of atrium Elasmobranchs may use ventricular suction to pull blood in from veins Ventricular Pressure Left ventricle contracts more forcefully and develops higher pressure Less pressure needed to pump blood through pulmonary circuit Resistance in pulmonary circuit low due to high capillary density in parallel (results in a large cross-sectional area) Low pressure protects delicate blood vessels of lung Systemic and pulmonary circuits have same blood flow Control of Contraction Vertebrate hearts are myogenic Cardiomyocytes produce spontaneous rhythmic depolarizations Do not require nerve signal Cardiomyocytes are electrically coupled via gap junctions to ensure coordinated contractions Action potential passes directly from cell to cell Pacemaker Characterized by a lack of a resting membrane potential Cells with fastest intrinsic rhythm In the sinus venosus in fish In the right atrium of other vertebrates Sinoatrial (SA) node Pacemaker Cells Derived from cardiomyocytes Characteristics of pacemaker cells Small with few myofibrils, mitochondria, or other organelles Do not contract Have unstable resting membrane potential pacemaker potential Figure 8.23 Contrast to Nerve and Skeletal Muscle ?t-type Ca2+ Control of Pacemaker Potentials Increasing heart rate Norepinephrine released from sympathetic neurons and epinephrine released from the adrenal medulla More Na+ and Ca2+ channels open Rate of depolarization and frequency APs ? Ephedrine and ephedra Control of Pacemaker Potentials Decreasing heart rate Acetylcholine released from parasympathetic neurons More K+ channels open Pacemaker cells hyperpolarize Time for depolarization ?, frequency APs ? Extended Action Potentials Action potentials in cardiomyocytes differ from those in skeletal muscle Plateau phase Extended depolarization that corresponds to refractory period and lasts as long as the contraction Due to voltage-gated Na+ channel inactivation Caused by Ca2+ entry via L-type channel Prevents tetanus Figure 8.26 Conducting Pathways (Mammalian Heart) Electrical Signals and Blood Flow Modified cardiomyocytes Elongated, pale appearance Do not contract Spread depolarization rapidly Can undergo rhythmic depolarizations Electrocardiogram (ECG or EKG) Composite recording of action potentials in cardiac muscle P wave Atrial depolarization QRS complex Ventricular depolarization T wave Ventricular repolarization Used for clinical diagnosis of problems with conducting system Figure 8.28 Electrical and Mechanical Events in the Cardiac Cycle Heart functions as an integrated organ Electrical and mechanical events are correlated Changes in pressure and volume of chambers Blood flow through chambers Heart sounds Closing of valves Blood Flow Through Your Heart and Lungs Cardiac Output Cardiac output (CO) Volume of blood pumped per unit time Can be modified by regulating HR and/or SV CO = HR ? SV Heart rate Rate of contraction (beats per minute) Modulated by autonomic nerves and adrenal medulla Decreased HR (bradycardia) Increased HR (tachycardia) Stroke volume Volume of blood pumped with each beat Modulated by nervous, hormonal, and physical factors Control of Stroke Volume The nervous and endocrine system can also cause the heart to contract more forcefully and consequently pump more blood with each beat (?SV) Also HR – fast depolarization (T-type Ca2+-channels and “funny” channels) Figure 8.27 These effects are as a result of stimulation from the sympathetic nervous system Extrinsic control Control of Stroke Volume, Cont. Frank-Starling effect – an increase in end-diastolic volume results in a more forceful contraction of the ventricle and an increase in SV Due to length-tension relationship for muscle Heart automatically compensates for increases in the amount of blood returning to the heart (autoregulation) Intrinsic regulation Level of sympathetic activity shifts the position of the cardiac muscle length-tension relationship Figure 8.28 Regulation of Blood Flow Arterioles control blood distribution Because arterioles are arranged in parallel, they can alter blood flow to various organs Vasoconstriction and vasodilation Changes in resistance alter flow Control of vasoconstriction and vasodilation Myogenic Autoregulation Direct response of the arteriolar smooth muscle Some smooth muscle cells sensitive to stretch and contract when blood pressure increases Acts as negative feedback loop Prevents excessive flow of blood into tissue Intrinsic (local) factors Metabolic state of the tissue Extrinsic factors Nervous and endocrine systems Metabolic Activity of Tissues - Intrinsic Smooth muscle cells in arterioles are sensitive to conditions of extracellular fluid Levels of metabolites alter vasoconstriction/vasodilation Blood flow matched to metabolic requirements Paracrine e.g. NO GC – cGMP - Vasodilation PDE (inactivates) Tissue damage ? release Sildenafil Figure 8.32 Neural and Endocrine Control of Flow Sympathetic neurons cause vasoconstriction of arterioles Decreased sympathetic tone causes vasodilation Other hormones affect vascular smooth muscle Vasopressin (ADH) from the posterior pituitary causes generalized vasoconstriction Angiotensin II produced in response to decreased blood pressure causes generalized vasoconstriction Atrial natriuretic peptide (ANP) produced in response to increased blood pressure promotes generalized vasodilation Extrinsic (nervous and endocrine) and Intrinsic (paracrine signals related to metabolic activity) work together to influence arteriolar diameter and blood flow. Pressure in Vertebrate Circulatory Systems BP in left ventricle changes with systole and diastole Pressure decreases as blood moves through system Pressure and pulse decrease in arterioles due to high resistance Relatively narrow (vs arteries) Relatively few (vs capillaries) Velocity of blood highest in arteries, lowest in capillaries, and intermediate in veins Figure 8.33 ?P Arteries Act as Pressure Dampeners Pressure fluctuations in arteries are smaller than those in left ventricle Aorta acts as a pressure reservoir Elasticity of vessel wall Expands during systole Elastic recoil during diastole Low compliance Dampens pressure fluctuations Also have thick walls Reduce stress Figure 8.34 Moving Blood Back to the Heart Blood in veins is under low pressure Two pumps assist in moving blood back to the heart Skeletal muscle Contraction squeezes vein Respiratory pumps Pressure changes in thoracic cavity during ventilation Valves in veins assure unidirectional flow Figure 8.35 Veins Act as a Volume Reservoir Thin, compliant walls Small ? BP lead to large changes in volume In mammals, veins hold more than 60% of blood Vein volume (and venous return) controlled by sympathetic nerves Venomotor tone Figure 8.36 Regulation of Blood Pressure Pressure is the primary driving force for blood flow through organs - Law of Bulk Flow Rearrange the equation: CO = MAP / TPR MAP = CO x TPR Body varies cardiac output (CO) and total peripheral resistance (TPR) to maintain a near constant mean arterial pressure (MAP) Maintaining MAP is the fundamental requirement TPR – state of vasoconstriction/vasodilation – metabolic state of tissue CO varies in response to changes in TPR to maintain MAP in narrow range Thus, metabolic demand of tissues is ultimate regulator Homeostatic regulation of Blood Pressure Figure 8.37 EPO Baroreceptor Reflex Baroreceptors Stretch-sensitive mechano- receptors in walls of many major blood vessels Especially carotid arteries and aorta Send nerve signals to medulla Baroreceptor reflex regulates MAP ? Parasympathetic ? Ag II and Vasopressin Figure 8.38 Kidneys Help Maintain Blood Volume ? in blood volume leads to ? in bp, and vice versa Kidneys excrete or retain water to adjust blood volume (and pressure) to counter changes in MAP Veins are compliant and can act as volume reservoirs but not infinitely so! Figure 8.39 Question? Suppose the flow of blood into the heart is obstructed. How will the cardiac output and systemic blood pressure change from normal? CO will fall; systemic arterial bp will fall CO will rise; systemic bp will rise CO will fall; systemic bp will rise CO will fall; systemic arterial bp will fall CO will remain unchanged; systemic bp will fall Venous return is impeded, atrial pressure decreases, reduced EDV, reduces CO. However, the fall in CO is compensated for by an increase in TPR, a fall in urine production and a rise in HR. Net Filtration Pressure (NFP) Normal 20 liters out 17 liters in Xs of 3?? Arteriolar blood pressure forces fluid out of capillaries Starling principle: NFP = (Pcap – Pif) – (?cap – ?if) Terms: hydrostatic pressure in the capillary (Pcap) and interstitial fluid (Pif); osmotic pressure in the capillary (?cap) and interstitial fluid (?if) May result in net filtration or net reabsorption The Lymphatic System Collects excess filtered fluid and returns it to circulatory system Lymph nodes filter lymph to remove pathogens Lymphocytes Lymphatic veins and ducts contain valves to prevent backflow Edema – accumulation of interstitial fluid Figure 8.41 Affect of Gravity on Blood Pressure Hydrostatic pressure Pressure of a column of fluid due to gravity DP = r ? g ? Dh DP = pressure difference between two points, r = density of the fluid, g = acceleration due to gravity, Dh = height of the fluid column Blood flow may be with or against force of gravity Body Position Changes in body position can alter bp and flow Changes relative to gravity Standing up causes pooling of blood in lower body ? venous return, ? in SV, ? MAP Baroreceptor reflex brings MAP back to normal ? firing ? ? sympathetic output ? HR and ? SV ? ? CO Vasoconstriction ? ? TPR ? MAP Orthostatic hypotension Low blood pressure upon standing when reflex is too slow Can lead to fainting What about Giraffes? Bending down ? hydrostatic pressure in head would tend to ? filtration Highly elastic blood vessels that serve as a pressure reservoir Jugular vein has one-way valves Standing up high bp and hydrostatic pressure would tend to ? filtration in lower extremities Thick-walled and muscular arterioles Skin on legs is extremely tight Increases interstitial fluid pressure Increases efficiency of skeletal muscle pump NFP = (Pcap – Pif) – (?cap – ?if) Composition of Blood Primarily water, containing Dissolved ions and organic solutes Blood cells (hemocytes) Dissolved proteins Invertebrates Primarily respiratory pigments Vertebrates Carrier proteins such as albumin and globulins Proteins involved in blood clotting Blood Proteins Blood Cells (Hemocytes) Functions Oxygen transport or storage Nutrient transport or storage Phagocytosis Immune defense Blood clotting Figure 8.44 Great variety of hemocytes, but recently all have GATA TF involved in their development Red Blood Cells (Erythrocytes) Most abundant cells in blood of vertebrates Contain high concentrations of respiratory pigments (such as hemoglobin) Major function is storage and transport of oxygen Erythrocytes have evolved independently several times Also found in various worms, molluscs, and echinoderms Size of erythrocytes varies among vertebrates Smaller in mammals than in fish and amphibians Generally round or oval in shape Mammalian erythrocytes are biconcave disks Increased surface area, facilitating oxygen transfer Lack nucleus, mitochondria, and ribosomes Cannot divide and have a limited lifespan Retrieved from http://www.moonbowmedia.com/ei/ct/facts0313.htm, 27/02/06 Vertebrate Blood Separates into three main components when centrifuged Plasma Erythrocytes Other blood cells and clotting cells Hematocrit – Fraction of blood made up of erythrocytes Figure 8.45 White Blood Cells (Leukocytes) Function in immune response All are nucleated Found both in blood and interstitial fluid Some able to move across capillary walls Five major types Neutrophil Eosinophil Basophil Monocyte / macrophage Lymphocyte Figure 8.46 Adaptive Immunity Thrombocytes Key role in blood clotting In mammals, thrombocytes are anucleated cell fragments called platelets In non-mammals, thrombocytes are spindle-shaped cells and classified as leukocytes Three steps in blood clotting Vasoconstriction Platelet plug formation Platelets stick to break in vessel Clot formation through coagulation cascade Blood Cell Formation (Hematopoiesis) Location of stem cells Adult mammals Only in red bone marrow Fishes Kidney Amphibians, reptiles, birds Spleen, liver, kidney, bone marrow Signaling factors regulate hematopoiesis For example, erythropoietin is a hormone released by the kidney in response to low blood oxygen Stimulates differentiation of stem cells into erythrocytes Circulatory system during exercise MAP = CO x TPR Patterns of blood flow Retrieved from http://btc.montana.edu/olympics/physiology/pb01.html, 24/03/08 Control of Vasoconstriction/Vasodilation Table 8.1 Mean Arterial Pressure (MAP) MAP = 2/3 diastolic pressure + 1/3 systolic pressure

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