Chapter 10 - The Endocrine System

C h a p t e r 10 The Endocrine System Homeostasis is preserved through intercellular communication The Endocrine System The Endocrine System Regulates long-term processes: Growth Development Reproduction Uses chemical messengers to relay information and instructions between cells The Endocrine System Endocrine Communication Endocrine cells release chemicals (hormones) into the bloodstream Alters metabolic activities of many tissues and organs simultaneously The Endocrine System Target Cells Are specific cells that possess receptors needed to bind and “read” hormonal messages Hormones Stimulate synthesis of enzymes or structural proteins Increase or decrease rate of synthesis Turn existing enzyme or membrane channel “on” or “off” The endocrine system regulates physiological processes through the binding of hormones to receptors The Endocrine System Figure 10-1 The Endocrine System Figure 10-1 The Structure of Hormones Hormones can be divided into three groups Amino acid derivatives Peptide hormones Lipid derivatives Circulate freely or bound to transport proteins Mechanisms of Hormone Action Hormone Receptor Is a protein molecule to which a particular molecule binds strongly Responds to several different hormones Different tissues have different combinations of receptors Presence or absence of specific receptor determines hormonal sensitivity Target Cells and Hormones Figure 10-2 Mechanisms of Hormone Action Hormones and Plasma Membrane Receptors Catecholamines and peptide hormones: Are not lipid soluble Are unable to penetrate plasma membrane Bind to receptor proteins at the outer surface of the plasma membrane (extracellular receptors) Mechanisms of Hormone Action Hormones and Plasma Membrane Receptors Bind to receptors in plasma membrane Cannot have direct effect on activities inside target cell Use intracellular intermediary to exert effects: First messenger: leads to second messenger may act as enzyme activator, inhibitor, or cofactor results in change in rates of metabolic reactions Mechanisms of Hormone Action Important Second Messengers Cyclic-AMP (cAMP): Derivative of ATP Cyclic-GMP (cGMP): Derivative of GTP Calcium ions Mechanisms of Hormone Action Hormones and Plasma Membrane Receptors G Protein: Enzyme complex coupled to membrane receptor Involved in link between first messenger and second messenger Binds GTP Activated when hormone binds to receptor at membrane surface and changes concentration of second messenger cyclic-AMP (cAMP) within cell: increased cAMP level accelerates metabolic activity within cell Nonsteroidal Hormones Figure 10-3a Mechanisms of Hormone Action Hormones and Intracellular Receptors Alter rate of DNA transcription in nucleus: Change patterns of protein synthesis Directly affect metabolic activity and structure of target cell Includes steroids and thyroid hormones Steroids and Thyroid Hormones Figure 10-3b The Control of Endocrine Activity Endocrine reflexes can be triggered by Humoral stimuli: Changes in composition of extracellular fluid Hormonal stimuli: Arrival or removal of specific hormone Neural stimuli: Arrival of neurotransmitters at neuroglandular junctions Hypothalamic Control over Endocrine Function Figure 10-4 The bilobed pituitary gland is an endocrine organ that releases nine peptide hormones The Pituitary Gland Also called hypophysis Lies within sella turcica Hangs inferior to hypothalamus Connected by infundibulum Pituitary Gland Figure 10-5 The Hypophyseal Portal System Figure 10-6 Pituitary Gland Two Classes of Hypothalamic Regulatory Hormones Releasing hormones (RH): Stimulate synthesis and secretion of one or more hormones at anterior lobe Inhibiting hormones (IH): Prevent synthesis and secretion of hormones from the anterior lobe Rate of secretion is controlled by negative feedback Pituitary Gland Anterior lobe (also called adenohypophysis) Hormones “turn on” endocrine glands or support other organs Feedback Control of Endocrine Secretion Figure 10-7a Feedback Control of Endocrine Secretion Figure 10-7b Figure 10-8 Pituitary Gland Posterior lobe (also called neurohypophysis) Contains unmyelinated axons of hypothalamic neurons Supraoptic and paraventricular nuclei manufacture: Antidiuretic hormone (ADH) Oxytocin (OXT) The thyroid gland lies inferior to the larynx and requires iodine for hormone synthesis The Thyroid Gland Lies anterior to thyroid cartilage of larynx Consists of two lobes connected by narrow isthmus Thyroid follicles: Hollow spheres lined by cuboidal epithelium Cells surround follicle cavity that contains viscous colloid Surrounded by network of capillaries that deliver nutrients and regulatory hormones accept secretory products and metabolic wastes The Thyroid Gland Thyroglobulin (Globular Protein) Synthesized by follicle cells Secreted into colloid of thyroid follicles Molecules contain the amino acid tyrosine Thyroxine (T4) Also called tetraiodothyronine Contains four iodide ions Triiodothyronine (T3) Contains three iodide ions The Thyroid Gland Figure 10-9a The Thyroid Gland Figure 10-9b The Thyroid Gland Thyroid-Stimulating Hormone (TSH) Absence causes thyroid follicles to become inactive: Neither synthesis nor secretion occurs Binds to membrane receptors Activates key enzymes in thyroid hormone production The Thyroid Gland Thyroid Hormones Enter target cells by transport system Affect most cells in body Bind to receptors in: Cytoplasm Surfaces of mitochondria Nucleus In children, essential to normal development of: Skeletal, muscular, and nervous systems The Thyroid Gland Calorigenic Effect Cell consumes more energy resulting in increased heat generation Is responsible for strong, immediate, and short-lived increase in rate of cellular metabolism The Thyroid Gland C (Clear) Cells of the Thyroid Gland Produce calcitonin (CT): Helps regulate concentrations of Ca2+ in body fluids The four parathyroid glands, embedded in the posterior surface of the thyroid gland, secrete parathyroid hormone to elevate blood calcium levels Parathyroid Glands Embedded in posterior surface of thyroid gland Parathyroid hormone (PTH) Produced by chief cells In response to low concentrations of Ca2+ Figure 18–12 Parathyroid Glands Figure 10-11 Parathyroid Glands Four Effects of PTH It stimulates osteoclasts: Accelerates mineral turnover and releases Ca2+ from bone It inhibits osteoblasts: Reduces rate of calcium deposition in bone It enhances reabsorption of Ca2+ at kidneys, reducing urinary loss It stimulates formation and secretion of calcitriol at kidneys: Effects complement or enhance PTH Enhances Ca2+, PO43- absorption by digestive tract Figure 18–12 Figure 10-10 The suprarenal glands, consisting of a cortex and a medulla, cap each kidney and secrete several hormones Suprarenal (Adrenal) Glands Lie along superior border of each kidney Subdivided into Superficial suprarenal cortex: Stores lipids, especially cholesterol and fatty acids Manufactures steroid hormones: adrenocortical steroids (corticosteroids) Inner suprarenal medulla: Secretory activities controlled by sympathetic division of ANS Produces epinephrine (adrenaline) and norepinephrine Metabolic changes persist for several minutes Suprarenal Glands Mineralocorticoids For example, aldosterone: Stimulates conservation of sodium ions and elimination of potassium ions Increases sensitivity of salt receptors in taste buds Secretion responds to: Drop in blood Na+, blood volume, or blood pressure Rise in blood K+ concentration Suprarenal Glands Glucocorticoids For example, cortisol (hydrocortisone) with corticosterone: Liver converts cortisol to cortisone Secretion regulated by negative feedback Has inhibitory effect on production of Corticotropin-releasing hormone (CRH) in hypothalamus ACTH in adenohypophysis Suprarenal Glands Produces androgens under stimulation by ACTH Suprarenal Glands Figure 10-12 Suprarenal Glands Suprarenal Medulla Contains two types of secretory cells: One produces epinephrine (adrenaline): 75% to 80% of medullary secretions The other produces norepinephrine (noradrenaline): 20% to 25% of medullary secretions The pineal gland, attached to the third ventricle, secretes melatonin Pineal Gland Lies in posterior portion of roof of third ventricle Contains pinealocytes Synthesize hormone melatonin Pineal Gland Functions of Melatonin Inhibiting reproductive functions Protecting against damage by free radicals Setting circadian rhythms The endocrine pancreas produces insulin and glucagon, hormones that regulate blood glucose levels Pancreas Lies between Inferior border of stomach And proximal portion of small intestine Contains exocrine and endocrine cells Pancreas Endocrine Pancreas Consists of cells that form clusters known as pancreatic islets, or islets of Langerhans: Alpha cells produce glucagon Beta cells produce insulin Pancreas Figure 10-13 Pancreas Blood Glucose Levels When levels rise: Beta cells secrete insulin, stimulating transport of glucose across plasma membranes When levels decline: Alpha cells release glucagon, stimulating glucose release by liver Figure 10-14 Many organs have secondary endocrine functions Endocrine Tissues of Other Systems Intestines (digestive system) Kidneys (urinary system) Heart (cardiovascular system) Thymus (lymphoid system and immunity) Gonads (reproductive system) Endocrine Tissues of Other Systems Intestines Produce hormones important to coordination of digestive activities Kidneys Produce the hormones calcitriol and erythropoietin Produce the enzyme renin Endocrine Tissues of Other Systems Heart Produces natriuretic peptides (ANP and BNP): When blood volume becomes excessive Action opposes angiotensin II Resulting in reduction in blood volume and blood pressure Thymus Produces thymosins (blend of thymic hormones): That help develop and maintain normal immune defenses Endocrine Tissues of Other Systems Testes (Gonads) Produce androgens in interstitial cells: Testosterone is the most important male hormone Secrete inhibin in nurse (sustentacular) cells: Support differentiation and physical maturation of sperm Endocrine Tissues of Other Systems Ovaries (Gonads) Produce estrogens: Principle estrogen is estradiol After ovulation, follicle cells: Reorganize into corpus luteum Release estrogens and progestins, especially progesterone Endocrine Tissues of Other Systems Adipose Tissue Secretions Leptin: Feedback control for appetite Controls normal levels of GnRH, gonadotropin synthesis Resistin: Reduces insulin sensitivity Hormones interact to produce coordinated physiological responses Hormone Interactions Antagonistic (opposing) effects Synergistic (additive) effects Permissive effects: one hormone is necessary for another to produce effect Integrative effects: hormones produce different and complementary results Hormones and Growth Growth Hormone (GH) In children: Supports muscular and skeletal development In adults: Maintains normal blood glucose concentrations Mobilizes lipid reserves Hormones and Growth Thyroid Hormones If absent during fetal development or for first year: Nervous system fails to develop normally Mental retardation results If T4 concentrations decline before puberty: Normal skeletal development will not continue Hormones and Growth Insulin Allows passage of glucose and amino acids across plasma membranes Parathyroid Hormone (PTH) and calcitriol Promote absorption of calcium salts for deposition in bone Inadequate levels cause weak and flexible bones Hormones and Growth Reproductive Hormones Androgens in males, estrogens in females Stimulate cell growth and differentiation in target tissues Produce gender-related differences in: Skeletal proportions Secondary sex characteristics Hormones and Stress General Adaptation Syndrome (GAS) Also called stress response How body responds to stress-causing factors Is divided into three phases: Alarm phase Resistance phase Exhaustion phase Figure 18–18 Hormones and Stress Figure 10-15 Hormones and Stress Figure 10-15 Hormones and Stress Figure 10-15 Hormone Interactions Hormones and Behavior Can alter intellectual capabilities, memory, learning, and emotional states Affect behavior when endocrine glands are over-secreting or under-secreting Aging Causes few functional changes Decline in concentration of: Growth hormone Reproductive hormones Extensive integration occurs between the endocrine system and other body systems The Endocrine System in Perspective Functional Relationships Between the Endocrine System and Other Systems Copyright © 2010 Education, Inc. The Integumentary System protects superficial endocrine organs; epidermis synthesizes vitamin D3 The Endocrine System’s sex hormones stimulate sebaceous glands, influence hair growth, fat distribution, and apocrine sweat glands; PRL stimulates development of mammary glands; suprarenal hormones alter dermal blood flow, stimulate release of lipids from adipocytes; MSH stimulates melanocytes The Integumentary System Copyright © 2010 Education, Inc. The Skeletal System protects endocrine organs, especially in the brain, chest, and pelvic cavity The Endocrine System regulates skeletal growth: PTH and calcitonin mobilize calcium; sex hormones speed growth and close epiphyseal cartilages at puberty, and help maintain bone mass in adults The Skeletal System Copyright © 2010 Education, Inc. The Muscular System The Muscular System provides protection for some endocrine organs The Endocrine System adjusts Muscle metabolism, energy production, and growth; regulates calcium and phosphate levels in body fluids; speeds skeletal muscle growth Copyright © 2010 Education, Inc. The Nervous System The Nervous System’s hormones control secretions by the pituitary, other endocrine organs, and suprarenal medullae; secretes ADH and oxytocin The Endocrine System’s hormones affect neural metabolism; help regulate fluid and electrolyte balance; reproductive hormones influence CNS development and behaviors Copyright © 2010 Education, Inc. The Cardiovascular System The Cardiovascular System’s Vessels distribute hormones throughout the body; heart secretes ANP The Endocrine System’s hormone EPO regulates production of RBCs; several hormones elevate blood pressure; Epinephrine elevates heart rate and contraction force Copyright © 2010 Education, Inc. The Lymphoid System The Lymphoid System’s lymphocytes defend against infection and, with other WBCs, assist in repair after Injury The Endocrine System’s hormones have anti-inflammatory effects (glucocorticoids), stimulate development of lymphocytes (thymosins), and affect immune function Copyright © 2010 Education, Inc. The Respiratory System The Respiratory System provides oxygen and eliminates carbon Dioxide generated by endocrine Cells The Endocrine System’s hormones Epinephrine and NE stimulate respiration and dilate respiratory passageways Copyright © 2010 Education, Inc. The Digestive System The Digestive System provides nutrients to endocrine cells; Pancreas secretes insulin and glucagon; liver produces angiotensinogen The Endocrine System’s hormones Epinephrine and NE constrict sphincters and depress activity along digestive tract; digestive tract hormones coordinate secretions along tract Copyright © 2010 Education, Inc. The Urinary System The Urinary System’s kidney cells (1) release renin and EPO when local blood pressure declines and (2) produce calcitriol The Endocrine System’s hormones (aldosterone, ADH, and ANP) adjust fluid and electrolyte reabsorption in kidneys Copyright © 2010 Education, Inc. The Reproductive System The Reproductive System’s steroid sex hormones and inhibin suppress secretion in hypothalamus and pituitary The Endocrine System’s hypothalamic and pituitary hormones regulate sexual development and function; oxytocin stimulates contractions of the uterus and mammary glands Copyright © 2010 Education, Inc.