Fundamentals of Anatomy & Physiology Eleventh Edition Chapter 18 The Endocrine System Lecture Presentation by Lori Garrett, Parkland College
Learning outcomes 18-1 Explain the importance of intercellular communication, describe the mechanisms involved, and compare the modes of intercellular communication that occur in the endocrine and nervous systems. 18-2 Compare the cellular components of the endocrine system with those of other systems, contrast the major structural classes of hormones, and explain the general mechanisms of hormonal action on target organs. 18-3 Describe the location, hormones, and functions of the pituitary gland, and discuss the effects of abnormal pituitary hormone production. 18-4 Describe the location, hormones, and functions of the thyroid gland, and discuss the effects of abnormal thyroid hormone production. 2
Learning outcomes 18-5 Describe the location, hormones, and functions of the parathyroid glands, and discuss the effects of abnormal parathyroid hormone production. 18-6 Describe the location, structure, hormones, and general functions of the adrenal glands, and discuss the effects of abnormal adrenal hormone production. 18-7 Describe the location of the pineal gland, and discuss the functions of the hormone it produces. 18-8 Describe the location, structure, hormones, and functions of the pancreas, and discuss the effects of abnormal pancreatic hormone production. 3
Learning outcomes 18-9 Describe the functions of the hormones produced by the kidneys, heart, thymus, testes, ovaries, and adipose tissue. 18-10 Explain how hormones interact to produce coordinated physiological responses and influence behavior, describe the role of hormones in the general adaptation syndrome, and discuss how aging affects hormone production and give examples of interactions between the endocrine system and other organ systems. 4
An Introduction to the Endocrine System Endocrine system Endocrine cells and tissues produce about 30 different hormones (chemical messengers) Controls and coordinates body processes 5
18-1 Intercellular Communication Mechanisms of intercellular communication Direct communication Exchange of ions and molecules between adjacent cells across gap junctions Occurs between two cells of the same type Highly specialized and relatively rare Paracrine communication Chemical signals transfer information from cell to cell within a single tissue 6
18-1 Intercellular Communication Mechanisms of intercellular communication Autocrine communication Messages affect the same cells that secrete them Chemicals involved are autocrines E.g., prostaglandins secreted by smooth muscle cells cause the same cells to contract Endocrine communication Endocrine cells release chemicals (hormones) that are transported in bloodstream Alters metabolic activities of many organs 7
18-1 Intercellular Communication Target cells Have receptors needed to bind and read hormonal messages Hormones Change types, quantities, or activities of enzymes and structural proteins in target cells Can alter metabolic activities of multiple tissues and organs at the same time Affect long-term processes like growth and development 8
18-1 Intercellular Communication Synaptic communication Neurons release neurotransmitters at a synapse Leads to action potentials that are propagated along axons Allows for high-speed messages to reach specific destinations Ideal for crisis management 9
18-2 Hormones Both endocrine and nervous systems Rely on release of chemicals that bind to specific receptors on target cells Share many chemical messengers (e.g., norepinephrine and epinephrine) Are regulated mainly by negative feedback Function to preserve homeostasis by coordinating and regulating activities 10
18-2 Hormones Endocrine system Includes all endocrine cells and tissues that produce hormones or paracrines Endocrine cells release secretions into extracellular fluid Unlike exocrine cells Endocrine organs are scattered throughout body 11
Figure 18 1 Organs and Tissues of the Endocrine System (Part 1 of 2). Hypothalamus Production of ADH, OXT, and regulatory hormones Pituitary Gland Anterior lobe ACTH, TSH, GH, PRL, FSH, LH, and MSH Pineal Gland Melatonin Parathyroid Glands (located on the posterior surfaces of the thyroid gland) Parathyroid hormone (PTH) Posterior lobe Release of oxytocin (OXT) and antidiuretic hormone (ADH) 12
Figure 18 1 Organs and Tissues of the Endocrine System (Part 2 of 2). Thyroid Gland Thyroxine (T 4 ) Triiodothyronine (T 3 ) Calcitonin (CT) Adrenal Glands Medulla Epinephrine (E) Norepinephrine (NE) Cortex Cortisol, corticosterone, cortisone, aldosterone, androgens Pancreas (Pancreatic Islets) Insulin, glucagon Organs with Secondary Endocrine Functions Heart Atrial natriuretic peptide (ANP) Brain natriuretic peptide (BNP) Thymus (undergoes atrophy during adulthood) Thymosins Adipose Tissue Leptin Digestive Tract Secretes numerous hormones involved in the coordination of system functions, glucose metabolism, and appetite Kidneys Erythropoietin (EPO) Calcitriol See Chapter 21 See Chapter 22 See Chapter 25 See Chapters 19 and 26 KEY TO PITUITARY HORMONES ACTH TSH GH PRL FSH LH MSH Adrenocorticotropic hormone Thyroid-stimulating hormone Growth hormone Prolactin Follicle-stimulating hormone Luteinizing hormone Melanocyte-stimulating hormone Testis Ovary Gonads Testes (male) Androgens (especially testosterone) Inhibin Ovaries (female) Estrogens Progesterone Inhibin See Chapters 28 and 29 13
18-2 Hormones Classes of hormones Amino acid derivatives Peptide hormones Lipid derivatives 14
18-2 Hormones Amino acid derivatives (biogenic amines) Small molecules structurally related to amino acids Derivatives of tyrosine Thyroid hormones Catecholamines (epinephrine, norepinephrine, and dopamine) Derivatives of tryptophan Serotonin and melatonin 15
18-2 Hormones Peptide hormones Chains of amino acids Most are synthesized as prohormones Inactive molecules converted to active hormones before or after they are secreted Glycoproteins Proteins more than 200 amino acids long that have carbohydrate side chains (e.g., TSH, LH, FSH) Short polypeptides/small proteins 16
18-2 Hormones Peptide hormones Short-chain polypeptides ADH and OXT are each 9 amino acids long Small proteins Insulin (51 amino acids) Growth hormone (191 amino acids) Prolactin (198 amino acids) Includes all hormones secreted by hypothalamus, heart, thymus, digestive tract, pancreas, posterior lobe of the pituitary gland, etc. 17
18-2 Hormones Lipid derivatives Eicosanoids derived from arachidonic acid, a 20- carbon fatty acid Paracrines that coordinate cellular activities and affect enzymatic processes (such as blood clotting) Some eicosanoids (such as leukotrienes) have secondary roles as hormones Prostaglandins coordinate local cellular activities Converted to thromboxanes and prostacyclins in some tissues 18
18-2 Hormones Lipid derivatives Steroid hormones derived from cholesterol Include Androgens from testes in males Estrogens and progesterone from ovaries in females Corticosteroids from adrenal cortex Calcitriol from kidneys Bound to specific transport proteins in the plasma Remain in circulation longer than peptide hormones 19
18-2 Hormones Transport and inactivation of hormones Hormones may circulate freely or travel bound to special carrier proteins Free hormones remain functional for less than an hour and are inactivated when they Diffuse out of bloodstream and bind to receptors on target cells, Are absorbed and broken down by liver or kidneys, or Are broken down by enzymes in blood or interstitial fluids 20
18-2 Hormones Transport and inactivation of hormones Thyroid and steroid hormones Remain functional much longer More than 99 percent become attached to special transport proteins in blood Equilibrium state exists between free and bound forms Bloodstream contains a substantial reserve of bound hormones 21
18-2 Hormones Mechanisms of hormone action Binding of a hormone may Alter genetic activity Alter rate of protein synthesis Change membrane permeability 22
18-2 Hormones Hormone receptor A protein molecule to which a particular molecule binds strongly Different tissues have different combinations of receptors Presence or absence of a specific receptor determines hormonal sensitivity of a cell 23
18-2 Hormones Down-regulation Presence of a hormone triggers a decrease in the number of hormone receptors When levels of a particular hormone are high, cells become less sensitive to it Up-regulation Absence of a hormone triggers an increase in the number of hormone receptors When levels of a particular hormone are low, cells become more sensitive to it 24
18-2 Hormones Catecholamines and peptide hormones Not lipid soluble Unable to penetrate plasma membrane Bind to receptor proteins on outer surface of plasma membrane (extracellular receptors) Steroid and thyroid hormones Lipid soluble Diffuse across plasma membrane and bind to receptors inside cell (intracellular receptors) 25
18-2 Hormones Hormones and extracellular receptors First messenger Hormone that binds to extracellular receptor Promotes release of second messenger in cell Second messenger Intermediary molecule that appears due to hormone receptor interaction May act as enzyme activator, inhibitor, or cofactor Results in change in rates of metabolic reactions E.g., camp, cgmp, Ca 2+ 26
18-2 Hormones Process of amplification When a small number of hormone molecules binds to extracellular receptors, Thousands of second messengers may appear Magnifies effect of hormone on target cell 27
18-2 Hormones G protein Enzyme complex coupled to membrane receptor Protein binds GTP Involved in link between first messenger and second messenger 28
18-2 Hormones G proteins and camp Steps involved in increasing camp level, which accelerates metabolic activity of cell 1. Activated G protein activates adenylate cyclase 2. Adenylate cyclase converts ATP to cyclic AMP 3. Cyclic AMP functions as a second messenger 4. Generally, cyclic AMP activates kinases that phosphorylate proteins Increase in camp level is usually short-lived Phosphodiesterase (PDE) converts camp to AMP 29
Figure 18 3a G Proteins and Second Messengers. The first messenger (a peptide hormone, catecholamine, or eicosanoid) binds to a membrane receptor and activates a G protein. Hormone Protein receptor G protein (inactive) A G protein is an enzyme complex coupled to a membrane receptor that serves as a link between the first and second messenger. Hormone Protein receptor G protein activated a Effects on camp Level Many G proteins, once activated, exert their effects by changing the concentration of cyclic AMP, which acts as the second messenger within the cell. Hormone Hormone Protein receptor Acts as second camp messenger G protein activated kinase adenylate cyclase Increased production of camp ATP Protein receptor G protein activated camp PDE Enhanced breakdown of camp AMP Opens ion channels Activates enzymes If levels of camp increase, enzymes may be activated or ion channels may be opened, accelerating the metabolic activity of the cell. Reduced enzyme activity In some instances, G protein activation results in decreased levels of camp in the cytoplasm. This decrease has an inhibitory effect on the cell. First Messenger Examples Epinephrine and norepinephrine Calcitonin Parathyroid hormone ADH, ACTH, FSH, LH, TSH First Messenger Examples Epinephrine and norepinephrine 30
18-2 Hormones G proteins and calcium ions 1. G protein activates phospholipase C (PLC) 2. Triggers receptor cascade beginning with production of diacylglycerol (DAG) and inositol triphosphate (IP 3 ) from phospholipids 3. IP 3 diffuses into cytoplasm and triggers release of Ca 2+ from intracellular reserves 4. Calcium ion channels open due to activation of protein kinase C (PKC), and Ca 2+ enters cell 5. Ca 2+ binds to calmodulin, activating enzymes 31
Figure 18 3b G Proteins and Second Messengers. The first messenger (a peptide hormone, catecholamine, or eicosanoid) binds to a membrane receptor and activates a G protein. Hormone Protein receptor G protein (inactive) A G protein is an enzyme complex coupled to a membrane receptor that serves as a link between the first and second messenger. Hormone Protein receptor G protein activated b Effects on Ca 2+ Level Hormone Protein receptor G protein activated PKC Calmodulin Activates enzymes First Messenger Examples Epinephrine and norepinephrine Oxytocin Regulatory hormones of hypothalamus Several eicosanoids 32
18-2 Hormones Hormones and intracellular receptors Steroid hormones can alter rate of DNA transcription in nucleus Alterations in synthesis of enzymes or structural proteins Directly affect activity and structure of target cell Thyroid hormones bind to receptors within nucleus and on mitochondria Activate genes or change rate of transcription Increase rates of ATP production 33
Figure 18 4a Effects of Intracellular Hormone Binding. a Steroid hormones diffuse through the plasma membrane and bind to receptors in the cytoplasm or nucleus. The complex then binds to DNA in the nucleus, activating specific genes. 1 Diffusion through membrane lipids CYTOPLASM Target cell response Alteration of cellular structure or activity 2 Receptor Binding of hormone to cytoplasmic or nuclear receptors 6 Translation and protein synthesis 5 Transcription and mrna production Nuclear pore Nuclear envelope Receptor 3 4 Gene activation Binding of hormone receptor complex to DNA 34
Figure 18 4b Effects of Intracellular Hormone Binding. b Thyroid hormones enter the cytoplasm and bind to receptors in the nucleus to activate specific genes. They also bind to receptors on mitochondria and accelerate ATP production. 1 Transport across plasma membrane Target cell response Increased ATP production Alteration of cellular structure or activity 2 Receptor Binding of receptors at mitochondria and nucleus 6 Translation and protein synthesis 5 Transcription and mrna production Receptor 4 Gene activation 3 Binding of hormone receptor complex to DNA 35
18-2 Hormones Hormone secretion Mainly controlled by negative feedback Stimulus triggers production of hormone that reduces intensity of the stimulus Can be triggered by Humoral stimuli (change in extracellular fluid), Hormonal stimuli (arrival or removal of hormone), or Neural stimuli (neurotransmitters) 36
18-2 Hormones Control of hormone secretion May involve only one hormone Humoral stimuli Control hormone secretion by heart, pancreas, parathyroid gland, and digestive tract Hormonal stimuli May involve one or more intermediary steps Two or more hormones involved Neural stimuli Hypothalamus provides highest level of control 37
18-3 The Pituitary Gland Pituitary gland (hypophysis) Lies within sella turcica Sellar diaphragm isolates pituitary gland from cranial cavity Hangs inferior to hypothalamus Connected by infundibulum Releases nine important peptide hormones Bind to extracellular receptors Use camp as second messenger 38
Figure 18 5a The Orientation and Anatomy of the Pituitary Gland. Third ventricle Mammillary body Hypothalamus Optic chiasm Infundibulum Sellar diaphragm Anterior Pituitary Lobe Pars tuberalis Pars distalis Pars intermedia Posterior pituitary lobe Sphenoid (sella turcica) a Relationship of the pituitary gland to the hypothalamus 39
Figure 18 5b The Orientation and Anatomy of the Pituitary Gland. Anterior Pituitary Lobe Pars distalis Pars intermedia Posterior pituitary lobe Secretes other pituitary hormones Pituitary gland Secretes MSH Releases ADH and OXT LM 77 b Histology of the pituitary gland showing the anterior and posterior lobes 40
18-3 The Pituitary Gland The hypothalamus Regulates functions of the pituitary gland Synthesizes ADH and OXT and transports them to posterior pituitary gland for release Secretes regulatory hormones that control secretory activity of anterior pituitary gland Contains autonomic centers that exert direct control over adrenal medulla 41
Figure 18 6 Three Mechanisms of Hypothalamic Control over Endocrine Function. Production of antidiuretic hormone (ADH) and oxytocin (OXT) Secretion of regulatory hormones to control activity of the anterior lobe of the pituitary gland Control of sympathetic output to adrenal medulla HYPOTHALAMUS Preganglionic motor fibers Infundibulum Adrenal Gland Adrenal cortex Adrenal medulla Anterior lobe of pituitary gland Posterior lobe of pituitary gland Hormones secreted by the anterior lobe control other endocrine organs Release of antidiuretic hormone (ADH) and oxytocin (OXT) from posterior lobe Secretion of epinephrine (E) and norepinephrine (NE) from adrenal medulla 42
18-3 The Pituitary Gland Anterior lobe of pituitary gland Also called adenohypophysis Hormones turn on endocrine glands or support functions of other organs Has three regions Pars distalis Pars tuberalis Pars intermedia 43
18-3 The Pituitary Gland Median eminence Swelling near attachment of infundibulum Where hypothalamic neurons release regulatory hormones into interstitial fluids Hormones then enter bloodstream through fenestrated capillaries (fenestra = window) 44
18-3 The Pituitary Gland Portal vessels Blood vessels that link two capillary networks Entire complex is a portal system Hypophyseal portal system Ensures that regulatory hormones reach cells in anterior pituitary before entering general circulation 45
Figure 18 7 The Hypophyseal Portal System and the Blood Supply to the Pituitary Gland. Supra-optic nuclei Paraventricular nuclei Neurosecretory neurons Mammillary body Optic chiasm The superior hypophyseal artery delivers blood to a capillary network in the upper infundibulum. Capillary network Anterior lobe of the pituitary gland Capillary network in the anterior lobe Posterior lobe of the pituitary gland Endocrine cells Infundibulum The portal vessels deliver blood containing regulatory hormones to the capillary network in the anterior lobe of the pituitary. The inferior hypophyseal artery delivers blood to the posterior lobe of the pituitary gland. Hypophyseal veins carry blood containing the pituitary hormones to the cardiovascular system for delivery to the rest of the body. 46
18-3 The Pituitary Gland Hypothalamic control of anterior lobe 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 anterior lobe Rate of secretion is controlled by negative feedback 47
Figure 18 8a Feedback Control of Endocrine Secretion. Typical pattern of regulation when multiple endocrine organs are involved a The hypothalamus produces a releasing hormone (RH) to stimulate hormone production by other glands. Homeostatic control occurs by negative feedback. Stimulation KEY Hypothalamus Inhibition The effects of hypothalamic releasing hormones that follow the typical pattern of regulation Pituitary gland RH Releasing hormone (RH) TRH CRH GnRH Anterior lobe Hormone 1 Negative feedback Hormone 1 (from pituitary) TSH ACTH FSH LH Endocrine organ Endocrine target organ Thyroid gland Adrenal cortex Testes Ovaries Testes Ovaries Hormone 2 Target cells Hormone 2 (from endocrine target organ) Thyroid hormones Glucocorticoids Inhibin Inhibin Estrogens Androgens Progesterone Estrogens 48
18-3 The Pituitary Gland Hormones of anterior lobe Thyroid-stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH) Released due to corticotropin-releasing hormone (CRH) Prolactin (PRL) Release inhibited by prolactin-inhibiting hormone (PIH) Release stimulated by prolactin-releasing hormone (PRH) Growth hormone (GH), or somatotropin Gonadotropins 49
18-3 The Pituitary Gland Gonadotropins Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) In females, it induces ovulation and stimulates secretion of estrogens and progesterone In males, it stimulates production of androgens Production of FSH and LH is stimulated by gonadotropin-releasing hormone (GnRH) Hypogonadism Caused by low production of gonadotropins 50
Figure 18 9 Pituitary Hormones and Their Targets (Part 1 of 2). Direct Control by Nervous System Hypothalamus Indirect Control through Release of Regulatory Hormones Regulatory hormones are released into the hypophyseal portal system for delivery to the anterior lobe of the pituitary gland KEY TO PITUITARY HORMONES: ACTH TSH GH PRL FSH LH MSH ADH OXT Adrenocorticotropic hormone Thyroid-stimulating hormone Growth hormone Prolactin Follicle-stimulating hormone Luteinizing hormone Melanocyte-stimulating hormone Antidiuretic hormone Oxytocin Adrenal gland Adrenal medulla Adrenal cortex Anterior lobe of pituitary gland ACTH TSH GH Epinephrine and norepinephrine Thyroid gland Liver Somatomedins PRL FSH LH MSH Glucocorticoids (cortisol, corticosterone) Thyroid hormones (T 3, T 4 ) Bone, muscle, other tissues Mammary glands Inhibin Testes of male Ovaries of female Testosterone Estrogen Progesterone Inhibin Melanocytes (uncertain significance in healthy adults) 51
Figure 18 8a Feedback Control of Endocrine Secretion. 52
Figure 18 8b Feedback Control of Endocrine Secretion. Variations on the typical pattern of regulation of endocrine organs by the hypothalamus and anterior pituitary lobe b The regulation of prolactin (PRL) production by the anterior lobe. In this case, the hypothalamus produces both a releasing hormone (PRH) and an inhibiting hormone (PIH). When one is stimulated, the other is inhibited. PIH Anterior lobe PRH Stimulation Inhibition PRL Stimulates mammary glands 53
18-3 The Pituitary Gland Growth hormone stimulates Liver cells to release somatomedins that stimulate tissue growth Somatomedins cause skeletal muscle fibers and other cells to increase uptake of amino acids Stem cells in epithelia and connective tissues to divide Breakdown of triglycerides in adipocytes, which leads to glucose-sparing effect Breakdown of glycogen by liver cells causing diabetogenic effect 54
18-3 The Pituitary Gland Production of growth hormone is regulated by Growth hormone releasing hormone (GH RH) Growth hormone inhibiting hormone (GH IH) 55
Figure 18 8c Feedback Control of Endocrine Secretion. Variations on the typical pattern of regulation of endocrine organs by the hypothalamus and anterior pituitary lobe c The regulation of growth hormone (GH) production by the anterior lobe. When GH RH release is inhibited, GH IH release is stimulated. GH IH GH RH Stimulation Inhibition Anterior lobe GH Epithelia, adipose tissue, liver Liver Somatomedins Stimulate growth of skeletal muscle, cartilage, and many other tissues 56
18-3 The Pituitary Gland Pars intermedia Secretes melanocyte-stimulating hormone (MSH) Stimulates melanin production Virtually nonfunctional in adults except in Pregnant women Those with certain diseases 57
18-3 The Pituitary Gland Posterior lobe of the pituitary gland Also called neurohypophysis Contains unmyelinated axons of hypothalamic neurons Supra-optic and paraventricular nuclei manufacture (respectively) Antidiuretic hormone (ADH) Oxytocin (OXT) Stimulates contraction of uterus during labor Promotes ejection of milk after delivery 58
Figure 18 9 Pituitary Hormones and Their Targets (Part 2 of 2). Hypothalamus KEY TO PITUITARY HORMONES: Direct Release of Hormones Sensory stimulation Posterior lobe of pituitary gland ADH Osmoreceptor stimulation ACTH TSH GH PRL FSH LH MSH ADH OXT Adrenocorticotropic hormone Thyroid-stimulating hormone Growth hormone Prolactin Follicle-stimulating hormone Luteinizing hormone Melanocyte-stimulating hormone Antidiuretic hormone Oxytocin OXT Kidneys Males: Smooth muscle in ductus deferens and prostate gland Females: Uterine smooth muscle and mammary glands 59
Figure 18 9 Pituitary Hormones and Their Targets. Direct Control by Nervous System Hypothalamus Indirect Control through Release of Regulatory Hormones Regulatory hormones are released into the hypophyseal portal system for delivery to the anterior lobe of the pituitary gland Direct Release of Hormones Sensory stimulation Osmoreceptor stimulation KEY TO PITUITARY HORMONES: ACTH TSH GH PRL FSH LH MSH ADH OXT Adrenocorticotropic hormone Thyroid-stimulating hormone Growth hormone Prolactin Follicle-stimulating hormone Luteinizing hormone Melanocyte-stimulating hormone Antidiuretic hormone Oxytocin Adrenal gland Adrenal medulla Adrenal cortex Anterior lobe of pituitary gland ACTH TSH GH Posterior lobe of pituitary gland OXT ADH Kidneys Epinephrine and norepinephrine Thyroid gland Liver Somatomedins PRL FSH LH MSH Males: Smooth muscle in ductus deferens and prostate gland Glucocorticoids (cortisol, corticosterone) Thyroid hormones (T 3, T 4 ) Bone, muscle, other tissues Mammary glands Inhibin Testes of male Ovaries of female Females: Uterine smooth muscle and mammary glands Melanocytes (uncertain significance in healthy adults) Testosterone Estrogen Progesterone Inhibin 60
18-4 The Thyroid Gland Thyroid gland Lies inferior to thyroid cartilage of larynx Consists of two lobes connected by narrow isthmus Thyroid follicles Hollow spheres lined by cuboidal epithelium Surrounded by capillaries Cells absorb iodide ions (I ) from blood Follicle cavity contains viscous colloid C (clear) cells, or parafollicular cells 61
Figure 18 10a Anatomy of the Thyroid Gland. Hyoid bone Superior thyroid artery Thyroid cartilage of larynx Superior thyroid vein Common carotid artery Right lobe of thyroid gland Middle thyroid vein Thyrocervical trunk Trachea Internal jugular vein Cricoid cartilage of larynx Left lobe of thyroid gland Isthmus of thyroid gland Inferior thyroid artery Inferior thyroid veins Outline of clavicle Outline of sternum a Location and anatomy of the thyroid gland 62
Figure 18 10b Anatomy of the Thyroid Gland. Thyroid follicles The thyroid gland LM 122 b Histological organization of the thyroid 63
Figure 18 10c Anatomy of the Thyroid Gland. Thyroid follicle Capillary Capsule Follicle cavities C cell Cuboidal epithelium of follicle Thyroglobulin stored in colloid of follicle Thyroid follicle C cell Follicles of the thyroid gland LM 260 c Histological details of the thyroid gland showing thyroid follicles and both cell types in the follicular epithelium ATLAS: Plate 18c 64
18-4 The Thyroid Gland Thyroglobulin Globular protein synthesized by follicle cells Secreted into colloid of thyroid follicles Contains the amino acid tyrosine The building block of thyroid hormones Thyroid hormones Thyroxine (T 4 ), or tetraiodothyronine Contains four iodine atoms Triiodothyronine (T 3 ) Contains three iodine atoms 65
Figure 18 11a Synthesis and Regulation of Thyroid Hormones. 1 Follicle cavity 2 3 Thyroglobulin (contains T 3 and T 4 ) Thyroglobulin 4 Follicle cavity Endocytosis Iodide ions are absorbed from the digestive tract and delivered to the thyroid gland by the bloodstream. 2 Iodide ions diffuse to the apical surface of each follicle cell where they are converted into an atom of iodine (I0). The tyrosine portion of thyroglobulin bind the iodine atoms. Iodine atoms (I 0 ) Diffusion Tyrosine 5 Other amino acids T 4 Lysosomal digestion T3 3 Iodine-containing thyroxine molecules become linked to form thyroid hormones (T 3 and T 4 ) 4 Follicle cells remove thyroglobulin from the follicles by endocytosis. 1 TSHsensitive ion pump CAPILLARY Follicle cell Diffusion 7 6 5 Lysosomal enzymes break down the thyroglobulin, and the amino acids and thyroid hormones enter the cytoplasm. 6 The released T 3 and T 4 diffuse from the follicle cell into the bloodstream. Iodide ions (I ) T 4 & T 3 TBG, transthyretin, or albumin 7 A majority of the T 3 and T 4 bind to transport proteins. a The synthesis, storage, and secretion of thyroid hormones. 66
Figure 18 11b Synthesis and Regulation of Thyroid Hormones. Homeostasis DISTURBED BY DECREASING STIMULUS HOMEOSTASIS Normal T 3 and T 4 concentrations, normal body temperature RESTORED Homeostasis RESTORED BY INCREASING T 3 and T 4 concentrations in blood or low body temperature Receptor Hypothalamus Anterior lobe T 3 and T 4 concentrations increase in blood and body temperature rises T 3 and T 4 concentrations in blood TRH Effector Anterior lobe Anterior lobe TSH Thyroid gland Hypothalamus releases TRH Anterior lobe releases TSH Thyroid follicles release T 3 and T 4 b The regulation of thyroid secretion. 67
18-4 The Thyroid Gland Thyroid-binding globulins (TBGs) Proteins that bind about 75 percent of T 4 and 70 percent of T 3 entering the bloodstream Transthyretin and albumin Bind most of the remaining thyroid hormones About 0.3 percent of T 3 and 0.03 percent of T 4 remain unbound and free to diffuse into tissues 68
18-4 The Thyroid Gland Thyroid-stimulating hormone (TSH) Absence causes thyroid follicles to become inactive Neither synthesis nor secretion occurs Binds to plasma membrane receptors Activates key enzymes in thyroid hormone production 69
18-4 The Thyroid Gland Thyroid hormones Affect almost every cell in body Enter target cells by transport system Bind to receptors In cytoplasm On surfaces of mitochondria In nucleus In children, essential to normal development of skeletal, muscular, and nervous systems 70
18-4 The Thyroid Gland Thyroid hormones activate genes involved in glycolysis and ATP production Results in calorigenic effect Increased energy consumption and heat generation of cells Responsible for strong, immediate, and short-lived increase in rate of cellular metabolism 71
18-4 The Thyroid Gland C cells Produce calcitonin (CT) Helps regulate concentrations of Ca 2+ in body fluids Stimulates Ca 2+ excretion by kidneys Prevents Ca 2+ absorption by digestive tract 72
18-4 The Thyroid Gland Effects of thyroid hormones Elevate oxygen and energy consumption; in children, may cause rise in body temperature Increase heart rate and force of contraction Increase sensitivity to sympathetic stimulation Maintain normal sensitivity of respiratory centers to oxygen and carbon dioxide concentrations Stimulate red blood cell formation Stimulate activity in other endocrine tissues Accelerate turnover of minerals in bone 73
18-5 Parathyroid Glands Parathyroid glands Two pairs Embedded in posterior surface of thyroid gland Altogether, the four glands weigh 1.6 g Parathyroid hormone (PTH) or parathormone Secreted by parathyroid (principal) cells in response to low concentrations of Ca 2+ in blood Antagonist for calcitonin 74
Figure 18 12a Anatomy of the Parathyroid Glands. Left lobe of thyroid gland Parathyroid glands a Thyroid gland, posterior view. The location of the parathyroid glands on the posterior surface of the thyroid lobes. (The thyroid lobes are located anterior to the trachea.) 75
Figure 18 12b Anatomy of the Parathyroid Glands. Blood vessel Connective tissue capsule of parathyroid gland Parathyroid gland LM 94 Thyroid follicle b Both parathyroid and thyroid tissues. 76
Figure 18 12c Anatomy of the Parathyroid Glands. Parathyroid (principal) cells Oxyphil cells Parathyroid cells and oxyphil cells LM 600 c Parathyroid gland cells. 77
18-5 Parathyroid Glands Major effects of parathyroid hormone Stimulates osteoclasts Accelerates mineral turnover and Ca 2+ release Enhances reabsorption of Ca 2+ by kidneys, reducing urinary losses Stimulates formation and secretion of calcitriol by kidneys 78
Figure 18 13 Homeostatic Regulation of the Blood Calcium Ion Concentration (Part 1 of 2). 79
Figure 18 13 Homeostatic Regulation of the Blood Calcium Ion Concentration (Part 2 of 2). 80
18-6 Adrenal Glands Adrenal glands Lie along superior border of each kidney Superficial adrenal cortex Stores lipids, especially cholesterol and fatty acids Manufactures steroid hormones (corticosteroids) Inner adrenal medulla Secretory activities controlled by sympathetic division of ANS Produces epinephrine and norepinephrine (catecholamines) 81
Figure 18 14a The Adrenal Gland and Adrenal Hormones. Right superior adrenal arteries Right and left inferior phrenic arteries Celiac trunk Right adrenal gland Right middle adrenal artery Right inferior adrenal artery Right renal artery Right renal vein a A superficial view of the kidneys and adrenal glands Left adrenal gland Left middle adrenal artery Left inferior adrenal arteries Left adrenal vein Left renal artery Left renal vein Superior mesenteric artery Abdominal aorta Inferior vena cava 82
18-6 Adrenal Glands Adrenal cortex Subdivided into three zones Outer zona glomerulosa Middle zona fasciculata Inner zona reticularis 83
18-6 Adrenal Glands Zona glomerulosa Outer region of adrenal cortex Produces mineralocorticoids (e.g., aldosterone) Aldosterone Stimulates conservation of sodium ions and elimination of potassium ions Increases sensitivity of salt receptors in taste buds Secreted in response to Drop in blood Na +, blood volume, or blood pressure Rise in blood K + concentration 84
18-6 Adrenal Glands Zona fasciculata Produces glucocorticoids E.g., cortisol, corticosterone, and cortisone Secretion is regulated by negative feedback Glucocorticoids have inhibitory effect on production of Corticotropin-releasing hormone (CRH) in hypothalamus ACTH in anterior pituitary 85
18-6 Adrenal Glands Effects of glucocorticoids Accelerate glucose synthesis and glycogen formation, especially in liver Have anti-inflammatory effects Inhibit activities of white blood cells and other components of immune system 86
18-6 Adrenal Glands Zona reticularis Branching network of endocrine cells Forms narrow band bordering each adrenal medulla Produces small quantities of androgens under stimulation by ACTH Some are converted to estrogens in bloodstream Stimulate development of pubic hair before puberty 87
Figure 18 14b The Adrenal Gland and Adrenal Hormones. Capsule Cortex Medulla b An adrenal gland in section 88
Figure 18 14c The Adrenal Gland and Adrenal Hormones. The Adrenal Hormones Region/Zone Hormones Primary Target Hormonal Effects Regulatory Control Adrenal capsule Zona glomerulosa Mineralocorticoids, primarily aldosterone Kidneys Increase renal reabsorption of Na + and water (especially in the presence of ADH), and accelerate urinary loss of K + Stimulated by angiotensin II, elevated blood K + or fall in blood Na + ; inhibited by ANP and BNP Zona fasciculata Adrenal cortex Glucocorticoids (cortisol, corticosterone, and cortisone) Most cells Increase rates of glucose and glycogen formation by the liver; release of amino acids from skeletal muscles, and lipids from adipose tissues; promote peripheral utilization of lipids; anti-inflammatory effects Stimulated by ACTH from the anterior lobe of the pituitary gland Zona reticularis Androgens Most cells Adrenal androgens stimulate the development of pubic hair in boys and girls before puberty. Androgen secretion is stimulated by ACTH. Adrenal gland LM 140 Adrenal medulla Epinephrine (E), norepinephrine (NE) Most cells Increases cardiac activity, blood pressure, glycogen breakdown, blood glucose levels; releases lipids by adipose tissue Stimulated by sympathetic preganglionic fibers c The major regions and zones of an adrenal gland and the hormones they produce 89
18-6 Adrenal Glands Adrenal medulla Contains two types of secretory cells One produces epinephrine (E) 75 80 percent of medullary secretion The other produces norepinephrine (NE) 20 25 percent of medullary secretion 90
18-6 Adrenal Glands Results of activation of adrenal medulla In skeletal muscles, E and NE trigger mobilization of glycogen reserves And accelerate breakdown of glucose In adipose tissue, stored fats are broken down into fatty acids In the liver, glycogen molecules are broken down In the heart, stimulation of β 1 receptors speeds and strengthens cardiac muscle contraction 91
18-7 Pineal Gland Pineal gland Lies in posterior portion of roof of third ventricle Contains pinealocytes Synthesize hormone melatonin Functions of melatonin Influence circadian rhythms Inhibit reproductive functions Protect against damage by free radicals 92
Figure 18 15 Anatomy of the Pineal Gland. Pinealocytes Pineal gland LM 280 93
18-8 Pancreas Pancreas Large gland Lies in loop between inferior border of stomach and proximal portion of small intestine Mostly retroperitoneal Contains exocrine and endocrine cells 94
Figure 18 16a Anatomy of the Pancreas. Common bile duct Pancreatic duct Body of pancreas Lobule Tail Accessory pancreatic duct Head of pancreas Small intestine (duodenum) a The gross anatomy of the pancreas 95
18-8 Pancreas Exocrine pancreas Consists of clusters of gland cells called pancreatic acini and their attached ducts Takes up roughly 99 percent of pancreatic volume Gland and duct cells secrete alkaline, enzyme-rich fluid Passes through a network of ducts to lumen of digestive tract 96
18-8 Pancreas Endocrine pancreas Consists of cells that form clusters known as pancreatic islets (islets of Langerhans) Alpha (α) cells produce glucagon Beta (β) cells produce insulin Delta (δ) cells produce peptide hormone identical to GH IH Pancreatic polypeptide cells (PP cells) produce pancreatic polypeptide (PP) 97
Figure 18 16b Anatomy of the Pancreas. Pancreatic acini (clusters of exocrine cells) Pancreatic islet (islet of Langerhans) Capillary Pancreatic islet LM 400 b A pancreatic islet surrounded by exocrine cells 98
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18-8 Pancreas When blood glucose level increases, Beta cells secrete insulin Stimulating transport of glucose into target cells When blood glucose level decreases, Alpha cells secrete glucagon Stimulating glycogen breakdown and glucose release by liver 100
Figure 18 17 Homeostatic Regulation of the Blood Glucose Concentration (Part 1 of 2). 101
Figure 18 17 Homeostatic Regulation of the Blood Glucose Concentration (Part 2 of 2). 102
18-8 Pancreas Insulin Peptide hormone released by beta cells Effects on target cells Accelerating glucose uptake Accelerating glucose use and enhancing ATP production Stimulating glycogen formation Stimulating amino acid absorption and protein synthesis Stimulating triglyceride formation in adipocytes 103
18-8 Pancreas Glucagon Released by alpha cells Mobilizes energy reserves Effects on target cells Stimulating breakdown of glycogen in skeletal muscle fibers and liver cells Stimulating breakdown of triglycerides in adipocytes Stimulating production and release of glucose in liver cells (gluconeogenesis) 104
18-8 Pancreas Hyperglycemia Abnormally high glucose levels in the blood Diabetes mellitus Characterized by high glucose concentrations that overwhelm reabsorption capabilities of kidneys Glucose appears in urine Polyuria Urine volume becomes excessive 105
18-8 Pancreas Type 1 diabetes mellitus Characterized by inadequate insulin production by pancreatic beta cells Patients require daily injections or continuous infusion of insulin Approximately 5 percent of cases Usually develops in children and young adults 106
18-8 Pancreas Type 2 diabetes mellitus Most common form Usually, normal amounts of insulin are produced, at least initially Tissues do not respond properly (insulin resistance) Associated with obesity Weight loss can be an effective treatment 107
18-8 Pancreas Complications of untreated or poorly managed diabetes mellitus include Kidney degeneration Retinal damage (diabetic retinopathy) May lead to blindness Early heart attacks (3 5 times more likely) Peripheral nerve problems (diabetic neuropathies) Peripheral tissue damage due to reduced blood flow Tissue death, ulceration, infection, and amputation 108
18-9 Secondary Endocrine Functions Organs with secondary endocrine functions Intestines (digestive system) Kidneys (urinary system) Heart (cardiovascular system) Thymus (lymphatic system) Gonads (reproductive system) 109
18-9 Secondary Endocrine Functions Intestines Release hormones that coordinate digestive activities Kidneys Release the hormones calcitriol and erythropoietin (EPO) Release the enzyme renin Renin converts angiotensinogen to angiotensin I In the lungs, angiotensin-converting enzyme converts angiotensin I to angiotensin II 110
Figure 18 19a Endocrine Functions of the Kidneys. Sunlight Food Cholesterol Epidermis Cholecalciferol Liver Intermediate form Parathyroid glands Dietary cholecalciferol Digestive tract Calcitriol Kidney PTH Stimulation of calcium and phosphate ion absorption a The production of calcitriol 111
Figure 18 19b Endocrine Functions of the Kidneys. Homeostasis DISTURBED BY DECREASING STIMULUS HOMEOSTASIS Normal blood pressure and volume RESTORED Homeostasis RESTORED BY INCREASING blood pressure and volume Receptor Increase in blood pressure and volume blood pressure and volume Kidney Decreasing renal blood flow and O 2 Endocrine Response of Kidneys Erythropoietin (EPO) is released Renin is released Increased red blood cell production Increased fluid intake and retention Aldosterone secreted ADH secreted Stimulation of thirst Angiotensinogen Angiotensin I ACE Angiotensin II b The release of renin and erythropoietin, and an overview of the renin-angiotensin-aldosterone system beginning with the activation of angiotensinogen by renin 112
18-9 Secondary Endocrine Functions Heart Produces natriuretic peptides (ANP and BNP) Thymus When blood volume becomes excessive Actions opposes those of angiotensin II Resulting in reduction in blood volume and blood pressure Produces thymosin (blend of several hormones) Promotes development and maturation of lymphocytes 113
18-9 Secondary Endocrine Functions Testes Interstitial endocrine cells produce androgens Testosterone is an important androgen Nurse cells (Sertoli cells) Support differentiation and physical maturation of sperm Secrete inhibin for negative feedback 114
18-9 Secondary Endocrine Functions Ovaries Produce estrogens Principal estrogen is estradiol After ovulation, follicle cells Reorganize into corpus luteum Release estrogens and progesterone 115
18-9 Secondary Endocrine Functions Adipose tissue Produces leptin (a peptide hormone) Provides feedback control of appetite Maintains normal levels of GnRH and gonadotropin synthesis 116
18-10 Hormone Interactions When a cell receives instructions from two hormones at the same time, four outcomes are possible Antagonistic effect Result depends on balance between two hormones Synergistic effect Additive effect Permissive effect One hormone is needed for another to produce effect Integrative effect Hormones produce different but complementary results 117
18-10 Hormone Interactions Hormones important to growth Growth hormone Thyroid hormones Insulin Parathyroid hormone and calcitriol Reproductive hormones 118
18-10 Hormone Interactions Growth hormone (GH) In children Supports muscular and skeletal development In adults Maintains normal blood glucose concentrations Mobilizes lipid reserves 119
18-10 Hormone Interactions Thyroid hormones If absent during fetal development or for first year after birth, Nervous system fails to develop normally Developmental delay results If T 4 concentrations decline before puberty, Normal skeletal development does not continue 120
18-10 Hormone Interactions Insulin Allows passage of glucose and amino acids across plasma membranes Important for growing cells Parathyroid hormone (PTH) and calcitriol Promote absorption of calcium salts from bloodstream for deposition in bone Inadequate levels result in weak, flexible bones 121
18-10 Hormone Interactions 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 122
18-10 Hormone Interactions Stress Any condition that threatens homeostasis General adaptation syndrome (GAS) Also called stress response How body responds to stress-causing factors Divided into three phases Alarm phase Resistance phase Exhaustion phase 123
18-10 Hormone Interactions General adaptation syndrome Alarm phase Immediate response to stress Directed by sympathetic division of ANS Energy reserves (mainly glucose) are mobilized Body prepares fight or flight responses Epinephrine is dominant hormone 124
18-10 Hormone Interactions General adaptation syndrome Resistance phase Occurs if stress lasts longer than a few hours May last for weeks or months Glucocorticoids are dominant hormones Lipids and amino acids are mobilized for energy Glucose is conserved for use by nervous tissue 125
18-10 Hormone Interactions General adaptation syndrome Exhaustion phase Begins when homeostatic regulation breaks down Drop in K + levels due to aldosterone produced in resistance phase Failure of one or more organ systems will be fatal 126
18-10 Hormone Interactions Hormone changes Can affect behavior, intellectual capabilities, memory, learning, and emotional states Few functional changes occur with age Reproductive hormones decline in concentration Some endocrine tissues become less responsive to stimulation 127
Figure 18 21 Integration of the ENDOCRINE system with the other body systems presented so far. Integumentary System The endocrine system secretes sex hormones that stimulate sebaceous gland activity, influence hair growth, fat distribution, and apocrine sweat gland activity; PRL that stimulates development of mammary glands; adrenal hormones that alter dermal blood flow; MSH that stimulates melanocyte activity Skeletal System The Skeletal System protects endocrine organs, especially in brain, chest, and pelvic cavity The endocrine system regulates skeletal growth with several hormones; calcium homeostasis regulated primarily by parathyroid hormone; sex hormones speed growth and closure of epiphyseal cartilages at puberty and help maintain bone mass in adults Nervous System The Nervous System produces hypothalamic hormones that directly control pituitary secretions and indirectly control secretions of other endocrine organs; controls adrenal medulla; secretes ADH and oxytocin The endocrine system secretes several hormones that affect neural metabolism and brain development; hormones that help regulate fluid and electrolyte balance; reproductive hormones that influence CNS development and behaviors Endocrine System The endocrine system provides long-term regulation and adjustments of homeostatic mechanisms that affect many body functions. It: regulates fluid and electrolyte balance regulates cell and tissue metabolism regulates growth and development regulates reproductive functions responds to stressful stimuli through the general adaptation syndrome (GAS) Muscular System The Muscular System provides protection for some endocrine organs The endocrine system secretes hormones that adjust muscle metabolism, energy production, and growth; regulate calcium and phosphate levels in body fluids; speed skeletal muscle growth 128