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Chapter 18 The Endocrine System Pages 603-635 Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Endocrine System Introduction Composed of glands and tissues that secrete chemical regulators called hormones Study of endocrine system is endocrinology What do you call a doctor who specializes in diseases of the endocrine system? Definitions Hormones are chemicals regulators Most are secreted into the blood and become circulating hormones They affect the functioning of other cells These “other cells” are called targets Definitions Hormones are specific for certain targets because hormones bind to specific receptors of target cells Targets range from specific tissues to widespread tissues Hormones Regulate Growth Metabolism Fluid, electrolyte, and acid-base balance Reproduction Blood pressure and other processes such as heart rate, digestion, etc. Endocrine Glands and Tissues Secrete hormones Examples Pituitary gland (hypophysis) Thyroid gland Parathyroid glands Adrenal glands Pancreas Gonads Endocrine tissues within other organs Chemistry of hormones Compounds that act as hormones are: Amino Acid Derivatives Thyroid hormones Epinephrine, Norepinephrine and Dopamine Peptide Hormones Small polypeptides and small proteins Glycoproteins Chemistry of Hormones Lipid Derivatives Eicosanoids Leukotrienes and prostaglandins Steroids Estrogen, testosterone and cortisol Hormone Secretion Stimulus (another hormone, changes in blood chemistry or nerve stimuli) Endocrine Gland ----------------Hormone Hormone secretion Blood Binds to Receptor-----------Target cell Actions Regulation of Hormone Secretion Hormone actions depend on cellular receptors Hormones that cannot enter the cell bind to cell membrane receptors Hormone acts as “first messenger” Hormone-receptor complex simulates formation of “second messenger” – usually cyclic-AMP Second messenger produces hormones action inside cell Hormone Actions – Hormone Cannot Enter Cell Hormone – 1st messenger Membranes Receptor ATP c-AMP – 2nd messenger Enzyme catalyzed reactions Actions Most Hormones such as peptides and proteins work this way Regulation of Hormone Secretion Some Hormones can enter cell Hormone binds to intracellular receptor Hormone-receptor complex enters nucleus DNA segments (genes) activated DNA codes for protein formation Protein produces hormone actions Steroids and thyroid hormones work this way Hormone Actions – Hormone Enters Cell Hormone Enters Cell Intracellular Receptor DNA in Nucleus Protein Actions Regulation of Hormone Secretion Hormone Concentration Affects Number of Receptors If hormone level high, receptor numbers decrease – called down-regulation If hormone levels low, receptor numbers increase – called up-regulation Cells become less sensitive to hormone Cells become more sensitive to hormone Up and down regulation help maintain endocrine homeostasis Control of Secretion Negative feed back Actions of Effector (Gland) decrease or inhibit stimulus Actions are usually hormone secretions Most common control Attempts to maintain normal levels of secretion Thermostat analogy Positive feed back Actions of Effector increase or continue stimulus What are two examples? Negative Feedback Pituitary Gland (Hypophysis) Small gland connected to hypothalamus Two parts Anterior pituitary (adenohypophysis) Posterior pituitary (neurohypophysis) Infundibulum – a funnelshaped structure connecting the pituitary to the hypothalamus hypothalamus ---------infundibulum anterior pituitary--------- -----posterior pituitary Pituitary Gland (Hypophysis) Posterior pituitary Hormones produced by hypothalamus and placed in posterior pituitary for secretion Secretes two hormones Oxytocin (OT) Antidiuretic hormone (ADH) Pituitary Gland Anterior pituitary largest part Produces and secretes most of the hormones Under indirect control of hypothalamus Hypothalamus secretes releasing hormones (RH) and inhibiting hormones (IH) Reach anterior pituitary through hypophyseal portal circulation Hormones of Anterior Pituitary Human Growth Hormone (hGH) Targets most cells especially skeletal and muscle tissue Actions ↑ rate of cell division for growth ↑ protein synthesis provides structure needed for growth ↑ use of fat for energy, especially during prolonged exercise ↑ rate of bone growth Growth Hormone Results in growth to adulthood and maintenance of skeleton and muscles in adults May work directly on tissues, but mostly works indirectly by stimulating formation of insulin-like growth factors (IGF’s) in liver that then target muscle, skeletal and other tissues Growth Hormone Imbalances Pituitary dwarfism Caused by hyposecretion in children Results in small body Giantism caused by hypersecretion in infants and children resulting in height of 7 to 8 feet Acromegaly caused by hypersecretion in adults resulting in distorted features Giantism Acromegaly Hormones of Anterior Pituitary Thyroid stimulating hormone (TSH) Targets thyroid gland Stimulates secretion of most thyroid hormones Adrenocorticotropic Hormone (ACTH) Targets suprarenal (adrenal) cortex Stimulates secretion of most steroids from suprarenal glands Hormones of Anterior Pituitary Prolactin (PRL) Targets mammary glands Stimulates milk production in mammary glands in concert with other hormones Gonadotropins Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) target the ovaries and testes (gonads) and control female and male reproductive physiology Hormones of the Posterior Pituitary Oxytocin (OT) Mostly targets smooth muscles of reproductive system of both sexes Actions in female Labor (uterine) contractions Release of milk from mammary glands (milk letdown) Actions in male Contraction of smooth muscle in reproductive tissue Hormones of Posterior Pituitary Antidiuretic Hormone (ADH) (vasopressin) Targets kidneys, sweat glands and arterioles Actions Causes kidneys and sweat glands to conserve water Constricts arterioles Do these actions affect blood pressure? Summary of Pituitary Hormones Question Which of the following hormones causes birth? 1. prolactin 2. oxytocin 3. ADH 4. FSH Thyroid Gland Large butterflyshaped gland in neck below voice box (larynx) Has Two lobes connected by an isthmus left lobe right lobe isthmus Histology of Thyroid Composed of many follicles filled with jellylike (colloidal) thyroglobulin protein • Thyroid hormones synthesized by follicle cells and stored in combination with thyroglobulin Thyroglobulin Thyroid Follicles Thyroid Hormones Formation Thyroglobulin protein made by follicular cells Thyroid hormones formed by addition of iodine to the thryroglobulin protein 3 or 4 iodine atoms added to thyroglobulin T3 (triiodothyronine) if 3 iodine atoms added T4 (tetraiodothyronine or thyroxine) if 4 iodine atoms added Thyroid Hormone Formation Synthesis and secretion stimulated by anterior pituitary hormone TSH (thyrotropin) When secreted, T3 and T4 combine with blood proteins for transport to target cells Once in target cells, produce metabolic effects to provide energy and stimulate growth Target Tissues and Actions of T3 & T4 Targets most tissues, but not all Actions ATP production and use of ATP for energy Normal growth Control by negative feedback Control of Thyroid Secretion Question Iodine is added to __________ to make T3 and T4. 1. thyroxine binding globulin 2. thyroglobulin 3. albumin 4. gamma globulin Imbalances of T3 & T4 Thyroid Too dwarfism (cretinism) little from birth Severe form Imbalances of T3 & T4 Hyperthyroidism Too much T3 & T4 Grave’s disease most common form Symptoms metabolic rate (MR) tachycardia body temperature (BT) anxiety & irritability goiter Exophthalmia (exophthalmos) heat intolerance weight loss Imbalances of T3 & T4 Hypothyroidism Too little T3 & T4 Symptoms metabolic rate (MR) bradycardia body temperature (BT) lethargy goiter weight gain cold intolerance swollen face (Myxedema) Imbalances of T3 & T4 Endemic goiter and iodine deficiency Insufficient dietary iodine to make T3 & T4 Endemic refers to ____________________ Lack of negative feedback causes overgrowth of thyroid Goiter results Thyroid Disorders Endemic Goiter Exophthalmia Parathyroid Glands Thyroid and parathyroid glands contol blood calcium Four parathyroid glands embedded in back of thyroid gland Control of Blood Calcium Calcitonin (CT) from thyroid lowers blood calcium by adding it to bones Parathyroid hormone from parathyroid glands increases blood calcium by removing it from bones Calcium Homeostasis Suprarenal (adrenal) Glands Located on top of kidneys Hormones adjust metabolism and affect use of nutrients ionic balance energy consumption Help maintain homeostasis against stress Suprarenal Layers Capsule Cortex – outer layer Outer CT covering Threes zones Secretes steroids Medulla – inner layer Secretes catecholamines Suprarenal Histology Cortex Secrete steroid hormones called corticoids Three Zones Glomerular (outer) zone Fascicular (middle) zone Cells in globular clusters Secretes mineralocorticoids such as aldosterone Cells form vertical elongated bundles Secrete glucocorticoids such as cortisol Reticular (inner) zone Cells form irregular, net-like pattern Secrete some sex steroids in both sexes Suprarenal Layers Capsule Cortical Zones Glomerular zone Fascicular zone Reticular zone Medulla Corticoids Mineralocorticoids from glomerular zone Aldosterone most important Regulates blood sodium, potassium and acid – increases plasma sodium and decreases plasma potassium Regulation affects fluid & electrolyte homeostasis Glucocorticoids from Fascicular Zone Principal one is cortisol Actions include: Mobilizing Body’s Resources to Resist Stress by Protein breakdown (catabolism) for energy Formation of new glucose from amino acids, lactic acid, and the glycerol part of fat molecules-gluconeogenesis Glucocorticoids from Fascicular Zone Actions include: Mobilizing Body’s Resources to Resist Stress Conversion of excess glucose to glycogen (glycogenesis) for storage in liver-provides energy reserve use of fat for energy assures glucose availability for brain Maintaining bp by making blood vessels sensitive to vasoconstriction Glucocorticoids from Fascicular Zone Actions include: Reducing inflammation Works with epinephrine (adrenaline) to reduce effects of inflammation. Various steroids including hydrocortisone, cortisone, and synthetic steroids are used medically to reduce inflammation Excess cortisol causes fat deposition in abdomen and face. Control is by negative feedback Imbalances of Glucocorticoids Addison’s disease Insufficient glucocorticoids Usually caused by own antibodies attacking suprarenal cortex Symptoms Lack of energy Weight loss Inability to resist stress John F. Kennedy had it Addison’s Disease – President Kennedy Before Steroid Treatment During Steroid Treatment Imbalances of Glucocorticoids Cushing’s Disease Excessive glucocorticoid secretion Muscle wasting Usually caused by tumors in adrenals or elsewhere Spindly arms & legs Fat redistribution Large abdomen with stretch marks Rounded face Fatty hump between shoulders Cushing’s Syndrome Before After Question Which of the following is one of the actions of cortisol? 1. increased blood Calcium 2. blood glucose 3. gluconeogenesis 4. use of fat for energy 5. 2&3 6. 3&4 Hormones of Suprarenal Medulla Catecholamines - epinephrine (adrenaline) and norepinephrine (noradrenaline) Targets – most cells React quickly to stress by: heart rate and strength blood flow to skeletal muscles, heart and brain dilation of airways (bronchodilation) fuel for energy-release of glucose from glycogen blood pressure Suprarenal Medulla Suprarenal medulla receives direct innervation from sympathetic nervous system Hormones are sympathomimetic develop from same tissue as Autonomic neurons effects mimic those of sympathetic NS cause fight-flight behavior Sympathetic stimulation increases hormone secretion by suprarenal medulla Question Which hormone increases cell division, protein synthesis and the use of fat for energy? 1. prolactin 2. hGH 3. TSH 4. ACTH Pancreas Large leaf-shaped Located in curve of small intestine and behind stomach Both endocrine and exocrine Endocrine part controls mostly blood sugar Exocrine part secretes digestive enzymes Anatomy of Pancreas Five inches long Consists of head, body & tail Most of pancreas is exocrine and secretes digestive enzymes Endocrine cells produce hormones that control blood sugar and affect metabolism and digestion Histology of Pancreas Exocrine acinar cells surround a small duct Endocrine cells form Pancreatic Islet (Islets of Langerhans) 1 to 2 million Islets Contain four types of cells Cell Types in the Pancreatic Islets Alpha cells (20%) produce glucagon Beta cells (70%) produce insulin Delta cells (5%) produce somatostatin F cells (5%) produce pancreatic polypeptide Will stress glucagon and insulin secretion Actions of Insulin Insulin lowers blood glucose by: uptake of glucose into cells synthesis of liver glycogen for storageglycogenesis Insulin also protein & fat synthesis Actions of Glucagon Glucagon increases blood glucose by: Synthesis of glucose from amino acids in liver-gluconeogenesis breakdown of liver glycogen into glucoseglycogenolysis release of glucose from liver into blood Regulation of Glucagon & Insulin Secretion High blood glucose after meal stimulates secretion of insulin and inhibition of glucagon Low blood glucose when fasting stimulates release of glucagon and inhibition of insulin Question Which of the following happens after you eat? 1. More glucose released into blood from liver 2. More glucose moves into cells 3. gluconeogenesis 4. breakdown (catabolism) of glycogen Diabetes Mellitus Insulin unavailable for uptake of glucose into cells Blood glucose becomes elevated – hyperglycemia Diabetes Mellitus Two Types: Type I (IDDM) or juvenile DM Beta cells destroyed by own immune system Insulin levels low Insulin injections required Usually develops in people younger than 20 Diabetes Mellitus Type II (NIDDM) or maturity onset DM Most common type (90%) Insulin may still be secreted but cells may be less sensitive to it Insulin injections may not be required Mostly in people over 35 who are obese May be controlled by diet Three Signs (P’s) of DM Polyuria Polydypsia Polphagia Complications of DM Cardiovascular disease Loss of vision Kidney disease Diabetic Coma Most complications linked to high glucose and acidosis Acidosis caused by excessive use of fat for energy instead of glucose