1. The Endocrine System lammertlab.org

2. Objectives Be able to define hormone Know the three major categories of hormones Know the major endocrine glands, the hormones they secrete and their actions

3. Endocrine System: Hormones Endocrine Glands: ductless organs Hormones: – Chemical messengers – Circulate in the bloodstream – Stimulate physiological response

4. Characteristics Access to every cell Each hormone acts only on specific cells (target cells) Endocrine control slower than nervous system Endocrine and nervous systems interact Three chemical classes – Steroids – Peptides – monoamines

5. Hormone Chemistry Steroids derived from cholesterol secreted by gonads and adrenal glands Peptides and glycoproteins created from chains of amino acids secreted by pituitary and hypothalamus Monoamines derived from amino acids secreted by adrenal, pineal, and thyroid glands all hormones made from either cholesterol or amino acids with carbohydrate added to make glycoproteins. S Thr S CH 3 Testosterone O Angiotensin II Insulin (c) Peptides (a) Steroids(b) Monoamines CH 3 OH Estradiol HO I I CH 3 CHCH 2 OH CH 2 C H COOH H2NH2N O OH HO Thyroxine Epinephrine CH 2 NH OH S S S S Lys Pro Thr Tyr Phe Gly Arg Glu Gly Cys Val Leu Tyr Leu Ala Glu Val Leu His Ser Gly Cys Leu His Gln Asn Val Phe Asn Cys Tyr Asn Glu Leu Gln Tyr Leu Ser Cys lle Ser Thr Cys Gln Glu Val lle Gly Asp Arg Val Tyr lle His Pro Phe I I Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

6. Major Endocrine Organs

7. Hypothalamus and Hypophysis technologysifi.blogspot.com

8. Adenohypophysis & Neurohypophysis adenohypophysis constitutes anterior three-quarters of pituitary – two segments: anterior lobe (pars distalis) pars tuberalis small mass of cells adhering to stalk – linked to hypothalamus by hypophyseal portal system primary capillaries in hypothalamus connected to secondary capillaries in adenohypophysis by portal venules hypothalamic hormones regulate adenohypophysis cells neurohypophysis constitutes the posterior one-quarter of the pituitary – has 3 parts: median eminence, infundibulum, and the posterior lobe (pars nervosa) – nerve tissue, not a true gland nerve cell bodies in hypothalamus pass down the stalk as hypothalamo- hypophyseal tract and end in posterior lobe hypothalamic neurons secrete hormones that are stored in neurohypophysis until released into blood

9. Hypophyseal Portal System hypothalamic releasing and inhibiting hormones travel in hypophyseal portal system from hypothalamus to anterior pituitary hormones secreted by anterior pituitary (b) Portal venules Posterior lobe Anterior lobe Hypothalamic hormones Anterior lobe hormones Primary capillaries Gonadotropin-releasing hormone Thyrotropin-releasing hormone Corticotropin-releasing hormone Prolactin-inhibiting hormone Growth hormone–releasing hormone Somatostatin Follicle-stimulating hormone Luteinizing hormone Thyroid-stimulating hormone (thyrotropin) Adrenocorticotropic hormone Prolactin Growth hormone Axons to primary capillaries Neuron cell body Hypophyseal portal system: Secondary capillaries Superior hypophyseal artery Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-9

10. Hypothalamic Hormones eight hormones produced in hypothalamus – six regulate the anterior pituitary – two are released into capillaries in the posterior pituitary when hypothalamic neurons are stimulated (oxytocin and antidiuretic hormone) six releasing and inhibiting hormones stimulate or inhibit the anterior pituitary – TRH, CRH, GnRH, and GHRH are releasing hormones that affect anterior pituitary secretion of TSH, PRL, ACTH, FSH, LH, and GH – PIH inhibits secretion of prolactin, and somatostatin inhibits secretion growth hormone & thyroid stimulating hormone by the anterior pituitary

11. Hypothalamic Hormones two other hypothalamic hormones are oxytocin (OT) and antidiuretic hormone (ADH) – both stored and released by posterior pituitary – right and left paraventricular nuclei produce oxytocin (OT) – supraoptic nuclei produce antidiuretic hormone (ADH) – posterior pituitary does not synthesize them

12. Histology of Pituitary Gland Chromophobe Basophil Acidophil (b) Posterior pituitary Unmyelinated nerve fibers Glial cells (pituicytes) (a) Anterior pituitary a: © Dr. John D. Cunningham/Visuals Unlimited; b: © Science VU/Visuals Unlimited Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

13. Synthesizes and secretes six principal hormones two gonadotropin hormones – FSH (follicle stimulating hormone) stimulates secretion of ovarian sex hormones, development of ovarian follicles, and sperm production – LH (luteinizing hormone) stimulates ovulation, stimulates corpus luteum to secrete progesterone, stimulates testes to secrete testosterone TSH (thyroid stimulating hormone) – stimulates secretion of thyroid hormone ACTH (adrenocorticotropic hormone) – stimulates adrenal cortex to secrete glucocorticoids PRL (prolactin) – after birth stimulates mammary glands to synthesize milk, enhances secretion of testosterone by testes GH (growth hormone) – stimulates mitosis and cellular differentiation Anterior Pituitary Hormones

14. Hypothalamo-Pituitary-Target Organ Relationships Figure 17.6 GH ACTHTSH Liver TRH GnRH CRH Hypothalamus Adrenal cortex OvaryTestis Thyroid IGF GHRH PRL Mammary gland Fat, muscle, bone LH FSH principle hormones and target organs Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

15. Posterior Pituitary Hormones Third ventricle of brain Median eminence Hypothalamo–hypophyseal tract Stalk (infundibulum) Neurohypophysis: Posterior lobe Pars tuberalis Anterior lobe Adenohypophysis: (a) Optic chiasm Nuclei of hypothalamus: Paraventricular nucleus Supraoptic nucleus Oxytocin Antidiuretic hormone Pineal gland Cerebral aqueduct Mammillary body AnteriorPosterior Floor of hypothalamus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

16. produced in hypothalamus – transported by hypothalamo-hypophyseal tract to posterior lobe – releases hormones when hypothalamic neurons are stimulated ADH (antidiuretic hormone) – increases water retention thus reducing urine volume and prevents dehydration – also called vasopressin because it can cause vasoconstriction OT (oxytocin) – surge of hormone released during sexual arousal and orgasm stimulate uterine contractions and propulsion of semen – promotes feelings of sexual satisfaction and emotional bonding between partners – stimulates labor contractions during childbirth – stimulates flow of milk during lactation – promotes emotional bonding between lactating mother and infant Posterior Pituitary Hormones

17. Control of Pituitary Secretion Rates of secretion are not constant – regulated by hypothalamus, other brain centers, and feedback from target organs Hypothalamic and Cerebral Control – anterior lobe control - releasing hormones and inhibiting hormones from hypothalamus – posterior lobe control - neuroendocrine reflexes neuroendocrine reflex - hormone release in response to nervous system signals suckling infant  stimulates nerve endings  hypothalamus  posterior lobe  oxytocin  milk ejection

18. Growth Hormone GH has widespread effects on the body tissues – especially cartilage, bone, muscle, and fat induces liver to produce growth stimulants – insulin-like growth factors (IGF-I) or somatomedins (IGF-II) stimulate target cells in diverse tissues

19. Thymus Thymus plays a role in three systems: endocrine, lymphatic, and immune Bilobed gland in the mediastinum superior to the heart – goes through involution after puberty T cell maturation secretes hormones (thymopoietin, thymosin, and thymulin) that stimulate development of other lymphatic organs and activity of T-lymphocytes Thyroid Thymus Lung Heart Trachea Diaphragm Liver (a) Newborn (b) Adult Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

20. Thyroid Gland Anatomy Largest true endocrine gland Thyroid follicles – sacs that compose most of thyroid – follicular cells – simple cuboidal epithelium that lines follicles – secretes thyroxine (T 4 ) and triiodothyronine (T 3 ) – Increases metabolic rate, O 2 consumption, heat production (calorigenic effect), appetite, growth hormone secretion, alertness and quicker reflexes Parafollicular (C or clear) cells secrete calcitonin with rising blood calcium – stimulates osteoblast activity and bone formation Inferior thyroid vein Isthmus (a) Thyroid cartilage Thyroid gland Trachea Superior thyroid artery and vein Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

21. Histology of the Thyroid Gland thyroid follicles are filled with colloid and lined with simple cuboidal epithelial cells (follicular cells). Follicle (b) Follicular cells Colloid of thyroglobulin C (parafollicular) cells © Robert Calentine/Visuals Unlimited Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

22. Parathyroid Glands Secrete parathyroid hormone (PTH) – increases blood Ca 2+ levels promotes synthesis of calcitriol increases absorption of Ca 2+ decreases urinary excretion increases bone resorption Thyroid gland Esophagus Trachea (a) Pharynx (posterior view) Parathyroid glands Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Adipose tissue Adipocytes (b) Parathyroid capsule Parathyroid gland cells © John Cunningham/Visuals Unlimited Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

23. Adrenal Medulla adrenal medulla – inner core, 10% to 20% of gland Neuroendocrine gland – innervated by sympathetic preganglionic fibers – Chromaffin cells – when stimulated release catecholamines and a trace of dopamine directly into the bloodstream – increases alertness and prepares body for physical activity – decreases digestion and urine production

24. Adrenal Cortex surrounds adrenal medulla and produces more than 25 steroid hormones called corticosteroids or corticoids secretes 5 major steroid hormones from three layers of glandular tissue – zona glomerulosa (thin, outer layer) cells are arranged in rounded clusters secretes mineralocorticoid – regulate the body’s electrolyte balance aldosterone – zona fasciculata (thick, middle layer) cells arranged in fascicles separated by capillaries secretes glucocorticoids cortisol – zona reticularis (narrow, inner layer) cells in branching network secretes sex steroids

25. Bile duct Duodenum Tail of pancreas Head of pancreas (a) (b) Pancreatic islet Pancreatic ducts Beta cell Delta cell Alpha cell (c)Pancreatic islet Exocrine acinus c: © Ed Reschke Pancreas exocrine digestive gland and endocrine cell clusters (pancreatic islets) found retroperitoneal, inferior and posterior to stomach. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

26. Pancreatic Hormones 1-2 million pancreatic islets (Islets of Langerhans) produce hormones – other 98% of pancreas cells produces digestive enzymes insulin secreted by B or beta (  ) cells – secreted during and after meal when glucose and amino acid blood levels are rising – stimulates cells to absorb these nutrients and store or metabolize them lowering blood glucose levels – insufficiency or inaction is cause of diabetes mellitus

27. Pancreatic Hormones glucagon – secreted by A or alpha (  ) cells – released between meals when blood glucose concentration is falling – in liver, stimulates gluconeogenesis, glycogenolysis, and the release of glucose into the circulation raising blood glucose level somatostatin secreted by D or delta (  ) cells – partially suppresses secretion of glucagon and insulin – inhibits nutrient digestion and absorption which prolongs absorption of nutrients pancreatic polypeptide secreted by PP cells or F cells) – inhibits gallbladder contraction and secretion pancreatic digestive enzymes

28. The Gonads ovaries and testes are both endocrine and exocrine – exocrine product – whole cells - eggs and sperm (cytogenic glands) – endocrine product - gonadal hormones – mostly steroids ovarian hormones – estradiol, progesterone, and inhibin testicular hormones – testosterone, weaker androgens, estrogen and inhibin

29. Histology of Ovary and Testis follicle - egg surrounded by granulosa cells and a capsule (theca) Granulosa cells (source of estrogen) Egg nucleus Egg Ovary (a) Theca 100 µm © Manfred Kage/Peter Arnold, Inc. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (b) Interstitial cells (source of testosterone) Connective tissue wall of tubule Germ cells Seminiferous tubule Blood vessels Testis Sustentacular cells 50 µm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © Ed Reschke

30. Endocrine Functions of Other Organs skin – keratinocytes convert a cholesterol-like steroid into cholecalciferol liver – involved in the production of at least five hormones – converts cholecalciferol into calcidiol – secretes angiotensinogen (a prohormone) – secretes 15% of erythropoietin – hepcidin – promotes intestinal absorption of iron – source of IGF-I kidneys – plays role in production of three hormones – converts calcidiol to calcitriol, active form of vitamin D increases Ca 2+ absorption by intestine and inhibits loss in the urine – secrete renin that converts angiotensinogen to angiotensin I angiotensin II created by converting enzyme in lungs – constricts blood vessels and raises blood pressure – produces 85% of erythropoietin

31. Endocrine Functions of Other Organs heart – cardiac muscle secretes ANP and BNP in response to an increase in blood pressure – decreases blood volume and pressure – opposes action of angiotensin II stomach and small intestine secrete at least ten enteric hormones secreted by enteroendocrine cells – coordinate digestive motility and glandular secretion – cholecystokinin, gastrin, Ghrelin, and peptide YY adipose tissue secretes leptin – slows appetite placenta – secretes estrogen, progesterone and others regulate pregnancy, stimulate development of fetus and mammary glands

32. Endocrine Disorders Gigantism, Acromegaly, Pituitary dwarfism Congenital hypothyroidism, myxedema Cushing syndrome Diabetes mellitus