Endocrine System

1. Endocrine System

2. Endocrine vs Exocrine Endo = within Exo = out Crine = to secrete • Exocrine glands (sweat, sebaceous, digestive) secrete products through ducts into body cavities or onto body surfaces • Endocrine glands are small, inconspicuous, ductless tissues that deposit products into the interstitial tissues that bathe the cells.

3. Hormonal Actions Regulate the metabolic function of other cells in the body • Reproduction • Growth and Development • Mobility of body defenses • Maintenance of blood electrolyte, water and nutrient balance • Regulation of cellular metabolism • Energy balance

4. Chemistry of Hormones • Body produces a large variety of hormones • Classified chemically as: • Amino acid based • Makes up the majority • Can be simple AA derivatives or long polymers • Steroids • derived from cholesterol • only gonadal and adrenocortical hormones • Prostaglandins/Eicosanoids • Derived from lipids • Leukotrienes • Protaglandins

5. Endocrine System • Focuses on the hormonal control of the body • Integrates with nervous system to maintain homeostasis milliseconds Muscle/Gland Activity Nerves stimulus received Increase in metabolic activity in most body cells Seconds to Days Endocrine Gland Stimulus received

6. Endocrine Hormones

7. Steroid Hormone Signaling

8. Amino Acid-Based Hormone Action: cAMP Second Messenger

9. Second Messenger Mechanisms • Cyclic AMP GTP in the cytoplasm binds to and “turns on” the G-protein Receptor changes shape and binds to an inactive G-protein Hormone binds to its receptor on the Target cell membrane cAMP now triggers cascade reactions to activate protein kinase, which can catalyze hundreds of reactions Activated G-protein moves along the membrane; binds and activates the enzyme Adenylate Cyclase Activated Adenylate Cyclase generates the second messenger cAMP from ATP ATP = Adenocine Triphosphate

10. How Hormones work? • Hormones signal a cell by binding to specific receptors on or in the cell • lock and key • alter chemical rxns in target cell (ex. Initiate synthesis of new protein) • different hormones can work together- synergism • different hormones can have opposite effect- antagonism

11. Prostaglandins • lipid molecules that are similar to, but do not meet usually definition of, a hormone • A through I • secreted by seminal vesicles, kidneys, lungs, iris, brain, thymus • varied functions. Ex: • PGE- regulate HCL secretion in stomach • PGF- cause uterus contractions; induce labor

12. Prostaglandins

13. Hormone Interaction at Target Cells • Multiple hormones acting upon target cells simultaneously = varied results • Permissiveness = one hormone depends upon another in order to have full effect (reproductive hormones need thyroid hormones) • Synergism = More than one hormone amplifies the desired effect (glucagon and epinephrine cause liver to release glucose) • Anatgonism = One hormone opposes the action of another(insulin and glucagon produce opposite effects on blood glucose levels)

14. Control of Hormone Release • Humoral Stimuli • Respond to blood levels of ions and nutrients • Aldosterone (Kidney) • Insulin (Pancreas) • Neural Stimuli • Respond to innervation • Sympathetic nervous system releases Epinephrine and Norepinephrine during stress • Hormonal Stimuli • Respond to release of other hormones

16. Endocrine Organs & Hormones

17. Overview of the hypothalamic-pituitary system

18. The pituitary gland (Hypophysis) hangs from diencephalon • “master gland” • stalk- infundibulum • 2 parts: • adenohypophysis (anterior pituitary)- secretes GH, TSH, PRL, LH, FSH, MSH- actually controlled by hypothalamus’ releasing hormones (ex. GnRH) • neurohypophysis (posterior pituitary)- secretes ADH and OT

19. Pituitary Gland Posterior pituitary: axons from hypothalamus Oxytocin & ADH

20. Pineal Body • Pineal Body- part of diencephalon • biological clock- sleeping; female reproductive cycle • secretes melatonin- induces sleep; secretion inhibited by sunlight

21. Thyroid Gland: Master of metabolism • below larynx • secretes Thyroid hormones • T4 • T3 • Calcitonin, CT

22. Thyroid Glands Cell Type Follicular cells Parafollicular cells Hormone Thyroid Hormones (T3,T4) Calcitonin Regulator TSH Calcitonin Target Tissue all tissues Bone Function Regulates basal metabolic rate Regulates blood Ca++ levels in and has important influences concert with parathyroid hormone. on growth and maturation. Calcitonin lowers Ca++ by inhibiting decalcification of bone.

23. Parathyroid Gland Parathyroid Glands- 4 or 5; posterior surface of thyroid; secrete PTH Acts on:  • Bone:  increases blood calcium by inhibiting osteoblast deposition of calcium and stimulating osteoclast removal of calcium.  • Kidney:  increases blood calcium by increasing calcium ion reabsorption by kidney tubular cells; inhibits reabsorption of phosphate ion from the glomerular filtrate • Small intestine:  increases the absorption of calcium from the small intestine

24. Calcium regulation • PTH - increases blood calcium by taking in out of bones, kidney, and small intestine • Calcitonin - decreases blood calcium by stimulating uptake into bone

25. Parathyroid Hormone & Ca2+

26. Adrenal Glands (aka suprarenal) top of kidneys; secrete corticosteroids which are divided into: • Mineralocorticoid- aldosterone • glucocorticoids- cortisol; cortisone • gonadocorticoids- androgens

27. What’s this stress mess?

28. The Endocrine Pancreas Islets of Langerhans • The endocrine pancreas is formed by the Islets of Langerhans that are scattered throughout the exocrine tissue. • Secretes the following: • glucagon • Insulin • Somatostatin • pancreatic polypeptide

29. A sweet battle: Insulin vs. Glucagon

30. What happens when there is no insulin?

31. Miscellaneous structures that produce hormones • Placenta- secretes hCG • thymus- thymosin and thymopoietin • gastric & intestinal mucosa- gastrin, secretin • heart- ANH