Regulates rate of metabolism Ion regulation: Regulates blood pH, Na+, K+, Ca+ conc. in blood

2. Functions of the Endocrine System • Regulates rate of metabolism • Ion regulation: Regulates blood pH, Na+, K+, Ca+ conc. in blood • Water balance : Regulates water balance by controlling solute conc. of blood • Immune system regulation • Heart rate and blood pressure regulation • Control of blood glucose and other nutrients • Control of reproductive functions • Uterine contractions and milk release

3. Hypothalamus Pituitary gland Thyroid Gland Parathyroid gland Adrenal glands Pancreas Pineal gland thymus gland Reproductive glands Endocrine glands

4. Part neuronal and part endocrine in function Located in the diencephalon below the thalamus Control the activities of pituitary gland Hypothalamus

5. It is also known as hypophysis Size of a pea It is attached to the hypothalamus of the brain by a stalk called infundibulum It is called the master gland because it releases hormones that affect the working of other glands such as thyroid, gonads etc. It is divided into two lobes: anterior pituitary posterior pituitary Pituitary Gland (Hypophysis)

6. Structure of the Pituitary Gland • Posterior pituitary (neurohypophysis): • extension of the hypothalamus via the infundibulum • Secretes neurohormones • Anterior pituitary (adenohypophysis) • Derive from embryonic oral cavity – Pituitary diverticulum or Rathke pouch • Synthesizes and secretes a number of hormones • Consists of three areas with indistinct boundaries: • pars distalis • pars intermedia • pars tuberalis

7. Pituitary-Hypothalamic Relationships: Posterior Lobe • The posterior lobe is a downgrowth of hypothalamic neural tissue • Has a neural connection with the hypothalamus (hypothalamic-hypophyseal tract) • Nuclei of the hypothalamus synthesize oxytocin and antidiuretic hormone (ADH) • These hormones are transported to the posterior pituitary

8. Pituitary-Hypothalamic Relationships: Anterior Lobe • The anterior lobe of the pituitary is derived from epithelial tissue of the embryonic oral cavity • There is no direct neural contact with the hypothalamus • There is a vascular connection, the hypophyseal portal system, consisting of: • Primary capillary plexus • Hypophyseal portal veins • Secondary capillary plexus

9. Activity of the Adenophypophysis • The hypothalamus sends a chemical stimulus to the anterior pituitary via Hypophyseal portal system • Releasing hormones stimulate the synthesis and release of hormones of ant. pituitary • Inhibiting hormones shut off the synthesis and release of hormones • Thus, by using neurohormones as chemical messenger Hypothalamus regulates the secretory activity of the Ant. Pituitary

10. Releasing and Inhibiting Hormones • Releasing hormones: • GHRH. Growth hormone-releasing hormone : Causes the ant. pituitary to release growth hormone • TRH. Thyrotropin-releasing hormone : Causes ant. pituitary to release thyroid-stimulating hormone (TSH) • CRH. Corticotropin-releasing hormone : Causes ant. pituitary to produce adrenocorticotropic hormone • GnRH. Gonadotropin-releasing hormone: Causes anterior pituitary to produce FSH (follicle stimulating hormone) and LH (luteinizing hormone) • PRH. Prolactin-releasing hormone : Causes the anterior pituitary to release prolactin

11. Releasing and Inhibiting Hormones • Inhibiting hormones: • GHIH. Growth hormone-inhibiting hormone, somatostatin : Causes the anterior pituitary to decrease release of growth hormone • PIH. Prolactin-inhibiting hormone : Causes the anterior pituitary to decrease release of prolactin.

12. Hormones of Posterior Pituitary: ADH • Antidiuretic hormone (ADH) : Also called vasopressin • It is an antiurination hormone • ADH helps to avoid dehydration or water overload • A. Osmoreceptors (specialized neurons of hypothalamus monitor changes in intercellular osmolality) monitor the solute concentration of the blood • With high solutes, ADH secretion increases • ADH stimulates kidney to retain water • With low solutes, ADH is not released, thus causing water loss

13. Hormones of Posterior Pituitary: ADH • Because ADH regulates blood volume its secretion is also controlled by BP changes • B. Baroreceptors (specialized neurons found in walls of atria of heart, large veins, carotid arteries, aortic arch) sense changes in blood pressure (BP) • If BP decreases, then ADH secretion is stimulated

14. Oxytocin • Oxytocin is a strong stimulant of uterine contraction • Regulated by a positive feedback mechanism to oxytocin in the blood • This leads to increased intensity of uterine contractions • Play imp. Role in the expulsion of the fetus during delivery by stimulating uterine smooth muscle contraction • Oxytocin triggers milk ejection in lactating women

15. Anterior Pituitary Hormones • Growth hormone (GH) or somatotropin • Thyroid-stimulating hormone (TSH) • Adrenocorticotropic hormone (ACTH) • Melanocyte-stimulating hormone (MSH) • Beta endorphins • Lipotropins • Luteinizing hormone (LH) • Follicle-stimulating hormone (FSH) • Prolactin

16. Growth Hormone (GH or Somatotropin) • Regulates metabolism • Regulates blood levels of nutrients after a meal and during periods of fasting • Stimulates uptake of amino acids; protein synthesis • Stimulates breakdown of fats to be used as an energy source • Stimulates glucose synthesis by liver ; which releases glucose into the blood

17. Growth Hormone • Functions in regulating growth, tissue maintenance, metabolism • Direct effect: GH binds to membrane-bound receptors on cells and causes changes within the cells • Eg. Adipose cells, Increased breakdown of lipids and decreased use of glucose as an energy source • Indirect effect: causes liver and skeletal muscle to produce somatomedins (polypeptide) • Somatomedins bind to receptors on membranes of target cells • Stimulate growth in cartilage, bone; increased synthesis of proteins in skeletal muscle

18. Growth Hormone • Two neurohormones released from hypothalamus regulate the secretion of GH • Growth hormone–releasing hormone (GHRH) stimulates GH release • Growth hormone–inhibiting hormone (GHIH) inhibits GH release • GHRH secretion in response to low blood glucose, stress, increase in certain amino acids in blood • GHIH secretions in response to high blood glucose • Peak GH levels during deep sleep; levels lower at other times of day

19. Growth hormone (GH) disorders Pituitary dwarfism results from hyposecretion of GH during childhood Gigantism results from hypersecretion of GH during childhood Acromegaly results from hypersecretion of GH during adulthood Growth hormone (GH) disorders

20. Gigantism Hypersecretion causes excessive growth as shown in these identical twins.

21. Acromegaly Face

22. TSH and Thyroid Hormones • TRH (thyrotropin-releasing hormone) from hypothalamus causes the release of TSH from anterior pituitary which causes secretion of thyroid hormones from thyroid gland • TSH secretion is controlled by TRH from hypothalamus and by thyroid hormones from thyroid gland • TRH binds to the membrane-bound receptors • Receptors respond through a G protein mechanism • and increase TSH secretion • Rising blood levels of thyroid hormones act on the pituitary and hypothalamus to block the release of TSH

23. Adrenocorticotrophic Hormone (ACTH) • CRH (Corticotropin-releasing hormone) from hypothalamus causes release of ACTH from anterior pituitary which • Causes cortisol secretion from the adrenal cortex • Causes aldosterone secretion from the adrenal cortex

24. Melanocyte Stimulating Hormone, Endorphins, and Lipotropins • ACTH, MSH, endorphins and lipotropins all derived from the same large precursor molecule when stimulated by CRH • MSH (Melanocyte-stimulating hormone) causes melanocytes to produce more melanin • Endorphins act as an analgesic; produced during times of stress • Lipotropins cause adipose cells to catabolize fat and release fatty acids into the blood

25. LH, FSH, Prolactin • Gonadotropins: glycoprotein hormones that promote growth and function of the gonads; ovaries and testes • Two gonadotrophins secrete from ant. Pituitary are: • LH (Luteinizing hormone) & FSH (Follicle stimulating hormone) : • Both hormones regulate production of gametes • sperm cells in testes and oocytes in ovaries • And reproductive hormones • Testosterone in males • Estrogen and progesterone in females • GnRH from hypothalamus stimulates LH and FSH secretion • Prolactin: role in milk production • Regulation of secretion: prolactin-releasing hormone (PRH) and prolactin-inhibiting hormones (PIH)

26. Thyroid Gland • The largest endocrine gland, located in the anterior neck, consists of two lateral lobes connected by a median tissue mass called the isthmus • Thyroid glands contains numerous follicles , filled with protein called thyroglobulin • Thyroid hormones are stored in the thyroglobulin molecules • Between the follicles other endocrine cells, the parafollicular cells are present which produces the hormone calcitonin (play imp. Role in reducing the conc. of calcium)

27. Thyroid Gland • Thyroid hormone – major metabolic hormone • Consists of two related iodine-containing compounds • T4 – thyroxine (tetraiodothyronine); has two tyrosine molecules plus four bound iodine atoms • T3 – triiodothyronine; has two tyrosines with three bound iodine atoms

28. Effects of Thyroid Hormone • TH plays a role in: • Maintaining blood pressure • Regulating tissue growth • Developing skeletal and nervous systems • Maturation and reproductive capabilities

29. Synthesis of Thyroid Hormone • Thyroglobulin is synthesized & discharged into follicle lumen • Iodides (I–) are actively taken into the cell, oxidized to iodine (I2), and released into the lumen • Iodine attaches to tyrosine (part of thyroglobulin), mediated by peroxidase enzymes, forming T1 (monoiodotyrosine, or MIT), and T2 (diiodotyrosine, or DIT)

30. Synthesis of Thyroid Hormone • Iodinated tyrosines link together to form T3 and T4 • Colloid is then endocytosed and combined with a lysosome, where T3 and T4 are cleaved and diffuse into the bloodstream

31. Transport and Regulation of TH • Both T4 and T3 bind to target receptors, but T3 is ten times more active than T4 • Peripheral tissues convert T4 to T3 • Regulation is by negative feedback

32. Thyroid hormone disorders Hyperthyroidism or Graves disease: Enlargement of thyroid gland Excess of thyroid secretion production caused by tumor Eyes bulge Patient is hyperactive, irritable, nervous etc BMR increases Treatable by surgery and radioactive Iodine Thyroid Hormone

33. Simple Goiter: ( Iodine deficiency and hormone deficiency) Thyroid over stimulated because of lack of usable thyroid hormone due to lack of iodine Results in hypothyroidism Enlarged thyroid gland

34. Hypothyroidism (Lack of stimulation by TSH): Crinitism: in child hood. Slow growth, mental retardation low body metabolism In adult: called as myxedema Results in physical and mental sluggishness puffiness of face, fatigue, obesity, dry skin

35. Regulation of Calcitonin Secretion • Produced by parafollicular cells • Secretion triggered by high Ca2+ concentration in blood; acts to decrease Ca2+ concentration • Primary target tissue: bone. Decreases osteoclast activity, lengthens life span of osteoblasts.

36. Parathyroid Glands • Embedded in thyroid • Two glands on each side • Secrete PTH: target tissues are bone, kidneys and intestines. • Increases blood calcium and phosphate levels • Stimulates osteoclasts • Promotes calcium reabsorption by kidneys, so that less calcium leaves the body in urine • Increases synthesis of vitamin D in kidney, which, in turn, increases absorption of Ca and PO4 by intestines • Regulation depends on calcium levels.

37. Adrenal Glands • Adrenal glands – paired, pyramid-shaped organs atop the kidneys • Inner medulla; outer cortex • Medulla: formed from neural crest; sympathetic. Secretes epinephrine and norepinephrine • Cortex: glandular tissue derived from embryonic mesoderm • three zones from superficial to deep • Zona glomerulosa • Zona fasciculata • Zona reticularis

38. Hormones of Adrenal Medulla • Secretory products are neurohormones: epinephrine and norepinephrine • Combine with adrenergic membrane-bound receptors • All function through G protein mechanisms • Secretion of hormones prepares body for physical activity • Effects are short-lived; hormones rapidly metabolized

39. Hormones of Adrenal Medulla • Epinephrine • Increases blood levels of glucose • Increases fat breakdown in adipose tissue • Causes dilation of blood vessels in skeletal muscles and cardiac muscles. • Epinephrine and norepinephrine increase heart rate and force of contraction; cause blood vessels to constrict in skin, kidneys, gastrointestinal tract, and other viscera

40. Hormones of Adrenal Cortex • Mineralocorticoids: Zona glomerulosa • Aldosterone produced in greatest amounts • Secreted under low BP condition • Increases rate of sodium reabsorption by kidneys thereby increasing sodium blood levels • Glucocorticoids: Zona fasciculata • Cortisol is major hormone. Increases fat and protein breakdown, increases glucose synthesis, decreases inflammatory response

41. Hormones of Adrenal Cortex • Androgens: Zona reticularis • Most gonadocorticoids secreted are androgens (male sex hormones), and the most important one is testosterone • Androgens contribute to: • The onset of puberty • The appearance of secondary sex characteristics • Sex drive in females • Androgens can be converted into estrogens after menopause

42. Pancreas • Located along small intestine and stomach; retroperitoneal • Exocrine gland • Produces pancreatic digestive juices • Endocrine gland • Consists of pancreatic islets • Composed of • Alpha cells; secrete glucagon • Beta cells; secrete insulin

43. Insulin and Glucagon • Glucagon • Target tissue is liver • Causes breakdown of glycogen and fats for energy • Insulin • Target tissues: liver, adipose tissue, muscle, and satiety center of hypothalamus • Increases uptake of glucose and amino acids by cells

44. Regulation of Blood Glucose Levels

45. Diabetes Mellitus (DM) • Results from hyposecretion or hypoactivity of insulin • The three cardinal signs of DM are: • Polyuria – huge urine output • Polydipsia – excessive thirst • Polyphagia – excessive hunger and food consumption • Hyperinsulinism – excessive insulin secretion, resulting in hypoglycemia

46. Hormones of the Reproductive System • Female: Ovaries • Estrogen and Progesterone • Uterine and mammary gland development and function, external genitalia structure, secondary sex characteristics, menstrual cycle • Inhibin • Inhibits FSH secretion • Relaxin • Increases flexibility of symphysis pubis during pregnancy • Male: Testes • Testosterone • Regulates production of sperm cells and development and maintenance of male reproductive organs and secondary sex characteristics • Inhibin • Inhibits FSH secretion • from ant. Pituitary gland

47. Pineal Gland • Small gland hanging from the roof of the third ventricle of the brain • Secretory product is melatonin • Melatonin is involved with: • Day/night cycles • Physiological processes that show rhythmic variations (body temperature, sleep, appetite)

48. Thymus • Lobulated gland located deep to the sternum • Secretes a hormone called thymosin • Essential for the development of the T lymphocytes (T cells) of the immune system

49. Other Hormone-Producing Structures • Heart – produces atrial natriuretic peptide (ANP), which reduces blood pressure, blood volume, and blood sodium concentration • Placenta – releases hormones that influence the course of pregnancy • GI tract: several hormones regulate digestion and enzyme secretion

50. Other Hormone-Producing Structures • Kidneys – secrete erythropoietin, which signals the production of red blood cells • Skin – produces cholecalciferol, the precursor of vitamin D • Adipose tissue – releases leptin, stimulates increased energy expenditure