The Endocrine System: Part B

1. 16 The Endocrine System: Part B

2. Pineal gland Hypothalamus Pituitary gland Thyroid gland Parathyroid glands (on dorsal aspect of thyroid gland) Thymus Adrenal glands Pancreas Ovary (female) Testis (male) Figure 16.1

3. Major Endocrine Organs: Pituitary (Hypophysis) • Pituitary gland – two-lobed organ that secretes nine major hormones • Neurohypophysis – posterior lobe (neural tissue) and the infundibulum • Receives, stores, and releases hormones from the hypothalamus • Adenohypophysis – anterior lobe, made up of glandular tissue • Synthesizes and secretes a number of hormones

4. Communication between hypothalamus and hypophysis • With the neurohypophysis via tracts (what are tracts) • With the adenohypophysis via blood portal system • The hypothalamus sends a chemical stimulus to the anterior pituitary • Releasing hormones stimulate the synthesis and release of hormones • Inhibiting hormones shut off the synthesis and release of hormones

5. Pituitary-Hypothalamic Relationships: anterior Lobe • The hypophyseal portal system, consisting of: • The primary capillary plexus in the infundibulum • The hypophyseal portal veins • The secondary capillary plexus

6. Neurohypophysis hormones Hormones that are produced in the hypothalamus and stored in the neurohypophysis

7. Anterior pituitary hormones • The hormones of the anterior pituitary (7) are called tropic/trophic hormones because they “turn on” other glands or organs

8. Anterior pituitary hormones

9. Thyroid Gland The thyroid gland on the anterior side of the neck. The thyroid gland has a right lobe and a left lobe connected by a narrow isthmus http://webanatomy.net/histology/endocrine_histology.htm

10. Thyroid gland histology • The thyroid gland contains thyroid follicles lined with simple cuboidal epithelium – follicular cells • The follicle cells surround a follicular cavity that contain the colloid; a fluid that contains a large amount of proteins - thyroglobulin that contain the amino acid tyrosine • Each follicle is surrounded by a capillary network. • Between the follicles C cells/parafollicular cells can be found

11. Other effects of Thyroid Hormone • TH is concerned with: • Activate genes that code for enzymes that are involved in glycolysis (Glucose oxidation) • Increasing metabolic rate of the cells • Increase heat production (calorigenic effect) • Although the major thyroid hormone that is being produced is the T4 (90%) T3 is the one responsible for the TH effects • Enzymes in the kidneys, liver and other tissues convert T4 to T3

12. Hypothalamus TRH Anterior pituitary TSH Thyroid gland Thyroid hormones Stimulates Target cells Inhibits Figure 16.7

13. Calcitonin • A peptide hormone produced by the parafollicular, or C cells • Lowers blood calcium levels • Antagonist to parathyroid hormone (PTH)

14. Calcitonin • Calcitonin targets the skeleton, where it: • Inhibits osteoclast activity (and thus bone resorption) and release of calcium from the bone matrix • Stimulates calcium uptake and incorporation into the bone matrix • Regulated by a humoral (calcium ion concentration in the blood) negative feedback mechanism

15. Parathyroid Glands • Four to eight tiny glands embedded in the posterior aspect of the thyroid • Contain oxyphil cells (function unknown) and chief cells that secrete parathyroid hormone (PTH) or parathormone • PTH—most important hormone in Ca2+ homeostasis

16. Effects of Parathyroid Hormone • PTH release increases Ca2+ in the blood as it: • Stimulates osteoclasts to digest bone matrix • Enhances the reabsorption of Ca2+ and the secretion of phosphate by the kidneys • Increases absorption of Ca2+ by intestinal mucosal • Rising Ca2+ in the blood inhibits PTH release

17. Adrenal (Suprarenal) Glands • Adrenal glands – paired, pyramid-shaped organs atop the kidneys • Structurally and functionally, they are two glands in one • Adrenal medulla – neural tissue; part of the sympathetic nervous system • Adrenal cortex - three layers of glandular tissue that synthesize and secrete corticosteroids

18. Adrenal Cortex • Synthesizes and releases steroid hormones called corticosteroids • Different corticosteroids are produced in each of the three layers • Zona glomerulosa – glumerulus- little ball. Secretes mineralocorticoids – main one aldosterone • Zona fasciculata – glucocorticoids (chiefly cortisol) • Zona reticularis – gonadocorticoids (chiefly androgens)

19. Zona glumerulosa - Mineralocorticoids • Aldosterone secretion is stimulated by: • Rising blood levels of K+ • Low blood Na+ • Decreasing blood volume or pressure • Increases Na+ and water in the kidneys

20. Zona fasciculata - Glucocorticoids • This adrenal layer responds to ACTH (which endocrine glands secretes ACTH?) • Main hormone secreted are the Cortisol • Glucocorticoids accelerate the rates of glucose synthesis and glycogen formation – especially in the liver • Clucocorticoids also have anti-inflammatory effect – inhibit the activities of WBC (use?)

21. Zona reticularis Gonadocorticoids (Sex Hormones) • Most gonadocorticoids secreted are androgens (male sex hormones), and the most important one is testosterone • Androgens can be converted into estrogens after menopause • Both hormones from the kidney origin do not effect sexual characteristics

22. Adrenal Medulla • Secrete epinephrine and norepinephrine • Epinephrine is the more potent stimulator of the heart and metabolic activities • Norepinephrine is more influential on peripheral vasoconstriction and blood pressure

23. Pancreas • A triangular gland, which has both exocrine and endocrine cells, located behind the stomach • Acinar cells produce an enzyme-rich juice used for digestion (exocrine product) • Pancreatic islets (islets of Langerhans) produce hormones (endocrine products)

24. Pancreas – islets of Langerhans cells • The islets contain two major cell types: • Alpha () cells that produce glucagon • Beta () cells that produce insulin • The islets also contain • Delta cells – produce a peptide hormone identical to GH inhibiting hormone (GH-IH). That hormone supresses the release of glucagon and insulin and slows food absorptopn and digestive enzyme secretion • F cells – Produce the hormone pancreatic polypeptide (pp) that inhibits gallbladder contractions and regulate the production of some pancreatic enzymes

25. Glucagon • A 29-amino-acid polypeptide hormone that is a potent hyperglycemic agent • Its major target is the liver, where it promotes: • Glycogenolysis – the breakdown of glycogen to glucose • Gluconeogenesis – synthesis of glucose from lactic acid and noncarbohydrates • Release of glucose to the blood from liver cells

26. Effects of Insulin Binding • Insulin effects: • Acceleration of glucose uptake as a result from an increase of the number of glucose carrier proteins • Acceleration of glucose utilization and increased ATP production • Stimulation of glycogen formation in the liver and muscle cells • Inhibits glycogenolysis (break down of glycogen) and gluconeogenesis (glucose building) • Stimulation of amino acid absorption and protein synthesis • Stimulation of triglyceride formation in adipose tissue • As a result glucose concentration in the blood decreases

27. Other Hormone-Producing Structures • Heart – produces atrial natriuretic peptide (ANP), which reduces blood pressure, blood volume, and blood sodium concentration • Gastrointestinal tract – enteroendocrine cells release local-acting digestive hormones • Placenta – releases hormones that influence the course of pregnancy • Kidneys – secrete erythropoietin, which signals the production of red blood cells • Skin – produces cholecalciferol, the precursor of vitamin D • Adipose tissue – releases leptin, which is involved in the sensation of satiety, and stimulates increased energy expenditure