PITUITARY GLAND ANATOMY ENDOCRINE SYSTEM

PITUARY GLAND ANATOMY

1. PITUITARY GLAND GROUP V mongera mwamba

2. PITUITARY GLAND Pituitary gland or hypophysis small endocrine gland with a d=1 cm, wt=0.5 -1 g . Located in ‘ sella turcica ’, sphenoid bone at the base of skull connected with the hypothalamus by the pituitary stalk or hypophyseal stalk ( hypothalamo-hypophysial tract/ hypothalomo -hypophyseal vessels) mongera mwamba

3. DIVISIONS OF PITUITARY GLAND Anterior pituitary or adenohypophysis Posterior pituitary or neurohypophysis Pars intermedia mongera mwamba

4. Divisions of pituitary mongera mwamba

5. DEVELOPMENT OF PITUITARY GLAND Adenohpophysis Anterior pituitary is ectodermal in origin arises from the pharyngeal epithelium as Rathke pouch neurohypophysis neuroectodermal in origin arises from hypothalamus as a downward diverticulum . mongera mwamba

6. DEVELOPMENT OF PITUITARY GLAND Rathke pouch and the downward diverticulum from hypothalamus grow towards each other and meet in the midway between the roof of the buccal cavity and base of brain. There, the two structures lie close together. mongera mwamba

7. REGULATION OF SECRETION Hypothalamo-hypophyseal Relationship Hormones secreted by hypothalamus are transported to anterior pituitary and posterior pituitary hypothalamo-hypophysial portal vessel - adenohypophysis hypothalamo-hypophyseal tract - neurohpopyhsis mongera mwamba

8. ANTERIOR PITUITARY master gland-secretes tropic hormones Parts of adenohypophysis Pars distalis Pars tuberalis Pars intermedia mongera mwamba

9. Histological structure Chromophobe cells aggranular Stain poorly form 50% of total cells in anterior pituitary cells are not secretory in nature are precursors of chromophil cells . mongera mwamba

10. Histological structure Chromaphil cells contain large number of granules darkly stained Classes of chromaphil cells a)Based on staining properties Acidophilic cells or alpha cells - 35% Basophilic cells or beta cells - 15%. mongera mwamba

11. Classification of anterior pituitary cells Based on secretory nature Somatotropes - growth hormone (GH) Corticotropes - adrenocorticotropic hormone (ACTH) Thyrotropes - thyroid-stimulating hormone (TSH) Gonadotropes - FSH and LH Lactotropes - prolactin mongera mwamba

12. Classification of anterior pituitary cells Somatotropes and lactotropes are acidophilic cells others are basophilic cells Somatotropes form 30 % to 40% of the chromophil cells NB: pituitary tumors that secrete large quantities of human growth hormone are called acidophilic tumors. mongera mwamba

13. REGULATION OF ANTERIOR PITUITARY SECRETION Hypothalamus control adenohypophysis by neurohormones releasing hormones inhibitory hormones (factors ) Special hypothalamic nerve cells send their nerve fibers (axons) to median eminence and tuber cinereum. mongera mwamba

14. REGULATION OF ANTERIOR PITUITARY SECRETION These nerve cells synthesize the hormones and release them into median eminence From here, the hormones are transported by blood via hypothalamo-hypophyseal portal vessels to anterior pituitary mongera mwamba

15. Hypothalamic hormones Growth hormone-releasing hormone ( GHRH)-Stimulates the release of growth hormone Growth hormone-releasing polypeptide ( GHRP)-Stimulates the release of GHRH and growth hormone Growth hormone-inhibitory hormone (GHIH) or somatostatin- Inhibits the growth hormone release Thyrotropic-releasing hormone ( TRH)-Stimulates- the release of thyroid stimulating hormone mongera mwamba

16. Hypothalamic hormones Corticotropin-releasing hormone (CRH)-Stimulates the release of adrenocorticotropic hormone Gonadotropin-releasing hormone (GnRH)-Stimulates the release of gonadotropins : FSH and LH Prolactin-inhibitory hormone (PIH): Inhibits prolactin secretion. It is believed that PIH is dopamine. mongera mwamba

17. ANTERIOR PITUITARY HORMONES Growth hormone (GH) or somatotropic hormone (STH) Thyroid-stimulating hormone (TSH) or thyrotropic hormone Adrenocorticotropic hormone ( ACTH ) Beta endorphins-synthesized from proopiomelanocortin (CRH-hypothalamus) Follicle-stimulating hormone ( FSH) mongera mwamba

18. ANTERIOR PITUITARY HORMONES Luteinizing hormone (LH) in females or interstitial cell- stimulating hormone (ICSH) in males Prolactin β- lipotropin mongera mwamba

19. ANTERIOR PITUITARY HORMONES Tropic Hormones First five hormones of anterior pituitary stimulate the other endocrine glands. Growth hormone also stimulates the secretory activity of liver and other tissues. Therefore, these five hormones are called tropic hormones. Prolactin is concerned with milk secretion. mongera mwamba

20. ANTERIOR PITUITARY HORMONES Gonadotropic Hormones Follicle-stimulating hormone (FSH) luteinizing hormone (LH) mongera mwamba

21. Posterior pituitary mongera mwamba

22. Neurohypophysis Parts of posterior pituitary Pars nervosa or infundibular process Neural stalk or infundibular stem Median eminence . Pars tuberalis of anterior pituitary and the neural stalk of posterior pituitary together form the hypophyseal stalk . mongera mwamba

23. Neurohypophysis HISTOLOGY Neural cells – pituicytes, derived from glial cells, supportive cell, non-secretory unmyelinated nerve fibers- magnocellular nuclei numerous blood vessels, hyaline bodies, neuralgia cells and mast cells. mongera mwamba

24. HORMONES OF POSTERIOR PITUITARY Neurohormones : Antidiuretic hormone (ADH) or vasopressin Oxytocin They are synthesized in the hypothalamus and transported in neurosecretory ganules as neurophysin complexes through hypothalamo-hypophysial tract Stored as Herring bodies , in intimate contact with blood capillaries, in neurohypophysis mongera mwamba

25. Neurohypophysis Source of posterior pituitary hormones ADH (vasopressin) Mainly from supraoptic nucleus Some produced by paraventricular cells Oxytocin mainly paraventricular nucleus supraoptic nucleus - small quantity mongera mwamba