The pituitary gland is located at the base of the brain and is composed of an anterior and posterior lobe. The anterior lobe secretes hormones that regulate other endocrine glands, while the posterior lobe stores and releases hormones from the hypothalamus. The pituitary is linked to and regulated by the hypothalamus via the pituitary stalk. It plays a central role in feedback systems controlling many physiological processes.

1. PITUITARY GLAND (Hypophysis)

2. PITUITARY AND HYPOTHALAMUS are morphologically and functionally linked in the endocrine and neuroendocrine glands. they play central roles in a number of regulatory feedback system “master organs” of the ES

3. PITUITARY GLAND a pea-sized, compound endocrine gland, centrally located at the base of the brain. Sellaturcica– saddle-shaped depression of the sphenoid bone where lies the pituitary gland develops in the embryo partly from oral ectoderm and partly from the developing brain A short stalk, the infundibulum, and a vascular network connect the pituitary gland to the hypothalamus.

4. 2 FUNCTIONAL COMPONENTS Anterior lobe (adenohypophysis) - the glandular epithelial tissue - derived from an evagination of the ectoderm of the oropharynx toward the brain (Rathke’s pouch) Posterior lobe (neurohypophysis) - the neural (secretory) tissue - derived from a downgrowth of neuroectoderm of the floor of the third ventricle (diencephalon) of the developing brain.

5. ANTERIOR LOBE3 derivatives of Rathke’s pouch: Pars distalis(distal lobe) - comprises the bulk of the anterior lobe; arises from the thickened anterior wall of the pouch Pars intermedia(intermediate lobe) - a thin remnant of the posterior wall of the pouch that abuts the pars distalis Pars tuberalis(tuberal lobe) - develops from the thickened lateral walls of the pouch and forms a collar or sheath around the infundibulum

6. Posterior lobe3 components: Neural lobe (Pars nervosa, Infundbular process) - lying behind the anterior pituitary in the sellaturcica Pituitary stalk (Infundibular stem) - where axons run from the brain above Median Eminence (Infundibulum) - a funnel shape extension of the hypothalamus; where the infundibulum with its stalk is attached.

8. PITUITARY GLAND infundibular stalk (IS); pars nervosa (PN); pars distalis (PD); pars intermediate (PI); and pars tuberalis (PT)

11. I. ADENOHYPOPHYSIS (Anterior Pituitary) The cells are organized in clumps and cords separated by fenestrated sinusoidal capillaries of relatively large diameter. Have cells that respond to signals from the hypothalamus and synthesize and secrete a number of pituitary hormones (4+2) 4 hormones (“tropic hormones”) ACTH, TSH, FH, LH regulate the activity of cells in other endocrine glands throughout the body Other 2 hormones (not tropic) GH, PRL act directly on target organs that are not endocrine in nature regulates other endocrine glands and some non-endocrine tissues

12. Hormones of the Anterior Pituitary

13. Pars distalis accounts for 75% of the adenohypophysis and is covered by a thin fibrous capsule. main components are cords of epithelial cells interspersed with fenestrated capillaries Fibroblasts are present and produce reticular fibers supporting the cords of hormone-secreting cells. Common stains suggest two broad groups of cells in the pars distalis based on staining affinity: chromophils and chromophobes. chromophils- are secretory cells in which hormone is stored in cytoplasmic granules. - are also called basophils and acidophils according totheir affinity for basic and acidic dyes chromophobes - stain weakly, with few or no secretory granules, and also represent a heterogeneous group, including stem and undifferentiated progenitor cells as well as any degranulated cells present. Acidophils include the somatotropic and mammotropic cells Basophilic cells are the gonadotropic, corticotropic, and thyrotropic cells Hormones produced by the pars distalis have widespread functional activities; they regulate almost all other endocrine glands, milk secretion, melanocyte activity, and the metabolism of muscle, bone, and adipose tissue.

14. Pars distalis: acidophils, basophils, and chromophobes (a,b):acidophil cells (A), basophils (B), and chromophobes (C) (c):acidophil cells (A), basophils (B), and chromophobes (C); Cords of acidophils and basophils vary in distribution and number in different regions of the pars distalis, but are always closely associated with capillaries and sinusoids (S) in the second capillary plexus of the portal system.

15. 5 Secretory Cell Types of the pars distalis

16. Hormones of the pars distalis and their targets

17. Pars tuberalis a funnel-shaped region surrounding the infundibulum of the neurohypophysis Highly vascular region containing veins of the hypothalamohypophyseal system Most of its cells are basophilic gonadotropic cells that secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

18. Pars Intermedia a thin zone of basophilic cells between the pars distalis and the pars nervosa of the neurohypophysis, which is often invaded by these basophils develops from the dorsal wall of the hypophyseal pouch and usually contains colloid-filled cysts that represent remnants of that structure's lumen

19. Pars intermedia The pars intermedia (PI) lies between the pars distalis (PD) and the pars nervosa (PN), with many of its basophilic cells (B) usually invading the latter. Remnants of the embryonic hypophyseal pouch's lumen are usually present in this region as colloid-filled cysts (C) of various sizes. Presence of different-sized follicles filled with colloid (CF)

20. Control of Secretion in the Adenohypophysis The activities of the cells of the anterior pituitary are controlled primarily by peptide hormones produced by specialized neurons in certain hypothalamic nuclei and stored in their axons that run to the median eminence Most of these hormones are hypothalamic-releasing hormones; liberated from the axons, they are transported by capillaries to the pars distalis where they stimulate hormone synthesis and/or release. Two of the hypothalamic factors, however, act to inhibit hormone release by specific cells of the pars distalis (hypothalamic-inhibiting hormones)

21. Hypothalamic hormones regulating the anterior pituitary

22. Negative feedback loops affecting anterior pituitary secretion Hypothalamic thyrotropin-releasing hormone (TRH) stimulates secretion of thyrotropin (TSH), which stimulates synthesis and secretion of thyroid hormone (TH). In addition to their effects on target organs, TH inhibits TSH secretion from the pars distalis and TRH secretion from the hypothalamus by negative-feedback.

23. II. Neurohypophysis (Posterior Pituitary) an extension of the CNS consists of the pars nervosa (which doesn’t have secretory cells) and the infundibular stalk is composed of neural tissue, containing some 100,000 unmyelinated axons of secretory neurons situated in the supraoptic and paraventricular nuclei of the hypothalamus presence of highly branched glial cells called pituicytes that resemble astrocytes and are the most abundant cell type in the posterior pituitary; serves a supporting role in the CNS NOT an endocrine gland; stores and releases secretory products from the hypothalamus

24. Pars nervosa: Neurosecretory bodies and pituicytes The pars nervosa of the posterior pituitary consists of modified neural tissues containing unmyelinated axons supported and ensheathed by glia cells called pituicytes (P), the most numerous cell type present. The axons run from the supraoptic and paraventricular hypothalamic nuclei and have swellings called neurosecretory (Herring) bodies (NB) from which either oxytocin or vasopressin is released upon neural stimulation. The released hormones are picked up by capillaries (C) for distribution throughout the body.

26. Hormones of the Posterior Pituitary