The pituitary gland, also known as the hypophysis, is a small gland located at the base of the brain. It has an anterior and posterior lobe with different developmental origins and functions. The anterior lobe produces several hormones that regulate other endocrine glands and other processes. These include growth hormone, thyroid stimulating hormone, adrenocorticotropic hormone, follicle stimulating hormone, luteinizing hormone, and prolactin. The posterior lobe stores and releases antidiuretic hormone and oxytocin, which are produced in the hypothalamus. The pituitary gland plays a key role in regulating many physiological processes through its interaction with the hypothalamus via the hypothalamic-hypophyseal portal system
3. Introduction Known as Hypophysis Small gland Weight is 0.5 – 1 gm Dimension is approximately (10×13×6)mm.
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5. Development Anterior pituitary Ectodermal in origin Arises from pharyngeal epithelium as an upward growth known as Rathke’s pouch Posterior pituitary Neuroectodermal in origin Arises from base of the Diencephalon as a downward diverticulumknown as Infundibulam
6. Continued… The Rathke’s pouch and downward diverticulum from hypothalamus meet midway between The roof of the buccal cavity and Base of the brain
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8. Anatomy Location Lies at the base of brain in Sella turcica. Connected with the Hypothalamus by the pituitary stalk or hypophyseal stalk.
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10. Continued… Divided into two portions: Anterior pituitary or Adenohypophysis Posterior pituitary or Neurohypopysis Between the two portions Pars intermedia is present. Very small in humans More functional in lower animals
11. Continued… Anterior and Posterior pituitary are situated in very close approximation But they are entirely different in their: Development Structure Function
12. Blood supply 2 pairs of vessels coming off the internal carotid artery Superior hypophyseal arteries Supply the Median eminence and the Infundibular stalk Inferior hypophyseal arteries Supply the Neurohypophysis with small supply to the stalk.
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14. Continued… Primary capillary network and Secondary capillary network are formed. Capillaries are fenestrated Hypothalamo-Hypophyseal portal system is formed. Carries neuropeptides from the median eminence to the Adenohypophysis where they either stimulate or inhibit hormone release
15. Continued… In Hypothalamo-Hypophyseal system there are 3 groups of hormones released at 3 sites 1. Peptide hormones synthesized by neurons by specific nuclei in hypothalamus Supraoptic Paraventricular Hormones are accumulated in the axons situated in Pars nervosa
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17. Continued… 2. Another group of peptides produced by neurons in other hypothalamic nuclei Carried in axons for temporary axonal storage and secretion in Median eminence These peptides enters primary plexus and transported to the Adenohypophysisand control hormone release
18. Continued… 3. Group of hormones consists of Proteins Glycoproteins Released from endocrine cells of Pars distalis and diffused into capillaries of the second portal system plexus
23. Continued… Chromophobe cells Do not possess granules Stained poorly Cells are not secretory in nature Believed to be the precursors of chromophil cells Comprises about 50% of total cells
24. Continued… Chromophil cells Contain large number of granules Darkly stained 2 types based on staining nature Acidophilic or Alpha cells - 35% Basophilic or Beta cells - 15%
25. Continued… 5 types based on secretory nature Somatotropeswhich secrete growth hormone Corticotropes which secrete adrenocorticotropic hormone Thyrotropes which secrete thyroid stimulating hormone Gonadotropes which secrete follicle stimulating and Luteinizing hormone Lactotropes which secrete prolactin
27. Regulation of secretion Hypothalamo-Hypophyseal Relationship Hypothalamus secretes several hormones to the Anterior pituitary Posterior pituitary Transportation of hormones To Anterior pituitary by Hypothalamo-Hypophyseal portal system To Posterior pituitary by nerve fibers of Hypothalamo-Hypophyseal tract
28. Continued… Regulation of Anterior Pituitary Secretion Hypothalamus controls Anterior Pituitary through releasing and inhibitory hormones called neurohormones
29. Continued… Releasing and Inhibitory Hormones by Hypothalamus Growth hormone releasing hormone (GHRH) Stimulates the release of growth hormone Growth hormone releasing polypeptide (GHRP) Stimulates release of GHRH and growth hormone Growth hormone inhibitory hormone (GHIH) or Somatostatin Inhibits growth hormone release
30. Continued… Thyrotropic releasing hormone (TRH) Stimulates the release of thyroid stimulating hormone Corticotropin releasing hormone (CRH) Stimulates the release of adrenocorticotropin Gonadotropin releasing hormone (GnRH) Stimulates the release of gonadotropins Prolactin inhibitory hormone (PIH) Inhibits prolactin secretion
31. Hormones Secreted by Adenohypophysis Growth hormone (GH) or Somatotropic hormone (STH) Thyroid stimulating hormone (TSH) or Thyrotropic hormone Adrenocorticotropic hormone (ACTH) Follicle stimulating hormone (FSH) Luteinizing hormone (LH in females) or Interstitial cell stimulating hormone (ICSH in males) Prolactin β- Lipotropin (recent)
