Pituitary gland.pptx functional anatomy of pituitary

functional anatomy of pituitary gland

1. Pituitary gland: Functional anatomy By Shama Praveen

2. Pituitary gland Physiologically, the pituitary gland is divisible into two distinct portions: the anterior pituitary, also known as the adenohypophysis , and the posterior pituitary, also known as the neurohypophysis . Adenohypophysis is divided into 3parts. Pars distalis Pars intemedia Pars tuberalis Neurohypophysis consists of 3 components: Median eminence Infundibular stem Infundibular process (pars nervosa)

3. Adenohypophysis is influenced by hormones which comes from the hypothalamus via the portal vessels: Hypothalamo - hypophyseal portal vessels. Neurohypophysis by neurons : Hypothalamo - hypophyseal neural tract which convey hormones directly from hypothalamic nuclei for storage in the posterior lobe. These unmyelinated nerve tracts arise from supraoptic and paraventricular nuclei within the hypothalamus. The origin of the anterior pituitary from the pharyngeal epithelium ( rathke’s pouch) explains the epithelioid nature of its cells, and the origin of the posterior pituitary from neural tissue explains the presence of large numbers of glial-type cells in this gland. An additional polypeptide, β-lipotropin (β-LPH), is secreted with ACTH, but its physiologic role is unknown. But helps in enkephalins synthesis. (AK jain )

4. Intermediate lobe: (pars intermedia) Secretes α & β melanocyte stimulating hormone (α & β MSH, melanotropin, intermedin ). Anterior pituitary hormones are all trophic hormones which means pertaining to food of nourishment.

5. 1. Somatotropes —human growth hormone ( hGH ) 2. Corticotropes—adrenocorticotropic hormone (ACTH) 3. Thyrotropes—thyroid-stimulating hormone (TSH) 4. Gonadotropes —gonadotropic hormones, which include both luteinizing hormone (LH) and folliclestimulating hormone (FSH) 5. Lactotropes —prolactin (PRL)

6. Portal system It is a specialized region of the circulation consisting of two sets of capillaries directly connected by the set of large blood vessels. Hormones secreted into portal system have a distinct advantage. A much small amount of hormone can be secreted into general circulation is rapidly diluted by total blood volume of 5L. In this way, a small number of neurosecretory neurons in the hypothalamus can effectively control the anterior pituitary The neurons found in the anterior lobe are mainly the post ganglionic sympathetic fibers that innervate the blood vessels. The blood supply to the anterior lobe is derived from portal vessels. This system begins and ends in capillaries without going through the heart and is therefore a true portal system.

7. Growth hormone The long arm of human chromosome 17 contains the growth hormone- hCS cluster that contains five genes: one, hGH -N, codes for the most abundant (“normal”) form of growth hormone; a second, hGH -V, codes for the variant form of growth hormone; two code for human chorionic somatomammotropin ( hCS ); and the fifth is probably an hCS pseudogene. Only hGH -N is secreted by the pituitary; hGH -V and hCS are primarily products of the placenta, and as a consequence are only found in appreciable quantities in the circulation during pregnancy. GH, also called somatotropic hormone or somatotropin, is a small protein molecule that contains 191 amino acids in a single chain and has a molecular weight of 22,005. It causes growth of almost all tissues of the body that are capable of growing. It promotes increased sizes of the cells and increased mitosis, The anterior pituitary also contains folliculostellate cells that send processes between the granulated secretory cells. These cells produce paracrine factors that regulate the growth and function of the secretory cells.

8. The secretion of growth hormone is highly episodic, varying on a minute to minute basis. Most normal children experience episodes or bursts of GH secretion throughout the day, most prominently within the first several hours of sleep. The circulating GH concentration may be upto 100 fold higher during the burst of GH secretion. The pattern of bursts depends on sleep- wake patterns not on light dark patterns.

9. The basal plasma growth hormone level measured by radioimmunoassay in adult humans is normally less than 3 ng/ mL. This represents both the protein-bound and free forms. Growth hormone is metabolized rapidly, at least in part in the liver. The half-life of circulating growth hormone in humans is 6–20 min, and the daily growth hormone output has been calculated to be 0.2–1.0 mg/d in adults. Mode of action: The receptor that mediates the cellular effects of growth hormone has a large extracellular portion, a transmembrane domain, and a large cytoplasmic portion. GH receptor belongs to cytokine family of receptors. its activation of the JAK2–STAT pathway. JAK2 is a member of the Janus family of cytoplasmic tyrosine kinases. STATs (for signal transducers and activators of transcription) are a family of cytoplasmic transcription factors that, upon phosphorylation by JAK kinases, migrate to the nucleus where they activate various genes. JAK–STAT pathways are known also to mediate the effects of prolactin and various other growth factors.

10. JAK2 -STAT PATHWAY

11. Control of growth hormone secretion The release of GH is under control of two hypothalamic hormones GHRH &GHIH Stimuli that increases GH secretion hypoglycemia 2- deoxy glucose Moderate to severe exercise Fasting Estrogen, androgens and decrease in FFA concentration. Increase in circulating levels of. Amino acids Glucagon Emotional and stressful stimulus Deprived of REM sleep Increase in dopamine and norepinephrine b) Stimuli that decrease GH secretion GHIH (somatostatin) found in δ -cells of pancreatic islets of Langerhans. It also blocks the secretion of insulin,glucagon and gastrin and inhibits the intestinal absorption of glucose producing a state of hypoglycemia.

12. Growth hormone also increases circulating IGF-I, and IGF-I in turn exerts a direct inhibitory action on growth hormone secretion from the pituitary. It also stimulates somatostatin secretion

13. Actions of GH Stimulation of growth of bone, cartilage and connective tissue.