pituitary gland is master gland
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- 1.pituitary gland is Master Gland
2. 3. anterior pituitary(adenohypophysis) classical gland composed predominantly of cellsthat secrete protein hormones.posterior pituitary(neurohypophysis) -not really an organ, but an extension of the hypothalamus. composed largely of the axons of hypothalamic neurons which extend downward as a large bundle behind the anterior pituitary. It also forms the so-calledpituitary stalk , which appears to suspend the anterior gland from the hypothalamus. 4. 5. 6. Hormones of the Pituitary pituitary gland - pea-sized structure located at the base of the brain. In humans-two lobes:Anterior LobePosterior Lobe 7. The Anterior Lobe Anterior lobe contains 6 types of secretory cells, all but one of which are specialized to secrete only one of the anterior lobe hormones.All of them secrete their hormone in response to hormones reaching them from the hypothalamus of the brain 8. Thyroid Stimulating Hormone (TSH) TSH (also known as thyrotropin) glycoportein consisting of:achain of 112 amino acids andanchain of 89 amino acids. chain is identical to that found in 2 other pituitary hormones, FSH and LH as well as in hCG. 9. The secretion of TSH is- stimulatedby the arrival of thyrotropin releasing hormone (TRH) from the hypothalamus.- inhibitedby the arrival of somatostatin from the hypothalamus. As name suggests, TSH stimulates the thyroid gland to secrete THs 10. Thyroid-Stimulating Hormone (Thyrotropin) TSH (thyrotropin)- is secreted fromthyrotrophs TSH receptors (GPCR) on epithelial cells in the thyroid gland, and stimulates that gland tosynthesize and release thyroid hormones. TSHis a glycoprotein hormone2 subunits which are non-covalently bound to one another. 11. Thyroid-Stimulating Hormone (Thyrotropin) Found in pituitaries of all vertebrates Most important role is control of thyroid gland to liberate thyroid hormones Also inducesmetamorphismin amphibians Important role inthermogenesisin mammals 12. The most important controller of TSH secretion isthyroid-releasing hormone. TRH is secreted by hypothalamic neurons into hypothalamic-hypophyseal portal blood, finds its receptors on thyrotrophs in the anterior pituitary and stimulates secretion of TSH.One interesting aspect of TRH is that it is only 3 amino acids long. Its basic sequence is glutamic acid-histidine-proline, althoughboth ends of the peptide are modified . 13. 14. Some people develop antibodies against their own TSH receptors. When these bind the receptors, they "fool" the cell into making more T4 causing hyperthyroidism. The condition is calledthyrotoxicosis or Graves' disease . 15. A deficiency of TSH causes hypothyroidism: inadequate levels of T4 (and thus of T3 ).Recombinant human TSHhas recently become available to treat patients with TSH deficiency.Some people inherit mutant TSH receptors. This can result in hypothyroidism. A deficiency of TSH, or mutant TSH receptors, have also been implicated as a cause of osteoporosis.Mice, whose TSH receptors have been knocked out, develop increased numbers of bone-reabsorbing osteoclasts. 16. Follicle-Stimulating Hormone (FSH) FSH is a heterodimeric glycoprotien consisting of- same chain found in TSH (and LH)-chain of 115 amino acids (gives it its unique properties) Synthesis and release of FSH is triggered by the arrival from the hypothalamus of gonadotropin releasing hormone GnRH 17. Effect of FSH depends on one's sexFSH in females In sexually-mature females, FSH (assisted by LH) acts on thefollicle to stimulate it to release estrogens FSH in males In sexually-mature males, FSH acts on spermatogonia (with the aid of testosterone) stimulating the production of sperm. 18. Luteinizing Hormone (LH) LH is synthesized within the same pituitary cells as FSH and under the same stimulus (GnRH).Heterodimeric glycoprotein-same 89 aasubunit found in FSH & TSH-chain of 115 aa that is responsible for its properties. 19. Effects of LH also depend on sex LH in females In sexually-mature females, LHstimulates the follicle tosecrete estrogenin the first of the menstrual cyclea surge of LHtriggers the completion of meiosis I of the egg and its release (ovulation) in the middle of the cyclestimulatesthe now-empty follicle to develop into thecorpus luteum , which secretes progesterone during the latter of the menstrual cycle. 20. LH in males LH acts on the interstitial cells (also known as Leydig cells) of the testes stimulating them to synthesize and secrete the male sex hormone, testosterone.LH in males is also known as interstitial cell stimulating hormone (ICSH). 21. Gonadotropins: Luteinizing and Follicle Stimulating Hormones LH and FSH are called gonadotropins becausestimulate the gonadsin males-the testes in females-the ovaries.**Not necessary for life*** Essential for reproduction.Both hormones are secreted fromgonadotrophsin the anterior pituitary. Most gonadotrophs secreteonlyLH or FSH, but some appear to secrete both hormones. 22. Physiologic Effects of Gonadotropins Physiologic effects of the gonadotrophins are known only in the ovaries and testes.Together, then regulate many aspects of gonadal function in both males and females. 23. Luteinizing Hormone In both sexes, LH stimulates secretion of sex steroids from the gonads.In thetestes,LH binds to receptors on Leydig cells, stimulating synthesis and secretion of testosterone.Theca cells in theovaryrespond to LH stimulation by secretion of testosterone, which is converted into estrogen by adjacent granulosa cells. 24. Control of Gonadotropin Secretion principle regulator of LH and FSH secretion isGnRH. GnRH is a 10 aa peptide that is synthesized and secreted from hypothalamic neurons and binds to receptors on gonadotrophs. 25. Control of Gonadotropin Secretion In a classical negative feedback loop, sex steroids inhibit secretion of GnRH and also have direct negative effects on gonadotrophs.This regulatory loop leads to pulsatile secretion of LH and, to a much lesser extent, FSH.The number of pulses of GnRH and LH varies from afewper day to one or more per hour.In females, pulse frequency is clearly related to stage of the cycle. 26. 27. Disease States Diminished secretion of LH or FSH can result in failure of gonadal function (hypogonadism).This condition is typically manifest in males as failure in production of normal numbers of sperm.In females, cessation of reproductive cycles is commonly observed.Elevated blood levels of gonadotropins usually reflectlack of steroid negative feedback . 28. 29. Prolactin (PRL) 198 aa During pregnancy it helps in the preparation of the breasts for future milk production.After birth- promotes the synthesis of milk.Prolactin secretion isstimulated by TRHrepressed by estrogens and dopamine In pregnant mice, prolactin stimulates the growth of new neurons in the olfactory center of the of the brain. 30. Growth Hormone (GH) also called somatotropin 191 aaGH-secreting cells are stimulated to synthesize and release GH by the intermittent arrival of growth hormone releasing hormone (GHRH) from the hypothalamus. 31. GHpromotes body growthby:binding to receptors on the surface of liver cellsthis stimulates them to release insulin-like growth factor-1 (IGF-1; also known as somatomedin)IGF-1 acts directly on the ends of the long bones promoting their growth 32. Things that can go wrong In childhood-hyposecretion of GH produces the stunted(but normally well-proportioned) growth of a midget.Growth retardation can also result from an inability to respond to GH. This can result from inheriting mutant genes encoding the receptors for GHRH or GH or a defect in STAT 5B. 33.
- Hypersecretion leads to gigantism
- In adults, a hypersecretion of GH leads to acromegaly.
34. Hormone-replacement therapy GH from domestic mammals like cows and pigs does not work in humans.So for many years, the only source of GH for therapy was that extracted from the glands of human cadavers. This supply was shut off when several patients died from a rare neurological disease attributed to contaminated glands.Now, with recombinant DNA methods, recombinant human GH (rHGH) is available . 35. While a great benefit to patients suffering from GH deficiency, there has also been pressure to use it to stimulate growth in youngsters who have no deficiency but whose parents want them to grow up tall.Summer of 2003, the U.S. FDA approved the use of human growth hormone (HGH) forboys predicted to grow no taller than 53 andfor girls, 411even though otherwise perfectly healthy. 36. ACTH the adrenocorticotropic hormone ACTH of 39 aa peptide.Produced from a larger precursor proopiomelanocortin (POMC).ACTH acts on the cells of the adrental cortex stimulating them to produceglucocortiocoids, like cortisolmineralcortiocoids, like aldosteroneAndrogens (male sex hormones, like testosterone 37. in the fetus, ACTH stimulates the adrenal cortex to synthesize a precursor of estrogen called dehydroepiandrosterone sulfate (DHEA-S) which helps prepare the mother for giving birth 38. Production of ACTH depends on the intermittent arrival of corticotropin-releasing hormone (CRH) from the hypothalamus. Hypersecretion of ACTH is a frequent cause ofCushing's disease . 39. Alpha Melanocyte-Stimulating Hormone (-MSH) another cleavage product POMC In fact, -MSH is identical to the first 13 amino acids at the amino terminal of ACTH. 40. Pituitary cell types of Rathke's pouchCorticotropes ,produce(POMC) and cleave it into adrenocorticotropic hormone (ACTH) needed for glucocorticoid synthesis in the adrenal glandMelanotropes , which produce POMC, but cleave it into MSH (for pigment formation, feeding regulation)Somatotropes , which produce growth hormone 41. Pituitary cell types of Rathke's pouchLactotropes , which make prolactin (for milk production, uterine contractions)Gonadotropes , which synthesize lutenizing hormone and follicle stimulating hormone (for gonad growth an