Hormonal basis of reproduction


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Hormonal basis of reproduction

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Hormonal basis of reproduction

  1. 2. Introduction- <ul><li>Hormone – </li></ul><ul><li>It is the Chemical messenger produced by a ductless gland i.e. Endocrine glands or tissue and carried in the blood to a target organ where it effects a change in cellular activity. </li></ul><ul><li>Cells communicate with each other via these chemical messengers . Hence These are the modes of intercellular communication.   </li></ul>
  2. 3. Endocrine glands of cow-
  3. 4. Classifications of hormones-
  4. 5. Classifications of reproductive hormones- <ul><li>Based on mode of action- </li></ul><ul><li>-primary hormones of reproduction : FSH & LH </li></ul><ul><li>-secondary hormones of reproduction : ACTH & TSH </li></ul><ul><li>Based on biochemical structures- </li></ul><ul><li>proteins- polypeptide hormones having MW of 300-70000 dalton </li></ul><ul><li>Eg- oxytocin –glycoprotein in nature </li></ul><ul><li>FSH & LH-polypeptide in nature </li></ul>
  5. 6. Cont… <ul><li>steroids -derived from cholesterol & have MW of 300 – 400 daltons </li></ul><ul><li>Eg- testosterone </li></ul><ul><li>Fatty acids- derived from arachidonic acid & have MW of about 400 daltons </li></ul><ul><li>eg-prostaglandins </li></ul><ul><li>Amines- derived from tyrosine or tryptophan </li></ul><ul><li>eg- melatonin </li></ul>
  6. 7. Diff. Modes of intercellular communication- <ul><li>4 basic modes </li></ul><ul><li>Neural communication- neuro transmitters are released at synaptic junctions from nerve cells & act across narrow synaptic clefts between as neurotransmitters. </li></ul><ul><li>Endocrine communication- hormones transported through blood circulation typical of most hormones. </li></ul><ul><li>Paracrine communication- products of cell diffuse through extracellular fluid to affect neighbouring cells that are at a distance . i.e. prostaglandins </li></ul><ul><li>Autocrine communication- cells secrete chemical messengers that bind to receptors on the same cell that secreted messenger. </li></ul>
  7. 8. Regulation of hormone secretion- <ul><li>Nervous system plays essential role in regulation of gonadal activities by means of </li></ul><ul><li>Endocrine feedback mechanism </li></ul><ul><li>Neuroendocrine reflex </li></ul><ul><li>Immunoendocrine control. </li></ul><ul><li>Endocrine feedback mechanism </li></ul><ul><li>A target gland hormone (i.e. estrogen) can influence secretion of tropic stimuli that causes its own release ( i.e. FSH) </li></ul><ul><li>Feed back control occurs at the level of hypothalamus & pituitary gland. </li></ul><ul><li>Depending upon conc. In blood steroid hormones may exert stimulatory (+ve) or inhibitory feed back(-ve). </li></ul>
  8. 9. Cont… <ul><li>Inhitory or negative feedback - </li></ul><ul><li>Stimulation of ovary increases estrogen secretion , FSH levels decline. </li></ul><ul><li>When pituitary hormones reach a certain level hypothalamic nuclei respond by decreasing the production of releasing hormones thereby decreasing production of pituitary tropic hormone & lower level of target gland function. </li></ul><ul><li>Stimulatory or positive feedback- </li></ul><ul><li>Increase level of estrogen during preovulatory phase increase release of pituitary LH leading to ovulation. </li></ul>
  9. 10. Cont… <ul><li>1. Long loop feedback- </li></ul><ul><li>involves interaction among gonads,pituitary & hypothalamus. </li></ul><ul><li>2. Short loop feedback- </li></ul><ul><li>permits pituitary gonadotropins to influence secretory activity of releasing hormones from hypothalamus without mediation of gonads. </li></ul>
  10. 11. General features- Group 1 Group 2 Types Steroids,iodothyronines, calcitriol ,retinoids Polypeptides,proteins, glycoproteins, catecholamines. Solubility Lipophilic Hydrophilic Transport protein Yes No Plasma half life Long (hours to days) Short(minutes) Receptor Intracellular Plasma membrane Mediators Receptor – hormone complex cAMP ,cGMP,Ca 2+, metabolites of complex phosphoinositols, kinase cascades.
  11. 12. Primary hormones of reproduction- <ul><li>Regulate various reproductive processes i.e.spermatogenesis,ovulation,sexual behavior , fertilization,implantation,maintenance of gestation , parturition,lactation & maternal behavior. </li></ul><ul><li>Secondary or metabolic hormones- </li></ul><ul><li>These indirectly influence reproduction. </li></ul>
  12. 13. Hypothalamic hormones- <ul><li>GnRH- </li></ul><ul><ul><li>Decapeptide (10 aminoacids) </li></ul></ul><ul><ul><li>MW 1183 dalton </li></ul></ul><ul><ul><li>Synthesised & stored in medial basal hypothalamus </li></ul></ul><ul><ul><li>In response to neural signals pulses of GnRH released into hypophyseal portal system for release of FSH & LH from anterior pituitary. </li></ul></ul><ul><li>PRH- (Prolactin releasing hormone) </li></ul><ul><ul><ul><li>Stimulate release of prolactin hormone </li></ul></ul></ul><ul><li>PIH-(Prolactin inhibiting hormone) </li></ul><ul><ul><ul><li>Inhibit release of prolactin hormone </li></ul></ul></ul><ul><ul><ul><li>It is a catecholamine i.e.dopamine which is a low MW amine synthesised from L-Tyrosine & secreted from nerve terminals in median eminence. </li></ul></ul></ul>
  13. 15. Adenohypophyseal hormones- <ul><li>FSH- </li></ul><ul><ul><li>Glycoprotein hormone having MW 32000 dalton </li></ul></ul><ul><ul><li>Consists of α & β subunits </li></ul></ul><ul><ul><li>Functions- </li></ul></ul><ul><ul><ul><li>Stimulates growth & maturation of ovarian follicle i.e. Graafian follicle </li></ul></ul></ul><ul><ul><ul><li>In presence of LH stimulates estrogen production </li></ul></ul></ul><ul><ul><ul><li>In males it is responsible for spermatogenesis( upto secondary spermatocyte stage) </li></ul></ul></ul><ul><li>LH- </li></ul><ul><ul><li>Glycoprotein composed of α & β subunits with a MW of 30000 daltons </li></ul></ul><ul><ul><li>Biological half life is 30 mins </li></ul></ul>
  14. 16. Cont… <ul><ul><li>In conjuction with FSH induce estrogen secretion from ovarian follicle. </li></ul></ul><ul><ul><li>Preovulatory LH surge responsible for rupture of follicle wall & ovulation. </li></ul></ul><ul><ul><li>In males stimulate interstitial cells (Leydig cells) to produce androgens. </li></ul></ul><ul><li>PROLACTIN- </li></ul><ul><ul><li>Polypeptide hormone consisting of 198 aminoacids & having MW of 24000daltons. </li></ul></ul><ul><ul><li>Functions- </li></ul></ul><ul><ul><ul><li>Initiates & maintains lactation </li></ul></ul></ul><ul><ul><ul><li>luteotropic in rodents i.e. maintains the C.L. </li></ul></ul></ul>
  15. 17. Neurohypophyseal hormones- <ul><li>These hormones are secreted from hypothalamus & stored in posterior pituitary until they are needed. </li></ul><ul><li>Transferred from hypothalamus to pituitary along the axons of nervous tissue. </li></ul><ul><li>Oxytocin- </li></ul><ul><li>An octapeptide </li></ul><ul><li>Functions- </li></ul><ul><ul><li>Stimulate uterine contraction </li></ul></ul><ul><ul><li>Facilitate spermatozoal transport </li></ul></ul><ul><ul><li>Induction of parturition (Ferguson’s reflex) </li></ul></ul><ul><ul><li>Reflex release of milk upon suckling & milking stimulation </li></ul></ul>
  16. 18. Release of oxytocin-
  17. 19. Melatonin- <ul><li>It is N-Acetyl-5-methoxy tryptamine synthesised in pineal gland. Synthesis- </li></ul><ul><li>Blood vessel Tryptophan pineal </li></ul><ul><li>parenchyma serotonin light N-Acetyl </li></ul><ul><li> Transferase </li></ul><ul><li>N-Acetyl serotonin dark Hydroxy indole- o-methyl transferase Melatonin </li></ul><ul><li>Blood vessel Melatonin </li></ul>
  18. 20. Gonadal steroid hormones- <ul><li>Ovaries,testes & to some extent adrenal & placenta secrete these steroids. </li></ul><ul><li>Major hormones are androgen,estrogen,progestin. </li></ul><ul><li>Have common nucleus called cyclopentanoperhydrophenanthrene ring i.e. consisting of 3 six membered fully hydrogenated (perhydro) phenanthrene rings & 1 five membered cyclo pentane ring. </li></ul><ul><li>18 –c steroid has estrogen activity,19-c steroid has androgen activity,21-c steroid has progestogen activity. </li></ul><ul><li>In blood plasma mostly bound to albumin protein. </li></ul>
  19. 21. Structures of steroid hormones- Natural steroids-
  20. 22. Synthetic steroids-
  21. 23. Synthesis-
  22. 24. Synthesis-
  23. 25. Cont…..
  24. 26. Conversion of testosterone to estradiol-
  25. 27. Mechanism of action-
  26. 28. Estrogen- <ul><li>Estradiol is biologically active. </li></ul><ul><li>Zeronal is a compound having estrogenic activity is produced by mold. </li></ul><ul><li>DES is synthetic non-steroidal estrogen used for growth promoting purpose in bovines. </li></ul><ul><li>Functions- </li></ul><ul><ul><li>Behavioral estrous signs in animals </li></ul></ul><ul><ul><li>Potentiate effect of oxytocin & PGF2 α </li></ul></ul><ul><ul><li>Develop female secondary sexual characteristics like development of mammary gland. </li></ul></ul><ul><ul><li>Control release of FSH & LH. </li></ul></ul>
  27. 29. Progestogens- <ul><li>Functions- </li></ul><ul><ul><li>Prepare endometrium for implantation & maintains pregnancy </li></ul></ul><ul><ul><li>Inhibit uterine motility </li></ul></ul><ul><ul><li>Inhibit estrus & ovulatory surge of LH </li></ul></ul><ul><li>Androgens- </li></ul><ul><li>19-c steroids with –OH or an oxygen group at position 3 & 17 & a double bond at position 4. </li></ul><ul><li>Called as 17-keto steroid when oxygen present at position 17. </li></ul>
  28. 30. Cont.. <ul><li>Secreted by leydig cells of testes & limited amount by adrenal cortex. </li></ul><ul><li>Functions- </li></ul><ul><ul><li>Stimulate late stage of spermatogenesis & prolong lifespan of epididymal sperm </li></ul></ul><ul><ul><li>Promote growth ,development, secretory activity of accessory sex glands </li></ul></ul><ul><ul><li>Maintains secondary sexual characteristics & sexual behaviour in males </li></ul></ul>
  29. 31. Hormones in males-
  30. 32. Other gonadal hormones- <ul><li>Relaxin- </li></ul><ul><ul><li>Secreted by CL of pregnancy </li></ul></ul><ul><ul><li>Polypeptide hormone consisting of α & β subunits connected by 2 disulfide bonds having MW of 5700 dalton. </li></ul></ul><ul><ul><li>Major function is dialation of cervix & vagina prior to parturition. </li></ul></ul><ul><li>Inhibin- </li></ul><ul><ul><li>Secreted from sertoli cells in male & granulosa cells in female. </li></ul></ul><ul><ul><li>Protein hormones consisting of α & β subunits connected by 2 disulfide bridge </li></ul></ul><ul><ul><li>Inhibit release of FSH without altering LH release. </li></ul></ul>
  31. 33. Cont….. <ul><li>Activin- </li></ul><ul><ul><li>Stimulates release of FSH. </li></ul></ul><ul><ul><li>Consists of two β subunits. </li></ul></ul><ul><ul><li>Present in follicular fluid & rete testes fluid. </li></ul></ul><ul><li>Follistanin- </li></ul><ul><ul><li>A protein </li></ul></ul><ul><ul><li>Inhibits secretion of FSH </li></ul></ul><ul><ul><li>Binds with activin thereby neutralises its biological activities. </li></ul></ul>
  32. 34. Placental hormones- <ul><li>PMSG or eCG – </li></ul><ul><ul><li>Is a glycoprotein with α & β subunits containing more sialic acid than FSH & LH that accounts for its long half life. </li></ul></ul><ul><ul><li>Has both FSH & LH biologic actions </li></ul></ul><ul><li>hCG- </li></ul><ul><ul><li>Glycoprotein consisting of α & β subunits & has MW of 40000daltons. α subunit have 92 aninoacids & 2 carbohydrate chain. β subunit has 145 AA & 5 carbohydrate chains. </li></ul></ul><ul><ul><li>It has luteinizing & luteotropic & little FSH properties. </li></ul></ul><ul><li>Placental lactogen- </li></ul><ul><ul><li>Protein with MW 22000-23000 daltons & has 192 AA </li></ul></ul><ul><ul><li>Has prolactin like properties </li></ul></ul><ul><li>Pregnancy specific protein B(PSPB)- </li></ul><ul><ul><li>Prevent destruction of CL in early pregnancy. </li></ul></ul>
  33. 35. Prostaglandins- <ul><li>Secreted from almost all body tissue </li></ul><ul><li>Are 20-c unsaturated hydroxy FAs with a cyclopentene ring. </li></ul><ul><li>Arachidonic acid ,an essential FA is precursor of PGF2 α & PGE2 those are more closely associated with reproduction. </li></ul><ul><li>Functions- </li></ul><ul><ul><li>Luteolytic agent that ends CL of estrous cycle & start a new cycle </li></ul></ul><ul><ul><li>Ends early pregnancy </li></ul></ul><ul><ul><li>Contraction of smooth msl in reproductive tract there by helps in erection,ejaculation,sperm transport etc </li></ul></ul><ul><ul><li>Ovulation,formation of CL ,parturition & milk ejection. </li></ul></ul>
  34. 36. Synthesis of prostaglandins-
  35. 37. Action of PGF2 α on CL-
  36. 38. Structures-
  37. 39. Figure 28.25 The Hormonal Regulation of Ovarian Activity-
  38. 40. In females-
  39. 42. Follicular development in ovary-
  40. 43. Figure 28.12 Hormonal Feedback and the Regulation of the Male Reproductive Function
  41. 44. In male animals-