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Hormonal Control of Reproduction

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Hormonal Control of Reproduction

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  1. Hormonal Control of Reproduction female male Dendrobates azureus

  2. Hormonal Control of Reproduction • 1. Critical importance to fitness • “its ability to perpetuate itself as measured • by its reproductive success” (Pianka 2000) • Energetically expensive • Therefore, must be precisely timed to insure maximal survival of young • young born at time most favorable for survival in cyclical environment

  3. 2. Control of Reproduction HYPOTHALAMUS MEDIAN EMINENCE ADENOHYPOPHYSIS GONAD: TESTIS OR OVARY

  4. DAYLENGTH

  5. DAYLENGTH TEMPERATURE

  6. DAYLENGTH TEMPERATURE NUTRITION

  7. DAYLENGTH TEMPERATURE NUTRITION ENDOGENOUS CLOCK

  8. DAYLENGTH TEMPERATURE NUTRITION ENDOGENOUS CLOCK Gonadotropin-Releasing Hormone (GnRH)

  9. GnRH Stimulates Gonadotropins: Luteinizing Hormone (LH) Follicle-Stimulating Hormone (FSH)

  10. 3. Functions of gonadotropins • a. Stimulate gametogenesis • production (meiosis) and maturation of gametes • Male: spermatozoa • Female: oocyte

  11. b. Stimulate steroidogenesis • steroid hormone production by gonads • Male: androgens (testosterone) • Female: estrogens (estradiol) • progestins (progesterone) • androgens • Actions similar in male and female, only timing and targets that differ

  12. 4. Female system • Precise, often brief, secretion of gonadotropins in regular cycles • Cycles range from multiannual to days

  13. a. Ovary Structure • (1) connective tissue capsule • (2) ovarian follicle (1 to millions) • oocyte: premeiotic gamete • follicle cells: two layers of steroidogenic cells surrounding oocyte • inner layer: granulosa • outer layer: theca • (3) Ducts for oocyte transport and packaging • oviduct, uterus

  14. b. Control of ovarian function + LH Theca Cells

  15. b. Control of ovarian function + LH Theca Cells Androgen

  16. b. Control of ovarian function + LH Theca Cells Androgen + FSH +LH Granulosa Cells

  17. b. Control of ovarian function + LH Theca Cells Androgen + FSH +LH Granulosa Cells Estrogen

  18. b. Control of ovarian function + LH Theca Cells Androgen + FSH +LH Granulosa Granulosa Cells Estrogen Blood

  19. b. Control of ovarian function + LH Theca Cells Androgen + FSH +LH Granulosa Granulosa Cells Estrogen Oogenesis Blood

  20. c. Estrogens • (1) Local effects (paracrine) • Stimulate oocyte and follicle cell growth • Oocyte and follicle size increase • (2) Distant effects (endocrine) • (a) Feedback: slight negative feedback on LH

  21. (b) Primary Sexual Characteristics • Growth of ducts and organs directly responsible for gamete production and transport: • ovary, oviduct, uterus • (c) Secondary Sexual Characteristics • Anatomical structures not directly involved in gamete production, but associated with reproductive activity • physical and behavioral: • mating receptivity

  22. (d) Metabolic effects • tissue growth • follicle, ducts, mammary gland • energy storage • appetite stimulant • fat deposition • yolk production • vitellogenin : precursor protein • of yolk proteins.

  23. VITELLOGENESIS Ovary FSH LH ESTROGEN LIVER

  24. VITELLOGENESIS Ovary FSH LH ESTROGEN VITELLOGENIN LIVER (calcium, lipids, carbohydrates, phosphorous)

  25. VITELLOGENESIS Ovary Follicular growth ESTROGEN VITELLOGENIN LIVER (calcium, lipids, carbohydrates, phosphorous)

  26. Vitellogenin concentration in blood plasma or serum can be measured by immunoassays known as ELISAs • Requires an antibody specific for vitellogenin.

  27. POST NESTING PRE MATING MATING NESTING

  28. Female Reproductive Cycles • (1) Follicular Phase of the cycle • oocyte and follicle growth under • influence of estrogen • Oocyte can not be fertilized in the follicle

  29. (2) Ovulation • rupture of follicle and release of oocyte • stimulated by LH surge • Regulation of LH surge: • (a) environmental cues • e.g., daylength, temperature, substrate, mates, etc. • (b) endocrine cues • e.g., estrogen positive feedback

  30. LH surge transforms follicle cells into new endocrine gland: • Corpus luteum (CL) • External fertilizers: • eggs shed, CL very brief • cycle ends here • Internal fertilizers: • eggs retained, CL persists

  31. (3) Luteal Phase , the CL is steroidogenic • Estrogens • maintain 1° and 2° sexual characteristics • Progestins • negative feedback on LH with estrogen • prepare female for embryo support • stimulate structures essential for • embryo survival • e.g., uterus, mammary gland, albumin glands • All preparation in anticipation of fertilization

  32. (4) No fertilization • CL regresses, negative feedback gone, cycle restarts if CNS permits • (5) Fertilization • CL persists: progesterone • New endocrine gland: placenta • Progestins maintained until termination • Cycle can be manipulated: GnRH, steroids