Reproduction - Hormonal Control Flashcards
What are the main classes of reproductive hormones based on their chemical structure?
Glycoproteins
Proteins/Peptides
Gonadal Steroids
Eicanosoids
Amines (derived from tyrosin or tryptophan)
Give examples of reproductive hormones that are glycoproteins.
Follicle Stimulating Hormone (FSH)
Luteinising Hormone (LH)
Human Chorionic Gonadotrophin (hCG)
These are synthesised by the gonadotrophs in the anterior pituitary.
Give examples of reproductive hormones that are protein- or peptide hormones.
Oxytocin
GnRH
Relaxin
Inhibin
Activin
Insulin
Prolactin
IFN-tau
Give examples of reproductive hormones that are gonadal steroids.
Oestradiols: Oestrogen (Oestradiol ß-17)
Progestagens: Progesterone
Androgens: Testosterone, 5α-dihydrotestosterone, androstenedione, dehydroepiandrosterone [DHEA])
Give examples of reproductive hormones that are eicanosoids.
PGF2a
PGE2
Give examples of reproductive hormones that are amines.
Dopamine
Melatonin
What are the main regulatory controls of glycoprotein hormone FSH, and what do this hormone do in male & female reproduction?
Control:
(-) feedback by gonadal steroids, ie., progesterone, testosterone & oestrogen
(-) feedback by inhibin, secreted by granulosa cells
secreted by gonadotrophs of anterior pituitary under influence of GnRH from hypothalamus
Function:
In female, induces granulosa cells to convert androgens (testosterone) from theca cells to oestradiol-17ß; very high levels intercycle between end-luteal & early follicular phases; critical for selection of antral follicles (fall in FSH results in atresia); induces selected antral follicles to express LH receptors; [FSH] drops as oestogen rises
In males, induces Sertoli cells to support/nourish spermatocytes up to second stage of spermatogenesis
What are the main regulators of the glycoprotein LH, and what does the hormone do?
Control:
synthesized by gonadotrophs in anterior pituitary under influence of GnRH from hypothalamus
(-) feedback by gonadal steroids progesterone & testosterone
(+) & (-) feedback by oestrogen; mostly (+) throughout folliculogenesis until pre-ovulatory stage, when [oestrogen] reaches threshold & switches to (+) feedback, selective for LH surge
Function:
In male, induces Leydig cells to synthesize & secrete testosterone
In female, induces theca cells to synthesize gonadal steroids (progesterone, testosterone), which are converted by aromatase in granulosa cells into oestrogen; critical for survival of dominant follicle, which has only LH receptors; LH surge sets in motion ovulation; in luteal phase, LH-stimulated theca cells become theca-lutein along with. granulosa-lutein in CL to synthesize progesterone
What are the regulatory controls of the peptide hormone inhibin, and what is its function in male & female reproduction?
*Most importantly, inhibin enables differential control of FSH vs. LH. *
In females, it is secreted by granulosa cells to negatively feedback on FSH secretion by the anterior pituitary. Ie., it inhibits FSH action on the granulosa cells, particularly in the later stages of folliculogenesis, when oestrogen is also negatively feeding back to FSH production.
In males, inhibin is secreted by Sertoli cells & inhibited by androgens (eg., testosterone) - less important in males.
What is the main role of progesterone in the pregnant female?
Provides (-) feedback to gonadotrophin
secretion ie., FSH & LH secretion so no new eggs are released during pregnancy
Prepares uterus to receive conceptus:
- induces changes in uterus so it can secrete
“goodies” ie., uterine milk to nourish egg as it travels down the oviduct - ↓ uterine activity (motility) during pregnancy
-
↑ growth of mammary glands, but
suppresses secretion of milk during pregnancy
What are the main roles of testosterone, the gonadal androgen secreted by Leydig cells in the testes, in spermatogenesis specifically and male sexual development in general?
Testosterone is required in large local concentrations to maintain spermatogenesis, which is achieved via the binding of testosterone by androgen-binding protein present in the seminiferous tubules.
- Leydig cells synthesize & secrete testosterone into seminiferous tubules & bloodstream
- Sertoli cells convert testosterone into 5α Dihydrotestosterone (more
potent form) & release into blood to act on gonadal & sex-trait development - induce & maintain differentiation of male somatic tissues
- induce secondary sex characteristics (eg., deep voice, body hair, penile growth); induce and maintain some secondary sex characteristics (eg., accessory sex organs)
- promote protein anabolism & somatic growth
- influence sexual & aggressive behaviour
- (-) feedback for gonadotrophins LH & FSH
What is aromatase and what is important about its role in female reproduction?
Aromatase is also called oestrogen synthase. It’s an enzyme responsible for a key step in the synthesis of oestrogen from testosterone in the granulosa cells of an ovarian follicle.
Basically, it cleaves one carbon from testosterone (19 carbon atoms) to produce oestradiol (18 C atoms).
What are the roles of oestrogen in the pregnant female?
- ↑ growth & activity of mammary gland & endometrium
- preps endometrium for progestagen action (uterine-milk production, reduced motility, induces progesterone receptors)
- ↑ vascular permeability & tissue oedema
- associated with sexual behaviour in some
species - stimulates secondary sex characteristics
What are the roles of oestrogen in the NON-pregnant female?
- provides (+) & (-) feedback on hypothalamus and anterior pituitary for differential secretion of LH & FSH (positive feedback for LH during pre-ovulatory LH surge; negative feedback for FSH)
- preps uterus for spermatozoal transport
- associated with sexual behaviour in some species (lordosis, standing behaviour)
- stimulates secondary sex characteristics
What are the roles of the eicanosoids PGF2a & PGE2 in female reproduction?
They both play an important role in ovulation, luteolysis & parturition.
Ovulation:
PGF2a synthesized in uterus causes contraction of ovarian smooth muscle, so the dominant follicle is “squeezed” out; causes release of lysozymes, which weakens the follicle wall.
PGE2 causes vasodilation of ovarian vessels, causing oedema, increased pressure on the follicular wall;
Luteolysis:
PGF2a is synthesized by the uterus under the influence of oxytocin, secreted by CL. PGF2a diffuses from uterine vein to ovarian artery, where it travels to CL
PGF2a leads to degradation of corpus luteum, turning it into corpus albicans. Thus, effectively reducing progesterone secretion & ↑ FSH secretion due to removal of negative feedback by progesterone
Parturition:
Under influence of hypothalamic oxytocin released by posterior pituitary, induces production by cervix of:
PGE2, PGF2a & prostacyclin (PGI2): soften cervix by breaking down collagen content, causes uterine (myometrial) contraction by stimulating liberation of Ca++ needed for contraction from SR, effectively stimulates progesterone secretion
