Physiology of Reproduction 3 Flashcards
GnRH is secreted by what? (Gonadotropin-releasing hormone AKA Luteinizing hormone-releasing hormone)
Hypothalamus
What gland does GnRH bind to?
Anterior Pituitary gland
What does the pituitary gland release in response to GnRH binding?
LH (luteinizing hormone) and FSH (follicle-stimulating hormone)
LH and FSH travel in bloodstream to where?
The ovaries
What is produced by ovaries after LH and FSH bind?
oestrogen and inhibin
What does inhibin do?
Inhibits activin (usually responsible for stimulating GnRH production)
What does progesterone do?
Stimulates endometrium to become receptive to implantation of fertilised ovum.
Follicular phase
Increased levels of FSH stimulate few ovarian follicles.
Maturing follicles compete for dominance.
First follicle to fully mature produces large amounts of oestrogen which inhibits growth of other competing follicles.
This fully mature follicle called Graafian follicle.
Continues secreting increasing amounts of oestrogen.
Causes endometrial thickening, thinning of cervical mucus
Inhibition of LH production by pituitary gland.
Oestrogen surpasses threshold level and stimulate LH production.
Day 12 = spike in LH levels.
Membrane of Graafian follicle thins then ruptures releasing secondary oocyte.
Oocyte matures into ootid then mature ovum.
Mature ovum released into peritoneal space and taken into fallopian tube via fimbriae (finger-like projections)
Luteal Phase
Once ovulation has occurred, LH and FSH stimulate remaining Graafian follicle to develop into corpus luteum.
Produces progesterone.
Endometrium becomes receptive to implantation of blastocyst.
Negative feedback causing decreased LH and FSH
Increase in woman’s basal body temperature.
Corpus luteum degenerates as levels of FSH and LH fall.
Therefore, loss of progesterone production causing cycle to begin again.
If fertilisation occurs…
Fertilised ovum produces hCG (similar to LH) which prevents degeneration of corpus luteum.
Continued progesterone production prevents menstruation.
Placenta eventually takes of role of corpus luteum
2 layers of the endometrium
Functional layer (shed during menstruation) and basal layer (not shed)
3 Phases of the uterine cycle
Proliferative phase, secretory phase and menstrual phase.
Proliferative phase
Endometrium exposed to increasing levels of oestrogen.
Stimulates repair and growth of functional endometrial layer (allows recovery from previous menstruation)
Secretory phase
Occurs once ovulation has occurred
Corpus luteum produces progesterone causing secretions of various substances by endometrial glands. More welcoming environment for embryo to implant.
Menstrual phase
End of luteal phase.
If no fertilisation occurs, corpus luteum degenerates.
Decreased progesterone production.
Contraction of spiral arteries in functional endometrium -> ischaemic/ necrotic.
Therefore, functional endometrium shed and exits vagina = menstruation.
