reproduction/sex steroid axis: physiology and biochem Flashcards
what gonadotrophic hormones does the pituitary gland secrete?
- FSH
- LH
what hormone produced by the hypothalamus triggers the pituitary to secrete LH/FSH?
GnRH
what is the role of FSH in males?
-causes the testes to produce sperm (spermatogenesis)
what is the role of FSH in females?
-causes the growth of the ovarian follicles (oogenesis) and it causes the ovary to secrete oestrogen
what is the role of LH in males?
-causes the testes to secrete testosterone
what is the role of LH in females?
-causes ovulation and it causes progesterone to be produced by the Corpus Luteum
what synthesizes and releases GnRH in the hypothalamus?
GnRH neurons within the hypothalamus
what is GnRH responsible for?
the release of LH and FSH
in what manner is GnRH released?
-a pulsatile manner
how is GnRH released in females compared to males?
- in males GnRH is secreted in pulses at a constant frequency
- in females the frequency of the pulses vary during menstrual cycle
what do high frequency GnRH pulses stimulate?
-LH
what do low frequency GnRH pulses stimulate?
-FSH
what effect does estrogen have on GnHR pulses?
-once oestrogen reaches a certain threshold then it will increase the GnRH pulsatility driving the release of LH
what effect does progesterone have on GnRH pulses?
-it decreases them
what hormones regulate GnRH pulsatility?
-oestrogen and progesterone
do GnRH producing neurons contain estrogen and progesterone receptor?
no- the receptors for estrogen and progesterone are found on kisspeptin neurons which then influence GnRH neurons
what are the 2 phases of the menstrual cycle?
- follicular phase
- luteal phase
how long is the average menstrual cycle?
28 days
what day does ovulation occur in the menstrual cycle?
14
what occurs in the follicular phase?
-follicular growth
what occurs in the luteal phase?
-the corpus luteum is formed under the influence of LH
what phase of the menstrual cycle is more variable?
follicular phase
describe the affect of hormones on the menstrual cycle?
- FSH stimulates growth of ovarian follicles, increasing oestrogen levels
- rising oestrogen levels exert negative feedback regulation to temporarily lower FSH
- once oestrogen reaches a certain concentration it exerts a positive feedback resulting in an increase in FSH and a surge of LH
- LH surge leads to ovulation and regulates the formation of the corpus luteum and progesterone production/secretion
- increasing progesterone increases the frequency of the GnRH pulses and so decreases LH levels
what effect does FSH have on the follicular cells?
-increases the number of follicular cells and accumulation of follicular fluid both resulting in an increase in diameter and overall size of the follicle
what effect does oestrogen have on the endometrium?
causes it to thicken
what part of the follicle is highlighted blue?
antrum
what part of the follicle is highlighted blue?
oocyte
what part of the follicle is highlighted blue?
zona pellucida
what part of the follicle is highlighted blue?
zona granulosa
what part of the follicle is highlighted blue?
theca interna
how is oestrogen produced in the follicles?
- LH allows cholesterol to be converted into androgens in the Theca cells
- FSH then converts androgen into estrogen in the granulosa cell
True or False follicle growth is always controlled by FSH
False
In early stages follicles are gonadotrophic independant and so do not require FSH
In later stages follicles are gonadotrophic dependant and so require FSH
when does ovulation occur after LH surge?
34-36 hours after
what hormone stimulates the formation of the corpus luteum?
LH
how does LH cause an increase in progesterone production?
-LH stimulates enzymes involved in conversion of cholesterol to progesterone
what is the effect of estrogen on vaginal pH?
-reduces vaginal pH through increase in lactic acid production
what effect does estrogen have on viscosity of cervical mucus?
-it decreases viscosity of cervical mucus to facilitate sperm penetration
what role does progesterone have on pregnancy?
-it maintains pregnancy
what effect does progesterone have on the endometrium?
-it maintains the thickness of the endometrium
what effect does progesterone have on mucus?
-it is responsible for infertile thick mucus to prevent sperm transport and help prevent infection
what effect does progesterone have on myometrium?
-relaxes the myometrium
how long does spermatogenic process take place?
70 days
what is most of testosterone taken up by?
-Sertoli cells (90%)
what role does testosterone play during spermatogenesis?
- maintains the integrity of the blood testes barrier
- releases mature spermatozoa from Sertoli cells by influencing peritubular myoid cells
