Repro 2 Flashcards
How often, and from where, is GnRH released?
Released from the hypothalamus.
Released in a pulsatile way, once an hour.
What effect does progesterone have on the release of oestrogen?
Progesterone potentiates the inhibitory effect oestrogen (low dose)
At moderate oestrogen levels, what effect does it have on GnRH release?
Decreases the amount of GnRH release per pulse
Progesterone decrease the frequency of the pulse frequency.
Overall decreases the amount of GnRH released.
At high levels of oestrogen alone, what effect does it have on GnRH release.
It increases the amount of GnRH released - which increases FSH and LH, which amplifies the amount of oestrogen released, which is a positive feedback cycle. The LH that is released causes an LH surge - binds to the theca interna - causing ovulation.
Inhibin has an effect on a particular hormone that is released from the AP. What is this hormone and what is the effect?
It influences the release of FSH, and the effect is to decrease the amount of FSH. Inhibin doesn’t have an effect on LH St all.
Where is inhibin released from in the female?
It is released from the Granulosa cells of the follicle.
Describe the relationship between the size of the follicle and the amount of inhibin released
The bigger the follicle, the more inhibin released.
Name the cells of the anterior pituitary and which hormone is produced by each
Thyrotrophs - TSH Lactotrophs - Prolactin Corticotrophs - ACTH Somatotrophs - Growth hormone Gonadotrophs - LH/FSH
What effect do LH and FSH have in the testes?
- LH acts upon the leydig cells to promote the production of testosterone
- testosterone acts on the Sertoli cells to promote spermatogenesis.
- testosterone also acts elsewhere in the body to maintain the reproductive systems.
- FSH acts upon Sertoli cells to make them responsive to testosterone.
How does the HPG act if the rate of sperm production is too high?
- Inhibin levels rise (from the Sertoli cells) but inhibit FSH release from the AP
- FSH makes the Sertoli cells responsive to testosterone, so less FSH means less responsiveness.
Describe the effect of LH and FSH in the ovaries
Antral phase
- LH binds to theca interna and FSH binds to Granulosa
- LH stimulates the thecal cells to produce androgens
- FSH stimulates Granulosa cells to create enzymes that will convert the androgen from the theca into oestrogens.
Pre-Ovulatory
- LH receptors develop on the Granulosa cells, and the surge of LH stimulates ovulation
Post-ovulation
- LH stimulates the CL to secret oestrogen and progesterone.
Describe the action of oestrogen in the follicular phase of the menstrual cycle.
- thin alkaline vaginal mucus, making it easier for penetration of sperm
- hair skin and calcium changes
- thickening of the endometrium
- growth and motility of the myometrium - causes contraction of the uterine wall which aids the movement of the sperm.
Describe the action of LH in the luteal phase of the menstrual cycle
- changes in mammary tissue, metabolism and increase temperature
- thick, acidic cervical mucus which helps to protect the inside of the uterus
- thickening of the myometrium but not on the motility.
Describe the changes seen throughout the follicular phase, in terms of hormone concentration
Early
- very little oestrogen (sub therapeutic) or inhibin so there is no inhibiton of the HPG. FSH and LH are released from the AP. FSH causes the development of one or two follicles, which then begin to increase in size. As size increases, [inhibin] increases too.
- FSH binds to Granulosa. Theca develops, which under the action of LH secretes androgens, that are converted to oestrogen by Granulosa.
Mid
- [oestrogen] increase as does [inhibin] so [FSH] decreases. No new follicles can develop. LH continues to rise as not inhibited by inhibin.
- oestrogen exerts positive feedback onto HPG so LH continues to rise but not FSH.
Pre Ovulatory
-LH continues to rise so chance of LH surge.
Describe what happens in the luteal phase
- CL forms spontaneously
- progesterone and oestrogen secreted but progesterone is higher and it potentiates the inhibitory effect of oestrogen so there is no LH or FSH released.
- waits for conceptus to implant; if nothing then after 14 days the CL shuts off its own blood supply and dies. This removes inhibition of hormones, menstruation occurs and new cycle begins.
