[Wangers]

Hey peeps,

can someone help please.

I have to do the Menstrual cycle yet again and dont understand this point:

My textbook says Oestrogen has a -ve feedback on the anterior lobe of the Pituitary gland. This stops another egg Oocyte maturing - fair point

But is this is the case - how can LH peak at day 14 to allow the release of the Primary Oocyte from the Graafian follicle?

Is it a case of just summation of [LH] despite lower production or something else? GnRH?

Thank you

[Revenged]

"In females, at the time of menstruation, FSH initiates follicular growth, specifically affecting granulosa cells.[2] With the rise in estrogens, LH receptors are also expressed on the maturing follicle that produces an increasing amount of estradiol. Eventually at the time of the maturation of the follicle, the estrogen rise leads via the hypothalamic interface to the “positive feed-back” effect, a release of LH over a 24-48 hour period. This 'LH surge' triggers ovulation hereby not only releasing the egg, but also initiating the conversion of the residual follicle into a corpus luteum that, in turn, produces progesterone to prepare the endometrium for a possible implantation. LH is necessary to maintain luteal function for the first two weeks. In case of a pregnancy luteal function will be further maintained by the action of hCG from the newly established pregnancy. LH supports thecal cells in the ovary that provide androgens and hormonal precursors for estradiol production."

http://en.wikipedia.org/wiki/Luteinizing_hormone

[Wangers]

[/translation]

FSH causes the follicle to mature from the granulosa precurser cells.
[LH] causes Oestrogen production
[Oestrogen] causes positive feedback to the pituitary causing peak in LH to release the Oocyte from the Graafian follicle
Does LH production stop here or carry on?
[LH] causes Corpus Luteum to secret Progesterone
low[progesterone] - stops FSH (and LH?)
if not pregnant high [progesterone] - inhibits LH - stopping the CL producing [P] therefore the lining is no longer maintained therefore menstruation.

If pregnant the fertilised egg produces hCG? to keep the lining.

I thought Thecal cells were there to protect the Graafian follicle and the Primary Oocyte?

Also - that last sentence implies LH is a precurser to Oestrogen production - how does that work?

Thanks Revenged

[Revenged]

ok, i've confused you with wikipaedia...

first of all it would be good to have a basic idea of how you get oestrogen... oestrogen production in the ovary is quite complicated but it will help you understand what is going on... the oestrogen produced in the normal menstrual cycle is oestrodiol and it is produced from a cholesterol precursor...

The theca and granulosa cells are cells on the outside of the oocyte... see picture...

http://upload.wikimedia.org/wikipedi...n_follicle.jpg

cholesterol -> androgen -> oestrogen

LH causes the first stage via activation of the enzyme c17 lyase in thecal cells... FSH causes the second stage via activation of the enzyme aromatase in granulosa cells (found on outside of oocyte)...

as for the functions of the hormones...

FSH: - stimulates development of follicle and stimulates oestrogen production in granulosa cells

LH: - stimulates androgen fomation in thecal cells, causes ovulation, causes formation of corpus luteum (forms progesterone)

Oestrogen: - Causes build up of endometrium for implantation of the embryo, negative feedback on anterior pituitary (inhibition of FSH and LH)

Progesterone: - Progesterone production continues through pregnancy, maintains lining on endometrium, inhibition of FSH and LH...

Progesterone secretion is produced by the corpeus luteum... After about 14 days the corpeus luteum stops production progesterone, which causes menstration...

If implantation occurs then hCG is produced... hCG is a horomone that causes the corpus luteum to keep producing progesterone... eventually after a few weeks the corpus luteum breaks down but in this time the placenta develops and produces progesterone...

Don't worry about the LH surge Wangers... No one really has a clue how it occurs... There are also other hormones involved during development and also in pregnancy such as inhibin, placental lactogen, oestriol, oestrone...etc. so it is more complicated but i doubt you'd need to know about them...

It may seem a bit pointless and daunting to know about all these hormones... but the hormones oestrogen and progesterone are both used as contraception... and you have various chemicals that you can take to effect levels of hormones... fertility and infertility treatment is a massive area... for example, clomiphene citrate is an infertility drug... it causes FSH levels to increase and causes ovulation occur... so i think this is where the idea that high oestrogen causes ovulation comes from... FSH -> increases oestrogen -> causes LH surge... i know this doesn't explain what is going on properly but as i said before, i don't think anyone really understands what causes the LH surge...

[Wangers]

Thank you D