The menstrual cycle has 2 phases when talking about the OVARIES. What are they. Nice and easy.
1. Follicular phase
2. Luteal phase
So the follicular phase is triggered by FSH release. Initially, what does this FSH do to the primordial follicle?
1. Proliferation of granulosa cells, which contain aromatase that converts androstenedione to estradiol. There is also some conversion of cholesterol to progesterone, which diffuses back to the theca cell to be converted to androtenedione, which then goes back to the granulosa cell.
2. Estradiol and FSH stimulate production of more FSH receptors (and later LH receptors)
The follicle secretes estrogen in response to FSH activating aromatase enzyme. What does this estrogen do?
Upregulate LH receptors on the theca cells, so that they respond more to LH and proliferate.
Now we have more LH receptors on the follicle. What does LH do to the follicle?
Direct action on theca cells to convert cholesterol to progesterone and then androstenedione (AD). AD diffuses across the basement membrane to the granulosa cells, where it gets converted to esterone/testosterone, which is converted to estradiol.
Where does the estrogen that LH helps produce go?
To the blood stream to reach:
Why it is important for estrogen from the follicle to reach the hypothalamus?
Because that is one of the major signals of positive feedback that tell the hypothalamus to produce lots of GnRH, leading to the ovulatory surge of LH and FSH.
During the folliclular phase, there is a sharp rise in estrogen (stimulated by FSH and LH's action on the follicle) but the level of FSH and LH don't actually rise very much. HOW IS THAT POSSIBLE?
Becauseeeee remember there is up regulation of FSH and LH receptors on the follicle, so it is able to increase its response to FSH and LH without an actual increase in FSH and LH
Also during the follicular phase, there is some "escape" of androstenedione and testosterone from the follicle. Why is that?
Roles in labido.
What is the role of the theca cells?
Convert cholesterol to androgen precursors. Remember these precursors are then convereted to estrogen by aromatse enzmye in the granulosa cells.
The granulosa cells are analogous to the ___________cells in the male. The theca cells are analogous to the ___________ cels in the male.
1. Sertoli (production of estrogen in males)
2. Leydig (testosterone in male)
What is a catecholestrogen and why do we give a shit about it?
In the hypothalamus, the A ring of estrogen is transformed into a catechol structure so that this new catecholestrogen can act in both catecholamine and estrogen pathways
What signals are involved in hypothalamus' cyclic control over LH/FSH secretion. What is telling the hypothalamus to secrete these hormones?
1. Signals from the ovary (estrogen anyone?)
2. Sleep wake cycle, emotions and nutrition status of mom
What is the "self-priming" pattern of GnRH release in the middle of the menstrual cycle?
It is still pulsatile, but there is an increase in frequency and amount of LH/FSH released with each GnRH stimulation of the anterior pituitary
What is the significance of the pulsatile release of GnRH
Without a pulsatile release, a constant stream of GnRH would lead to feedback inhibition of the hypothalamus, and a block of LH and FSH production. **Remember that GnRH analog leuprolide was used to treat prostate cancer by inhibition LH/FSH production.
Describe the differences in the amount of GnRH made in the stages of female development (prepubertal, reproductive, postmenopausal)
1. prepubertal: low
2. reproductive: cyclic and elevated
3. post-menopausal: highest (because follicles/corpus luteum aren't providing negative feedback with progesterone and estrogen anymore)
Where does the estrogen rise in the luteal phase come from?
The corpus luteum
How long does the corpus luteum last after ovulation?
How does the loss of progesterone and estrogen production from the corpus luteum lead to menstruation
1. Vasospasm of spiral arteries of the functional layer of the endometrium
2. Prostaglandins cause vasoconstriction leading to tissue hypoxia.
At puberty, what changes occur that bring about the start of the menstrual cycle?
1. The hypothalamus undergoes desensitization to the negative feedback of the gonadal steroids LH/FSH
2. Positive feedback of estrogen is established.
3. Ovulation starts up, mostly due to the mid-cycle estrogen surge
What causes the small rise in FSH in the beginning of the menstrual cycle?
The involution of the corpus luteum means that there is no negative feedback of progesterone to the hypothalamus. GnRH can start being produced again.
What causes a temperature rise in the female after ovulation ( in the middle of the luteal phase)?