What are the main functions of the ovaries?
oogenesis and secretion of the female sex hromones, progesterone and estrogen
What are the zones of an ovary?
1) The cortex- the outer and largest zone, containing all occytes, each of which is enclosed in a follicle
3) The hilum, the inner most zone, through which blood and lymph passes
In developing ovaries, primordial germ cells produce oogonia by mitotic divisions until gestational weeks 20-24 to produce roughly 7 million oogonia. Beginning at gestational weeks 8-9, some of these oogonia enter prophase of meiosis and become primary oocytes. The meiotic process continues until approx. 6 mos after birth when all oogonia have become oocytes suspended in prophase. Simultaneously, many oocytes degenerate, leaving only about 2 million oocytes at birth and 400K at puberty
Describe the early development of ovarian follicles
1) As a primary oocyte develops, the granulosa cells in the follicle proliferate and nurture the oocyte. During this stage, the primordial follicle develops into a primary follicle, theca cells develop, and granulosa cells begin to secrete fluid.
2) During each menstrual cycle a few follicles enter the next phase in which a fluid containing steroid hormones, proteins, and FSH accumulates in a central area of the follicle called the antrum and granulosa and theca cells continue to proliferate to form a graafian follicle
3) 5-7 days after menese a single graafian follicle gains dominance and proliferates until ovulation occurs
After ovulation, the residual elements of the ruptured primary follicle form ________
the corpus luteum (primarily composed of granulosa cells, and some theca cells and capillaries)
What does the corpus luteum do?
What happens to the corpus luteum if fertilization doesn occur?
It regresses during the luteal phase and is replaced by the corpus albicans
Where is progesterone made in women?
How is testosterone (and estradiol) made in women?
Theca cells produce androstenedione which diffuses to nearby granulosa cells, which contain 17B-HSD and aromatase.
T or F. Like testicular function in men, ovarian function in the female is driven by pulsatile activity activity of the HPO axis
What are the phases of the menstrual cycle?
The follicular phase - Days 1-14 (or 21)
Luteal Phase (Days 15-28)
What ovarian cells have FSH receptors?
only granulosa cells
How does FSH act initially on granulosa cells?
It stimulates growth of granulosa cells in primary follicles and stimulates estradiol synthesis, which then also supports more granulosa cell growth
What hormones promotes the formation of the corpus luteum?
What kind of feedback is in play during the follicular phase of the menstrual cycle?
In this phase, FSH and LH stimulate estradiol production in the follicular cells of the ovaries, which negatively feedbacks on the anterior pituitary (only)
How does feedback change midcycle?
Estradiol levels rise sharply due to proliferation of follicular cells and the stimulation of estradiol, such that, when a critical level of estradiol is met (200 picograms/ml), estradiol switches to positive feedback on the anterior pitutiary by upregulating GnRH receptors on the anterior pituitary, triggering even more release of FSH and LH from the anterior pituitary which stimulates ovulation
Describe the feedback in place during the luteal phase of the menstrual cycle?
Progesterone becomes the major hormone of the ovaries and negatively feedbacks on the anterior pitutiary
What are some functions of estrogen?
-stimulation of prolactin secretion
-decreasing LDL cholesterol
How would the administration of estrogen affect progesterone activity? Vice-versa?
Estrogen has the tendency to upregulate progesterone receptors to enhance its effect while progesterone typically attenuates estrogen response