Endocrinology5

Endocrinology5 - The menstrual cycle: prior to day 1, under...

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The menstrual cycle : From the Latin word menses (month). - Day 1 considered as the first day of detectable vaginal bleeding, represents a deterioration of the uterine endometrium . -Prior to day one endometrium proliferates and becomes thick under the influence of estradiol . - Progesterone induces the appearance of glycogen-secreting glands. - Menses (bleeding) begins when estradiol and progesterone very low in circulation, when the blood vessels supplying the endometrium constrict reducing the blood supply - endometrium deteriorates, flows through the cervix into the vagina - day one -Bleeding occurs for about 5 days during which, ovaries are endocrinologically rather inactive. Figure 5.6
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-Low estradiol and progesterone leads to increased secretion of FSH by pituitary. Usually, moderate levels of estradiol block FSH release . -Also, decrease in non-steroid ovarian hormones, inhibins , which selectively inhibit secretion of FSH and may in part raise FSH levels during 5-6 days -Under influence of FSH, cohort of ovarian follicles develop . FSH stimulates granulosa cell s of follicles to proliferate, and induces production of aromatase , converts androgens to estrogen. Local production of estrogen stimulates granulose cell proliferation. -D ay 8 , one of the follicles becomes dominant and committed to further development. The remaining follicles begin to degenerate by atresia. In humans, how one follicle becomes dominant still unknown. - Dominant follicle produces increasingly more estradiol, and estradiol becomes important in late stages of cycle - increased estradiol produced by growing follicle causes uterine endometrium proliferation. -By day 13 the endometrium very thick. Under the influence of estradiol, there is an induction of progesterone receptors in the endometrium. Figure 5.7
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Estradiol effects on brain and pituitary. -Rising estradiol - negative feedback on FSH release - Moderate concentrations, estrogen also stimulates synthesis of LH by pituitary and increases sensitivity of the pituitary to GnRH, which stimulates synthesis of LH. Although moderate estradiol concentrations stimulate LH synthesis, they inhibit LH release. LH accumulates to high levels within pituitary. - Under influence of the developing follicle estrogen concentrations continue to build. Elevated estrogen concentrations stimulate LH release - LH surge on or about day 14 . Small increase in FSH release also occurs. -Stimulation of LH synthesis by estradiol and increased sensitivity of the anterior pituitary to GnRH leading to increased LH synthesis by anterior pituitary known as the estrogen (+) feedback control mechanism. -Thus estrogens exert both a negative feedback such as decreased GnRH and LH release and a positive feedback such as increased sensitivity of the anterior pituitary cells to GnRH and increased LH synthesis. -Meanwhile, at the ovarian level the follicle has become
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This note was uploaded on 04/26/2011 for the course PHGY 210 taught by Professor Trippenbach during the Winter '08 term at McGill.

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Endocrinology5 - The menstrual cycle: prior to day 1, under...

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