Final Reproduction

Primordial eggs mature each month but only one

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: es undergo apoptosis (atresia): die • 99.99% of follicles undergo atresia • Cumulus oophorus • Secondary oocyte (out of meiotic arrest) Ovulation • • • • Ovulation (exiting of egg from follicle) occurs in 15 minutes (just the egg popping out part) The secondary oocyte, the zona pullida, the granulosa cells, and the cumulus all leave the follicle If 2 follicles mature= fraternal twins The granulosa cells get big as the follicle grows Phases of the Menstrual Cycle • 2 main parts: – Follicular phase (first 2 weeks) • Estrogen is secreted from granulosa cells • Progesterone is secreted from granulosa and theca cells • Multiple follicles develop, one dominant follicle matures completely • Bleeding occurs during the first few days of this stage as a result of the previous luteal phase • Marked by increased estrogen levels How the cycle is controlled • • • • • The brain! Neural inputs stimulate the hypothalamus to secrete GnRH GnRH stimulates the anterior pituitary to secrete FSH and LH LH and FSH stimulates the gonads to secrete sex hormones (estrogen and progesterone) Estrogen and Progesterone have positive Hormone Control of the Menstrual Cycle • • Small increase in LH and FSH (gonadotropins) cause follicular maturation, and cause increate in the synthesis and secretion of estrogen (from the granulosa cells) Ovulation is produced More on Female Hormones • • • • LH acts on theca cells (acted on Leydig cells in males) to synthesize androgens FSH acts on granulosa cells (acted on Sertoli cells in males) converts androgens (from the theca cells) into estrogen Notice how the path moves inward from the theca to the granulosa cells Once the effects of the LH surge and FSH wear off (about day 16) then the levels of Dominant Follicle Hormones • • • After the initial FSH wears off (around day 6) most of the follicles, beside the dominant follicle, degenerate The dominant follicle can keep going because it has more granulosa cells and granulosa cells have more FSH receptors and it gains LH receptors so it can last longer on less FSH/LH The dominant follicle secretes estrogen (where the large surge in estrogen (not Negative Feedback • The estrogen produced by the granulosa cells with the help of androgens from the theca cells has a negative feedback on FSH and LH (b/c both play a role in producing estrogen) – • Until a lot is produced, then it switched to positive feedback The granulosa cells also produce inhibin, which has negative feedback on FSH mostly The LH surge • The feedback relationship between the on the hypothalamus and anterior pituitary reverses (goes from negative to positive) during mid-cycle, causing a huge surge in LH (high levels of estrogen cause positive feedback on LH so that increases a lot). Day 7 – – – Increased GnRH and LH release FSH also increased but has no physiological effects Luteal Phase • • After ovulation, LH levels from the LH surge remain sufficient to sup...
View Full Document

Ask a homework question - tutors are online