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Lecture 5

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McGill University
PHGY 210
Ann Wechsler

Lecture 5 The menstrual cycle Unlike the males, the females have several positive feedback loops. LH and FSH stimulate follicular receptor development, which then ups estrogen. Estrogen then makes follicles more sensitive to gonadotropin hormones. On day one, vaginal bleeding begins. Progesterone and estrogen levels from the previous cycle drops off. Negative feedback loop ups FSH levels from pituitary. FSH will cause follicles to begin development. Very rapid development of the follicles. By day 8, only 1 follicle remains to further develop. Bleeding stops. This then increases estrogen levels. Day 14. Estrogen acts locally to affect follicular development. Also act systemically to affect pituitary. Reduce feedback FSH release, but increases GnRH receptors on the pituitary, to increase LH production. Ups synthesis, but prevents release. LH accumulates to a very high level within the pituitary. This leads to ovulation. Follicle becomes the corpus luteum. Oral Contraceptives – the pills contains estrogen and progesterone, maintains a leveled level of estrogen and progesterone, which supress LH and FSH release. The corpus luteum under LH increases levels of progesterone. Estrogen induces proliferation, progesterone allows specialization. If fertilization does not happen in 14 days, the corpus luteum degenerates, levels drops and the endometrium degenerates as well. Restarts cycle as FSH levels are upped while everything else becomes low. The egg, when released, it goes down the fallopian tube. When fertilized, it becomes a blastocyst, and then is implanted into the endometrium. Differentiation of the blastocyst leads to trophoblast, becoming the placenta, and the inner cell mass becomes the embryo. Trophoblast produce human chorionic gonadotropin (HCG), LH like, causes corpus luteum to hang around, the corpus luteum of pregnancy. 3 months later, the placenta takes over and the corpus luteum of pregnancy is no longer the major player. HCG level is a good indicat
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