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Lecture 12

Lecture 12 - Mar 1.doc

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PSYC 342
Jens C Pruessner

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PSYC342 Lecture 12 - Mar. 1 Female Reproductive Organs: • Vagina: Tubular tract leading from uterus to exterior of body • Cervix: Lower, narrow portion of the uterus • Uterus: Muscular reproductive organ, located in the pelvis • Fallopian tubes: Two tubes leading from the ovaries into the uterus • Ovaries: Oocyte-producing organs The Menstrual Cycle: • Involves the monthly release of hormones that help to mature an oocyte (egg) and prepare the body for fertilization and pregnancy • When fertilization does not occur, the endometrium (lining of uterus which grows during menstrual cycle to prepare the attaching of the egg) breaks down and menstruation occurs What is Menstruation? • Monthly bleeding, “menses”, as a result of the shedding of the endometrium lining Hormonal Activity: GnRH (Gonadotropin Releasing Hormone) released from hypothalamus acts on pituitary gland, • leads to the release of FSH & LH • Follicle-Stimulating Hormone (FSH) & Luteinizing Hormone (LH) released by the anterior pituitary, control the maturation and release of an egg by the ovaries. FSH acts on ovaries to promote devel- opment of follicles (maturing eggs of the female ovary) • LH causes the mature follicle to release an egg. This is called Ovulation • Estrogen and progesterone, secreted by the ovary, build up the endometrium (the lining of the uterus) Follicular Phase: • Between days 5 and 13 (but interindividual variations) • Otherwise known as the proliferative phase • Stage ends with ovulation • Main hormone controlling this stage is estrogen Step 1: • FSH + LH levels will begin to rise at the end of the menstrual period. These rising levels of FSH will causes ovarian follicles to start growing Step 2: • The granulose cells surrounding the follicles begin to proliferate and increase their expression of lut- enizing hormone (LH) receptors. • These follicles also start producing estrogen Step 3: • As estrogen levels increases they will feedback negatively not he pituitary and hypothalamus, there- by lowering GnRH, FSH and LH levels Eventually one follicle will become dominant • Selection of the Dominant Follicle: How does a follicle gain dominance? • • Near the end of the follicular phase, the level of FSH is low, due to inhibition exerted by estro- gen • As a result of this scarcity in FSH, only the follicle with the most FSH receptors expressed can acquire enough FSH to continue growing • The other follicles eventually atrophy Step 4: • The dominant follicle continues to secrete more amounts of estrogen which will eventually lead into the LH surge...and then ovulation Ovulation: • The release of a mature ovum (egg) from the ovary • It varies in the individual, but typically occurs on day 14 or 15 of the menstrual cycle The Hormones Involved: • Estrogen is synthesized in the ovaries • GnRH is synthesized in the hypothalamus • LH is produced by the anterior pituitary gland Positive Feedback and the LUteal Surge: Just before ovulation, the ovary secretes estrogen which emits positive feedback on the hypothala- • mus and anterior pituitary gland • Estrogen causes the hypothalamus to secrete GnRH, and the anterior pituitary to secrete LH • Furthermore, GnRH also stimulates the release of LH from the anterior pituitary • LH travels through the bloodstream and promotes the further secretion of estrogen from the ovaries • This positive feedback mechanism creates a dramatic increase in LH secretion known as the luteal surge • The luteal surge causes the follicle to burst, releasing the gig into the body cavity towards the Fal- lopian tubes The Dual Nature of Estrogen: • Estrogen in the Follicular Stage: • Estrogen suppresses production of LH from the anterior pituitary gland • Estrogen just prior to Ovulation: • Estrogen reaches a threshold. Above this threshold it stimulates production of LH • The Dual nature of Estrogen Estrogen receptor Alpha: responsible for the negative feedback estrogen-LH loop in the follic- • ular stage Estrogen receptor Beta: responsible for the positive estrogen-LH relationship • The Luteal Phase: Occurs after ovulation thus it constitutes the last half of the menstrual cycle (day 14-28) • • Begins with the formation of the corpus luteum • Ends with either • Luteolysis • Pregnancy • Follicle transforms into luteum The Corpus Luteum: • The corpus luteum continues to grow for some time, secreting progesterone and some estrogen • Progesterone makes the endometrial lining ready for implantation of an embryo • Estrogen helps m
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