Lecture 40: Female reproductive cycle

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Female Reproductive Cycle

--- --- ---:
-Controlled by monthly cycle of hormones from anterior pituitary, hypothalamus and ovary
-Consists of coordinated monthly cycle of changes in the ovary and uterus
-Ovarian cycle: changes in the ovary during and after maturation of the oocyte
-Uterine cycle
-Preparation of the uterus to receive fertilized ovum
-If Impantation does not occur, the stratum functionalis is shed during menstruation

Menstual Phase

--- ---:
-Menstruation lasts for 5 days
-First day is considered beginning of 28 day cycle
-In ovary: 20 follicles that began to develop 6 days before are now beginning to secrete estrogen
-Fluid is filling the antrum from granulosa cells
-In uterus:
-declining levels of progesterone causes spiral arteries to constrict and glandular tissue degenerates
-Stratum functionalis layer is sloughed off along with 50-150ml of blood

Preovulatory Phase

--- ---:
-Lasts from day 6-13 (most variable timeline)
-In the ovary (follicular phase)
-Follicular secretion of estrogen and inhibin has slowed the secretion of FSH
-dominant follicle emerges by day 6
-by day 14, graafian follicle has enlarged and bulges at surface
-increasing estrogen levels trigger the secretion of LH
-In the uterus (proliferative phase)
-increasing estrogen levels have repaired and thickened the stratum functionalis to 4-10mm in thickness

Ovulation

---:
1) High levels of estrogens from almost mature follicle stimulate release of more GnRH and LH
2) GnRH promotes release of FSH and more LH
3) LH surge brings abour ovulation

Postovulatory Phase

--- ---:
-Most consistent timeline: 14 days
-In the ovary (luteal phase)
-If fertilization does not occur, corpus albicans is formed: as a hormone levels drop, secretion of GnRH, FSH, and LH rise
-If fertilization does occur, developing embryo secretes human chorionic gonadotropin (hCG) which maintains health of corpus luteum and its hormonal secretions
-In the uterus (secretory phase)
-Hormones from corpus luteum promote thickening of endometrium to 12-18mm: formation of more endometrial glands and vascularization
-If no fertilization occurs, menstrual phase will begin

Hormonal Regulation of Reproductive Cycle

--- --- --- --- ---:
-GnRH secreted by the hypothalamus controls the female reproductive cycle: stimulates anterior pituitary to secrete FSH and LH
-FSH initiates growth of follicles that secrete estrogen: estrogen maintains reproductive organs
-LH stimulates ovulation & promotes formation of the corpus luteum which secretes estrogens, progesterone, relaxin and inhibin
-Progesterone prepares uterus for implantation and the mammary glands for milk secretion
-Relaxin facilitates implantation in the relaxed uterus
-inhibin inhibits the secretion of FSH

Estrogens

---:
-Promote development and maintenance of female reproductive structures, feminine secondary sex characteristics and breasts
-Increase protein anabolism
-Lower blood cholesterol
-Moderate levels inhibit release of GnRH, FSH, and LH

Progesterone

---:
-Works with estrogens to prepare endometrium for implantation
-Prepares mammary glands to secrete milk
-Inhibits release of GnRH

Relaxin

---:
-Inhibits contractions of uterine smooth muscle
-During labor, increases flexibility of pubic symphysis and dilates uterine cervix

Inhibin

Inhibits release of FSH and, to a lesser extent, LH

Follicular

Ovarian Cycle: --- Phase: 1-14 days
-Cohort of 8-15 primary follicles
-FSH stimulates development of antral follicles
-Antral follicles secrete estradiol
-Around day 6 one antral follicle becomes dominant and the rest undergo atresia
-Estradiol peak precedes LH surge

Ovulatory

Ovarian Cycle: --- Phase: day 14
-LH surge stimulates ovulation of mature follicle within 24-36 hours

Luteal

Ovarian Cycle: --- Phase: 15-28 days
-Corpus luteum (CL) forms
-CL secretes progesterone and estradiol
-Luteolysis begins day 25 in non-pregnant women

Menstrual

Uterine Cycle: --- Phase:
-1st day of menstruation is day 1
-Discharge of blood and endometrial tissue

Proliferative

Uterine Cycle: --- Phase:
-Estradiol stimulates growth of endometrium
-Thickening of endometrium

Secretory

Uterine Cycle: --- Phase:
-Nutrients capable of sustaining embryo
-Decline of progesterone and estradiol at end of secretory phase permit release of prostaglandins

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