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Tuesday, September 1, 2020

Menstrual Cycle, Ovarian and Uterine Changes

 Menstrual Cycle 

Ovarian Changes

Preovulatory Phase

  • Hypothalamus release gonadotropin-releasing hormone through the portal system to the anterior pituitary system. 
  • Secretion of follicle-stimulating hormone (FSH) by the anterior lobe of the pituitary gland stimulates growth of follicles. 
  • Most follicles die,  leaving 1 to mature into a large Graafian follicle.
  • Estrogen produced by the follicle stimulates increased secretion of luteinizing hormone (LH) by the anterior lobe of the pituitary gland.
  • The follicle ruptures and releases an ovum into the peritoneal cavity. 
Luteal phase

  • Begins with ovulation. 
  • Body temperature decreases and then increases by 0.5°F to 1° F around the time of ovulation 
  • Corpus luteum is formed from follicle cells that remain in the ovary after ovulation. 
  • Corpus luteum secretes estrogen and progesterone during the remaining 14 days of the cycle. 
  • Corpus luteum degenerates if the ovum is not fertilized,  and secretion of estrogen and progesterone declines. 
  • Decline of estrogen and progesterone stimulates the anterior pituitary to secrete more FSH and LH,  initiating a new reproductive cycle. 
Uterine Changes

Menstrual phase
  • Consists of 4 to 6 days of bleeding as the endometrium break down because of the decreased levels of estrogen and progesterone. 
  • The level of FSH increases,  enabling the beginning of a new cycle. 
Proliferative phase 
  • Lasts about 9 days
  • Estrogen stimulates proliferation and growth of the endometrium.
  • As estrogen, it suppresses secretion of FSH and increases secretion of LH.
  • Secretion of LH stimulates ovulation and the development of the corpus luteum. 
  • Ovulation occurs between days 12 and 16.
  • Estrogen level is high, and progesterone level is low.
Secretory phase 
  • Lasts about 12 days and follows ovulation. 
  • This phase is initiated in response to the increase in LH level.
  • The Graafian follicle is replaced by the corpus luteum. 
  • The corpus luteum secretes progesterone and estrogen. 
  • Progesterone prepares the endometrium for pregnancy if a fertilized ovum is implanted.

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