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.