CHAPTER 22: THE REPRODUCTIVE SYSTEMS
V.THE FEMALE REPRODUCTIVE SYSTEM
Female Reproductive/Menstrual Cycle:
See Fig 22.33, page 911 and Table 22.4, page 910.
The female reproductive cycle is approximately 28 days in length and involves the interaction between several glands, hormones, and target sites.
Beginning at puberty, on Day 0, the hypothalamus secretes a releasing hormone that targets the anterior pituitary gland to secrete FSH.
FSH is secreted from Days 0-14.
FSH targets a primordial follicle and causes it to mature.
The maturing follicle secretes estrogen.
1.Estrogen is secreted from Days 1-14.
2.Estrogen targets the secondary sex organs to develop at puberty, and then maintains them throughout life.
On Day 14, the hypothalamus secretes a second releasing hormone that targets the anterior pituitary gland to secrete LH
LH is secreted on Day 14 only.
LH targets the mature secondary follicle and causes it to burst.
The secondary oocyte is released into the fallopian tube.
The follicle becomes the corpus luteum.
1.The corpus luteum secretes progesterone.
Progesterone is secreted from Days 14-24.
Progesterone targets the uterine endometrium to prepare for implantion.
Progesterone causes the endometrium to become thick, glandular, and vascular.
If implantion does not occur by Day 24, the corpus luteum degenerates and levels of progesterone (and estrogen) decline.
This decline occurs from Days 24-28.
The hypothalamus detects this decrease and initiates a new cycle by secreting a releasing hormone that targets the anterior pituitary gland to secrete FSH on Day 0.
FSH begins new cycle by maturing follicle.
FSH ends previous cycle through menstruation of the endometrium.
4.If implanation does occur by Day 24, the corpus luteum continues to secrete progesterone to maintain the developing embryo, until the placenta is formed (end of month 3).