Anatomy and Physiology / Unit 10: The Urinary and Reproductive Systems
10.6 Reproductive Hormones and the Cycles
Notes
- Male: the hypothalamus releases GnRH, so the anterior pituitary releases FSH (supports sperm production) and LH (stimulates testosterone). Testosterone causes male secondary sex characteristics and sperm production. Negative feedback regulates it.
- Female ovarian cycle (about 28 days): follicular phase (FSH grows a follicle, which makes estrogen), ovulation (around day 14, caused by a sharp LH surge), luteal phase (the empty follicle becomes the corpus luteum, which makes progesterone and estrogen).
- Menstrual (uterine) cycle: menstruation (days 1-5, shedding of endometrium), proliferative phase (estrogen rebuilds endometrium), secretory phase (progesterone prepares it for implantation). If there is no pregnancy, the corpus luteum degenerates, hormone levels drop and menstruation begins.
- Menopause is the end of cycles, usually around age 50, when ovaries stop responding.
- Puberty begins when GnRH increases, usually between ages 8 and 14.
Practice
Which hormone surge triggers ovulation?
A surge of LH around day 14 causes the follicle to release the egg.
Which structure makes progesterone during the second half of the cycle?
The corpus luteum forms from the ruptured follicle and secretes progesterone.
What causes menstruation to begin if fertilization has not occurred?
Falling hormone levels cause the endometrium to shed.
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