Question

The reproductive cycle in the female primates is called menstrual cycle. The first menstruation begins at puberty.

Answer the following questions:

1. Name the four phases of menstrual cycle in a proper sequence.
2. How long does the menstrual phase last in a menstrual cycle?
3. When and why hormones estrogen and progesterone reach their peak levels respectively, in the menstrual cycle?
4. Give the significance of LH surge.

Answer 1

1. The menstrual phase (period), follicular phase, ovulation, and luteal phase are the four stages of the menstrual cycle.
2. The menstrual phase lasts from the first to the fourth day of the menstrual cycle and lasts for three to five days.
3. During the follicular phase, estrogen levels progressively rise and peak approximately one day prior to ovulation, usually on days 12-14 of a 28-day cycle. A spike in luteinizing hormone (LH) causes this peak. Following ovulation, progesterone levels increase throughout the luteal phase, peaking five to nine days later (about day 21 in a 28-day cycle). This happens because the burst follicle becomes the corpus luteum, which generates progesterone, following ovulation.
4. The significance of the LH surge:
   • Ovulation is brought on by the LH surge, which causes the mature follicle to burst and release the egg. About 28-36 hours after the LH surge begins and 10-12 hours after it peaks, ovulation takes place.
   • Also, it induces the granulosa and theca cells to luteinize, creating the corpus luteum, which is in charge of producing progesterone.