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Question
What is menstrual cycle? Describe it in brief.
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Solution
- The menstrual cycle is a series of cyclic changes that occur at intervals of about 28–30 days in a mature woman.
- It is controlled by pituitary hormones, namely FSH (Follicle Stimulating Hormone) and LH (Luteinizing Hormone), and ovarian hormones, estrogen and progesterone.
- Under the influence of FSH, the ovarian follicle containing the oocyte grows and matures.
- The growing follicle secretes estrogen.
- Estrogen stimulates the growth and regeneration of the inner lining of the uterus, called the endometrium.
- LH causes the mature follicle to burst and release the ovum. This process is called ovulation.
- After ovulation, the empty follicle is transformed into the corpus luteum, which secretes progesterone.
- Progesterone stimulates the endometrial glands to secrete nutrients and prepares the uterus for implantation of the fertilized ovum.
- If fertilization does not occur, the corpus luteum degenerates into the corpus albicans and stops secreting estrogen and progesterone.
- Due to the decrease in these hormones, the endometrium breaks down and is shed along with the unfertilized ovum through the vagina as menstrual flow, which lasts for about 3–5 days.
- If pregnancy does not occur, the menstrual cycle repeats regularly.
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