Question

When an ovum gets fertilized, the menstrual cycle stops temporarily in a woman. Give reason.

Answer 1

Hint: Menstrual cycle is defined as cyclic events that take place in a rhythmic fashion during the reproductive period of a woman’s life. Ovum is released from the Graafian follicle of the ovary into the abdominal cavity at the time of ovulation.

Complete answer:
After ovulation, if pregnancy does not occur, the thickened endometrium is shed or desquamated. This desquamated endometrium is expelled out through the vagina along with blood and tissue fluid. The process of shedding and exit of uterine lining along with blood and fluid is called menstruation or menstrual bleeding. At the end of the cycle, there is a sudden reduction in the release of estrogen and progesterone from the ovary. The decreased level of these two hormones is responsible for menstruation.

After the ovum is fertilized Follicular changes do not appear in the ovary and ovulation does not occur because the secretion of FSH and LH from the anterior pituitary is inhibited. Corpus luteum enlarges and secretes a large quantity of progesterone and a little estrogen, which are essential for maintaining the pregnancy. Increased secretion of progesterone and little estrogen prevents endometrium from shedding.

Note:When the ovum is released into the abdominal cavity during ovulation, it is in the secondary oocyte stage with a haploid number of chromosomes. Immediately after fertilization, the ovum, which is in the secondary oocyte stage, divides into a mature ovum and a second polar body. The second polar body is expelled. The nucleus of the matured ovum becomes a female pronucleus with 23 chromosomes, which include 22 autosomes and one sex chromosome called the X chromosome.