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What is Menstrual Cycle-Definition, And Fertilization

August 25, 2022
written by Sidra Batool

The menstrual cycle is the time between ovulation and menstruation. During this period, the lining of the uterus sheds every month. This shedding is called menstruation. Menstruation usually lasts for two weeks.

Women go through their menstrual cycles every 28 days. Each cycle consists of four phases: the follicular phase, ovulatory phase, luteal phase, and menstruation. In the follicular phase, the egg matures and grows into a mature egg.

Then, during the ovulatory phase, the mature egg is released from the ovary. Finally, the luteal phase begins after the release of the mature egg. During this phase, the uterine lining thickens and prepares itself for implantation. If fertilization occurs, the embryo develops into a fetus. After the development of the fetus, the luteal tissue breaks down and menstruation starts.

What is Menstrual Cycle?

The cycle which involves the periodic proliferation of the inner lining of the uterus and maturation of egg accompanied by menses if fertilization does not occur is called the menstrual cycle. The menstrual cycle of female humans, apes (gorilla and chimpanzee),  and monkeys are similar to the estrus.

The periodic proliferation of the inner lining of the uterus and maturation of the ovum occurs in both cases. But if fertilization does not occur before the end of the cycle, menses occurs. The sloughing of the uterine lining is called menses.


Fertilization occurs in the upper region of the oviduct within hours of copulation. Fertilization is delayed in a few mammals.

1. Coitus (copulation) occurs in autumn in some bats. But fertilization is delayed until spring. Females store sperm in the uterus for two months. This delayed fertilization is an adaptation for winter dormancy. The females emerge from dormancy and fertilization occurs immediately.

2. In many other mammals, fertilization occurs immediately after coitus. But development is delayed for one or two weeks.

3. The embryonic diapause occurs in sea lions. It also occurs in some bats, bears, martens, and marsupials. The adaptive significance of embryonic diapause is different in different species. In the sea lion, embryonic diapause allows the mother to give birth and mate within a short interval. But her resources are not lost during nursing and pregnancy.

Similarly the young are born at a favorable time. 4. In some bats, fertilization occurs in the fall before hibernation. But birth is delayed to spring. The resources become abundant in the spring.

4. Menopause is the end of a woman’s reproductive years. It is characterized by the cessation of menstruation and the loss of ovarian function.

Premenstrual syndrome or PMS is a condition that occurs during the luteal phase of the menstrual cycle. Symptoms include mood swings, irritability, bloating, breast tenderness, fatigue, headaches, food cravings, acne, and cramps.

It is believed that women who suffer from PMS are more likely to experience depression, anxiety, stress, and other mental health issues.

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