Menstrual Cycle

MENSTRUAL CYCLE

The reproductive cycle of females is called the menstrual cycle. The first menstruation begins at puberty and is called menarche. This cycle is repeated at an average interval of 28 days. During this cycle various changes occur simultaneously in the ovary and the uterus.

This cycle consists of four phases.

• Menstrual Phase or Bleeding Phase
• Follicular Phase (Proliferative Phase)
• Ovulatory Phase
• Luteal Phase or Secretary Phase

Menstrual Phase or Bleeding Phase

The cycle starts with the menstrual phase. This phase lasts for about 3 – 5 days. During this cycle bleeding occurs from the uterus of the females. The bleeding occurs due to breakdown of endometrial lining of the uterus and it’s blood vessels which form liquid that comes out through vagina.

Menstruation occurs only if the fertilization does not occur. The decreased LH production causes degeneration of corpus luteum which results in degeneration of uterine endometrium and the cycle starts.

Follicular Phase (Proliferative Phase)

The menstrual phase is followed by follicular phase. During this phase the primary follicles in the ovary grow to become a mature Graafian follicles. The endometrium of the uterus regenerates through proliferation. During this phase production of FSH increases. This stimulates follicular development and also secretion of oestrogen by growing follicles. This phase lasts from 6th to 13th day.

Ovulatory Phase

The production of LH and FSH reaches at peak level in the middle of the cycle. The mature Graafian follicle ruptures and the secondary oocycte (ovum) is released. It is called ovulation. It occurs on the 14th day.

Luteal Phase or Secretary Phase

This phase lasts for 10 – 12 days. After ovulation the remaining cells of the ovarian follicle are stimulated by the LH to develop corpus luteum. The corpus luteum secretes large amount of progesterone. It stimulates uterine glands to produce large amount of watery mucus. Progesterone also maintains endometrium of uterine wall which is necessary for implantation.

In the absence of fertilization, the corpus luteum degenerates. This causes degeneration of uterine endometrium and the new cycle begins.

HORMONAL CONTROL OF MENSTRUAL CYCLE

GnRH from hypothalamus causes release of FSH and LH. FSH stimulates growth of follicles and their secretion of oestrogen. LH stimulates corpus luteum to secrete progesterone.

Hormones show their effect as under:

Withdrawal of progesterone causes menstruation.

Increase in FSH and oestrogen causes follicular development.

LH causes ovulation and

The secretary phase is caused by increase in progesterone production.