Menstrual cycle is the series of cyclic changes that occur in the reproductive tract of human females with a periodicity of 28 days. It is characterized by loss of vaginal blood for a few days.

Occurs from 13 years till 50-55 years. It is influenced by certain hormones, secreted by pituitary gland and ovary.

The menstrual cycle can be divided into three phases: 

1) Menstrual Phase (Bleeding Phase)

2) Proliferative or Follicular or Ovulatory Phase

3) Luteal or Secretory phase.

1) Menstrual Phase:

It is the phase of menstrual flow (menses) which continues for 3-5 days and involves discharge of blood, connective tissue, and mucus. It is due to the cast off the epithelium lining of endometrium. At this time, the level of oestrogen and progesterone is very low in blood.

Menstruation is observed only when the ovum remains unfertilized. The level of progesterone in blood decreases. It results in breaking down of the blood vessels of endometrium and loss of about 50-100 ml of blood, along with some mucus through the vaginal orifice. Also known as weeping of uterus.

2) Proliferative or Follicular Phase.

It involves the rapid proliferation of endometrial cells after the menstrual cycle. It lasts for 9-10 days from (Fifth day- Fourteenth day). It involves following changes:

a) It begins with the repair and proliferation of the damaged endometrium of reproductive tract and ruptured blood vessels after the menstrual cycle.

b) The release of FSH (follicular Stimulating Hormone) from anterior pituitary stimulates the development of the Graafian Follicles. Hence, this phase is also known as the follicular phase.

c) Graafian follicular cells secrets hormone called oestrogen. Its level increases gradually maximum on the 12th day of the cycle.

d) Oestrogen enhances proliferation of endometrium of the uterus and fallopian tubes. Endometrium becomes 2-3 mm thick and more vascular ready for implantation.

3) Secretory or Luteal or Ovulatory Phase.

It lasts for 12-14 days from the 14th-28th day of the menstrual cycle. This phase is characterized as follows:

a) It is the phase in which the luteinizing hormone (LH) is secreted by pituitary gland, hence called as luteal phase.

b) LH and FSH stimulates the ovulation (release of Ova). Ovulation is marked by a high concentration of both L.H. and F.S.H.

c) The cells of ruptured follicles form corpus luteum. It secrets a progesterone hormone.

d) Progesterone hormone inhibits the further maturation of any follicles or ovulation from ovary.

e) Progesterone inhibits the thickening of the endometrium for the implantation of the fertilized ovum. It also stimulates the uterine glands to secrete watery mucus. Progesterone also inhibits the mammary gland.

If the ovum is not fertilized, corpus luteum starts degenerating and the level of both the hormones progesterone and oestrogen decrease. At an about 28th day the progesterone level falls, the blood vessels constrict and prevent the blood supply to the endometrium.