What is the menstrual cycle?
Menstruation is a monthly physiological bleeding from the endometrium that lasts from about 4 days from the time of menarche to menopause. The occurrence of monthly menstrual flow is known as menstrual cycle.
Physiology of menstruation
The uterine changes which relate to menstruation occur in the corpora endometrium, as a result of its stimulation of the ovarian hormones; oestrogen and progesterone. These takes form of:
- Proliferative phase: in this phase the endometrium is under the influence of oestrogen.
- Secretory phase: the endometrium is under the influence of oestrogen and progesterone.
- Menstrual phase: the secretion of oestrogen and progesterone falls.
The Proliferative Phase
This begins at the end of menstrual phase and lasts for about 10 days ie until ovulation. During this period, a graffian follicle starts to develop in the ovary. FSH from anterior pituitary stimulates the cells of the graffian follicle to secrete oestrogen which is responsible for the growth of the endometrium from unchanged deeper layer.
At the conclusion of these phase, the endometrium consist of three layers:
A basal layer: lies immediately above the myometrium about 1mm in thickness. This layer never alter during the menstrual cycle. It contains all the necessary rudimentary structures for building up new endometrium
A functional layer: which contains tubular glands and is 2.5mm thick. This layer changes constantly according to the hormonal influences of the ovary.
A layer of cuboidal: ciliated epithelium Covers the functional layer. It deeps down to line the tubular glands.
The Secretory Phase
After the proliferative phase, ovulation takes place and corpus luteum is formed. The corpus luteum is under the influence of luteinizing hormone(LH) from anterior pituitary, secretes progesterone. This cause the endometrium which was being growing under the influence of oestrogen to undergo further growth and glands increase in size, become more tertous and secrete more mucus. Blood supply is also increased giving a red corrugated surface. This is in preparation for the fertilized ovum.
The Menstrual Phase
Should fertilization not take place the ovum dies, the corpus luteum disintegrates. The secretion of oestrogen and progesterone falls. The endometrium shows degenerative changes which is followed by bleeding lasting for 3-4 days.