MENSTRUAL CYCLE -
It occurs only in Primates. Start at the age of 13 yrs. upto menopouse.
During this period, generally one egg is released every 28 dyas or so alternately from the two ovaries. Since the female is fertile for about 32 years and about 13 eggs mature each year, only about 466 eggs have a chance of reaching maturity.
Menstrual cycle consists of 3 phases.
1. FOLLICULAR (PROLIFERATING) PHASE -
It lasts for about 14 days.
It comprises the following events -
1. Level of FSH is increased in the blood early in the cycle.
2. FSH stimulates the grwoth of the selected primary ovarian follicle.
3. FSH stimulates follicle to secrete estradiol.
4. Estradiol inhibit secretion of FSH & stimulate secretion of LH.
5. LH induces graffian follicle to burst & eject its egg in to fallopian tube. It occurs after about 14 days.
6. Estradiol stimultes the uterus to prepare for implantation & nourishment of foetus.
7. Lining of fallopian tube becomes thick to move ova into uterus.
2. LUTEAL OR SECRETORY PHASE -
This phase lasts for 10 days. It involves following events -
1. LH stimulates graffian follicle to convert into corpus luteum.
2. Corpus luteum secretes progesteron and little amount of estradiol.
3. Progesteron inhibits the release of FSH so that it may not develop additional follicle & eggs.
3. MENSTRUAL OR BLEEDING CYCLE -
It lasts about for 4 days.
It involves following events -
(i) If fertilization does not occur, secondary oocyte undergoes autolysis.
(ii) In some wall of uterus secretes a luteolysine. It reaches to ovary where it causes autolysis of corpus luteum.
(iii) Stratum functionalis of endomatrium is given out with bleeding.
(iv) Menstrual flow continues for 3-5 days.
(v) Endomatrium tissue, unfertilised egg & 500-600 ml of blood are lost during this period.
Menstural is often described as funeral of unfertilized egg or weeping of uterus for the last ovum.