Reproductive cycle of Female

Ovulation and all related phenomenon of ovary and uterus occur in cyclic manner. Period of cycle varies in different mammals, like, in rat every 5 - 6 days; rabbit 8 - 10 days; cow 15 days ; human 28 days.

It is two types :

• Estrous cycle and
• Menstrual cycle.

Estrous cycle : It occurs in non-primate mammals (cow, rat, rabbit etc.) ‘Estrous’ means ‘heat’ which denotes the ovulation time with very high level of estrogen in the female body.

The entire period is divided into four phases :

• Proestrous phase – Vaginal epithelium proliferates, follicles are near maturing stage, the estrogen level starts increasing.
• Estrous phase – The ‘heat phase’, when female develops strong desire for sex; the estrogen level is at its peak ; vaginal epithelium thickens and becomes keratinized; ovulation takes place. In some animals like cat, rabbit the ovulation does not occur without copulation hence, they are induced ovulators.
• Metestrous phase – Corpus luteum starts developing, the keratinized layer of vaginal epithelium breaks off. In monoestrous animals (e.g. bitch) hypertrophic mucosa of uterus breaks down and is discharged.
• Diestrous phase – The quiescent period, without any activity in the ovary and other parts. In monoestrous animals the period may be as long as the next breeding season (after one year) hence called as anestrous phase. In polyestrous animals it is the gap between two cycles like rat.