Answer following question is short.

What is menstrual cycle? Describe it in brief.

The menstrual cycle is the reproductive cycle in all primates and begins at puberty (menarche).
? In human females, menstruation occurs once in 28 to 29 days. The cycle of events starting from one menstruation till the next one is called the menstrual cycle. 
? During the middle of the menstrual cycle, one ovum is released (ovulation). 
? The cycle starts with the menstrual flow (3 to 5 days), caused due to the breakdown of the endometrium of the uterus. Blood vessels in the liquid state are discharged, but this occurs only when the ovum is not fertilised. 
? It is followed by the follicular phase. In this phase, the primary follicles mature into the Graafian follicles. This causes the regeneration of the endometrium, follicular growth, and the growing follicles to produce oestrogen. 
? The LH and FSH are at their peak in the middle of the cycle ($14^{th}$ day) and cause the rupture of the Graafian follicles to release an ovum. This phase is called the ovulatory phase. ? In the absence of fertilisation, the corpus luteum degenerates, thereby causing the disintegration of the endometrium and the start of a new cycle.