A. If fertilisation fails to occur menstrual phase starts. The endometrium (the lining of the uterus) breaks and its blood vessel form the liquid that comes out through the vagina is called menstrual flow. It lasts for 3 to 5 days.
During menstrual phase, the levels of hormones secreted by corpus luteum and hormones secreted by pituitary gland are low.
B. The follicular phase begins just after menstrual phase. In this phase, the primary follicles mature into the Graafian follicle under the influence of follicle stimulating hormone (FSH) and Luteinising hormone (LH). As the follicles and the endometrium proliferate during the follicular phase, it is also known as the proliferative phase.
C. The LH and FSH are at their peak in the middle of the cycle (14th day) this causes the rupturing of the Graafian follicle to release the ovum (secondary oocyte) and the remaining parts of the Graafian follicle changed to the corpus luteum.
D. Structure of a Graafian follicle:
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