A follicle is a small fluid sac of the ovary that contains a developing egg.
The mature follicle has a diameter between 17-28 mm.
At puberty, women have about 300,000 - 400,000 eggs. In the monthly menstrual cycle, a set of follicles, each containing an egg, is selected for growth and maturity. However, most of the follicles in this group do not reach maturity but decline.
One follicle is selected and matures each month.
When the follicle matures and grows to the correct size, the follicle ruptures and releases an egg, ready for fertilization.
This is usually about 14 days from the start of the menstrual cycle.
The follicle secretes hormones that cause various stages of the menstrual cycle.
The journey to ovulation begins in the late luteal phase of the previous menstrual cycle, where certain 2-5 mm healthy follicles form a population, from which the predominant follicles are selected for the next cycle. This process is called "recruitment." The normal number of such follicles is 3-11.
From the first to the fifth day of the menstrual cycle, the second process of "follicle selection" is to select a specific growing follicle with a size of 5-10 mm from all the recruited follicles and the rest. It begins when the follicle regresses or closes.
On the 5th to 7th day of the menstrual cycle, the "dominant process" begins when a particular 10mm follicle takes control and becomes dominant.
It also suppresses the growth of the remaining selected follicles and is, in a sense, destined for ovulation.
The follicle begins to grow at a rate of 2-3 mm per day and reaches a size of 17-27 mm shortly before ovulation.
The rapid growth of the follicle occurs shortly before ovulation, where the follicle begins to protrude from the ovarian cortex, reaches the notched edge, and literally explodes, releasing the follicle with some cystic fluid.
