Women often find the term "follicular phase" in the medical literature and ask what it means.
What is the follicular phase?
This is the name for the first phase of the menstrual cycle before the onset of ovulation. The entire menstrual cycle is divided into several phases:
- the follicular phase;
- ovulatory phase;
- luteal phase .
The follicular phase begins with the first day of menstruation, and ends with ovulation. The ovulatory phase coincides with the release of the oocyte from the follicle, and after it begins the luteal phase.
How long does the follicular phase last?
The follicular phase lasts from 7 (short) to 22 days (long), its average duration is 14 days. During this phase, the endometrium is rejected and the menstrual period begins. Then, under the influence of the follicle-stimulating hormone (FSH) of the pituitary gland, the growth of the follicle begins in the ovary.
In the maturing follicle, estradiol is produced, under the influence of which the phase of proliferation of the endometrium in the uterus begins. With an increase in the concentration of estradiol in the follicle, inhibin B is released releasing the level of FSH with the maximum amount of estradiol at the onset of ovulation.
In the first 5 days of the phase, several follicles grow, in which several layers of cells around the oocyte and the follicular fluid appear. On the 5th-7th day of the follicular phase, one of the follicles becomes dominant, it overtakes others in growth, and it is in it that the greatest amount of estradiol and also inhibin B is synthesized. The non-dominant follicles that start with it undergo reverse development and their cavity overgrows. From this moment and before the onset of ovulation, the amount of follicular fluid and the level of hormones contained in it increase, which have a retarding effect on the pituitary gland. Thus, the level of FSH decreases, and this prevents the growth and maturation of other follicles.
Influence of the follicular phase on the endometrium
The change in the level of estrogens in the follicles, and the increase in their content in the blood, has a regulating effect on the growth of the endometrium in the uterus. With a low estrogen content, the desquamation (menstrual bleeding) phase begins. But, with an increase in their content, bleeding stops and the regeneration phase begins (simultaneously with the growth of follicles) and the proliferation (growth) of the endometrium in the uterus (coinciding with the growth of the dominant follicle ). In the ovulatory phase, by the time the egg leaves the follicle, the endometrium of the uterus is ready to attach a fertilized egg to the uterine cavity.