Even during intrauterine development, more than 500,000 follicles are embryonic in girls' bodies. Upon reaching adulthood, about 40,000 such structures remain in the reproductive system. During life, no more than 500 eggs are fully matured, and the rest of the microscopic oocyte rudiments undergoes atresia.
What does follicle mean?
A follicle is a structural element of the female reproductive glands, which consists of an oocyte surrounded by a layer of connective and epithelial tissue. It contains only one oocyte of the 1st order, inside which there is a small nucleus - the "germ bladder".
The oocyte (egg cell) is enclosed in a dense glycoprotein capsule surrounded by granulosa cells. Their surface is covered with a thin acellular matrix layer around which the theca-cell is located.
Follicles in the ovaries
Inside the ovaries, oocytes mature, ready for sperm fertilization. Conception is possible only in the case of their full development and maturation. Often hormonal disorders lead to the appearance of abnormalities that provoke the formation of a cyst or infertility.
The main task of the follicle is to protect oocytes from destruction and the negative influence of endogenous factors. The eggs in the female reproductive glands are still immature. That is why the success of conception and the course of pregnancy largely depend on the degree of protection of oocytes from the influence of destructive factors.
Follicle development stages
Folliculogenesis is the continuous maturation of follicles, which begins in the antenatal period and ends in the menopause. Due to apoptosis, most immature female germ cells die. Only a small part of them goes through the entire cycle of maturation and takes part in ovulation.
The types of structural elements of the ovaries are determined by the stage of their development:
- primordial (embryonic);
- preantral (primary);
- antral (secondary);
- preovulatory (graafian vesicles).
24 hours before ovulation, the production of estrogen increases, stimulating the flow of luteinizing hormone into the blood. It is peptide hormones that initiate the formation of a bulge in the follicular sac, from which the oocyte subsequently emerges (ovulation).
Follicle cycle
Throughout the entire menstrual cycle, changes occur in a woman's reproductive system that precede ovulation. The size and location of follicular sacs is determined by the phases of this cycle:
- menstrual (duration 3-6 days) - bleeding from the uterus caused by endometrial rejection;
- follicular (duration 14 days) - the process of development of new structural elements of the ovaries, which begins with the production of luteinizing and follicle-stimulating hormones, which accelerate their growth;
- ovulatory (duration 3 days) - rupture of the dominant follicle with the subsequent release of the oocyte, ready for fertilization;
- luteal (duration 16 days) - intensive production of progesterone and estrogen, preparing the female body for pregnancy.
Ripe oocytes are visible with the naked eye on the screen of an ultrasound scanner. Normally, in one menstrual cycle, from 1 to 3 dominant follicles mature.
Follicles grow poorly
Underdevelopment of the structural components of the ovaries is one of the main causes of female infertility. In the absence of a dominant follicle, luteinizing hormones do not enter the bloodstream, which stimulates the onset of ovulation. The main reasons for insufficient development of germ cells include:
- pathology of the hypothalamus;
- violation of the generative function of the ovaries;
- contraceptive abuse;
- the consequences of infection in small genital organs;
- pathology of the thyroid gland;
- endocrine disorders;
- depression and emotional instability;
- the formation of tumors in the pituitary gland.
Adequate hormone therapy can restore the menstrual cycle and the maturation of oocytes. With the ineffectiveness of conservative treatment, ovarian cauterization is prescribed, which consists in the surgical removal of underdeveloped cells from the gonads.
Follicles with IVF
The probability of conception is influenced by the number of antral follicles in the female reproductive glands. In the absence of pathologies, their number is on average 16-26 pieces. In this case, the probability of successful maturation of the dominant follicle is almost 100%.
An increased content of oocytes in the ovaries often indicates the development of polycystic disease. Gynecological pathology is diagnosed in 65% of cases in patients suffering from infertility. With polycystic disease, there is no ovulation phase, so a woman cannot get pregnant.
If there are no more than 6 immature follicles in the ovaries, the probability of ovulation is reduced to 5%. In this case, natural conception is almost impossible, therefore women are recommended to undergo in vitro fertilization (IVF).
Follicle puncture with IVF
Follicle puncture is a minimally invasive procedure, the purpose of which is to extract an egg from the gonads. In vitro fertilization of the oocyte and embryo transfer into the patient's uterus are carried out.
The process of extracting female germ cells is carried out according to the following scheme:
- under general anesthesia, a thin needle is inserted into the ovary;
- after the penetration of the needle into the follicle, the oocyte is taken;
- the egg cell is cleaned of epithelium and placed in a special incubator.
The prepared oocyte is fertilized with a sperm, after which the embryo is transplanted into the patient's uterus.
Stimulation of follicles with IVF
With hormonal infertility, it is impossible to extract a mature egg from the ovary due to the absence of ovulation and the biochemical processes preceding it. It is possible to increase the chances of successful conception with the help of IVF if several mature eggs are selected at once.
To stimulate the growth of germ cells, hormonal preparations are used, due to which from 8 to 15 follicles are formed in the ovaries. During the puncture, specialists select only the largest of them, the diameter of which is 15-20 microns.
Follicle growth with IVF
In the process of stimulating superovulation, doctors control the growth rate of germ cells, which is carried out using transvaginal ultrasound. The survey begins five days after the start of hormone therapy. With insufficient development of organic structures of the ovaries, the dose of drugs taken increases.
The growth rate of female germ cells is no more than 2 mm per day. When the diameter of the follicles reaches 16 mm, the patient is prepared for a puncture to collect the oocyte. By the time the procedure begins, the state of the endometrium is assessed, the thickness of which should be in the range from 7 to 9 mm.
