Graaf's follicle is otherwise known as a mature ovarian follicle or a pre-ovulatory follicle. Graaf's follicle is the last stage of the ovarian follicle development phase. how is a Graaf bubble built? What happens to a ruptured Graaf follicle when fertilization occurs, and what happens when it is not?

Graaf's follicleis a mature ovarian follicle - the last stage of follicular development, whose task is to secrete.

In order for a Graaf follicle to form, the primary follicle must transform into a growing ovarian follicle, and this into a maturing ovarian follicle.
A woman's entire reproductive period lasts from the first menstruation to menopause, i.e. the cessation of menstruation. It is divided into the so-called menstrual (menstrual) cycles, in which the following phases can be distinguished:

  • menstrual bleeding
  • follicular phase (lasts approx. 14-17 days)
  • ovulation
  • luteal phase (lasts approx. 14 days)

In each menstrual cycle, under the influence of hormones of the hypothalamic-pituitary-ovary axis, periodic changes occur throughout the reproductive system - including the ovaries.

They are used, among others generation of second order oocytes, i.e. cells capable of fertilization. They are secreted by the so-called mature ovarian follicle (Graaf's follicle).

Graaf's bubble - construction

Graaf's follicle is located in the cortex of the ovary and is usually 15-25 mm in diameter. It contains an egg whose chromosomes are in the late prophase of the first meiotic division. This is called 1st order oocyte.

The peak of luteinizing hormone (LH) secretion, around 36 hours before ovulation, leads to the completion of meiotic division I.

As a result, a second-order oocyte is formed, inhibited in the metaphase stage with 23 chromosomes (the so-called haploid number of chromosomes) and the first polar body which then degenerates - it contains the genetic material remaining after the division.

The resulting 2nd order oocyte is located on the cumulus ovary and is surrounded by the following layers (from the egg to the outside):

  • transparent cover
  • radiant wreath
  • granular layer
  • inner basement membrane - contains numerous cells with propertiesendocrine and blood vessels
  • outer basal membrane - contains collagen fibers and smooth muscle fibers
  • bubble cover

Interestingly, intima cells synthesize androgens, which are transported to the granular layer of the follicle, where they are converted to estrogens - then released into the bloodstream.

In contrast, cells that make up the granular layer synthesize the so-called inhibin F, which is responsible for the inhibition of follitropin (FSH) secretion.

At the beginning of the cycle, under the influence of follicle stimulating hormone (FSH), about 20 out of several hundred primary follicles begin to grow. Only one of them (less frequently 2 or 3) reaches the stage of a Graaf bubble.

In the middle of the menstrual cycle, the Graafian follicle ruptures and the ovum (second-order oocyte) is released into the peritoneal cavity and then captured into the fallopian tube by its hyphae.

In the case of fertilization, the second meiotic division is completed, the second polar body is separated and karyogamy, i.e. the genetic material of the oocyte fuses with the genetic material of the sperm.

Graaf's vesicle: hemorrhagic corpus, yellow, whitish

After the release of the egg, the ruptured Graaf follicle fills with a blood clot - the so-called hemorrhagic corpuscle.

At the site of the clot, luteal cells begin to appear, which come from the rapidly dividing cells of the granulosa layer and the inner basement membrane.

Then the follicle together with the luteal cells forms the corpus luteum. It produces progesterone and oestradiol under the control of pituitary gonadotrophins.

If fertilization does not take place, the corpus luteum undergoes lytic and degenerative changes after about 11 days, and finally atrophy. It gradually loses its secretory functions and turns into scar tissue, forming the so-called whitish corpuscle.

Graaf vesicle after fertilization - gestational corpus luteum

When the released egg is fertilized and the embryo is implanted - the corpus luteum under the influence of the syncytiotrophoblast of the chorionic gonadotropin undergoes further proliferation and enlargement.

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They are then referred to as the gestational yellow body. It synthesizes steroid hormones (progesterone and estrogens) that are necessary for the proper maintenance and development of pregnancy.

This continues until the gestational corpus luteum takes over the function of the gestational corpus, i.e. around 9-10 weeks of pregnancy. Then the gestational corpus luteum slowly disappears and becomes whitish after delivery.

Category:

Female diseases