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ovarian follicle

Sunday 18 February 2007

ovarian follicles


Definition: A follicle is an anatomical structure in which the primary oocyte develops. The primary role of the follicle is oocyte support.


- antral ovarian follicle

Ovarian follicles are the basic units of female reproductive biology, each of which is composed of roughly spherical aggregations of cells found in the ovary.

Ovarian follicles contain a single oocyte (immature ovum or egg).

These structures are periodically initiated to grow and develop, culminating in ovulation of usually a single competent oocyte in humans. These eggs/ova are only developed once every menstrual cycle (e.g. once a month in humans).


The cells of the ovarian follicle are the oocyte, granulosa cells and the cells of the internal and external theca layers. A follicle is an anatomical structure in which the primary oocyte develops.

- oocyte

  • Each month, one of the ovaries releases a mature egg, known as an oocyte. The nucleus of such an oocyte is called a germinal vesicle.

- granulosa

  • The granulosa cells are located within the follicle surrounding the oocyte.
  • Their numbers increase directly in response to heightened levels of circulating gonadotropins or decrease in response to testosterone.
  • The granulosa cells produce peptides involved in ovarian hormone synthesis regulation.
  • Follicle-stimulating hormone (FSH) induces granulosa cells to express luteinizing hormone (LH) receptors on their surfaces; when circulating LH binds to these receptors, proliferation stops.

- theca

  • The granulosa cells are enclosed in a thin layer of extracellular matrix: the follicular basement membrane or basal lamina (fibro-vascular coat in picture).
  • Outside the basal lamina, the layers theca interna and theca externa are found.


- primordial follicles

  • 400,000 primordial follicles containing primary oocytes are present at birth in ovarian stroma.
  • The primordial follicles travels from yolk sac endoderm to ovary, develops into oogonia and oocytes, arrests at prophase of mitosis

- maturing follicles

  • A maturing follicle is an oocyte with granulosa layer.
  • A maturing follicle lacks reticulum and are immunoreactive for vimentin, keratin, desmoplakin.
  • Types
    • primary follicles
    • secondary follicles
    • tertiary follicles
    • graafian follicles.
  • They contains Call-Exner bodies (rosette-like formations with central filamentous / eosinophilic material consisting of excess basal lamina), theca cells (within follicle, luteinized cells that produce sex hormones; external to follicle).

See also

- folliculogenesis
- oocyte development


- cystic follicles

  • Prominent cystic follicles are present at birth and puberty.

- atretic follicles


Any ovarian follicle that is larger than about two centimeters is termed an "ovarian follicular cyst" or "ovarian functional cyst".

Ovarian function may be measured by gynecologic ultrasonography of follicular volume. Nowadays, ovarian follicle volumes can be measured rapidly and automatically from three-dimensionally reconstructed ultrasound images.

Rupture of the follicle can result in abdominal pain (mittelschmerz) and is to be considered in the differential diagnosis in women of childbearing age.

Cryopreservation and culture

Follicles can develop from ovarian tissue after cryopreservation. Cryopreservation of ovarian tissue is of interest to women who want to preserve their reproductive function beyond the natural limit, or whose reproductive potential is threatened by cancer therapy, for example in hematologic malignancies or breast cancer.

For in vitro culture of follicles, there are various techniques to optimize the growth of follicles, including the use of defined media, growth factors and three-dimensional extracellular matrix support.

Molecular methods and immunoassay can evaluate stage of maturation and guide adequate differentiation.

See also

- Ovaries

  • folliculogenesis

- ovarian cyst

  • ovarian follicualr cyst