Urogenital System › Female Reproductive

Ovarian Follicle Histology

Notes

Ovarian Follicle Histology

Ovarian Follicles

Primordial Follicle

  • Comprises:
    • The primary oocyte, which is arrested in meiosis I
    • A single layer of flat granulosa cells; the granulosa cells and oocyte interact to guide follicular maturation
    • A basement membrane (aka, lamina) surrounds the follicle
    • In puberty, follicles are cyclically "recruited" for further development
  • Primordial follicles are found towards the outermost portion of the ovary

Primary follicle

  • Comprises:
    • The growing primary oocyte
    • Newly formed zona pellucida, which is thick a-cellular coat that covers the oocyte; It displays sperm receptors and facilitates the acrosome reaction necessary for fertilization; after fertilization, the zona pellucida prevents additional sperm from joining with the oocyte.
    • Single layer of granulosa cells transition from flat to cuboidal, which reflects their greater cellular activity.

Secondary follicle

  • Comprises
    • Primary oocyte; has achieved meiotic and developmental competence (it is capable of completing meiosis and preparing for implantation).
    • Zona pellucida, and,
    • Multiple layers of cuboid granulosa cell (typically 6-9 layers)
    • Theca cells, which arise from the ovarian interstitium, begin to accumulate around the basement membrane of the secondary follicle.

Tertiary follicle

  • Comprises
    • Secondary oocyte, which is the product of meiosis I (we've omitted the polar body)
    • Zona pellucida
    • Granulosa cells separated by the antrum
    • Cumulos oophorus is the collection of granulosa cells that support the secondary oocyte
    • Corona radiata is a subset of the cumulus oophorus that directly surround the zona pellucida.
    • Theca cells have diversified, and now form the theca interna and externa layers.
    • Of the late tertiary follicles, only one, the so-called "dominant follicle," is ovulated.

Ruptured follicle

  • Transitions physiologically and morphologically to become the corpus luteum, which acts as a temporary endocrine gland.
  • Ovulated secondary oocyte takes the corona radiata with it; in most cases, it is swept into the uterine tube and transported to the uterus for menstruation or implantation.

Images:

Histology (Mark Braun, MD, & Indiana University: http://medsci.indiana.edu/c602web/602/c602web/toc.htm; http://www.indiana.edu/~anat215/virtualscope2/start.htm)