Talk:BGDA Practical - Female Reproductive Tract Histology

Primordial Follicle

are located in the cortex just beneath tunica albuginea. One layer of flattened follicular cells surround the oocyte (about 30 µm in diameter). The nucleus of the oocyte is positioned eccentric in the cell. It appears very light and contains a prominent nucleolus. Most organelles of the oocyte aggregate in the centre of the cell, where they form the vitelline body (probably not visible in any of the available preparations).

Primary Follicle

(preantral)

is the first morphological stage that marks the onset of follicular maturation (Which hormone stimulates follicular maturation and where is this hormone produced?). The previously flattened cell surrounding the oocyte now form a cuboidal or columnar epithelium surrounding the oocyte. Their cytoplasm may have a granular appearance, and they are for this reason also called granulosa cells. The continued proliferation of these cells will result in the formation of a stratified epithelium (with a distinct basement membrane) surrounding the oocyte. The zona pellucida (glycoproteins between interdigitating processes of oocyte and granulosa cells) becomes visible. Parenchymal cells of the ovary surrounding the growing follicle become organised in concentric sheaths, the theca folliculi.

Secondary Follicle

(antral)

Small fluid-filled spaces become visible between the granulosa cells as the follicle reaches a diameter of about 400 µm. These spaces enlarge and fuse to form the follicular antrum, which is the defining feature of the secondary follicle. The oocyte is now located eccentric in the follicle in the cumulus oophorus, where it is surrounded by granulosa cells. The theca folliculi differentiates with the continued growth of the follicle into a theca interna and a theca externa. Vascularization of the theca interna improves, and the spindle-shaped or polyhedral cells in this layer start to produce oestrogens. The theca externa retains the characteristics of a highly cellular connective tissue with smooth muscle cells. The oocyte of the secondary follicle reaches a diameter of about 125 µm. The follicle itself reaches a diameter of about 10-15 mm.

Tertiary Follicle

(mature, preovulatory or Graafian follicle)

increases further in size (in particular in the last 12h before ovulation). The Graafian follicle forms a small "bump" on the surface of the ovary, the stigma (or macula pellucida). The stigma is characterised by a thinning of the capsule and a progressive restriction of the blood flow to it. Prior to ovulation the cumulus oophorus separates from the follicular wall. The oocyte is now floating freely in the follicular antrum. It is still surrounded by granulosa cells which form the corona radiata. The follicle finally ruptures at the stigma and the oocyte is released from the ovary.