Page 846 - Atlas of Histology with Functional Correlations

Smaller follicles with cuboidal, columnar, or stratified cuboidal cells that

surround the primary oocytes (12) are called primary follicles (12). As the
follicles increase in size, a fluid, called liquor folliculi (follicular liquid), begins
to accumulate between the follicular cells, now called the granulosa cells (5).
The fluid areas eventually coalesce to form a fluid-filled cavity, called the
antrum (4, 20). Follicles with antral cavities are called secondary (antral)

follicles (21). They are larger and are situated deeper in the cortex (10). All
larger follicles, including primary follicles (12), secondary follicles (21), and
mature follicles exhibit a granulosa cell layer (5), a theca interna (6), and an

outer connective tissue layer, the theca externa (7).

The largest ovarian follicle is the mature follicle. It exhibits a large antrum
(4) filled with liquor folliculi (follicular fluid); a cumulus oophorus (1), the
mound on which the primary oocyte (2) is situated; a corona radiata (3), the
cell layer that is attached directly to the primary oocyte (2); granulosa cells (5)

that surround the antrum (4); the inner layer theca interna (6); and the outer theca
externa (7).

After ovulation, the large follicle collapses and transforms into a temporary
endocrine organ, the corpus luteum (16). The granulosa cells (5) of the follicle

transform into light-staining granulosa lutein cells (17), and the theca interna
(6) cells become the darker-staining theca lutein cells (18) of the functioning
corpus luteum (16). If fertilization and implantation do not occur, the corpus
luteum (16) regresses, degenerates, and turns into a connective tissue scar called
the corpus albicans (9, 14). This illustration shows a recent larger corpus

albicans (9) and an older smaller corpus albicans (14).

Most ovarian follicles do not attain maturity. Instead, they undergo
degeneration (atresia) at all stages of follicular growth and become atretic
follicles (22), which eventually are replaced by the connective tissue.

845