Theca of follicle

The theca folliculi comprise a layer of the ovarian follicles. They appear as the follicles become tertiary follicles.

The theca are divided into two layers, the theca interna and the theca externa.

The theca interna is responsible for the production of androstenedione, and indirectly the production of 17β estradiol, also called E2, by supplying the neighboring granulosa cells with androstenedione that with the help of the enzyme aromatase can be used as a substrate for this type of estradiol.