Hyperthecosis is hyperplasia of the theca interna of the ovary.

Outside the basal lamina, the layers theca interna and theca externa are found.

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

In females, synthesis of estrogens starts in theca interna cells in the ovary, by the synthesis of androstenedione from cholesterol.

They surround the follicle's outermost layer, the basal lamina, and undergo cytodifferentiation to become the theca externa and theca interna.

After rupture of the mature ovarian follicle, the theca interna cells differentiate into the theca lutein cells of the corpus luteum.

Theca interna cells express receptors for luteinizing hormone (LH) to produce androstenedione, which via a few steps, gives the granulosa the precursor for estrogen manufacturing.

Theca interna (ti) showed more distinct LHR immunoreactivity, characterized by accumulation of LHR cytoplasmic granules.

Our results demonstrate for the first time that the theca interna of healthy follicles is composed of two distinct populations of theca interstitial cells (TIC).

The late-term secondary follicle is marked histologically by a fully grown oocyte surrounded by a zona pellucida, approximately nine layers of granulosa cells, a basal lamina, a theca interna, a capillary net, and a theca externa.

One group, which expresses BMP-4, is present as an outer layer of cells juxtaposed to the theca externa (TE), and another, which expresses BMP-7, is present at the proximal side of the theca interna near the basal lamina of the follicle.

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.

Porcine tissues (Figure 3) Porcine preovulatory follicles showed distinct LHR staining of theca interna, lack of LHR expression in vascular layer under the follicular membrane, and transition of granular cytoplasmic to surface LHR immunoreactivity in granulosa cells (Fig.