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The anterior pituitary complex and hypophyseal portal system, where FSH and LH are released. Theca cells are responsible for synthesizing androgens, providing signal transduction between granulosa cells and oocytes during development by the establishment of a vascular system, providing nutrients, and providing structure and support to the follicle as it matures.
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. [ 1 ] After rupture of the mature ovarian follicle , the theca interna cells differentiate into the theca lutein cells of the corpus luteum .
Each type of cell behaves differently in response to FSH. Theca interna cells express receptors for luteinizing hormone . LH induces the production of androgens by the theca cells, most notably androstendione, which are aromatized by granulosa cells to produce estrogens, primarily estradiol. Consequently, estrogen levels begin to rise.
Androstenedione is released into the blood by theca cells. Conversion of androstenedione to estrone requires the enzyme aromatase. Androstenedione is a substrate for estrogen production in granulosa cells which produce aromatase. Thus, theca cells and granulosa cells work together to form estrogens. [8]
The luteinized cells produce androgens, which may lead to hirsutism and virilization (or masculinization) in affected women. [2] The term hyperthecosis refers to the presence of nests of luteinized theca cells in the ovarian stroma due to differentiation of the ovarian interstitial cells into steroidogenically active luteinized stromal cells.
Cell culture of granulosa cells can be performed in vitro. Plating density (number of cells per volume of culture medium) plays a critical role for the differentiation. A lower plating density makes granulosa cells exhibit estrogen production, while a higher plating density makes them appear as progesterone producing theca lutein cells. [12]
The theca externa is the outer layer of the theca folliculi. It is derived from connective tissue, the cells resembling fibroblasts , and contains abundant collagen . [ 1 ] During ovulation, the surge in luteinizing hormone increases cAMP which increases progesterone and PGF2α production.
The theca cells form mainly the androgens androstenedione and testosterone. These hormones may then be converted by aromatase in the granulosa cells into estrogens, including estradiol. The corpus luteum normally grows to about 1.5 centimeters in diameter, reaching this stage of development 7 to 8 days after ovulation.