The theca folliculi comprise a layer of the

ovarian follicle An ovarian follicle is a roughly spheroid cellular aggregation set found in the ovaries. It secretes hormones that influence stages of the menstrual cycle. At the time of puberty, women have approximately 200,000 to 300,000 follicles, each with t ...

s. They appear as the follicles become secondary follicles. The theca are divided into two layers, the theca interna and the theca externa. Theca cells are a group of endocrine cells in the ovary made up of connective tissue surrounding the follicle. They have many diverse functions, including promoting folliculogenesis and recruitment of a single follicle during ovulation. Theca cells and granulosa cells together form the stroma of the

ovary The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the bod ...

Androgen synthesis

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. Testosterone estradiol conversion

Theca cells are responsible for the production of

androstenedione Androstenedione, or 4-androstenedione (abbreviated as A4 or Δ4-dione), also known as androst-4-ene-3,17-dione, is an endogenous weak androgen steroid hormone and intermediate in the biosynthesis of estrone and of testosterone from dehy ...

, and indirectly the production of 17β estradiol, also called E2, by supplying the neighboring granulosa cells with

that with the help of the enzyme aromatase can be used as a substrate for this type of estradiol. FSH induces the granulosa cells to synthesize aromatase, an enzyme that converts the androgens made by the theca interna into estradiol.

Signaling cascade

Gonadotropin releasing hormone (GnRH) is released by projections of the hypothalamus into the anterior pituitary gland. Gonadotrophs are stimulated to produce

follicle-stimulating hormone Follicle-stimulating hormone (FSH) is a gonadotropin, a glycoprotein polypeptide hormone. FSH is synthesized and secreted by the gonadotropic cells of the anterior pituitary gland and regulates the development, growth, pubertal maturation, ...

(FSH) and

luteinizing hormone Luteinizing hormone (LH, also known as luteinising hormone, lutropin and sometimes lutrophin) is a hormone produced by gonadotropic cells in the anterior pituitary gland. The production of LH is regulated by gonadotropin-releasing hormone (Gn ...

(LH), which are released into the bloodstream to act upon the ovaries. Luteinizing hormone serves to directly stimulate theca cells. Together, these organs comprise the HPG axis. Within the ovaries, transmembrane G-protein coupled receptors (GPCRs) bind to LH in the bloodstream, and the signal is transduced to the interior of theca cells through the action of the second messenger cAMP and third messenger protein kinase A (PKA). Theca cells are then stimulated to produce

testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate, as well as promoting secondary sexual characteris ...

, which is sent in a paracrine fashion to neighboring granulosa cells for conversion to estradiol.

Disorders

Hyperactivity of theca cells causes hyperandrogenism, and hypoactivity leads to a lack of estrogen. Granulosa cell tumors, while rare (less than 5% of ovarian cancers), may both granulosa cells and theca cells. Thecomas are benign proliferations of theca cells that may present with hormonal dysfunction. Theca cells (along with granulosa cells) form the corpus luteum during oocyte maturation. Theca cells are only correlated with developing ovarian follicles. They are the leading cause of endocrine-based infertility, as either hyperactivity or hypoactivity of the theca cells can lead to fertility problems.

Folliculogenesis

Anatomy and physiology of animals Ovarian cycle showing from top left clockwise

In human adult females, the primordial follicle is composed of a single

oocyte An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The femal ...

surrounded by a layer of closely associated granulosa cells. In early stages of the ovarian cycle, the developing follicle acquires a layer of connective tissue and associated blood vessels. This covering is called the ''theca.'' As development of the secondary follicle progresses, granulosa cells proliferate to form the multilayered ''membrana granulosum.'' Over a period of months, the granulosa cells and thecal cells secrete antral fluid (a mixture of hormones, enzymes, and anticoagulants) to nourish the maturing

ovum The egg cell, or ovum (plural ova), is the female reproductive cell, or gamete, in most anisogamous organisms (organisms that reproduce sexually with a larger, female gamete and a smaller, male one). The term is used when the female gamete i ...

. In tertiary follicles, the single-layered theca differentiates into a ''theca interna'' and ''theca externa.'' The ''theca interna'' contains glandular cells and many small blood vessels, while the ''theca externa'' is composed of dense connective tissue and larger blood vessels.

References

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