Theca interna cells are a specialized cell layer within the ovary, playing a key role in female reproduction and hormone regulation. Their activity is fundamental to the development of ovarian follicles and the production of hormones that orchestrate the menstrual cycle and potential pregnancy.
Where Theca Interna Resides
Theca interna cells are situated as an inner layer of cells that surround a developing ovarian follicle. They are located adjacent to a structure called the basement membrane, which separates them from the innermost layer of cells, known as granulosa cells. Theca interna cells exhibit characteristics typical of cells that produce steroid hormones. This layer is richly supplied with blood vessels, forming an autonomous capillary network within the follicle. This vascularization is important for the transport of precursors for hormone synthesis and for the delivery of hormones to the bloodstream.
Its Central Role in Hormone Production
The primary function of theca interna cells is the synthesis of androgens, which are a group of male hormones. This process begins when luteinizing hormone (LH) binds to specific receptors on the surface of theca interna cells. This binding stimulates a signaling pathway that leads to the production of androgens from cholesterol.
Once synthesized, these androgens are then transported across the basement membrane to the adjacent granulosa cells. Inside the granulosa cells, an enzyme called aromatase, which is stimulated by follicle-stimulating hormone (FSH), converts these androgens into estrogens, primarily estradiol. This cooperative interaction between theca interna cells and granulosa cells, involving both LH and FSH, is often referred to as the “two-cell, two-gonadotropin” concept of estrogen biosynthesis. The estrogen produced then plays a role in stimulating the proliferation of granulosa cells, contributing to the growth of the follicle.
What Happens After Ovulation
After the mature egg is released from the ovarian follicle during ovulation, the remaining follicular cells undergo a transformation to form a temporary endocrine structure called the corpus luteum. Within this new structure, theca interna cells differentiate into “theca lutein cells.” These theca lutein cells, along with granulosa lutein cells, are responsible for the continued production of hormones within the corpus luteum.
Theca lutein cells primarily contribute to the production of progesterone, although they also continue to secrete some androgens. Progesterone is an important hormone that prepares the lining of the uterus for a potential pregnancy, making it receptive for the implantation of a fertilized egg. If pregnancy does not occur, the corpus luteum degenerates, leading to a decrease in progesterone levels and the onset of menstruation. If conception does occur, human chorionic gonadotropin (hCG) signals the corpus luteum to continue producing progesterone, sustaining the early stages of pregnancy until the placenta takes over hormone production around 12 weeks of gestation.