Inhibin is a protein hormone that plays a regulatory role in various bodily processes. It is involved in the endocrine system, particularly in areas related to reproduction. Inhibin primarily functions by influencing the secretion of other hormones, maintaining hormonal balance.
Main Production Centers
The primary sites for inhibin production are the gonads, which are the testes in males and the ovaries in females. In males, inhibin is mainly produced by Sertoli cells located within the seminiferous tubules. Inhibin B is the predominant form produced in males, and its levels correlate with the function of Sertoli cells and the process of sperm production.
In females, inhibin is produced by the granulosa cells in the ovarian follicles. The two main forms, inhibin A and inhibin B, are produced at different stages of the menstrual cycle. Inhibin A is primarily secreted by the dominant follicle and later by the corpus luteum, while inhibin B is produced by the small, developing antral follicles.
Its Role in Reproductive Hormones
Inhibin’s main function involves a feedback mechanism with the pituitary gland, specifically regulating Follicle-Stimulating Hormone (FSH) secretion. This hormone helps to control reproductive processes in both sexes. Inhibin acts to suppress the release of FSH.
In males, inhibin B is important for regulating FSH levels, which in turn supports the process of spermatogenesis, or sperm development. This feedback ensures that FSH levels are appropriate for sperm production without overstimulation. In females, inhibin B helps regulate FSH during the early follicular phase, influencing the growth and development of ovarian follicles. Inhibin A, produced by the dominant follicle and corpus luteum, also contributes to FSH suppression, which is important for regulating the menstrual cycle and ensuring balanced follicular maturation.
Other Production Locations
While the gonads are the main sites of inhibin production, it is also produced in other tissues throughout the body. During pregnancy, the placenta secretes inhibin A in significant quantities. Other locations that produce inhibin include the adrenal glands and the pituitary gland itself. Certain tumors can also produce inhibin, leading to elevated levels that can be used for diagnostic purposes.
Monitoring Inhibin Levels
Measuring inhibin levels in the blood can serve as a diagnostic tool. Inhibin B levels are used to assess ovarian reserve in females, providing an indication of ovarian function and the number of remaining follicles. Elevated levels of inhibin A or inhibin B can also function as tumor markers, particularly for granulosa cell tumors and some mucinous epithelial ovarian tumors.
Inhibin A is part of prenatal screening tests, such as the quad screen, used during the second trimester to assess the risk of certain chromosomal conditions, including Down syndrome. Abnormal inhibin levels can suggest underlying issues in the organs where it is primarily produced.