テストステロン: 機能と調節

Gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates the pituitary gland to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH). LH travels through the bloodstream to the testes, where it stimulates Leydig cells to produce and release testosterone. This hormonal cascade initiates the entire male reproductive hormone system.

FSH and LH stimulate Sertoli cells to release androgen-binding protein (ABP) around spermatogenic cells. ABP binds testosterone and increases its concentration within the seminiferous tubules, creating a high local testosterone environment essential for supporting sperm cell maturation and development throughout the spermatogenic process.

During prenatal development, testosterone drives differentiation of male internal reproductive structures, including the Wolffian ducts into seminal vesicles and vas deferens, and development of external genitalia. During puberty, testosterone promotes testicular growth and maturation while supporting secondary sexual characteristics like facial hair, deeper voice, increased muscle mass, and heightened libido.

When blood testosterone levels rise, they inhibit the release of gonadotropin-releasing hormone, FSH, and LH, reducing testosterone production. Additionally, inhibin produced by Sertoli cells suppresses FSH secretion specifically. This dual feedback system maintains hormonal homeostasis and prevents testosterone overproduction in males.

Leydig cells respond to LH stimulation by producing and releasing testosterone. Sertoli cells respond to FSH by releasing androgen-binding protein, which concentrates testosterone around developing sperm. Together, these cell types coordinate testosterone production and localization to support both hormone regulation and spermatogenesis.

Inhibin is produced by Sertoli cells when sperm production is adequate. It specifically suppresses FSH secretion from the anterior pituitary without affecting LH levels. This targeted feedback allows precise regulation of spermatogenesis while maintaining testosterone production, ensuring optimal reproductive function.

Testosterone directs structural development of internal ducts and external genitalia during fetal development. During puberty, it promotes functional maturation of the testes and drives secondary sexual characteristics including facial hair growth, voice deepening, and increased muscle mass. Both processes are essential for complete male reproductive development.