Leydig cell
Summary
Leydig cells are testosterone-producing interstitial cells located in the testes, adjacent to the seminiferous tubules. They respond to luteinizing hormone (LH) from the anterior pituitary to synthesize testosterone from cholesterol. They are essential for male sexual differentiation, puberty, and spermatogenesis support.
Detail
Leydig cells are found in the interstitium between seminiferous tubules in the testis. LH from the anterior pituitary binds to LH receptors on Leydig cells, activating the cAMP/PKA pathway, which upregulates StAR protein and desmolase (CYP11A1) to convert cholesterol into pregnenolone, the precursor for testosterone synthesis. Testosterone produced by Leydig cells has both endocrine effects (virilization, libido, secondary sexual characteristics, bone/muscle growth) and local paracrine effects on Sertoli cells to support spermatogenesis (though Sertoli cells require FSH and testosterone together). Histologically, Leydig cells have abundant eosinophilic cytoplasm with lipid droplets and Reinke crystals (crystalloid inclusions), a useful diagnostic feature on pathology. Clinically relevant conditions include: Leydig cell tumors (usually benign, can secrete androgens or estrogens, causing precocious puberty in boys or gynecomastia in men due to peripheral aromatization); Klinefelter syndrome (47,XXY) where Leydig cell dysfunction leads to low testosterone and elevated LH/FSH; and hypogonadotropic hypogonadism where LH deficiency leads to Leydig cell dysfunction and low testosterone. Distinguishing Leydig cell disorders from Sertoli cell disorders is a common exam theme: Leydig cells make testosterone (stimulated by LH), Sertoli cells support spermatogenesis and secrete inhibin B (stimulated by FSH) and are the source of anti-Müllerian hormone in fetal development.
Sources
- First Aid for the USMLE Step 1
- Guyton and Hall Textbook of Medical Physiology
- Robbins and Cotran Pathologic Basis of Disease
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