Figure 2: Schematic representation of the association between testicular volume and hormonal changes during postnatal development.

During infancy and childhood, there is little change in testicular volume, which depends mainly on Sertoli cell number. From a clinical standpoint, when testicular volume reaches 4 cc the boy is said to have started pubertal development (Tanner stage two). This is due mainly to Sertoli cell proliferation in response to increased FSH activity. Concomitantly, LH induces Leydig cell testosterone secretion, resulting in an increase in intratesticular testosterone concentration. This leads to Sertoli cell maturation (reflected by a decrease in AMH secretion and an increase in inhibin B, during Tanner stages two to three) and the development of full adult spermatogenesis, the main responsible for testicular volume growth between pubertal Tanner stages two to five. Subsequently, testosterone also increases in serum (Tanner stages three to five). AMH = anti-Müllerian hormone; FSH = follicle-stimulating hormone; LH = luteinizing hormone; T = testosterone; TV = testicular volume. Modified with permission from Edelsztein et al., 2016.³¹