In multicellular organisms, and particularly in mammals, both gonadal and germ cell development are essential for the transmission of genetic information to the next generations. The testes are paired ovoid organs located inside the scrotum but outside the abdominal cavity. They have two major functions: spermatogenesis and steroidogenesis. The former corresponds to the production of male gametes, spermatozoa; the latter, to the production of hormones that will influence spermatogenesis and consequently male reproductive function and health. The male and female reproductive organs have the same precursor tissues. Initially, the embryo has a bipotential gonad which may have a testicular or ovarian fate. Accordingly, Müllerian ducts form the uterus and fallopian tubes in females and Wolffian ducts form the epididymis, vas deferens, and ejaculatory duct in males. On the other hand, male sex determination is triggered by sex-determining region Y (SRY), which is located on the Y chromosome and works as a master regulator, initiating SOX9 expression. The latter causes urogenital development, a highly complex process, through a complex cascade of transcription factors and signaling events. These will promote testis differentiation and ultimately the production of hormones that will lead to male development and testicular function during adulthood. In this chapter, we will provide a brief overview of the testicular anatomy and functional organization, as well as its embryonic development.
Keywords: Genital ridge, Interstitial compartment, Leydig cells, Male reproductive tract, Peritubular myoid cells, Prenatal development, Pre-Sertoli cells, Sex-determining region Y, Sex differentiation, Testis cords, Tubular compartment.