Development of Normal Testis

Abstract

The embryological development of the male genital apparatus comprises two major stages. The first lasts from the middle of the third week to the end of the sixth week of embryonic life, and is the period of construction of the primordia of the genital apparatus. This is called the indifferent stage because the nature of the development is common to both the male and the female sex. At the end of this period, when both the gonads and the systems of canals (Wolffian ducts and Mullerian ducts) which connect them with the urogenital sinus are present, there is still no morphological feature which indicates the eventual destiny of the embryo as male or female; this is only revealed by the chromosome complement which is, of course, determined at fertilization. The second stage begins at the seventh week and consists initially of testicular differentiation by the transformation of the undifferentiated gonad in genetically male embryos. This testicular differentiation is controlled by the Y-heterochromosome and passes through several phases before its completion at puberty. The testicular hormone secretions are responsible, from a very early stage, for the differentiation of the male reproductive tract from the Wolffian ducts, the urogenital sinus and the primordia of the external genitalia.