Describe briefly the processes involved in the differentiation of male and female internal genitalia.

Outline:

·        Formation of indifferent gonad

·        Role of hormones

·        Differentiation of genital ducts

Essay:

            Sex differentiation is a complex process that involves many genes, including some that are autosomal. The key to sexual dimorphism is the Y chromosome, which contains the testis-determining factor (TDF) gene on its sex-determining region (SRY). In the presence of this factor, male development occurs; in its absence, female development is established.

            Gonads appear initially as a pair of longitudinal ridges, the genital or gonadal ridges, and are formed by proliferation of the coelomic epithelium and a condensation of underlying mesenchyme. In human embryos, primordial germ cells appear at an early stage of development among endoderm cells in the wall of the yolk sac. They migrate to the primitive gonads at the beginning of the 5th week and invading the genital ridges in the 6th week of development.

            Initially, both male and female embryos have two pairs of genital ducts: wofflian and mullerian ducts. In the male, testosterone produced by the Leydig cells stimulates the growth and differentiation of the wolffian ducts into the epididymis, vas deferens, seminal vesicles and ejaculatory duct. This system is responsible for delivering sperm from the testis to the penis and into the vagina. Sertoli cells produce antimullerian hormone (AMH) which causes the mullerian ducts to atrophy.

            In the female, no AMH is produced, and in its absence the mullerian duct system is retained and differentiate into fallopian tubes at the upper ends, whereas at the lower ends they join to form the uterus, cervix and upper vagina.