Question

What is the difference between the development of the male reproductive tract and the female reproductive tracts? (think ducts)

Biology

Answer 1

The development of male and female reproductive system begins soon after the fertilization. Primordial cells starts to develop after 1 month of conception. Without much prompting all fertilized egg will develop in females.To become a male, an individual must be exposed to the cascade of factors initiated by a single gene on the male Y chromosome. This is called the SRY (Sex-determining Region of the Y chromosome). Because females do not have a Y chromosome, they do not have the SRY gene. Without a functional SRY gene, individual develop into female.

Indifferent Stage-development of gonads

During the first stage of gonadal development, it is impossible to distinguish between the male and female gonad. Thus, it is known as the indifferent stage.

The gonads begin as genital ridges – a pair of longitudinal ridges derived from intermediate mesoderm and overlying epithelium. They initially do not contain any germ cells.

In the fourth week, germ cells begin to migrate from the endoderm lining of the yolk sac to the genital ridges, via the dorsal mesentary of the hindgut. They reach the genital ridges in the sixth week.

Simultaneously, the epithelium of the genital ridges proliferates and penetrates the intermediate mesoderm to form the primitive sex cords. The combination of germ cells and primitive sex cords forms the indifferent gonad – from which development into the testes or ovaries can occu

Testes

In a male embryo, the XY sex chromosomes are present. The Y chromosome contains the SRY gene, which stimulates the development of the primitive sex cords to form testis (medullary) cords. The tunica albuginea, a fibrous connective tissue layer, forms around the cords.

A portion of the testis cords breaks off to form the future rete testis. The remaining cords contain two types of cells:

• Germ cells
• Sertoli cells (derived from the surface epithelium of the gland).

In puberty, these cords acquire a lumen and become the seminiferous tubules – the site within which sperm will be formed.

Located between the testis cords are the Leydig cells (derived from the intermediate mesoderm). In the eighth week, they begin production of testosterone – which drives differentiation of the internal and external genitalia.

Ovaries

XX sex chromosomes are absent in the female embryo. As there is no Y chromosome, there is no SRY gene to influence development. Without it, the primitive sex cords degenerate and do not form the testis cords.

Instead, the epithelium of the gonad continues to proliferate, producing cortical cords. In the third month, these cords break up into clusters, surrounding each oogonium (germ cell) with a layer of epithelial follicular cells, forming a primordial follicle.

The Internal Genitalia

Indifferent Stage

During the first weeks of urogenital development, all embryos have two pairs of ducts, both ending at the cloaca. These are the:

• Mesonephric (Wolffian) ducts
• Paramesonephric (Mullerian) ducts

Male

In the presence of testosterone (produced by the Leydig cells), the mesonephric ducts develop to form the primary male genital ducts. They give rise to the efferent ductules, epididymis, vas deferens and seminal vesicles.

Meanwhile, the paramesonephric ducts degenerate in the presence of anti-Mullerian hormone – produced by sertoli cells in the testes. Its developmental remnant is the appendix testis; a small portion of tissue located on the upper pole of each testicle, which has no physiological function.

Female

In the female, there are no Leydig cells to produce testosterone. In the absence of this hormone, the mesonephric ducts degenerate, leaving behind only a vestigial remnant – Gartner’s duct.

Equally, the absence of anti-Mullerian hormone also allows for development of the paramesonephric ducts. Initially, these ducts can be described as having three parts:

• Cranial – becomes the Fallopian tubes
• Horizontal – becomes the Fallopian tubes
• Caudal – fuses to form the uterus, cervix

The lower 2/3 of the outer cervix is formed by sinovaginal bulbs (derived from the pelvic part of the urogenital sinus).