The development of the male reproductive system explained in a very simple way.
In this video we focus on the embryological development of the testis. In a future video we will discuss development of the external genitalia (both males and females), and the development of the ovaries, and uterus.
CORRECTION @ 13:36: The paramesonephric duct does not become the ovaries. It becomes the uterus and fallopian tubes. Sorry!
If you are completely new to embryology, and you have no idea whats going on, let this be the first video you watch:
→ kzfaq.info/get/bejne/opuXiKSDzb67hI0.html
The development of the kidney and gonads are very closely linked. I recommend you watch the embryology of the kidney video first to get the most out of the above video:
→ kzfaq.info/get/bejne/bpepdtOqq5i6mIU.html
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SUMMARY OF THE VIDEO FOR YOUR NOTES:
Sex differentiation is complex and involves many genes, e.g. Sex differentiating Region on the Y chromosome (SRY). The sex of the embryo is determined genetically at the time of fertilisation, but the gonads aren't either male or female until the 7th week of development. The gonads appear as a pair of longitudinal ridges (the genital or gonadal ridges), which are formed by the proliferation of the epithelium of the underlying mesenchyme (nephrogenic cord). Testis are derived from the intermediate mesoderm, and from germ cells that migrate from the epiblast.
The germ cells appear in the 6th week. They migrate through the primitive streak from the epiblast, by ameboid movement (explained in video) finally reach the gonadal ridge via the dorsal mesentery of the hindgut. if they fail to reach the gonadal ridges, the gonads will not be developed. The underlying mesenchyme proliferates and forms the primitive sex cords and it is impossible to differentiate between male and female at this point (thus the indifferent gonad).
Under the influence of SRY which encodes the testis-determining-factor, the primitive sex cords continue to proliferate and penetrate deep into the medulla to form the testis (or medullary cords). Toward the hilum, the cords break up into a network of cell strands that later give rise to the rete testis. Additional development sees the appearance of the tunica albuginea. Leydig and Sertoli cells are also differentiating at this time.
Leydig cells begin to produce testosterone and the testis is able to influence sexual differentiation of the genital ducts and the external genitalia (penis). Testis cords remain solid until puberty, when they acquire a lumen, thus forming the seminiferous tubules. Once canalised, they join the rete testis tubules which in turn enter the ductus efferentes (efferent ductules). These ductules link the rete testis and the mesonephric duct which becomes the ductus deferens.