Male Genital System – Genital System Development

by John McLachlan, PhD

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    00:01 third of the vagina. Now, let?s have a look at the developing male genital system.

    00:04 In this image, we can see the primary sex cords that are penetrating into the underlying mesoderm of the developing gonad. The primordial germ cells will arrive and take out position with respect to these initial cords. The primary sex cords will give rise to the Sertoli cells and the rete testis in the adult male. A little later still, we can see the efferent tubules that have been formed, and the spermatogonia are beginning to develop in association with these.

    00:39 There is going to be a significant shift of the testis during the course of development.

    00:45 The reasons for this are perhaps less clear than you might think. Most people know that sperm do not survive well at body temperature, but the key question here is, why do they not survive well at body temperature? All the other cells in your body survive at this temperature.

    01:00 And when the developing sperm cells aren?t mature, they also survive perfectly happily inside the body. So there?s a mystery here which remains unexplained. But they will undergo a significant shift in their position down towards the testicles. It will actually lie outside the body wall. In the female, the paramesonephric ducts persist, as we see, but in the male, the paramesonephric ducts are going to degenerate. And the mesonephric ducts are going to give rise to the ductus deferens. So here?s our equivalent summary for the male genital system. Starting again with the gonadal ridge, the mesoderm is going to give rise to the interstitial cells of the testis. And these will be the cells of Leydig. And the coelomic epithelium is going to give rise to the primary sex cords, which in males persist and will give rise to the seminiferous tubules, and to the Sertoli cells and the rete testis. The nephrons of the mesonephric system will give rise to the efferent ductules.

    01:59 And the mesonephric ducts themselves will develop under the influence of androgens in the developing male embryo into the epididymis, the vas deferens, and the seminal vesicles.

    02:10 The paramesonephric ducts, as we said, will degenerate, but there may be occasional remnants just as there were corresponding mesonephric remnants in the female. So the remnants of the paramesonephric system in the male may well be the, what?s called the appendix testis and the prostatic utricle. Again, surgeons may come across this during the course of operations. Now, let?s look at this process of the testis. At its lower end, the testis is connected to the body by a long ligament, which will become known as the gubernaculum.

    02:45 This is from the Latin word for a guvnor or controller. And as the body begins to expand through normal growth processes, the gubernaculum effectively tethers the testis.

    02:57 So it?s dragged further down the body with respect to the rest of the tissue. Note in this diagram that although it may appear as if the testis is inside the body cavity, in fact, it?s covered by a layer of mesoderm. So it?s slipping down behind the mesodermal wall to achieve this process. Then it will pause roundabout position of the pubic bone. Later on in development towards the time of birth, what will happen is that the gubernaculum will become actively contractile, and it will pull the testes down into this testicular sack. In front of where this happens, there is an open space called the processus vaginalis or vaginal process.

    03:40 Curiously, this is present in both males and females. As we?ll see, this can lead to difficulties later on. Once the testis is fully pulled down into its normal position, then the vaginal process will normally close leaving perhaps a patent space in front of where the testicle lies. Now, let?s have a look at the external genitalia. Again, in

    About the Lecture

    The lecture Male Genital System – Genital System Development by John McLachlan, PhD is from the course System-Specific Embryology with John McLachlan.

    Author of lecture Male Genital System – Genital System Development

     John McLachlan, PhD

    John McLachlan, PhD

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