Spermatogenèse

The spermatogenèse is the whole of the phenomena which, of the Spermatogonie S, original cells diploïdes (2n chromosomes), lead to the haploid spermatozoa, gamètes male (N chromosomes).

The Spermiogenèse is the differentiation of the spermatides in spermatozoa.

The spermatogenèse takes place in the seminiferous tubes of the Testicule S

Introduction

The spermatogenèse begins with puberty, reaches its maximum towards 20-30 years, slows down gradually towards forty but can continue until a advanced age. The spermatogenèse is a slow and continuous process requiring 74jours approximately at the man; it is held by thorough or vague successive along the seminiferous tube.

General outline

Seminiferous tube

The seminiferous Tube is limited by a formed thin tubular sheath of the blade or basal membrane, fibroblasts. Some of these fibroblasts contain contractile filaments and collagen fibers and constitute the cells myoïdes or myofibroblastes -

  • the tubular sheath is called clean membrane of the seminiferous tube or membrana propria .
  • These tubes are surrounded by conjunctive fabric (of “filling”) and also of formed fabric intersticiel of Cellules of Leydig which is, of course, traversed by small arteries and veinules bringing oxygen. (v. Testicle) These endocrine cells or cells of Leydig secrete primarily Testostérone (and dihydrotestostérone); they constitute interstitial gland of the testicle.
  • the wall of the seminiferous tube is made of a laminated epithelium including/understanding two types of cells
    • the cells of the germinal line laid out on 4 to 8 layers
    • the cells of Sertoli, cells high being pressed on the basal membrane and reaching the light of the tube by their apical pole;
  • In the adult seminiferous tubes, the various layers of germinal cells represent the phases of the spermatogenèse which are carried out in a centripetal way, since the spermatogonie located against the basal membrane until the spermatozoon released in the light: Under the microscope, one observes that these tubes “are filled” with apparently different cells, organized out of rings. With the periphery, one finds original cells (spermatogonies, while in the center the spermatozoa are. In fact, the not differentiated cells develop for finally becoming male gamètes:
    • Spermatogonie
    • Spermatocyte I
    • Spermatocyte II
    • Spermatide
    • Spermatozoon

Spermatogenèse

First of all, through multiples mitoses, starting from a spermatogonie, one obtains a stock from it. Then the spermatogonie grows and becomes spermatocyte I. At this stage, they are always original cells with 2n chromosomes. The Méiose of the spermatocytes I produces spermatocytes II which have nothing any more but N chromosomes (v. Méiose). The continuation of the Méiose leads to spermatides which migrate towards the " lumière" tube. The differentiation of those gives finally the spermatozoon, in the center of the tube. It is thus said that the spermatogenèse is “centripetal” .

This process is continuous, i.e. the cells change successively and are replaced by news spermatogonies obtained by Mitose.

In the seminiferous tubes, one notices also the presence of large cells, the cells of Sertoli, which support and nourish the spermatogonies and which are thus essential to the spermatogenèse.

The seminiferous tubes lead, by a system of drainage, with the epididymal Canal which becomes Vas deferens while leaving the testicles. The cells are propelled in this channel, and are mixed with the seminal liquid in the Prostate, to form the Sperme during ejaculation.

Hormones

Three hormones play a big role at the time of the spermatogenèse:

  • the Testosterone
  • LH (hormone lutéinisante)
  • FSH (hormone folliculostimulante)

LH and FSH are produced by the pituitary gland while the Testostérone is produced in the Cellules of Leydig.

The FSH acts directly on the spermatogonies and the cells of Sertoli to accelerate the spermatogenèse (by increased testosterone assimilation). The LH, as for it, increases the production of Testostérone which also acts on the spermatogonies (and allows in particular final differentiation) and on the cells of Sertoli. If the production of testosterone reaches a certain threshold, the cells of Leydig send a negative rétrocontrôle to the pituitary gland which inhibits the production of LH and FSH. It is thus a system autorégulé which does not allow the excessive production of testosterone, and thus of spermatozoa.

See too

External bonds

  • Summarized with diagrams
  • more technical Explanations

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