Maturation of sperm

Maturation of sperm

1. Maturation of Sperm Dr. Ghizal Fatima

2. The Sperm Development Process The sperm development process follows a series of steps involving phases of cell divisions and differentiations. Inside the testes millions of tubules simultaneously produce sperm at different maturation stages. This assembly line architecture ensures that mature sperm is available at all times. Nevertheless, overall sperm quality (male fertility) can fluctuate significantly. Throughout this development, sperm needs access to certain nutrients such amino acids, vitamins, trace elements, hormones, enzymes etc to ensure healthy development. At the same time, sperm needs to be safeguarded from oxidative stress which can significantly disrupt development and maturation.

3. How long does it take? While most of this development takes place in the testicles, sperm must migrate into the epididymis before it can fully mature. The maturation process inside the testicles’ tubules takes a total of 64 days. While still in the tubules, sperm is immobile and unfertile. Only in the finally maturation stages within the epididymis does the sperm gain fertility and mobility. After this, transportation and final maturation phase into the epididymis  takes another 2 weeks. The sperm cells are stored here for ejaculation and gain their full motility. The entire process therefore takes 78 days or 11 weeks to complete.

4. Sperm maturation occurs  in the epididymis . The optimal environment for sperm maturation is determined by the epididymal epithelial cells. Gene expression in the epididymis is under the control of androgens and other testicular factors, and it is tightly regulated in a region-specific manner.

5. Processes in the testis The spermatozoa are produced from the spermatogonia of the testis. They arise through mitotic and meiotic divisions in the seminiferous tubules ( see spermatogenesis ). Around 600 - 800 seminiferous tubules build the main part of the testis parenchyma and are arranged in over 300 tiny, incompletely partitioned lobules. With a length of roughly 50 - 60 cm for an individual seminiferous tubule it can be calculated that in a single testis a total canal length of around 300 m is accommodated. In addition, the cells that produce the hormone testosterone ( Leydig's cells) are present in the interstitial tissue as well.

6. Processes in the epididymis Following their production in the seminiferous tubules of the testis, the sperm cells are collected and stored in the ductus epididymidis . Maturation steps of the spermatozoa in the epididymis : Through the deposition of new proteins in the nucleus, the  DNA becomes more condensed . The sperm head becomes smaller, thereby, and more compact. This is an important step for the later correct decondensation of the paternal DNA in the maternal oocyte . The   cytoplasma is further reduced , making the sperm cells more slender. The  ability for motility  is achieved but at the same time inhibited by the milieu. The structure of the  plasma membrane  is altered. This has effects on the motility, the capacitation ability and the ability for the acrosome reaction.

7. Only spermatozoa that have passed through the epididymis are mature enough to be capable of motility.

8. Maturation steps There are parallels between getting the spermatozoa ready and the maturation of an oocyte but there are also clear differences. The spermatozoa have to go through several  temporal maturation steps in a series of different locations  in order to be capable of penetrating into the oocyte . While the oocyte's maturation steps involve the storing of yolk and the process of meiosis, functional maturation steps are required with the spermatozoa, which mainly involve their  motile abilities  along with their  ability to penetrate  through the egg covering.

9. The spermatozoa experience an initial maturation step during the time they are "stored" in the  epididymis . When the  ejaculation  occurs, a second step follows that leads to a  sudden activation of their motility . The third step takes place during their  stay  in the female genital tract, especially during the  ascension  towards the ovary through the uterus and fallopian tube. The spermatozoa experience thereby the so-called  capacitation . Finally, the last activation step follows: the  acrosome reaction  in the immediate  vicinity of the oocyte .

10. The maturation and activation of the spermatozoa occur in the following four steps : Storage in the epididymis Maturation Ejaculation Activation Ascension to the ovary Capacitation Near the oocyte Acrosome reaction