Sperm capacitation is the final phase of sperm development, necessary for fertilization.
In vivo it occurs after ejaculation, when spermatozoa come into contact with the secretions of the female genital tract. Different spermatozoa undergo the capacitation process at different times. Thus, when they meet the oocyte, only some will have already completed this process.
During capacitation, spermatozoa undergo a series of changes such as:
- Modifications at the level of the head (acrosome) facilitating the ability to attach to the zona pellucida of the oocyte and carry out the acrosome reaction. During the acrosome reaction, enzymes contained in the acrosome are releases and facilitate the passage of the spermatozoon through the zona pellucida and reach the oocyte cell surface.
-The movement of capacitated spermatozoa is no longer rectilinear and changes to an oscillatory pattern characterized by strong lateral excursions of the sperm head (hyperactive movement). This movement, much more vigorous than the pre-capacitation movement, facilitates the entry of the spermatozoon into the oocyte.
In vitro capacitation is carried out in the laboratory by washing and subsequent centrifugation of the semen sample. In this way, it is possible to recover the morphologically normal and hyperactive progressive motile spermatozoa from the total sample.
In vitro sperm capacitation, in addition to serving as a diagnostic test, is also performed to prepare spermatozoa for artificial insemination or in vitro fertilization, in any of its variants.