SPERM CAPACITATION AND ACROSOMAL REACTION

SPERM CAPACITATION:

Sperm can enter the uterus within minutes of ejaculation. Furthermore, the sperm can usually survive for up to a day or two within the cervical mucus, but the sperm are not able to fertilize the egg until they have resided in the female tract for several hours and been acted upon by secretions of the tract. This process, is called sperm capacitation.

Capacitation causes:

• The previously wavelike regular beats of the sperm's tail to be replaced by a more whip like action that propels the sperm forward in strong surges.
• The sperm's plasma membrane to become altered so that it will be capable of fusing with the surface membrane of the egg,

ACROSOME REACTION:

Many sperm, after moving between the granulosa cells of the corona radiata still surrounding the egg, bind to the zona pellucida. The zona pellucida glycoprotein functions as receptors for sperm surface proteins. The sperm head has many of these proteins and so becomes bound simultaneously to many sperm receptors on the zona pellucida. This binding triggers what is termed as acrosome reaction in the bound sperm.

The plasma membrane of the sperm head is altered so that the underlying membrane-bound acrosomal enzymes are now exposed to the outside- that is, to the zona pellucida. the enzymes digest a path through the zona pellucida as the sperm, using its tail, advances through this coating.