capacitation /kəpas′itā″shən/ , the process in which the spermatozoon, after it reaches the ampulla of the fallopian tube, undergoes a series of changes that lead to its ability to fertilize an ovum. Capacitation accomplishes three changes in sperm requisite to their fertilizing an ovum. First is the ability to undergo the acrosome reaction. In the acrosome reaction the seminal plasma factors that coat the sperm are removed, and receptor mobility is restricted, all associated with decreased stability of the acrosomal membrane. As the sperm approaches the ovum, a rapid breakdown of the outer acrosomal membrane occurs, completing the acrosomal reaction. The second changes involve the egress of the enzyme contents of the acrosome, including hyaluronidase, corona-disposing enzyme, and the protease acrosin, all of which facilitate sperm penetration and fusion with the ovarian membrane. Third, the sperm become hypermotile, and this increased velocity is thought to be crucial in zona penetration by the sperm.
