Capacitation

Capacitation

Capacitation is a crucial physiological process that spermatozoa must undergo to gain the ability to fertilize an egg. This process occurs after ejaculation when sperm are exposed to the female reproductive tract, although it can also be induced in vitro. Capacitation involves a series of biochemical and physiological changes that prepare the sperm for successful fertilization.

Overview

Capacitation is a complex process that involves several changes in the sperm cell, including alterations in the sperm plasma membrane, changes in motility patterns, and the activation of signaling pathways. These changes are essential for the sperm to penetrate the zona pellucida of the egg and achieve fertilization.

Biochemical Changes

During capacitation, the sperm plasma membrane undergoes significant changes. Cholesterol is removed from the membrane, increasing its fluidity. This change is facilitated by albumin and other factors present in the female reproductive tract. The removal of cholesterol is thought to be a key step in preparing the sperm for the acrosome reaction, which is necessary for penetrating the egg.

Changes in Motility

Capacitated sperm exhibit a change in motility known as "hyperactivation." This is characterized by increased flagellar beat amplitude and asymmetrical tail movement, which enhances the sperm's ability to navigate through the viscous environment of the female reproductive tract and reach the egg.

Signaling Pathways

Capacitation involves the activation of several signaling pathways, including the increase of intracellular calcium levels and the activation of protein kinases. These pathways lead to the phosphorylation of proteins that are critical for the acrosome reaction and other processes necessary for fertilization.

In Vitro Capacitation

In vitro capacitation can be achieved by incubating sperm in a defined medium that mimics the conditions of the female reproductive tract. This medium typically contains bicarbonate, calcium, and albumin, which are necessary for the capacitation process.

Importance in Fertility

Capacitation is a vital step in the fertilization process, and any defects in this process can lead to infertility. Understanding the mechanisms of capacitation can help in the development of treatments for infertility and in the improvement of assisted reproductive technologies such as in vitro fertilization.

Also see

• Acrosome reaction
• Sperm motility
• Fertilization
• Zona pellucida
• In vitro fertilization