Acrosome Reaction

Definition - What does Acrosome Reaction mean?

The acrosomal reaction is the process of two sex gametes, known as the egg cell and the sperm cell, fusing together, causing fertilization. Acrosomal reactions are an essential step of conception, and any abnormality can prevent fertilization and cause infertility.

FertilitySmarts explains Acrosome Reaction

After intercourse, sperm swim through the female reproductive system in search of an egg. When the sperm locates the egg, fertilization is attempted. An egg released during ovulation is coated in a thick layer of clear membranes, called the zona pellucida (ZP). In order to penetrate the egg, the sperm has to break down the ZP coating. The tip of a sperm’s head, known as the acrosome, is filled with enzymes that release when an egg is located. The enzymes have digestive abilities, and dissolve the coating on the egg, creating a vulnerable gap for the sperm to enter. Once completed, the sperm is able to fuse to the egg through the gap in the ZP. This results in fertilization.

In some cases, the acrosomal reaction cannot occur, preventing fertilization from occurring. When the prevention is caused by health factors off the egg or sperm, it can lead to infertility.

Complications of the acrosomal reaction include:

  • Abnormal or missing acrosome
  • Tough or thick ZP (more common with advanced maternal age)
  • Spontaneous acrosomal reaction (when the acrosome of a sperm releases enzymes without being triggered by an egg)
  • Low sperm count or low functioning sperm

In some cases, treatment may be required to address conditions of the acrosomal reaction, including:

  • Intracytoplasmic sperm injection (ICSI), a lab based procedure that injects sperm directly into the egg, circumventing the acrosomal reaction
  • Assisted reproductive technology (ART) procedure involving lab based fertilization, increasing the chances of a healthy sperm reaching the egg, including intrauterine insemination (IUI) or in vitro fertilization (IVF)
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