Acrosome Reaction

Reviewed by Dr. Oreoluwa Ogunyemi, UrologistCheckmark
Published: December 31, 2016

What Does Acrosome Reaction Mean?

The acrosomal reaction is the process of the egg and sperm cells fusing together during 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 (typically in a fallopian tube), fertilization is attempted.

Sperm Meets Egg

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. A cap over the 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 enter the egg through the gap in the ZP. This allows the sperm to fertilize the egg.

Acrosomal Reaction Complications

In some cases, the acrosomal reaction cannot occur, preventing fertilization from occurring. When the prevention is caused by health factors of 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

Treatment Options

In some cases, treatment may be required to address the conditions of the acrosomal reaction. Intracytoplasmic sperm injection (ICSI), a lab-based procedure that injects sperm directly into the egg, can circumvent the acrosomal reaction.

Acrosome Reaction Diagram1. Sperm contacts the surface of an egg. 2. Acrosome reaction. 3. Sperm nucleus enters the cytoplasm of an egg. 4. The fusion of two gametes.

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