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Acrosome Medically Reviewed

Last Updated: April 7, 2020

Definition - What does Acrosome mean?

The acrosome is a cap that covers the head of the sperm. The acrosome facilitates the acrosomal reaction, which occurs when an egg cell and a sperm cell fuse together, leading to fertilization. Abnormal acrosomes can prevent fertilization and cause male-factor infertility.

FertilitySmarts explains Acrosome

The acrosome is important during the earliest stages of fertilization, in a phase known as the acrosomal reaction. During natural conception, sperm travel through a woman’s reproductive system looking for an egg. Once the egg has been located, the sperm attempts fertilization.

During this stage, the egg is coated with a thick membrane layering called the zona pellucida. The acrosome releases a digestive enzyme called acrosine, which dissolves the zona pellucida, allowing the sperm to penetrate the egg’s membrane. The head of the sperm then fuses with the egg, and fertilization occurs.

Acrosomal Reaction

What causes abnormalities?

Abnormalities of the acrosome can prevent this process from occurring. Misshapen or dysfunctional acrosomes can impede penetration, as they may not excrete the appropriate enzymes needed to break down the zona pellucida. This can be caused by:

  • Genetic conditions
  • Health disorders that impact sperm quality
  • Lifestyle choices that damage sperm quality, such as stress, smoking, drug use, or excessive alcohol intake

How is it evaluated?

There are several tests that evaluate sperm. While a standard sperm analysis can visually test the sperm for the presence of a typical acrosome, it cannot test the acrosome’s ability to function normally when introduced to an egg.

The acrosome reaction test uses a trigger, such as hormones or certain electrolytes to trigger the acrosome reaction sequence in a lab and evaluates the sperm’s performance. The results of this test indicate the quality of the sperm’s acrosome.

This test of sperm function can explain infertility in the cases of normal semen analysis when no female infertility factors are present. Additionally, it can predict the level of intervention required during assisted reproductive treatments.

Treatment Options

If the acrosome reaction is not functioning in vitro fertilization (IVF) with intracytoplasmic sperm injection (ICSI), in which the sperm is injected in the egg may be necessary, whereas intrauterine injection (IUI) in which the sperm is placed within the cervix, will not be effective.

Acrosome Sperm

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