Infertility in Men - Introduction

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Click the icon to see an image of the vas deferens.

Semen. In addition to providing the fluid that transports the sperm, semen also has other benefits:

• It provides a very short-lived alkaline environment to protect sperm from the harsh acidity of the female vagina. (If the sperm do not reach the woman's cervix within several hours, the semen itself becomes toxic to sperm and they die.)
• It contains a gelatin-like substance that prevents it from draining from the vagina too quickly.
• It contains sugar in the form of fructose to provide instant energy for sperm locomotion.

The Path to the Egg. The sperm's passage to the egg is a difficult journey.

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• Usually about 100 - 300 million sperm are delivered into the ejaculate at any given time. Even under normal conditions, however only about 15% of these millions of sperm are strong enough to fertilize an egg.
• To compound the problem, after the stress of ejaculation, only about 400 sperm survive the orgasm to complete the journey.
• Out of this number, a mere 40 or so sperm survive the toxicity of the semen and the hostile environment of the vagina to reach the vicinity of the egg. Normally, the cervical mucus forms an impenetrable barrier to sperm. However, when a woman ovulates (releases her egg, the oocyte), the mucous lining thins to allow sperm penetration.
• Sperm that manage to reach the mucus lining in the woman's cervix (the lower part of her uterus) must survive about four more days to reach the woman's fallopian tubes. (Here, the egg is positioned for fertilization for only 12 hours each month.)
• The few remaining sperm that penetrate the cervical mucus and are able to reach the fallopian tubes become capacitated.
• Capacitation is a one-time explosion of energy that completes the sperm's journey. It boosts the motion of the sperm and triggers the actions of the acrosome, a membrane that covers the head of the sperm and resembles a warhead. The acrosome is dissolved, and enzymes contained within it are released to allow the sperm to drill a hole through the tough outer coating of the egg.
• In the end, only one sperm gets through to fertilize the egg.

Review Date: 10/21/2010
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).