Infertility in Men - Introduction

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Sperm are manufactured in several hundred microscopic tubes, known as seminiferous tubules, which make up most of the testicles.

Surrounding these tubules are clumps of tissue containing so-called Leydig cells. Here, testosterone is manufactured.

Sperm

Sperm Development. The life cycle of sperm takes about 74 days:

• Sperm begin partially embedded in nurturing Sertoli cells, which are located in the lower parts of the seminiferous tubules.
• As they mature and move along, they are stored in the upper part of the tubules. Young sperm cells are known as spermatids.
• When the sperm has completed the development of its head and tail, it is released from the cell into the epididymis. This C-shaped tube is 1/300 of an inch in diameter and about 20 feet long. It loops back and forth on itself within a space that is only about one and a half inches long. The sperm's journey through the epididymis takes about 3 weeks.
• The fluid in which the sperm is transported contains sugar in the form of fructose, which provides energy as the sperm matures. In the early stages of its passage, the sperm cannot swim in a forward direction and can only vibrate its tail weakly. By the time the sperm reaches the end of the epididymis, however, it is mature and looks like a microscopic squirming tadpole.
• At maturity, each healthy sperm consists of a head that contains the man's genetic material, his DNA, and a tail that lashes back and forth at great speed to propel the head forward at about four times its own length every second. The ability of a sperm to move forward rapidly and straight is probably the most significant determinant of male fertility.

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Ejaculation. When a man experiences sexual excitement, nerves stimulate the muscles in the epididymis to contract, which forces the sperm out through the penis:

• After being produced in the testicle, the sperm first pass through the epididymis and then into one of two rigid and wire-like muscular channels, called the vasa deferentia. (A single channel is called a vas deferens.)
• Muscle contractions in the vas deferens from sexual activity propel the sperm along past the seminal vesicles. These are clusters of tissue that contribute fluid, called seminal fluid, to the sperm. The vas deferens also collects fluid from the nearby prostate gland. This mixture of various fluids and sperm is the semen.
• Each vas deferens then joins together to form the ejaculatory duct. This duct, which now contains the sperm-containing semen, passes down through the urethra. (The urethra is the same channel in the penis through which a man urinates, but during orgasm, muscles close off the bladder so that urine cannot enter the urethra.)
• The semen is forced through the urethra during ejaculation, the final stage of orgasm when the sperm is literally shot out of the penis.