September 10, 2010
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Male InfertilityTesticular Function
Ninety percent of the volume of the testes is taken up by the seminiferous tubules, which is where sperm are generated. Germ stem cells, called spermatogonia, provide sperm cells throughout a man's life. Each spermatogonium ultimately produces four spermatozoa.
As sperm cells develop, they go through several stages, from spermatogonia to spermatocytes, to spermatids, and finally to spermatozoa. As the spermatid matures, it is surrounded by a Sertoli cell, often called a "nurse" cell. Here the sperm develops its characteristic features — the head, the midpiece and the tail. The whole process from spermatogonium to spermatozoa, or sperm, takes about 74 days. As the sperm exit the seminiferous tubules, they have very little ability to move (motility), and cannot yet fertilize an egg on their own. The spermatozoa then move to the epididymis, a long, tightly packed convoluted tubule that can be felt along the outside of the testis. As the sperm traverse the epididymis, further maturation takes place; this takes another 10-15 days. So from germ cell to active spermatozoon there is about a 90-day development period. That means that if spermatogenesis were to stop completely at the germ cell level, the actual effect on sperm count would not be seen for three months. Conversely, recovery and resumption of spematogenesis may not be detectable by measuring sperm count for three months or so. Semen Production
The secretions containing sperm that exit the epididymis make up only about 10% of the total volume of the semen. These sperm are transported via a tube called the vas deferens. Each vas deferens joins the duct from the seminal vesicle to form the ejaculatory duct, which enters the urethra and crosses over the prostate gland.
The seminal vesicles contribute about 70% of the volume of semen. These consist of secretions that are alkaline and rich in fructose; they also contain coagulating factors. The prostate contributes another 20% of semen volume. Its secretions are acidic and contain certain enzymes. During ejaculation, the bladder neck closes and the secretions from the vas, the seminal vesicles and the prostate are propelled through the urethra. "Retrograde ejaculation" is a condition that occurs when the bladder neck does not close and the secretions are propelled into the bladder. This can be detected through urinalysis, which will show sperm in the urine. Fertilization
Once sperm are deposited in the vagina, they must pass through the cervical mucus, swim through the uterus and enter into the fallopian tubes. During this passage, the sperm undergo a series of changes and reactions that attract the sperm to the egg and make them capable of penetrating the layer of cells that surrounds the egg, as well as the zona pellucida, the thick coating of the egg. Part of this process is what is called the acrosome reaction, during which the cap over the head of the sperm dissolves, exposing enzymes that aid in penetrating the layers around the egg.
As a sperm is attracted to the egg and makes contact, it becomes much more vigorous. When one sperm penetrates the zona pellucida, it fuses with the egg cell membrane and enters the cytoplasm. The "zona reaction" then occurs; this is a release of substances just below the cell membrane that prevent penetration by another sperm. Clearly, there is a complex series of steps and reactions that must take place in the sperm to allow it to reach and penetrate the egg. Any one of these reactions can go wrong. The bottom line is that the more numerous the sperm, the better their motility, and the more normal they appear, the better the chance that fertilization will take place. Defects in Male Fertility: First Step - Semen Analysis
In most cases, when a couple is having trouble conceiving, they will consult their primary care physician or the woman's gynecologist for a preliminary evaluation. The next step would be for the man to have a semen analysis. This should be done at a facility that has the technical expertise and depth of experience to do a reliable test. For an optimal specimen, the man is advised to abstain from ejaculation for 2-3 days. It is better if the sample is then given to the laboratory as soon as possible after ejaculation. The sample is examined for volume, pH, sperm concentration, motility and morphology, and other characteristics. The normal ranges for these results are given below.(2)(3)(4)
Table 1.
Semen Analysis Values: Normal and Subfertile.
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