Sperm and male reproduction
Sometimes a man has a normal sperm count but is still infertile. When this happens, many, if not half, of this person's sperm are abnormally shaped, have two heads, a head abnormality, or a body abnormality.
Abnormal spermatogenesis and male infertility
The seminiferous tubule epithelium can be destroyed by many causes. For example, bilateral orchitis caused by mumps can be a cause of infertility in some men. In addition, some male children are born with tubal epithelium due to narrowing of the vas deferens or other abnormalities. Finally, one cause of male infertility, which is often temporary, is an excessive increase in temperature in the testicles.
The effect of temperature on spermatogenesis
An increase in temperature can inhibit spermatogenesis because it can destroy most cells in the seminiferous tubules except for spermatozoa. That's why the testicles hang in two scrotum sacs outside the body even though there's only 2°C below body temperature. On cold days, the scrotal reflex pulls the testicles closer to the body to maintain this 2°C temperature difference. The scrotum, therefore, acts as a cooling mechanism for the testicles (controlled cooling), otherwise, spermatogenesis would be impaired during hot days.
An undescended testicle refers to the failure of the testicle to move from the abdomen to the scrotum during or near the time of birth. Along with the maturation of the male foetus, the testicles originate from the intra-abdominal sex germ. However, for about 3 weeks to 1 month after birth, the testicles move along the channels in the groin into the scrotum. Sometimes this process is incomplete, resulting in one or even both testicles remaining in the abdomen, in the inguinal canal, or anywhere else along the way.
A testicle that remains in the abdomen over time loses its ability to produce sperm. The epithelial cells of the seminiferous tubules will gradually degenerate, leaving only the interstitial organization of the testis. It is a testament to the fact that high intra-abdominal temperatures are responsible for the degeneration of seminiferous tubule cells and thus infertility, although this effect is uncertain. Nevertheless, transfer of testes from the abdomen to the scrotum before the onset of adult sexual life can be performed in men with undescended testicles.
The foetal testes secrete normal testosterone, which stimulates the testicles to move from the abdomen to the scrotum. Therefore, some, but not all, cases of undescended testicles are caused by abnormalities in the testicles that do not secrete enough testosterone. Surgery to transfer the testicle into the scrotum in such patients is unsuccessful.
The impact of sperm counts on fertility
A normal ejaculation male produces about 3.5ml of semen, and in 1ml of semen contains about 120 million sperm, (between 35 million and 200 million sperm). That means one ejaculation will release about 400 million sperm that are present in a few millilitres of semen. When the sperm count per millilitre falls below 20 million, the person may be infertile. Thus, although only a single sperm is required for fertilization, for some unknown reason, ejaculation requires such many sperm.
Figure. Infertile abnormal sperm compared with normal sperm on the right.
Effects of sperm morphology and motility on fertility
Sometimes a man has a normal sperm count but is still infertile. When this happens, many, even half of this person's sperm are abnormally shaped, have two heads, a head abnormality, or a torso abnormality as depicted in the figure. In other cases, the sperm may be structurally normal, but for some unknown reason, they are less motile or completely non-motile. Whenever a part of the sperm is irregularly shaped or not motile, the person may be infertile even though the rest of the sperm is completely normal.