Physiology

Male infertility and CaSa System

Male infertility—the inability of sperm cells to fertilize an egg cell—has several causes. if, during fetal development, the testes do not descend into the scrotum, the higher temperature of the abdominal cavity or inguinal canal impedes development of sperm cells in the seminiferous tubules. Certain diseases, such as mumps, may infl ame the testes (orchitis), impairing fertility. The quality and quantity of sperm cells are essential factors in the ability of a man to father a child. if a sperm head is misshapen, if the acrosome is too tough to burst and release enzymes, or if too few sperm cells reach the well-protected egg, fertilization may not happen. The structure of the sperm tail is particularly important. Male infertility can result from sperm tails that are irregularly shaped, coiled, bent, shortened, or absent.


Computer-aided sperm analysis (CaSa) is a technique used to evaluate a man’s fertility. it can analyze the pathways of up to 200 moving sperm in a few seconds. CaSa assesses the number of cells per milliliter of seminal fl uid (density), sperm motility, and the size and shape of sperm cell parts (morphology).

a computer tracks sperm cell movements. in semen, sperm cells swim in a straight line
(a), but as they are activated by biochemicals in the woman’s body, their trajectories widen (b). The sperm cells in (c) are in the mucus of a woman’s cervix, and the sperm cells in (d) are attempting to digest through the structures surrounding an egg cell.

In a sperm analysis, a man abstains from intercourse for two to three days, then provides a sperm sample. This may be done either in a clinical setting or at home using a kit ordered from the internet, with the sample mailed to a lab. The man provides information about his reproductive history and possible exposure to toxins. The CaSa system captures images with a digital camera and analyzes and integrates information on sperm density, motility, and morphology. a computer may also be used to track sperm progress,
in a woman’s body, toward fertilizing an egg cell.


Devices are being developed that will enable a man to estimate his sperm count at home. They indicate whether a man’s sperm count is above or below the World health Organization’s designation of 20 million sperm per milliliter of ejaculate as the lower criterion for normal fertility. if several tests performed days apart fall below this level, the man should consult a fertility specialist for further testing. It indicates characteristics of a man’s sperm output that are the lowest for which he is still likely to be fertile. it is clear that the male body manufactures many more sperm than are necessary to fertilize an egg.

Ranges of Semen and Sperm Characteristics in Healthy Men

CharacteristicRange
Volume/ejaculate1.5–5.0 mL
Number of sperm20–150 million/mL
Concentration of sperm12–16 million/mL
Sperm vitality55–63%
Morphologically normal3–4%

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