Sperm cells form from undifferentiated male germ cells, the so-called spermatogonia. The cycle of sperm forming and maturing lasts for approximately 72 days. A mature spermatozoon consists of a head which contains genetic material, i.e. DNA, and a tail which flagellates, thus propelling the head forward at a speed equal to four its lengths per second.
The sequence of all cytological phenomena leading to sperm formation is called spermatogenesis. This process takes place after reaching sexual maturity in the seminiferous tubules of the testicles.
The proper quantity of spermatozoa in ejaculate is >20 million/mL, according to WHO standards.
Each human cell contains the diploid number of chromosomes (46), while each sperm cell has a half of it, i.e. haploid number of chromosomes (23).
At the same time, it is the spermatozoon which decides whether the created embryo will be male or female.
The impact on the proper course of spermatogenesis can be exerted both by genetic (mutations) and non-genetic factors including stress, infections, hormone disorders, temperature, toxins.
Disorders can occur at any stage of spermatogenesis and can manifest as the lower number of mature sperm cells (oligospermia), abnormal structure (teratozoospermia), or deviation observed during the evaluation of sperm motility (asthenozoospermia). In about 1 to 2% of all infertility cases, sperm cells do not develop at all – this condition is called azoospermia.