Sperm is made by a complex hormonally regulated process that involves both rounds of cell division to produce identical clones and genetic rearrangement and duplication to produce genetically unique cells capable of fertilizing an egg.
Processes
Sperm cell production, or spermatogenesis, requires two processes. In the first process, called spermatogoniogenesis, sperm stem cells called spermatogonia undergo repeated rounds of cell division, or mitosis, to form a population of identical cells or clones. In the second process, called spermiogenesis, individual sperm undergo meiosis, which rearranges and halves the number of chromosomes and remodels the shape of the sperm cell to make it capable of fertilizing an egg.
Time Frame
It takes approximately 60 to 80 days for a human sperm to finish both spermatogoniogenesis and spermiogenesis and become fully functional. Different batches of sperm stem cells start to divide at different times, creating waves of staggered groups of sperm production throughout the testicles.
Anatomy
The testicle is made up of coiled seminiferous tubules containing two main cell types: Sertoli and Leydig cells. Sertoli cells line the tubules and enclose and nourish each developing sperm cell. Leydig cells lie in the spaces between the seminiferous tubules and produce male hormones called androgens. Testosterone produced by Leydig cells regulate the function of Sertoli cells.
Warnings
Physical trauma, prolonged high heat, toxins, radiation, chemotherapy, bacterial infection and some medications can prevent spermatogenesis, resulting in temporary or permanent infertility. Genetic errors in chromosome rearrangement during meiosis can produce abnormal sperm that cannot fertilize an egg or else produce abnormal embryos if fertilization does occur.
Fun Fact
A sperm cell is approximately 55 micrometers long, similar in scale to the width of a human hair, which is between 40 to 100 microns. A micrometer, or micron, is one millionth of a meter.
