Obviously for the creation of new life, the female egg cell and the male semen (sperm) need to come together. Yet how is semen formed?
The formation of sperm, the male germ cells, takes place in successive phases in the testicles. Unlike female eggs, they are produced permanently throughout a man’s life.
This process is known as spermatogenesis.
In sexually mature testicles there is a continual supply of spermatogonial stem cells. During the proliferation phase, two other types are generated from these: Type A and B spermatogonia. Type A cells remain with the stem cells in order to ensure a constant supply of spermatogonia. Only type B cells enter into the maturation phase.
B spermatogonia migrate to the seminiferous tubules and are referred to there as spermatocytes. Following two stages of meiosis, spermatids are produced. Now the actual maturation takes places and the spermatids develop into spermatozoa. This maturation process is referred to as spermiogenesis.
The entire generation of sperm – beginning with the formation of spermatogonia to the development of mature sperm – takes around 64 days.
Sperm formation is primarily controlled by the hormone testosterone, which is active above all in the brain and in the sexual organs. Testosterone is mainly produced in the what are known as the Leydig cells of the testicles as well as to a lesser extent in the adrenal cortex.