Location
Sperm are created in the testes, also called testicles, the male sex glands found in the scrotum, the sac-like bags of skin on either side of the penis. Testicles hang outside the body because sperm need to be kept 1.5 to 2.5 degrees Celsius cooler than the rest of body. The testes contain the seminiferous tubules, which are the site of sperm production. The seminiferous tubules are lined with Sertoli cells, which contain primitive sperm cells called spermatogonia. Testes also manufacture the male hormone testosterone in cells called Leydig cells, which are found between the seminiferous tubules.
Production
At puberty, spermatogonia begin to divide to make two kinds of cells: exact copies of themselves (a process known as mitosis) which will make more spermatogonia, and spermatocytes. Spermatocytes, which contain 46 chromosomes, undergo two meiotic divisions that produce four spermatids, each containing 23 chromosomes,according to the SUNY Downstate Medical Center Histology Lab Manual. This cell division is necessary because sperm can only supply half the chromosomes to create a new person; the other half come from the maternal egg. The process of meiosis takes about 3 weeks, and requires the production of hormones such as testosterone, and GnRH (gonadotropin releasing hormone).
Spermatids change into spermatozoa, which are sperm cells with a head, midpiece and tail. The head contains DNA, the midpiece contains the sperm's energy source, and the tail will assist the sperm in swimming to the egg after ejaculation.
Maturation
After spermatids become spermatozoa in the seminiferous tubules, they move from the testes to the epididymis, a tightly coiled tube which lies on top of the seminiferous tubules. In the epididymis, sperm gain the ability to move and to penetrate the egg, a maturing process that takes two weeks. At this point, mature sperm move to the vas deferens, two long curved tubes that connect the epididymis to the ejaculatory ducts. Sperm are stored in the vas deferens until ejaculation.
During ejaculation, sperm move through the vas deferens to the ejaculatory ducts, where sperm mixes with thick, alkaline fluid from the seminal vesicles and thinner milky fluid from the prostate. The seminal fluid contains fructose, a sugar that gives sperm additional energy, according to urologist Harry Fisch, M.D. The mixture of sperm and seminal fluid, called semen, exits from the urethra, the thin tube that runs through the penis and is also used for urination.
