Sperm is made up of sperm cells suspended in fluid called semen. Sperm is produced, stored and released by a group of tissues that make up the male reproductive system. Sperm is released by a process, called ejaculation, during sexual intercourse. Mature and adequately motile sperm cells within the sperm are responsible for fertilization of the female ovum, giving rise to the beginning of a viable pregnancy.The development and maturation of sperm cells is called spermatogenesis.
How Sperm Is Formed
Sperm cells are formed by germ cells (also called spermatocytes) within the seminiferous tubules of the testes. The germ cells undergo a special cell division called meiosis to give rise to spermatids. These spermatids embark on a maturation process as they float about in the seminiferous tubules in fluid produced by sertoli cells of the testes. The full development to mature sperm cells (also known as spermatozoa) takes place in the epididymis. The epididymis is a very long tubular system that also serves as temporary storage for the mature sperm cells. In the epididymis, the sperm cells fully develop their motility (ability to swim) as well as their potential to penetrate and fertilize the mature female ova. The mature cells possess an oval head and a tail that acts as a propeller. The main storage site of the mature spermatozoa is the vas deferens, which has a widened upper part called the ampulla. The vas deferens narrows into the ejaculatory duct as it passes through the prostate gland to open into the urethra.
The fluid portion of sperm is made up of secretions from the seminal vesicles, the prostate gland and Cowper's gland. The seminal vesicles produce a considerable bulk of the fluid, which is rich in fructose, a form of sugar used as an energy source by the sperm cells. Other portions of the fluid act as lubricants and also break down mucus barriers to ease the movement of the sperm cells.
Problems in Sperm Formation
A high number of sperm cells are produced at any point in time, increasing the chances of producing a pregnancy. Standards from the NIH indicate a sperm count within the range of 20 to 150 million sperm cells per milliliter of sperm, of which 60 percent are expected to be motile, as normal. Seminal analysis is the study of sperm to determine the number of sperm cells and viability.
The production and maturation of sperm cells are driven by the presence of testosterone, produced by the Leydig cells of the testes under the influence of luteinizing hormone. The luteinizing hormone comes from the pituitary gland in the brain. Thus, hormonal imbalances will affect sperm cell maturation and eventual numbers or function of sperm cells in ejaculated semen.
Injury to the testes by disease or drugs also has a direct effect on sperm cell maturation and the eventual number and function of the sperm cells. Cutting or tying off the vas deferens is used as a form of male contraception (called vasectomy), leading to production of semen without sperm cells.
