The male genital tract consists of the testes, a system of ducts and some other glands opening into the ducts. The testes produce sperm and the male sex hormone, testosterone. Sperm are produced by repeated division of cells in small coiled tubules within the testes at an average rate of approximately 100 million per day in healthy young men. Sperm production is a lengthy process; from the beginning of division of the stem cell to the appearance of mature sperm in the semen takes about 3 months.
Leading from each testis is a long highly coiled tube called an epididymis. The sperm spend 2 to 10 days passing through the epididymis, during which time they mature and become motile. At the beginning of ejaculation sperm are transported from the tail of the epididymis via the vas deferens to the urethra.
The seminal vesicles, prostate gland and Cowper’s glands secrete most of the volume of semen – these secretions help deliver the sperm during ejaculation. The volume of liquid coming from the two epididymides is less than 5% of the total semen volume. About 60% of the semen volume comes from the seminal vesicles and 30% from the prostate gland.
The average semen volume for healthy men ejaculating every two days is 3.8 ml, and the sperm concentration 100 million per mL. During ejaculation, usually the sperm and the prostatic fluid come out first and the seminal vesicle fluid follows. The seminal vesicle fluid coagulates giving the semen a lumpy gel-like appearance. Liquefaction occurs after 20 minutes or so and the gel disappears.
Under usual conditions with sexual intercourse during the fertile phase of the woman’s menstrual cycle, sperm quickly enter cervical mucus and ascend the uterus and Fallopian tubes to the site of fertilisation in the outer third of the tube. Sperm require motility to swim into cervical mucus and to penetrate the outer coverings of the oocyte. They also require normally shaped heads to bind to the surface of the oocyte. In addition, release of enzymes from the acrosome on the head of the sperm and vigorous motility are needed to penetrate into the oocyte.
The function of the testes is dependant upon hormones from the pituitary gland, follicle stimulating hormone (FSH) and luteinizing hormone (LH). The blood levels of these hormones rise during the early stages of puberty and stimulate testicular development. LH controls production of the male sex hormone testosterone which in turn is responsible for the growth that occurs at puberty: development of the genitals, beard and body hair, prostate and seminal vesicles, and also development of bone, muscle and other aspects of masculine physique.
If LH and FSH are deficient, the testes do not develop or function properly. In contrast, if the testes are damaged directly, the levels of these hormones in the blood rise. Thus the measurement of FSH, LH and testosterone in blood may help in the diagnosis of testicular disorders.