|This section covers those disorders which affect the male reproductive organs. Infections are the commonest kind of disorder, for although the male urethra is relatively long and less prone to invasion than the female, it has direct communication with the testes, epididymides, and prostate. This means that kidney, bladder, or urethral infections can spread to the organs concerned with reproduction. The testicles manufacture sperm and also produce the male sex hormone testosterone. They lie outside the body, the left usually lower than the right, because sperm production requires slightly cooler conditions than those which reign inside the body. Normally, both testicles descend into the scrotum, the pouch of skin behind the penis, shortly before birth. At puberty they enlarge and begin to produce sperm.
Each testicle consists of an almond-shaped testis, where sperm are manufactured at the rate of 10,000-30,000 million a month, and a much coiled tube called the epididymis, inside which the sperm mature for about 3 weeks. In all it takes 60-72 days for a sperm to develop fully. From the epididymides, sperm move into the vasa deferentia and seminal vesicles for storage; in the seminal vesicles a sugar-rich fluid is added to provide the sperm with energy. If mature sperm are not ejaculated, they disintegrate and are reabsorbed into the body, but if psychological conditions are right and orgasm occurs, the seminal vesicles and prostate gland contract powerfully, expelling about 3 ml (half a teaspoonful) of semen into the urethra and out of the end of the penis; this is ejaculation. Once in the female reproductive tract, sperm have a maximum life of 3 days. It is not possible to urinate and ejaculate at the same time because the reflexes which cause the bladder to empty automatically shut off entry of semen into the urethra.
The prostate gland is bulb-shaped and completely encircles the urethra at the point where it leaves the bladder. Its role is to add acids, trace elements, and enzymes to seminal fluid at the moment of ejaculation. These activate the sperm and also give semen its distinct smell. For reasons which are not known, the prostate tends to enlarge and stiffen with age, narrowing the exit from the bladder; this obliges the bladder muscles to work harder to expel urine, and can make urination slow and painful.
The penis relies, for its hydraulic power, on three cylinders, two hollow and one spongy. These are arranged protectively around the urethra and only fill with blood during sexual arousal. Erection is maintained by strands of muscle at the base of the penis which slow the rate at which blood drains back into general circulation. The head of the penis is most sensitive to touch, the shaft to pressure.