Disorders of the Urethra
Congenital anomalies may involve the urethra as well as other parts of the urinary tract. The opening of the urethra to the outside may be too small, or the urethra itself may be narrowed. Occasionally, an abnormal valve-like structure is found at the point where the urethra enters the bladder. If it is not removed surgically, it can cause back pressure of the urine, with serious consequences. There is also a condition in the male in which the urethra opens on the undersurface of the penis instead of at the end. This is called hypospadias (Fig. 18-15).
Urethritis, which is characterized by inflammation of the mucous membrane and the glands of the urethra, is much more common in men than in women. It is often caused by infection with gonococci or chlamydias, although many other bacteria may be involved.
“Straddle” injuries to the urethra are common in men. This type of injury occurs when, for example, a man walking along a raised beam slips and lands with the beam between his legs. Such an accident may catch the urethra between the hard surfaces of the beam and the pubic arch and rupture the urethra. In accidents in which the bones of the pelvis are fractured, rupture of the urethra is fairly common.
The Effects of Aging
Even without kidney disease, aging causes the kidneys to lose some of their ability to concentrate urine. With aging, progressively more water is needed to excrete the same amount of waste. Older people find it necessary to drink more water than young people, and they eliminate larger amounts of urine (polyuria), even at night (nocturia). Beginning at about 40 years of age, there is a decrease in the number and size of the nephrons. Often, more than half of them are lost before the age of 80 years. There may be an increase in blood urea nitrogen (BUN) without serious symptoms. Elderly people are more susceptible than young people to urinary system infections. Childbearing may cause damage to the musculature of the pelvic floor, resulting in urinary tract problems in later years. Enlargement of the prostate, common in older men, may cause obstruction and back pressure in the ureters and kidneys. If this condition is untreated, it will cause permanent damage to the kidneys. Changes with age, including decreased bladder capacity and decreased muscle tone in the bladder and urinary sphincters, may predispose to incontinence. However, most elderly people (60% in nursing homes, and up to 85% living independently) have no incontinence.
Figure 18-15 Hypospadias. A ventral view of the penis is shown here.