Kidneys and Urinary Tract

As people age, the kidneys tend to become smaller (because the number of cells decreases), and less blood flows through them. Beginning at about age 30, the kidneys begin to filter blood less well. As years pass, they may remove waste products from the blood less well. They may also excrete too much water, making dehydration more likely. Nonetheless, they almost always function well enough to meet the body's needs.

The urinary tract changes in several ways that may make controlling urination more difficult. The maximum volume of urine that the bladder can hold decreases. Older people may be less able to delay urination after they first sense a need to urinate. The bladder muscles may contract sporadically, apart from any need to urinate. The bladder muscles weaken. As a result, more urine is left in the bladder after urination is finished. These changes are one reason that urinary incontinence (the uncontrollable loss of urine) becomes more common as people age.

As women age, the urethra (which carries urine out of the body) shortens and its lining becomes thinner. The muscle that controls the passage of urine through the urethra (urinary sphincter) is less able to close tightly and prevent leakage. These changes may result from the decrease in the estrogen level that occurs with menopause.

As men age, the prostate gland tends to enlarge. In many men, it enlarges enough to partly block the passage of urine.