The excretory system includes the kidneys, ureters, bladder, and urethra. The most significant changes due to aging occur in the kidneys and bladder.
The kidney loses weight in the aging process-as much as 20%. As a result there is about a 30% decrease in the number of nephrons. The nephron, which makes urine, is the functioning unit of the kidney. At birth a person has about one million nephrons in each kidney.
A nephron consists of a glomerulus, which is a cluster of capillaries partially enclosed in a capsule called Bowman`s capsule, its tubule, and a blood supply. Filtration takes place from the blood in the glomeruli into the Bowman`s capsules. The tubules extend from the capsules and, by various mechanisms, they reabsorb the substances needed by the body; they also excrete water and waste substances.
Thickening of membranes in the nephrons and degeneration in the vascular system occur with age. The rates of filtration, excretion, and reabsorption decline. This affects the amount of a drug that is reabsorbed or excreted and helps account for problems older people have with medications. Blood flow to the kidney is decreased. Formation of urine is lower in the aging kidney, but the filtration process remains efficient, keeping the acid-base balance stable in the body.
The bladder is a collapsible muscular bag lined with a muscous membrane; it stores urine. Fibrous changes in the lining and weakened muscles can be attributed to aging. Capacity for holding urine is decreased. The reflex that brings about contraction of the bladder muscles and relaxation of the internal sphincter to begin the urinating process is delayed.
Reference :
Farrell J : Nursing Care of the Older Person, J.B. Lippincott Company, Philadelphia, 1990.
