Effects of Aging on the Urinary System

Effects of Aging on the Urinary System

Three different sets of kidneys develop in the embryo from the urogenital ridges. These are paired elevations of the intermediate mesoderm that will form the urinary and reproductive organs. Only the final set will persist and become the adult kidneys. In the fourth week of development, the pronephros or prekidney forms as a tubule system, then quickly degenerates when a second and lower system forms. The pronephros is completely gone by the sixth week, but its pronephric duct, con-necting it to the cloaca, persists. It will be used later by the developed kidneys. The second system, called the mesonephros or middle kidney, claims the prone-phric duct and is eventually called the mesonephric duct. This system also degenerates, when the third system or metanephros develops. It begins at about five weeks as hollow ureteric buds. These push supe-riorly from the mesonephric duct into the urogenital ridge, causing the local mesoderm to form nephrons. The ureteric buds’ distal ends form the renal pelvises, calyces, and collecting ducts. The unexpanded proxi-mal parts of the ureteric buds, which are later called ureteric ducts, form the ureters.

The kidneys develop in the pelvis and then ascend to their final locations. Because of this, they receive blood from continually higher sources. Lower blood vessels usually degenerate, but some-times persist. When they do, multiple renal arteries are common. By the third month, the metanephric kidneys excrete urine. The majority of the amni-otic fluid surrounding the fetus is fetal urine. The fetal kidneys do not operate nearly as efficiently as they will following birth, since placental exchange allows the urinary system of the mother to clear most unwanted substances from fetal blood. During metanephros development, the cloaca subdivides, forming the rectum, anal canal, and urogenital sinus. The urinary and genital ducts will empty into the urogenital sinus, and the urinary bladder and urethra­ will develop from this structure.

Kidney problems increase with age, includ-ing the formation of calculi or kidney stones, also called nephrolithiasis. Other changes because of aging include a decline in the number of functional nephrons, up to 40% in some individuals. Patients may experience a reduction in the glomeruli, dam-age to the filtration apparatus of the glomeruli that remain, and lessened renal blood flow. The nephrons and collecting system may become less responsive to the ADH, and both water and sodium reabsorp-tion is lower. More sodium ions are lost in the urine. The sphincter muscles lose tone, which can lead to incontinence. Ability to control urination may be partially or completely lost after Alzheimer’s dis-ease, stroke, or other central nervous system events.Urinary­ retention in males may develop because of an enlarged prostate gland that compresses the ­urethra and restricts urine flow.