Urinary System Disorders

Kidney Function and Urological Disorders

Functioning of the body's systems to filter wastes.

The kidneys filter waste materials and excess fluid from the blood and also produce hormones that are important for blood formation, blood pressure, and bone formation. Entering the kidneys through the renal artery, blood is processed in tiny tubes called nephrons and returned to circulation through the renal veins. The waste substances that are filtered out are turned into urine, which collects in the central part of the kidney (called the renal pelvis) and passes through the ureters to the bladder. When a half pint or more of urine has collected in the bladder, it is emptied from the body through the urethra.

The kidneys and ureters begin to form when an embryo is about four or five weeks old and are complete, in a rudimentary form, by the eighth week. However, they still need to travel to their correct place in the lower back, an activity that occurs throughout the rest of the prenatal period. Urine is produced and excreted before birth, forming part of the amniotic fluid, but it is the mother's placenta that filters out most of the waste products produced by the fetus. Upon birth, the baby's kidneys, which weigh about half an ounce each, have to take over this function on their own.

Most infants urinate for the first time within 24 hours of birth and between 8 and 20 times or more a day after that. Infants' urine generally ranges from clear to pale yellow in color, although foods, vitamins, and even urate (one of the salts contained in the urine) may cause it to change color. The urine of infants under the age of two has practically no odor but then becomes stronger due to higher concentrations of ammonia (especially when it is allowed to collect in a diaper for a while). Children cannot control urination until the sphincter muscles and the nerves at the base of the bladder are sufficiently developed, which does not occur until at least the age of two. Most children learn to control their bladders during the daytime by the age of three. However, enuresis (bedwetting) may occur in a healthy child (especially one who is a sound sleeper) until the age of four or five.

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Author Info: , Thomson Gale, Detroit, Gale Encyclopedia of Childhood and Adolescence, 1998

This feature is for informational purposes only and should not be used to replace the care and information received from your healthcare provider. Please consult a healthcare professional with any health concerns you may have.