Parent & Patient Information System 06/09/2015 Page40 / 51 Each of the nephrons contain a filter called the glomerulus, which contains a network of tiny blood vessels known as capillaries. The fluid filtered from the blood by the glomerulus then travels down a tiny tube-like structure called a tubule, which adjusts the level of salts, water, and wastes that are excreted in the urine. Filtered blood leaves the kidney through the renal vein and flows back to the heart. Urine is a concentrated solution of waste material containing water, urea, (a waste product that forms when proteins are broken down), salts, amino acids, byproducts of bile from the liver, ammonia, and any substances. Urine also contains urochrome, a pigmented blood product that gives urine its yellowish color. The renal pelvis, located near the hilus, collects the urine flowing from the calyxes. From the renal pelvis, urine is transported out of the kidneys through the ureters, tubes that carry the urine out of each kidney to be stored in the urinary bladder — a muscular collection sac in the lower abdomen. The bladder expands as it fills and can store the urine until proper time for micturition. When the bladder is full, nerve endings in its wall send impulses to the brain. When a child is ready to urinate, the bladder wall contracts and the sphincter (a ring-like muscle that guards the exit from the bladder to the urethra) relaxes. The urine is ejected from the bladder and out of the body through the urethra, another tube-like structure. The male urethra ends at the tip of the penis; the female urethra ends just above the vaginal opening. Problems of the Kidneys and Urinary Tract Like other systems in the body, the entire urinary tract is subject to diseases and disorders. In kids, the more common problems include: Congenital problems of the urinary tract. As a fetus develops, any part of the urinary tract can grow to an abnormal size or in an abnormal shape or position. One common congenital abnormality (an abnormality that exists at birth) is duplication of the ureters, in which a kidney has two ureters coming from it instead of one. This defect occurs in about 1 out of every 125 births and can cause the kidney to develop problems with repeated infections and scarring over time.
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