The Basics of Children’s Urinary Tract
ByThe urinary tract has the important task of making urine and removing it from the body. Urine consists of ninety-five per cent water and five per cent solids in solution. The solids include salts and the waste products from various metabolic processes (such as urea from the breakdown of protein). The concentration of urine can be altered by the kidneys to keep the composition, volume and acidity of the body’s fluids within normal limits. Some drugs and other foreign substances are also disposed of via the urinary tract.
The two bean-shaped kidneys lie in the abdomen on the muscles of the back, one either side of the spine and roughly at the level of the tummy button (umbilicus). The right kidney lies slightly lower than the left one. They are well cushioned by fat and are separated from the abdominal organs by a sheet of tissue called the peritoneum. On top of each kidney sits an adrenal gland that produces hormones. The kidneys have relatively the greatest blood flow of any organ – together they receive one fifth of all the blood leaving the heart.
Inside each kidney are about a million minute units called nephrons. These are made up of a series of membranes and little tubes which filter the blood, reabsorb what is necessary and concentrate the urine. Urine collects from these units and runs down the long muscular tube (ureter) which empties from the kidney into the bladder.
The bladder is a thin-walled muscular container which expands as it fills with urine. Urine is prevented from flowing down the urinary passage (urethra) out of the body by a muscular valve, the sphincter, at the top of the urethra. This can be relaxed at will to allow urine to be passed. In a baby, urine is passed automatically every so often until she is old enough to learn how to control her bladder.
The urethra is five times as long in boys as it is in girls. It passes through the pelvis to open at the tip of the penis in a boy and in front of the vaginal opening in a girl.
When things go wrong
A bacterial infection of the urine is a fairly common problem. The infection may affect primarily the bladder (cystitis) or the kidneys (pyelonephritis), but in practice it’s often not possible to distinguish one from the other, and urine infections are commonly known as urinary tract infections. Such infections are more common in girls than boys, perhaps because bacteria can more easily travel up their shorter urethra and because infection can easily pass from the back passage to the urethral opening. Any abnormality in the urinary tract increases the possibility of infection and boys are more likely to be affected by this. Urinary tract infections in babies can be difficult to recognize because they can’t tell you it hurts to pass water. Symptoms can include poor weight gain, vomiting and persistent crying.
A vaginal infection or a foreign object pushed into the urethra can lead to infection in girls. Poor washing of the area around the vulva makes infection more likely, but some children may simply be more prone to infection than others, however clean they are. Bacteria can also reach the kidneys via the bloodstream from an infection elsewhere in the body, causing pyelonephritis.
Sometimes a throat or skin infection by particular streptococcal bacteria can cause a kidney reaction called glomerulonephritis. The increase in use of antibiotics has helped to control these infections.
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