How does the urinary system use the kidneys?

Answer 1

Function * Ultrafiltiration: the process by which fluid is filtered out of the blood by the glomerulus. * The blood pressure in a glomerulus causes part of the blood plasma to leak through the capillary walls. The red blood cells and plasma proteins are too big to pass out of the capillary, so the fluid that does filter through is plasma without the protein. The fluid thus consists mainly of water with dissolved salts, glucose, urea and uric acid. * Selective Reabsorption: the process of absorbing back the substances needed by the body. * The filtrate from the glomerulus collects in the renal capsule and trickles down the renal tubule. * As it does so, the capillaries which surround the tubule absorb the substance the body needs back into the blood. * ** The glucose is reabsorbed with much of the water. ** Some of the salts are taken back to keep the correct concentration in the blood. ** *** Salts not needed by the body are left to pass down the kidney tubule with the urea and uric acid. *** They continue down the renal tubule into the pelvis of the kidney, passes down the ureter and to the bladder. * Urine cannot escape from the bladder because a band of circular muscle, called a sphincter, is contracted, so shutting off the exit. When it relaxes, the muscular walls of the bladder expel the urine through the urethra. * ** Adults can control this sphincter muscle and relax it only when they want to urinate. ** In babies, the sphincter muscle relaxes by a reflex reaction, set of off by pressure in the bladder. Water balance and osmoregulation * The body: * ** Gains water from food and drink ** Loses water by evaporation, urination and defececation. ** *** Evaporation from the skin takes place all the time but is particularly rapid when we sweat. *** Air from the lungs is saturated with water vapor which is lost in the atmosphere when we exhale. * Despite these gains and losses of water, the concentration of body is kept within very narrow limits by the kidneys, which adjust the concentration of blood flowing through them. * ** If the blood is too dilute, less water is reabsorbed from the renal tubules, leaving more to enter the bladder. ** If the blood is too concentrated, more water will be absorbed back into the blood from the kidney tubules. * A rise in blood concentration is thought to stimulate a thirst center in the brain. The drinking which follows this stimulation restores the blood to its correct concentration. * Osmoregulation: the regulatory processes that keep the blood at a steady concentration. * ** One example of the process of homeostasis

Answer 2

It filters blood plasma to make urine. And then it stores it in the bladder until ready to come out.