The kidneys are a pair of organs about the size of a human fist and in the shape of beans. Their main function is to process and filter out waste and unwanted materials in the blood.
When food is digested in the stomach, the digested parts go into the blood and are transported around the body to cell that need the materials. These materials include, glucose, amino acids and fatty acids. As the blood with the materials is transported around the body, cells use up what they require from it. After all that is needed by the body has been taken out, the main materials left are waste (cannot be used by the body) or unwanted (the body has enough of the substance, for example water). The blood flows into the kidneys and into tiny parts called nephrons. In a nephron, capillaries enter into a ‘Bowman’s capsule’ where they form a glomerulus. The blood is filtered so that excess water and waste passes through the membrane but the blood cells and large proteins stay in the blood. Glucose passes through as well as ions of minerals and excess water. The filtrates pass down through the proximal tubule where the substances and water that is needed are reabsorbed into the blood. The remainder carry on down to the collecting duct and eventually to the bladder, where it is turned into urine.
Urine can be analysed to see what amounts of certain substances it contains. Certain types of dipstick can be used to show the presence and quantities of substances such as protein, glucose, blood and nitrates. If too much protein is present in the urine, it could mean a kidney problem. If too much glucose is present it could mean that you have diabetes. If there are high levels of nitrates, it could mean a urinary tract infection. These are but a few examples of how urine analysis can indicate if people have certain diseases.