Urine is a fluid which is continously formed in and excreted from the body.
Urine has been referred to as a mirror which reflects activities within the
body. It has also been identified as presenting a biopsy of the kidney.
It is the principal route of waste removal of products of metabolism from
the body .
Examination of urine to diagnose a number of diseases is the oldest among tests in the history of Medical Laboratory Technology, It has been known for centuries that abnormalities in urine may indicate disease. Perhaps, one of the earliest known record of urine test was the technique of pouring urine on the ground and observing whether or not it attracted insects, The attraction of insects indicates (honey urine) which was known to be excreted by people with boils, Today checking sugar in urine is a test to detect diabetes .
• Function of kidneys :
1. Regulation of water and electrolyte balances .
2. Regulation of acid base balance of the blood .
3. Regulation of body fluid osmolality and electrolyte concentrations .
4. Regulation of arterial pressure .
5. Excretion of metabolic waste products and forein chemicals .
6. Secretion of hormones such as renin .
7. Gluconeogenesis: The kidneys synthesize glucose from amino acids and other precursors, like lactate and glycerol, during prolonged fasting by the process called gluconeogenesis .
Per day about 150 – 200 liters of blood enters the kidney each day and only 2 liters of urine are excreted daily, urine is ultra filtrated plasma which consist the substance of plasma but in small amount. This filtrated through glomeruli "filtration of all substance and water except substance have large molecular weight and negative charge(-ve), and this filtration process has certain rate"glomerular filtration rate {GFR}",
About 85% of the water filtrated by glomeruli is reabsorbed by proximal tubule, the reminder passes through lobe of henle, where a little is reabsorbed in distal convoluted tubule and collecting duct, The amount of water reabsorbed depending on the body need under control of ADH.