Urinalysis

Urinalysis, a portmanteau of the words urine and analysis, is a panel of medical tests that includes physical (macroscopic) examination of the urine, chemical evaluation using urine test strips, and microscopic examination. Macroscopic examination targets parameters such as color, clarity, odor, and specific gravity; urine test strips measure chemical properties such as pH, glucose concentration, and protein levels; and microscopy is performed to identify elements such as cells, urinary casts, crystals, and organisms. Urine is produced by the filtration of blood in the kidneys. The formation of urine takes place in microscopic structures called nephrons, about one million of which are found in a normal human kidney. Blood enters the kidney though the renal artery and flows through the kidney's vasculature into the glomerulus, a tangled knot of capillaries surrounded by Bowman's capsule. The glomerulus and Bowman's capsule together form the renal corpuscle. A healthy glomerulus allows many solutes in the blood to pass through, but does not permit the passage of cells or high-molecular weight substances such as most proteins. The filtrate from the glomerulus enters the capsule and proceeds to the renal tubules, which reabsorb water and solutes from the filtrate into the circulation and secrete substances from the blood into the urine in order to maintain homeostasis. The first destination is the proximal convoluted tubule. The filtrate proceeds into the loop of Henle, then flows through the distal convoluted tubule to the collecting duct. The collecting ducts ultimately drain into the renal calyces, which lead to the renal pelvis and the ureter. Urine flows through the ureters into the bladder and exits the body through the urethra. Besides excreting waste products, the process of urine formation helps to maintain fluid, electrolyte and acid-base balance in the body. The composition of urine reflects not only the functioning of the kidneys, but numerous other aspects of the body's regulatory processes.