urine

Urine is a liquid waste product produced by the kidneys and excreted through the urinary system. It consists primarily of water and dissolved substances such as urea, creatinine, uric acid, electrolytes, and other metabolites. The exact composition varies with hydration, diet, and metabolic activity.

Urine formation occurs in the nephrons of the kidneys through glomerular filtration, followed by selective reabsorption and secretion along the renal tubules. The kidneys regulate body water and salt balance, maintain pH, and help eliminate waste products and toxins. Collected urine flows from the kidneys into the ureters, is stored in the bladder, and is expelled via the urethra during urination.

Normal urine in adults is typically pale yellow to amber, clear, and has a mild odor. The pH generally ranges from about 4.5 to 8.0, and the specific gravity usually lies around 1.005 to 1.030. Daily urine volume varies with fluid intake and environmental conditions, commonly about 0.5 to 2 liters. Most of the substance is water, with dissolved ions, urea, creatinine, and other organic compounds contributing to its chemical profile.

Laboratory analysis of urine (urinalysis) can assess appearance, color, odor, pH, specific gravity, and the presence of substances such as glucose, protein, ketones, blood, nitrites, and leukocytes. Abnormal findings may indicate infections, kidney disease, diabetes, dehydration, or other medical conditions. Urine cultures can identify bacterial infections when indicated.

Specimens are typically collected by midstream clean-catch or other validated methods, with proper handling to preserve sample integrity.