Urine Formation
Excretion is a biological process, which plays a vital role in eliminating toxins and other waste products from the body. The kidneys filter unwanted substances from the blood and produce urine to excrete them. Constituents of normal human urine include 95 per cent water and 5 per cent solid wastes. It is produced in the nephron, which is the structural and functional unit of the kidney. There are three main steps of urine formation: glomerular filtration, reabsorption, and secretion. These processes ensure that only waste and excess water are removed from the body. Urine is about 95% water and 5% waste products. Nitrogenous wastes excreted in urine include urea, creatinine, ammonia, and uric acid. Ions such as sodium, potassium, hydrogen, and calcium are also excreted. 1. The Glomerular Filtration Each kidney contains over 1 million tiny structures called nephrons. Each nephron has a glomerulus, the site of blood filtration. The glomerulus is a network of capillaries surrounded by