Formation in Human

Formation in Human The nitrogenous waste formed as a result of breakdown of amino acids is converted to urea in the liver by the Ornithine cycle or urea cycle (Figure . ). Mitochondria Glutamine Glutamine NH Carbamoyl phosphate Carbamoyl phosphate synthetase I Carbamoyl phosphate synthetase III Citrulline Citrulline Ornithine Ornithine Arginine Argininasuccinate Fumarate Cell Cytoplasm Urea Figure . Ornithine cycle Urine formation involves three main processes namely, glomerular filtration, tubular reabsorption and tubular secretion. i ) Glomerular Filtration : Blood enters the kidney from the renal artery, into the glomerulus. Blood is composed of large quantities of water, colloidal proteins, sugars, salts and nitrogenous end product. The first step in urine formation is the filtration of blood that takes place in the glomerulus. This is called glomerular filtration which is a passive process. The fluid that leaves the glomerular capillaries and enters the Bowman’s capsule is called the glomerular filtrate. The glomerular membrane has a large surface area and is more permeable to water and small molecules present in the blood plasma. Blood enters the glomerulus faster with greater force through the afferent arteriole and leaves the glomerulus through the efferent arterioles, much slower. This force is because of the difference in sizes between the afferent and efferent arteriole (afferent arteriole is wider than efferent arteriole) and glomerular hydrostatic pressure which is around 55mm Hg. Kidneys produce about 180L of glomerular filtrate in hours. The molecules such as water, glucose, amino acids and nitrogenous substances pass freely from the blood into the glomerulus. Molecules larger than 5nm are barred from entering the tubule. Glomerular pressure is the chief force that pushes water and solutes out of the blood and across the filtration membrane. The glomerular blood pressure (approximately mmHg) is much higher than in other capillary beds. The two opposing forces are contributed by the plasma proteins in the capillaries. These includes, colloidal osmotic pressure ( mmHg) and the capsular hydrostatic pressure ( mmHg) due to the fluids in the glomerular capsule. The net filtration pressure of mmHg is responsible for the renal filtration. XI Std Biology-Zoology