How is urine formed

There are three steps/ process involved in the formation of urine , Glomerular Filtration Selective Reabsorption Tubular Secretion Filtration in the kidney through glomerulus The substance get filtrate in glomerulus is similar to the component of plasma with exception of proteins and blood cells. Blood cells, plasma proteins and other large molecules are too large in size to filter and remain in the capillaries. Process of filtration take place through glomerulus & glomerulus capsule through semipermeable membrane. Water and other small molecules readily get absorbed. Why filtration take place in the body? Filtration occure due to difference between the blood pressure in the glomerulus & filtrate pressure in glomerular capsule. The volume of filtrate formed by both kidneys each minute is called glomerular filtration rate. In a healthy adult, Normal gfr is about 125ml/min. i.e. 180 litres of filtrate is formed of which only 1% get excreted as urine. Selective Reabsorption Process of reabsorption is done through two processes, Active Transport Passive Transport Active transport take place at a carrier site in the epithelial membrane by using chemical energy to transport the substance. Some ions, Chloride and sodium absorption in the kidney done by both active and passive mechanism. Water, electrolytes and organic nutrients are passively absorbed in renal tubule. Renal tubule are of distal convoluted tubule and proximal convoluted tubule.