180 litres of filtrate are formed each day by the two kidneys In a healthy adult the GFR is about 125 mL/min, i.e. The volume of filtrate formed by both kidneys each minute is called the glomerular filtration rate (GFR). The filtrate containing large amount of water, glucose, aminoacids, uric acid, urea, electrolytes etc in the glomerular capsule is known as nephric filtrate of glomerular filtrate.Water and other small molecules readily pass through the filtration slits but Blood cells, plasma proteins and other large molecules are too large to filter through and therefore remain in the capillaries.By the net filtration pressure of 10mmHg, blood is filtered in the glomerular capsule.However this pressure is opposed by the osmotic pressure of the blood, provided mainly by plasma proteins, about 4 kPa (30 mmHg), and by filtrate hydrostatic pressure of about 2 kPa (15 mmHg in the glomerular capsule. A capillary hydrostatic pressure of about 7.3 kPa (55 mmHg) builds up in the glomerulus. The glomerular hydrostatic pressure forces the blood to leaves the glomerulus resulting in filtration of blood.Due to this difference in diameter of arteries, blood leaving the glomerulus creates the pressure known as hydrostatic pressure. The diameter of efferent arterioles is narrower than afferent arterioles.The useful substances are glucose, aminoacids, vitamins, hormones, electrolytes, ions etc and the harmful substances are metabolic wastes such as urea, uric acids, creatinine, ions, etc. The afferent arterioles supplying blood to glomerular capsule carries useful as well as harmful substances.This takes place through the semipermeable walls of the glomerular capillaries and Bowman’s capsule.Glomerular filtration or ultra-filtrationģ. There are three stages involved in the process of urine formation.
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