Question

In spite of the kidneys making 180 litres of filtrate each day, an average adult secretes only 1.5 litres of urine per day Give reasons

Answer 1

It is because about 70 - 80% of the glomerular filtrate is normally reabsorbed in the proximal convoluted tubule before reaching the loop of Henle. In the descending limb of loop of Henle, water is reabsorbed. In the ascending limb of loop of Henle, ions such as sodium, potassium, calcium, magnesium and chloride are reabsorbed. In distal convoluted tubules, water and chloride ions are reabsorbed. From distal convoluted tubule filtrate enters the collecting duct where further reabsorption of water takes place. Some substances such as glucose and amino acids are reabsorbed actively into the blood. Thus the overall volume of the glomerular filtrate reduces so much that kidneys excrete only about 1.5 liters in a day.