As the glomerular filtrate flows through the renal tubules, various substances are reabsorbed by the cells of the tubular wall and enter the blood. This is called selective reabsorption. 80% of the required material is reabsorbed from the glomerular filtrate.
(i) Proximal tubular reabsorption: The proximal tubule reabsorbs 60% of the glomerular filtrate. It reabsorbs water, glucose, amino acids, vitamins, hormones, sodium, potassium, chloride, phosphate, bicarbonate, urea etc. These substances are called high quality storable substances.
(ii) Reabsorption of Henle’s loop: Water, sodium, potassium, magnesium, calcium, chloride etc. are reabsorbed by the loop of Henle.
(iii) Distal tubular reabsorption: Water, sodium, potassium, hydrogen and chlorine ions are reabsorbed by the distal tubule. These substances are called intermediate quality storable substances.
(iv) Reabsorption of collecting ducts: Water, urea, sodium and chlorine ions are reabsorbed by collecting ducts.
After 4-5 minutes the blood of the body passes through the kidneys to filter it. Human body filters 170 liters of water in 24 hours. Of this, 99% or 168.50 liters of water is reabsorbed by the renal tubules. The remaining 1.5 liters of water is excreted as urine. 80% of water is reabsorbed by the proximal convoluted tubule and 20% by the loop of Henley and distal convoluted tubule. Sulfate and creatinine are not reabsorbed. For this reason, they are called non-preservable substances.