 Dear students, in this topic we shall discuss the tubular reabsorption, that is reabsorption process in the kidney tibule. The glomerular filtrate flows sequentially through the various or successive parts of the renal tibule. On the tibule, useful substances are selectively reabsorbed back into the blood. Reabsorption occurs in every segment, however the substance is absorbed and their relative concentration changes with the segment. First we shall discuss reabsorption in the proximal convoluted tibule. The cells of proximal convoluted tibule reabsorb about 60 to 70 percent volume of the ultrafiltrate. That means the ultrafiltrate is reabsorbed in proximal convoluted tibule. In ratio wise this portion reabsorbs about 99 percent or even more than 99 percent of glucose, amino acids and other organic nutrients. This reabsorption involves diffusion, facilitated diffusion, active transport and co-transport mechanisms. Proximal convoluted tibule also actively absorbs various ions like sodium, potassium, magnesium, phosphate, bicarbonate and sulphate ions. It also reabsorbs some ions passively. These reabsorbed materials enter the paritubular fluid, which is reabsorbed in the tibule. They diffuse into the paritubular capillaries, which quickly return these substances back to the blood flow or circulation. Now we shall discuss reabsorption in the loop of Henley. Loop of Henley is important for the reabsorption of water. Reabsorption is a proximal convoluted tibule that continues in the descending limb of loop of Henley, because this loop is freely permeable to water. It has numerous water channels which are made by aquaporin protein. The descending limb has no channel for solute, so it is not permeable for solutes. For solute reabsorption, descending limb of loop of Henley does not exist. Now unlike the descending limb, the ascending limb contains ion channels, but not water channels. Therefore, the reabsorption of ions from this limb does not reabsorbs water from this limb. Overall, the loop of Henley reabsorbs about half of the water and two-thirds of the sodium and chloride ions which enter into it in the filtrate form from the proximal convoluted tibule. This absorption takes place by a special mechanism which is called counter-crunt exchange or counter-crunt multiplication. Now we shall discuss reabsorption in the distal convoluted tibule. The initial filtrate of the distal convoluted tibule is about 15 to 20 percent distal convoluted tibule. The cells of the distal convoluted tibule actively reabsorb sodium and chloride ions. This distal convoluted tibule contains ion pumps which reabsorb tubular sodium in exchange for potassium ions. This portion of the distal convoluted tibule also reabsorbs bicarbonate ions to regulate the urine pH.