 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. From 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 60-70% volume of the ultrafiltrate, meaning that the ultrafiltrate is approximately 60-70% of the part that is reabsorbed in proximal convoluted tibule. In ratio wise this portion reabsorbs about 99% or even more than 99% 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. Reabsorption occurs in a large quantity of water as well as in proximal convoluted tibule. These reabsorbed materials enter the paritubular fluid, meaning the fluid which is present in the tibule. These reabsorbed substances enter where 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 Henle. Loop of Henle is important for the reabsorption of water. Reabsorption is a proximal convoluted tibule that continues in the descending limb of loop of Henle because this loop is freely permeable to water. It has numerous water channels which are made by aquaporin protein. So this limb of the descending limb has no channel for solute so it is not permeable for solutes. For solute reabsorption, descending limb of loop of Henle does not exist. Now unlike the ascending limb that contains ion channels but not water channels, that is why the reabsorption of ions in this limb does not reabsorbs water from this limb. So overall the loop of Henle 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. Because proximal convoluted tibule has played its role. Now we shall discuss reabsorption in the distal convoluted tibule. The initial filtrate is about 15 to 20 percent of the distal convoluted tibule. The distal convoluted tibule cells actively reabsorb sodium and chloride ions. Distal convoluted tibule contains ion pumps which reabsorb tubular sodium in exchange for potassium ions. Distal convoluted tibule also reabsorbs bicarbonate ions to regulate the urine pH.