Reabsorption

This is the process by which the useful substances are taken back into the blood so that they are not lost.

As the glomerular filtrate flows along, most of the ultrafiltered substances which are useful to the body are selectively reabsorbed back into the blood

This selective reabsorption occurs in three parts of the renal tubules i.e. Bowmans capsule, Loop of Henle, Distal convoluted tubule.

Proximal convoluted tubule

In the Proximal convoluted tubule, all glucose  and all amino acids  are actively reabsorbed against the concentration gradient, a process that requires energy  and refered to as active transport.

NB It is not all substances that are reabsorbed, its only those which are useful to the body that are reabsorbed hence it is refered to as selective Reabsorption.

How the Proximal convoluted tubule is adapted for efficient selective Re-absorption.

1. Cells lining the tubules have numerous mitochondria which provides the necessary energy in the form of ATP.
2. Cells of the tubules have micro-villi which increases the surface area.
3. The tube is long and highly coiled to provide a large surface area for Re-absorption.
4. The coiling of the tubule reduces the speed of flow of the filtrate thereby giving more time for efficient Reabsorption.
5. The tubule is well supplied with blood capillaries.

Describe how a large surface area facilitate re-absorption.