The main role of the proximal convoluted tubule is to reabsorb substances like glucose, amino acids, chloride ions, sodium ions, and some water back into the blood.

1. Microvilli - provide a large surface area
2. Infoldings at their bases - provide a large surface area to transfer reabsorbed substances
3. High density of mitochondria - provide ATP for active transport
4. Co-transporter proteins in the plasma membrane - allow co-transport of substances from filtrate into epithelial cells

1. Sodium ions (Na⁺) are actively transported into blood capillaries, reducing the Na⁺ concentration in epithelial cells lining the PCT
2. Na⁺ moves from the PCT lumen into the epithelial cells, down its concentration gradient
3. Na⁺ is co-transported with substances like glucose and amino acids into the epithelial cells
4. These reabsorbed molecules can then diffuse into blood capillaries

Molecules like glucose, amino acids, and water diffuse into the blood from the epithelial cells.

The blood then quickly transports the substances away, maintaining a steep concentration gradient.

The main function of the loop of Henle is to decrease the water potential in the medulla by actively transporting ions out of filtrate in the ascending limb into the surrounding tissues of the medulla.

This establishes a water potential gradient that allows water to be reabsorbed into the blood from filtrate in the collecting duct.

The main role of the distal convoluted tubule is to reabsorb water and salts, to make final adjustments to the filtrate that will enter the collecting ducts.

It can also help to control the pH of the blood by selecting which ions to reabsorb.