Now, these epithelial cells basically contain foldings on the membrane, and these foldings are known as the microvilli. And the microvilli greatly increases the surface area of the inner lining of our Proximal Convoluted tubule, and this increases the rate of reabsorption as well as secretion along the entire Proximal Convoluted tubule. Now, the epithelial cell membranes also contain special type of integral proteins found within our membrane. And these integral proteins aid they allow the movement of our ions and molecules across the membrane. So we have two types of movement that takes place inside the proximal convoluted tubial. We have active transport, which utilizes ATP, and we have passive transport which does not utilize ATP.