reabsorption in the nephron

selective reabsorption takes place in the proximal convoluted tubule

all of the useful molecules such as glucose are reabsorbed, as well as a large amount of water

in the epithelial cells of the proximal convoluted tubule, Na+ ions are pumped out of the cytoplasm and into the bloodstream via active transport

• these sodium ions are carried away by the blood

• so the epithelial cells have a low concentration of sodium ions in the cytoplasm

• sodium ions diffuse into the epithelial cells from the fluid in the PCT - through carrier proteins (facilitated diffusion)

• at the same time the carrier proteins also transport glucose into the epithelial cell - cotransport

• the glucose molecules diffuse out of the epithelial cells and into the bloodstream

there are different types of carrier proteins and each carrier protein carries a different type of molecule along with sodium ions

adaptations of epithelial cells:

• the membrane on the lumen side is covered with microvilli

• there are infoldings on the membrane near the blood capillary - large surface area for the transfer of molecules into the blood

• contain large number of mitochondria