Hello Moiz,

The kidney organ is made up of tubules (distal tubule, proximal tubule, collecting duct, loop of henle) where the transporters/channels will insert to reabsorb and excrete substances. The peritubular capillaries are the blood vessels that run in parallel to pick up the work done by the tubules. You can just always assume reabsorption from the tubules will get into systemic circulation via the peritublar capillaries.

Try not to overcomplicate the topics!