Secretion is similar to Reabsorption because in both substances cross endothelial cells lining the glomerulus and epithelial cells of Bowman's capsule.
Secretion is the movement of the molecules which are selective from the blood and then added to the filtrate in the tubule lumen by an active process. The secretion process enhances excretion by removal of the solutes from the peritubular capillaries.
Reabsorption is a process of movement of the substances in filtrate from lumen of proximal tubule back to the blood which flows through the peritubular capillaries and the cells of the proximal tubule transport the solutes out of the lumen and then water follows through the process of osmosis.
