Active transport
In order to achieve continued absorption when there is a grea ter concen tra tion in the cell or in the blood than in the lumen, a nutrient must be actively transported or pumped across the membrane barrier. These "pumps," which probably involve carriers, require energy to operate, but they do permit a very large and rapid transfer into the body of such nutrients as glucose, galactose, many amino acids, sodium, and several vitamins and minerals.
