USMLE Step 1: Physiology Primary and Secondary Transport In primary active transport, ATP is consumed directly by the transporting protein,(e.g, the Na/K-ATPase pump, or the calcium pump of the sarcolemma). econdary active transport depends indirectly on aTP as a source of energy, as in the cotran port(molecules move in the same direction)of Nat and glucose in the renal tubules and gut This process depends on ATP utilized by the Na/K-ATPase pump. s mucose Lumin Membrane Glucose moved up a concentration adient via secondary activ FIgure 1-1-3 Renal Tubule or Small Intestine Figure 1-1-3 represents a renal proximal tubular cell or a cell lining the small intestine. In this figure, the Na/K-ATPase pump maintains a low intracellular sodium concentration, which cre- ates a large gradient across the cell membrane. It is this sodium gradient across the luminal membrane that drives secondary active transport of glucose In summary, the secondary active transport of glucose Depends upon luminal sodium Is stimulated by luminal sodium(via increased sodium gradient Is linked to the uptake of sodiumr'" USMLEStep1: Physiology 6 meClical Primary and Secondary Transport In primary active transport, ATP is consumed directly by the transporting protein, (e.g., the Na/K-ATPasepump, or the calcium pump of the sarcolemma). Secondary active transport depends indirectly on ATP as a source of energy,as in the cotrans￾port (molecules move in the same direction) of Na+ and glucose in the renal tubules and gut. This process depends on ATP utilized by the Na/K-ATPasepump. ISF Na Na+ Glucose K+ Luminal Membrane Basal Membrane Glucose moved up a concentration gradient via secondary active transport Figure 1-1-3.Renal Tubule or Small Intestine Figure 1-1-3 represents a renal proximal tubular cell or a cell lining the small intestine. In this figure, the Na/K-ATPase pump maintains a low intracellular sodium concentration, which cre￾ates a large gradient across the cell membrane. It is this sodium gradient across the luminal membrane that drives secondary active transport of glucose. In summary, the secondary active transport of glucose Depends upon luminal sodium Is stimulated by luminal sodium (via increased sodium gradient) Is linked to the uptake of sodium