Page 9 of 28
Back Next

Primary Active Transport

figurePrimary active transport is a process in which a specific ATPase is an integral component of the carrier. Splitting ATP provides the energy required to move the ion or molecule uphill against its electrochemical concentration gradient across the membrane. Examples of primary active transport systems in the renal tubule include the Na+,K+-ATPase, The Ca++-ATPase and the H+,K+-ATPase. The figure illustrates the primary active transport of Na+. Na+ enters the cell passively down its concentration gradient from lumen to ICF where its concentration is lower than in the filtrate or the renal ISF. It diffuses across the cell and is transported uphill against its concentration gradient from cell to renal ISF using energy derived directly from the splitting of ATP. The restriction of the Na+, K+-ATPase pump to the basolateral membrane allows Na+ to be transported unidirectionally from lumen to renal ISF.