How are amino acids and sodium ions taken into the epithelial cells?
The correct answer and explanation is:
Correct Answer:
Amino acids and sodium ions are taken into epithelial cells by co-transport (symport) using active transport mechanisms.
Explanation:
Amino acids and sodium ions enter epithelial cells through a process known as secondary active transport. This process involves a co-transporter protein located on the apical membrane of epithelial cells, especially those lining the small intestine. The transporter binds both a sodium ion and an amino acid at the same time. The movement of sodium ions into the cell is driven by the concentration gradient of sodium, which is kept low inside the cell by the sodium-potassium pump (Na⁺/K⁺-ATPase) on the basolateral membrane.
This pump actively transports sodium ions out of the cell and potassium ions into the cell using energy from ATP. Because sodium concentration is lower inside the cell and higher in the intestinal lumen, sodium ions naturally move back into the cell through the co-transporter. When a sodium ion binds to the co-transporter, it enables the transport of an amino acid into the cell along with it.
The co-transport of amino acids with sodium does not require direct use of ATP but relies on the sodium gradient created by the sodium-potassium pump. This makes the transport indirectly active.
Once inside the epithelial cell, amino acids may move into the bloodstream by facilitated diffusion through transport proteins located on the basolateral membrane. Sodium ions, after entering the cell, are pumped out again by the sodium-potassium pump to maintain the concentration gradient and allow continued absorption.
This efficient transport system ensures that essential amino acids and sodium are absorbed from the intestine into the body for use in various physiological processes including protein synthesis, nerve function, and fluid balance.