Amino acids are primarily absorbed in the small intestine through a specific mechanism involving sodium ions.
The Intestinal Absorption of Amino Acids
The absorption process for amino acids mainly occurs within the jejunum, with a smaller contribution from the ileum. This process isn't simply passive; it involves a special transport system.
Co-transport Mechanism with Sodium Ions
- Amino acids are absorbed via a co-transport mechanism with sodium ions (Na+).
- Both the amino acid and a sodium ion bind to a cell surface protein receptor on the cells lining the intestinal wall.
- This binding allows both substances to move together into the cell. This relies on the electrochemical gradient of sodium ions generated by the sodium-potassium pump, indirectly fueling amino acid entry.
- Once inside the cell, the sodium is actively pumped out through the basolateral membrane, while the amino acids move into the capillaries.
Steps in Amino Acid Absorption:
- Binding: Amino acid and sodium ion bind to a specific cell surface protein receptor.
- Co-transport: Both molecules are transported together across the cell membrane into the intestinal cell (enterocyte).
- Sodium Removal: The sodium ion is actively pumped out of the cell to maintain the gradient.
- Amino Acid Transfer: The amino acids move out of the cell and into the bloodstream.
Practical Insights:
- The co-transport mechanism ensures efficient absorption of amino acids, even when their concentration in the intestinal lumen is low.
- This process highlights the importance of sodium levels in the body for proper nutrient absorption.
- Dietary factors and gut health can influence the efficiency of amino acid absorption.
