4.5 Co-transport and absorption of glucose in the ileum

Increasing the movement across membranes

• Epithelial cells lining the ileum possess microvilli collectively forming a brush boarder. The microvilli provide a larger surface area for the intersection of carrier proteins through which diffusion, facilated diffusion, and active transport can take place.

The role of diffusion in absorption

• As carbohydrates and proteins are being digested continously there is normally a greater concentration of glucose and amino acids within the ileum and the blood.
• Thetre is a concentration gradient down which moves the glucose via facilitated diffusion.

Role of active transport in the blood

• Diffusion only results in an equalibrium is reached in the intestinal epithelium. This leads to not all amino acids being absorbed.
• All amino acids or glucose are pulled into the cell by co-transport of sodium ions that have been actively transported out by the sodium potassium pump. . 

• 1. Sodium ions are actively transported out of epithelial cell, by the sodium-potassium pump. This takes place in one type of protein-carrier molecuel found in the membrane of epithelial cells.
• 2. This maintains a much higher concentration of sodium ions in the lumen of the intestine and that of the epithelial cells.
• 3. Sodium ions diffuse into the epithelial cells through a different type of protein carrier in the cell surface membrane.As the sodium ions diffuse in through the seocnd carrier protein , they carry either amino acids or gluecose molecuels. 
• 4. The glucose/amino acid molecuels move into the blood plasma by facilitated diffusion using another type of carrier protein.