Final answer:
Glucose is initially absorbed from the small intestine into the blood via simple diffusion, but as the concentration gradient decreases, active transport takes over.
Step-by-step explanation:
Glucose absorption in the small intestine is an essential process for providing energy to the body. Initially, glucose is transported via simple diffusion, moving from a higher concentration in the intestinal lumen to a lower concentration in the blood.
However, once the concentration gradient is diminished, glucose is absorbed through active transport, a process requiring energy.
Active transport involves a carrier protein located on the intestinal cell membrane, which binds to glucose and two Na+ ions. As glucose and Na+ are bound, the complex moves into the cell, releasing its contents into the cytoplasm; glucose then diffuses into the blood.
The Na+/K+ ATPase pump actively exports Na+ ions out of the cell, keeping internal Na+ concentrations low to maintain the gradient necessary for the co-transport mechanism. This exchange uses ATP to pump out Na+ in exchange for K+, making it an energy-consuming process and thus classified as active transport.
Glucose and galactose share a similar absorption mechanism, leveraging a co-transport system with sodium ions. Importantly, glucose transportation can also be seen in the kidneys, highlighting the body's need for efficient glucose reabsorption systems to prevent valuable energy sources from being wasted.