Here’s a completion of your text regarding nutrient absorption in the small intestine with appropriate terminology filled in:
- The process called digestion occurs in the small intestine.
- Nutrients are absorbed through the lining of the small intestine via a variety of mechanisms. Most nutrients require facilitated diffusion where a specific carrier protein is utilized, but no energy is required.
- Some smaller molecules can cross via simple diffusion. Like with facilitated diffusion, no energy is required because the concentration of a nutrient is higher inside the GI tract than in the enterocyte. Unlike with facilitated diffusion, however, no specific carrier protein is needed.
- Nutrients like glucose and amino acids are absorbed through active transport, which requires both a carrier protein and energy in the form of ATP.
- A fourth method is called endocytosis, which involves a vesicle that forms from the enterocyte's cell membrane, engulfing the nutrient and then drawing the nutrient into the cell.
- Once absorbed, water-soluble nutrients like carbohydrates and amino acids enter capillaries and travel to the liver via the hepatic portal vein.
- Fat-soluble nutrients initially travel via the lymphatic system before entering the bloodstream.
This provides a comprehensive overview of nutrient absorption mechanisms in the small intestine.