Describe four mechanisms of nutrient absorption from the small intestine?

Answer 1

ABSORPTION is accomplished by one of four mechanisms:

1) Active transport is a process requiring energy (ATP) and a nutrient carrier to move an essential nutrient against a gradient. Most carriers are nutrient-specific, and almost all required nutrients are actively transported. Minerals are the exception, as they require both passive diffusion and carrier-mediated transport. Amino acids are actively transported, but also require a carrier.

2) Passive diffusion is a movement of compounds across the cell membrane so as to equalize the concentration of the substrate on both sides of the membrane. This process applies only to such small molecules as electrolytes, water, and small sugars. It does not apply to such large molecules as starch or large proteins. Almost all the water-soluble nutrients are absorbed in this manner or by osmosis (passive absorption).

3) Facilitated diffusion is a movement of nutrients against a concentration gradient and usually does not require energy, but does require a carrier. Fructose absorption uses a carrier without expending energy pulling water with it upon entering the intestines.

4) Pinocytosis or phagocytosis happens when the absorptive cell engulfs the material. This process is used for fat absorption.

Answer 2

1. Passive diffusion: Nutrients like water, electrolytes, and lipid-soluble compounds can pass through cell membranes without requiring energy.
2. Active transport: Nutrient absorption against a concentration gradient, utilizing carrier proteins and ATP for movement.
3. Facilitated diffusion: Utilizes carrier proteins to move specific molecules down their concentration gradient.
4. Endocytosis: Larger molecules or particles are engulfed by the cell membrane and brought into the cell in vesicles.