Understand that absorption (by diffusion, osmosis and active transport) is the movement of nutrients from the intestines into cells lining the digestive system and then into the blood

SouravNovember 2, 2024

Answered step-by-step

Absorption is the process by which nutrients move from the intestines into the cells lining the digestive system and subsequently into the blood. This process occurs through three primary mechanisms: diffusion, osmosis, and active transport. Here’s a detailed explanation of each mechanism:

1. Diffusion

• Definition: Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached.
• Mechanism in Absorption:
  • In the small intestine, nutrients such as simple sugars (e.g., glucose) and amino acids are absorbed by diffusion. For example, when digested food enters the small intestine, the concentration of glucose in the intestinal lumen is higher than in the blood. This concentration gradient drives glucose to diffuse across the intestinal cell membranes into the bloodstream.
  • Facilitated Diffusion: Some nutrients, like glucose and certain amino acids, require specific transport proteins to assist their movement across cell membranes. This process is known as facilitated diffusion, which still relies on the concentration gradient but requires no energy.

2. Osmosis

• Definition: Osmosis is a specific type of diffusion that refers to the movement of water molecules across a selectively permeable membrane from an area of higher water concentration (lower solute concentration) to an area of lower water concentration (higher solute concentration).
• Mechanism in Absorption:
  • In the intestines, water is absorbed alongside nutrients. As nutrients are absorbed into the cells lining the intestine, they create a higher solute concentration within these cells compared to the intestinal lumen. This difference prompts water to move by osmosis from the lumen into the cells and then into the bloodstream, helping to maintain fluid balance and support nutrient transport.

3. Active Transport

• Definition: Active transport is the movement of molecules across a cell membrane from an area of lower concentration to an area of higher concentration using energy (usually in the form of ATP).
• Mechanism in Absorption:
  • Certain nutrients, such as amino acids and some ions (e.g., sodium), are absorbed through active transport mechanisms. For instance, sodium ions are often actively transported into intestinal cells against their concentration gradient using ATP. This process creates a favorable environment for other nutrients to be co-transported into the cells.
  • Active transport allows for efficient absorption of essential nutrients even when their concentrations are lower in the intestinal lumen compared to inside the cells.