Absorption & the Small Intestine: How Nutrients Enter Your Body

After chemical digestion breaks down food into small, soluble molecules, these nutrients need to enter the bloodstream for use by the body. This process is called absorption, and the small intestine is the star of the show.

 

What is Absorption?

Absorption is the process of moving small, soluble molecules (like glucose, amino acids, fatty acids, and glycerol) from the digestive system into the blood or lymph.

 

The Role of the Small Intestine

 

 

The small intestine is where most absorption happens. It has special features that make it highly efficient:

 

1. Villi and Microvilli

• The inner wall of the small intestine is covered in tiny finger-like structures called villi, and each villus is covered in even smaller projections called microvilli.
• These structures:
  • Increase Surface Area: More area means more absorption.
  • Contain Capillaries: For glucose and amino acids to enter the blood.
  • Contain Lacteals: For transporting fatty acids and glycerol from small intestine to the lymph.

 

2. Thin Walls

• The walls of the villi are just one cell thick, making it easier for nutrients to pass through.

 

3. Rich Blood Supply

• Capillaries in the villi carry absorbed nutrients away quickly, maintaining a steep concentration gradient for efficient diffusion.

 

 

Fun Analogy

Think of villi as a sponge.

• A sponge’s tiny holes soak up water efficiently.
• Similarly, the villi’s large surface area absorbs nutrients efficiently.