IGCSE Biology 0610

7.2 Human Nutrition – The Digestive System

Objective: Explain how the structure of a villus helps absorption of digested food in the small intestine.

The small intestine is the primary site for the absorption of digested food. Its structure is highly adapted to maximize surface area for efficient absorption. A key adaptation is the presence of villi.

What are Villi?

Villi are finger-like projections that line the inner wall of the small intestine. They greatly increase the surface area available for nutrient absorption.

Structure of a Villus

Each villus has a rich network of blood capillaries and lacteals (lymphatic vessels). This arrangement ensures that absorbed nutrients are quickly transported away from the epithelial cells of the villus.

Component	Function
Epithelial Cells	Cover the villus; have microvilli on their surface.
Blood Capillaries	Absorb carbohydrate and protein molecules.
Lacteals	Absorb fat molecules.
Lymphatic Vessels	Carry fats absorbed by the lacteals.

Microvilli

The epithelial cells that make up the villi also have tiny projections called microvilli. These further increase the surface area available for absorption. This creates a 'brush border' effect.

How Villi Enhance Absorption

1. Increased Surface Area: Villi and microvilli significantly increase the surface area of the small intestine. This allows for more efficient absorption of nutrients.
2. Short Diffusion Distance: The close proximity of blood capillaries and lacteals to the epithelial cells ensures that digested food molecules have a short distance to diffuse into the bloodstream or lymphatic system.
3. Efficient Transport: The extensive network of blood capillaries and lacteals provides a rapid transport system for absorbed nutrients.

In summary, the structure of the villus – with its increased surface area, short diffusion distance, and efficient transport network – is crucial for the effective absorption of digested food in the small intestine.