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

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Villus Structure and Absorption

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: A Site of Absorption

The small intestine is the primary site for the absorption of digested food in the digestive system. Its structure is highly adapted to maximize the surface area available for this crucial process.

The Villi: Increasing Surface Area

One of the key adaptations of the small intestine is the presence of tiny, finger-like projections lining its inner wall. These projections are called villi.

Villus Structure

Each villus has a complex structure designed for efficient absorption:

  • Epithelial cells: The surface of each villus is covered by a single layer of epithelial cells. These cells have microvilli on their surface.
  • Microvilli: These are even smaller projections on the surface of the epithelial cells, further increasing the surface area.
  • Capillaries: A network of capillaries runs through each villus. These capillaries absorb sugars and amino acids.
  • Lacteal: A lacteal, a lymphatic vessel, is also present in the center of each villus. The lacteal absorbs fats.

How the Villi Enhance Absorption

The structure of the villi significantly increases the surface area available for absorption. This is because:

  1. Increased Surface Area: The villi dramatically increase the surface area of the small intestine. It is estimated that the total surface area of the villi is about 250 square meters – roughly the size of a tennis court!
  2. Efficient Absorption: The large surface area allows for more efficient absorption of digested nutrients.
  3. Close Proximity to Blood and Lymph: The capillaries and lacteal within each villus are in close contact with the epithelial cells, facilitating rapid absorption of nutrients into the bloodstream and lymphatic system.

Table Summarizing Villi Structure and Function

Structure Function
Villi Increase surface area for absorption
Epithelial cells Cover the villi and have microvilli
Microvilli Further increase surface area
Capillaries Absorb sugars and amino acids
Lacteal Absorb fats
Suggested diagram: A cross-section of the small intestine showing villi, epithelial cells, microvilli, capillaries, and a lacteal.