Difference Between Villi and Alveoli | Villi vs Alveoli


The key difference between villi and alveoli is that villi are the finger-like projections present on the inner lining of the small intestine and facilitate nutrient absorption while alveoli are the tiny sac-like structures present in the lung that facilitate rapid exchange of oxygen and carbon dioxide.

Villi and alveoli are two important structures present in our body. Villi are present in the inner lining of the small intestine while alveoli are present at the end of the respiratory tree. In fact, villi are the basic units of nutrient absorption of the gastrointestinal tract while alveoli are the basic units of the ventilation of the respiratory tract. Both structures have a higher surface area in order to carry out their respective functions rapidly and efficiently. The purpose of this article is to discuss the difference between villi and alveoli in detail.

CONTENTS

1. Overview and Key Difference
2. What are Villi
3. What are Alveoli 
4. Similarities Between Villi and Alveoli
5. Side by Side Comparison – Villi vs Alveoli in Tabular Form
6. Summary

What are Villi?

Villi are tiny finger-like structures present in the inner lining of the small intestine. They extend to the small intestine lumen and facilitate the absorption of nutrients into the bloodstream. Villi have many microvilli projecting from the epithelium.

Difference Between Villi and Alveoli | Villi vs Alveoli

Figure 01: Intestinal Villi

Since the absorption of nutrients occurs via the surface area of the villi, they possess a higher surface area for absorption. Similar to gaseous exchange that occurs in the alveoli of the respiratory tract, nutrient absorption also occurs via diffusion.

What are Alveoli?

Alveoli are tiny sac-like structures that allow rapid gaseous exchange in the lungs. In simple words, they are the basic units of ventilation. They are present at the end of the respiratory tree of mammals. There is a network of blood capillaries around the alveoli.

Difference Between Villi and Alveoli | Villi vs Alveoli

Figure 02: Alveoli

Alveoli carry out the transporting of oxygen from the respiratory system to bloodstream and removing carbon dioxide from the blood to the respiratory system in order to exhale from the body. This gaseous exchange occurs through the one-cell-thick alveoli membrane by diffusion. Hence, alveoli have a higher surface area to carry out a rapid and efficient gaseous exchange inside our bodies. Our lungs have 600 million alveoli and the total surface area of the alveoli is about 75 m2.

What are the Similarities Between Villi and Alveoli?

  • Villi and alveoli are vital structures present in our body.
  • Both structures have a higher surface area to carry out their respective functions.
  • Moreover, blood cells are present in both structures.
  • Besides, gaseous exchange and nutrient absorption occur through diffusion in both structures.

What is the Difference Between Villi and Alveoli?

Villi are present in the small intestine while alveoli are present in the lungs. Thus, the location is the key difference between villi and alveoli. Furthermore, villi carry out nutrient absorption in the GI tract while alveoli carry out the gaseous exchange in the lungs. Therefore, their function is another significant difference between villi and alveoli.

Moreover, villi are finger-shaped while alveoli are sac-like structures. So, the shape also contributes to the difference between villi and alveoli.

Below is a comparison summary of the difference between villi and alveoli.

Difference Between Villi and Alveoli | Villi vs Alveoli

Summary – Villi vs Alveoli

Villi are small finger-shaped structures present in the small intestine inner lining. They facilitate nutrient absorption from the lumen. Furthermore, they have very tiny structures called microvilli projecting from their epithelium. They have a greater surface area in order to maximize the nutrient absorption in the small intestine. On the other hand, alveoli are tiny sac-like structures present in the lungs. Gaseous exchange occurs via alveoli membranes. Hence, alveoli also have a greater surface area. Thus, this is a summary of the difference between villi and alveoli.

Reference:

1. “Pulmonary Alveolus.” Wikipedia, Wikimedia Foundation, 24 Feb. 2019, Available here.
2. Britannica, The Editors of Encyclopaedia. “Villus.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 27 June 2018, Available here.

Image Courtesy:

1. “Gray1058” By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body (See “Book” section below)Bartleby.com: Gray’s Anatomy, Plate 1058 (Public Domain) via Commons Wikimedia
2. “Alveolus diagram” By LadyofHats – self-made(extracted from Image:Respiratory system complete.svg) (duplicate of Image:Respiratory system complete en.svg) (Public Domain) via Commons Wikimedia