What is the Difference Between Villi and Microvilli

The main difference between villi and microvilli is that villi are small projections on the mucous membrane, particularly in the small intestine. But, microvilli are tiny extensions that mainly occur on the cell membrane of different organs. Furthermore, villi increase the surface area while microvilli are responsible for absorption and secretion, increasing the surface area. 

In brief, villi and microvilli are two types of projections that occur on the internal surfaces of different organs. Generally, both are responsible for increasing the surface area. 

Key Areas Covered 

1. What are Villi
     – Definition, Anatomy, Function
2. What are Microvilli
     – Definition, Anatomy, Function
3. What are the Similarities Between Villi and Microvilli
     – Outline of Common Features
4. What is the Difference Between Villi and Microvilli
     – Comparison of Key Differences  

Key Terms 

Absorption, Lumen of Intestine, Micovilli, Surface Area, Villi

What are Villi 

Villi are small, finger-like projections extending into the lumen of the small intestine. In humans, the villus is approximately 0.5–1.6 mm in length. Each villus contains many microvilli, projecting from the epithelial cells of the intestine. Moreover, villi and microvilli collectively form the brush border. Within the brush border, microvilli form the smallest folds on the comparatively larger folds called villi. However, the lumen of the intestine contains circular folds, which are much larger than villi. 

Figure 1: Villi and Microvilli

Furthermore, the main function of the villi is to increase the internal surface area of the intestinal wall. It produces a greater surface area for the absorption of nutrients. Generally, the digested nutrients such as amino acids and monosaccharides pass into the villi through diffusion. Besides, villi increase the effectiveness of diffusion by the average distance traveled by nutrient molecules by increasing the surface area. 

What are Microvilli 

Microvilli are microscopic protrusions on the cell surface, increasing the surface area of the cell. Therefore, they minimize any increase in the volume of the cell. Generally, microfilaments form the core of the microvillus. Moreover, they are typically held together by cross-linking of proteins such as fimbrin, villin, and epsin. 

Figure 2: Low Magnification Micrograph of Small Intestinal Mucosa

However, microvilli are shorter and narrower when compared to cilia. Typically, they are 0.5 to 1.0 µm long and 0.1 µm thick. The main function of microvilli is to enhance the absorption of nutrients from the small intestine. Meanwhile, the glycocalyx layer, which covers microvilli, allows the binding of substances to the microvilli in order to get absorbed. On the other hand, microvilli facilitate carbohydrate digestion. Furthermore, microvilli occur on the surface of egg cells as well. Basically, they allow the anchoring of the sperm cells to the egg cell. Microvilli also occur on the surface of white blood cells, allowing them to migrate. Besides, they are present in sensory organs like nose, mouth, and ears.  

Similarities Between Villi and Microvilli  

• Villi and microvilli are two types of small projections that occur on the internal surfaces or lumens of organs.  
• Furthermore, their main function is to increase the surface area. 

Difference Between Villi and Microvilli 

Definition 

Villi refer to the finger-like projections from the surface of the certain membranous structures, typically serving to increase surface area and facilitate the passage of fluid or nutrients. But, microvilli refer to a large number of minute projections from the surface of some cells. 

Size 

The size of the villi is 0.5–1.6 mm in length in humans while the size of the microvilli is 1 µm in length. 

Occurrence 

Villi extend to the lumen of the small intestine while microvilli occur on the cell membrane of epithelial cells. 

Correspondence 

Intestinal villi are made up of many cells while epithelial cells of the intestine have many microvilli. 

Function 

Moreover, villi increase the surface area for absorption while microvilli increase the surface area for diffusion and take part in a wide variety of functions, including absorption, secretion, cellular adhesion, and mechanotransduction.  

Conclusion 

Villi are finger-like projections that mainly occur as extensions on the lumen of the intestine. Their main function is to increase the absorptive surface area of the lumen. In contrast, microvilli are microscopic projections on the surface of the epithelial cells. They increase the surface area without increasing the volume of the cell. In addition, this increment of the surface area aids many functions such as absorption, secretion, cellular adhesion, etc. Therefore, the main difference between villi and microvilli is size and occurrence. 

References:

1. “Villi in the Small Intestine – Biology: Socratic.” Socratic.org, Available Here.
2. Aryal, Sagar. “Microvilli- Structure and Functions: Cell Biology.” Microbe Notes, 29 Mar. 2019, Available Here.

Image Courtesy:

1. “Villi & microvilli of small intestine” By BallenaBlanca (CC BY-SA 4.0) via Commons Wikimedia     
2. “Small intestine low mag” By Nephron – Own work (CC BY-SA 3.0) via Commons Wikimedia