Describe the structure of a villus

The structure of a villus (plural: villi) in the small intestine is specifically adapted to maximize nutrient absorption. Here’s a detailed description of its components and organization:

Structure of a Villus

1. Shape and Size:
   • Villi are small, finger-like projections that extend into the lumen of the small intestine. Each villus typically measures about 0.5 to 1.6 mm in length, giving the intestinal lining a velvety appearance due to their abundance.
2. Core Composition:
   • Each villus contains a central core made up of:
     • Blood Vessels: A network of capillaries, including an arteriole and a venule, which transport absorbed nutrients (such as amino acids and simple sugars) into the bloodstream.
     • Lymphatic Capillary (Lacteal): This structure collects absorbed fats (in the form of chylomicrons) and transports them into the lymphatic system.
     • Connective Tissue: Provides structural support to the villus.
3. Muscle Strand:
   • A strand of smooth muscle runs through the villus, allowing it to contract and sway. This movement is believed to enhance nutrient absorption by increasing blood and lymph flow.
4. Epithelial Layer:
   • The surface of each villus is covered by a layer of epithelial cells, primarily composed of enterocytes, which are specialized for absorption. These cells have numerous tiny projections called microvilli on their apical surface, forming what is known as the brush border.
   • The brush border significantly increases the surface area available for absorption and contains enzymes that assist in the final stages of digestion.
5. Goblet Cells:
   • Interspersed among the enterocytes are goblet cells, which secrete mucus. This mucus lubricates the intestinal contents and provides protection to the epithelial lining.

Functional Significance

• The structural adaptations of the villi—such as their large surface area, thin walls, and presence of microvilli—facilitate efficient nutrient absorption from digested food. The extensive vascular network within each villus ensures that absorbed nutrients are rapidly transported away for use by the body.
• The combination of villi and microvilli increases the absorptive surface area of the small intestine approximately 40-fold (for villi) and an additional 600-fold (for microvilli), making it exceptionally effective in nutrient uptake.