Microvillus

Microvillus (plural: microvilli) is a microscopic cellular membrane protrusion that extends from the surface of many types of cells, especially those involved in absorption and secretion functions. These structures are particularly prominent in the epithelial cells lining the intestine and the kidney tubules. Microvilli increase the surface area of cells, thereby enhancing their ability to absorb substances from the external environment.

Structure and Function

A microvillus is composed of a core of actin filaments that are cross-linked by various proteins, including fimbrin, villin, and myosin I. This actin core is surrounded by a plasma membrane that contains specific lipids and integral membrane proteins. The dense packing of microvilli on the cell surface creates a brush border appearance, especially notable in the intestinal epithelium.

The primary function of microvilli is to increase the surface area of the cell, facilitating efficient absorption and secretion. In the small intestine, for example, microvilli play a crucial role in the absorption of nutrients from digested food. They contain enzymes like disaccharidases and peptidases that aid in the final steps of nutrient breakdown. In the kidney, microvilli are involved in the reabsorption of water and vital ions from the filtrate.

Associated Disorders

Alterations in the structure or function of microvilli can lead to various medical conditions. One such condition is Microvillus Inclusion Disease (MVID), a rare genetic disorder characterized by severe diarrhea and malabsorption due to the atrophy and abnormal function of intestinal microvilli. Another condition, Celiac disease, involves an immune response to gluten that damages the microvilli in the small intestine, impairing nutrient absorption.

Research and Clinical Significance

Understanding the molecular composition and function of microvilli has implications for treating and diagnosing diseases associated with their dysfunction. Research into the genetic and molecular basis of microvillus inclusion disease, for example, offers hope for new therapeutic strategies. Additionally, the role of microvilli in drug absorption is a key area of pharmacological research, with implications for the design of drug delivery systems.

See Also

• Cell membrane
• Cytoskeleton
• Epithelium
• Villi