What are Microvilli?
Microvilli are microscopic cellular membrane protrusions that increase the surface area of cells and are involved in a wide array of functions, predominantly absorption. These structures are most commonly found on the apical surface of epithelial cells in organs such as the
small intestine and
kidney.
Structure of Microvilli
Each microvillus is supported by a core of
actin filaments, which are cross-linked by various actin-binding proteins such as
fimbrin and
villin. The actin core is anchored into the
terminal web, a network of filaments located just beneath the plasma membrane. This structural organization provides both stability and flexibility to the microvilli.
Functions of Microvilli
Microvilli primarily serve to increase the surface area of the cell, thereby enhancing its ability to absorb substances. This is especially critical in absorptive cells of the
digestive tract and
renal tubules. In addition, microvilli play a role in
cell signaling and mechanotransduction, the process by which cells convert mechanical stimulus into chemical activity.
Histological Identification
Under a light microscope, microvilli appear as a brush border, which is a dense, fuzzy line on the apical surface of epithelial cells. This brush border is best seen using special staining techniques such as
Periodic acid-Schiff (PAS) stains, which highlight the glycoproteins present on the microvilli. Electron microscopy provides a more detailed view, revealing the individual microvilli and their actin filament cores.
Clinical Significance
Defects in microvilli can lead to various diseases. For example,
Microvillus inclusion disease (MVID) is a rare genetic disorder characterized by a lack of functional microvilli in the intestinal epithelium, resulting in severe diarrhea and malabsorption. Additionally, changes in the structure and function of microvilli are often observed in cancers, where they can influence cell proliferation and metastasis.
Research and Advances
Ongoing research is exploring the roles of
proteins involved in the formation and maintenance of microvilli, as well as their potential as therapeutic targets. Advances in super-resolution microscopy and molecular biology techniques are shedding new light on the dynamic nature of microvilli and their involvement in health and disease.
Conclusion
Microvilli are crucial for enhancing the absorptive capacity of cells, particularly in the intestinal and renal systems. Their intricate structure, supported by a network of actin filaments and associated proteins, is key to their function. Understanding the histological characteristics and clinical significance of microvilli can provide insights into various diseases and potential therapeutic approaches.
