Final answer:
Microvilli are tiny, bristle-like projections on the plasma membrane of mucosal epithelial cells, increasing surface area for better absorption of nutrients and aiding in digestion and secretion processes.
Step-by-step explanation:
The projections of the plasma membrane of a mucosal epithelial cell are called microvilli. These microscopic cylindrical extensions increase the cell's surface area, aiding absorption and secretion in epithelial tissues.
In mucosal epithelial cells, microvilli play a crucial role. They appear as tiny, fine projections on the apical surface of the plasma membrane. Their primary function is to increase the surface area for absorption significantly. This increase allows for a more efficient absorption process of nutrients and other substances within the intestines. Each microvillus contains a core of actin filaments that help maintain its shape and are essential for the proper function of microvilli. Furthermore, certain enzymes that complete the digestion of proteins and carbohydrates reside on the microvilli, making them integral to the digestive process. Considering there are approximately 200 million microvilli per square millimeter in the small intestine, the cumulative effect on absorption capabilities is tremendous. These structures, sometimes referred to as the brush border, also help in the action of the mucociliary escalator in the respiratory tract that moves mucus, trapping particles and pathogens to be expelled or swallowed.