The apical surface refers to the uppermost layer of cells in a tissue, particularly in epithelial tissues. It is the side of the cell that faces the lumen (the inside space of a tubular structure) or the outside of the body. This surface is crucial for various functions, including absorption, secretion, and sensation in different organs.
In the context of epithelial cells, the apical surface is often specialized with structures like microvilli or cilia. Microvilli increase the surface area for absorption, as seen in the intestinal lining, while cilia serve to move substances along the surface, such as mucus in the respiratory tract. Understanding the apical surface’s structure and function is essential for appreciating how epithelial tissues contribute to the overall function of organs and body systems.