Here's why:
* Apical surface: This is the free surface of the epithelial tissue that faces the external environment or an internal cavity. It often has specialized structures like cilia, microvilli, or even a layer of mucus, depending on the tissue's function.
* Basal surface: This is the bottom layer of the epithelial tissue, attached to the underlying connective tissue. It's often characterized by a basement membrane that provides support and acts as a barrier.
The presence of these distinct surfaces is a defining feature of epithelial tissue and is directly related to its function as a protective barrier, secretion, absorption, and filtration.
