What are the surfaces of epithelial cells?

Epithelial cells have three distinct surfaces – apical, lateral, and basal. 

1. The apical surface refers to the top of the epithelial cell, which faces the lumen or the external environment. It is also known as the free surface. The apical surface often features specialized structures related to the function of the cell, such as cilia that help substances move along in the respiratory tract, microvilli that increase surface area for absorption in the small intestines, and stereocilia that are associated with hearing and balance in the inner ear. 
2. The lateral surface faces adjacent cells on either side, facilitating connections with neighboring cells through four different types of epithelial cell junctions, namely tight junctions, gap junctions, desmosomes, and adherens. 
3. The basal surface refers to the bottom edge of the epithelial cell, which lies adjacent to the basement membrane. 

In a stratified epithelium, which is made up of multiple layers of epithelial cells, the apical layer forms the topmost superficial layer of cells while the basal layer forms the deepest layer of cells at the bottom.