Epithelial cells are enclosed within a cell membrane and may be flat, cuboidal or columnar in shape. Each cell contains 1 cell nucleus and a number of organelles including ribosomes, endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, and peroxisomes. Epithelial cells typically have 3 domains or regions in their structure:

1. The apical region, which is located on the side facing the external environment (the side of the lumen). The apical region may feature various structures related to the functions of that particular cell. For example, the epithelial cells in the respiratory tract contain motile hair-like structures called cilia that trap dust and other particles that you breathe in, preventing them from entering the lungs. The epithelial cells in the inner ear contain stereocilia on the apical region, which help with hearing and balance. The intestinal epithelial cells contain small finger-like projections called microvilli that increase the surface area for more efficient absorption and transport of fluids. 
2. The basal region, which is located at the lower edge of the cell, lies against the basal lamina of the extracellular matrix, which keeps the epithelium separate from the surrounding connective tissue.  
3. The lateral region or the sides of the cells allow neighboring cells to connect with each other via four types of cell junctions – tight junctions, gap junctions, adherens, and desmosomes.