Epithelial Tissue
Epithelial tissue is one of four basic types of animal cells, along with nervous tissue, muscle tissue and connective tissue. Epithelial tissue lines all organs and lumens in an animal's body. Their role is to act as a barrier to protect the rest of the cells from environmental conditions such as sunlight, or the acid in the stomach. Due to the two sides of the barrier being in contact with different conditions, epithelial cells are often polar. Polarity means that there is an asymmetrical distribution of the internal and membrane proteins in the cell. A variety of cell-to-cell junctions help maintain the barrier function of epithelial cells. While epithelial cells are always strongly adhered to each other through cell-to-cell junctions, they often have different cell morphologies. There are three main shapes of epithelial cells:
- Squamous - flat
- Cuboidal - square
- Columnar - tall, rectangular