Epithilial cells are characterized by a range of shapes (squamous, cuboidal, columnar) and by the pattern of adhering tightly to each other to form sheets. Cellular junctions are abundant in epithelial tissues, i.e. zonulae adherens, desmosomes and tight junctions.. The increasing or decreasing prominence of certain organelles are associated with specific cellular functions within certain tissues and organs.

An old MCAT trick is to see if you think that simply because a tissue is epithelial tissue, it must derive from ectoderm. Epithelial tissues may derive from either of the three germ layers. For example, the epithelial tissue of the skin derives from ectoderm. The inner linings of body cavities derives from mesoderm, and the lining of the gastrointestinal tract derives from endoderm. All are epithelial tissue.

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