General Characteristics Of Epithelial Tissue

There are many characteristics common to all epithelial tissue making it easy to recognize. However, students sometimes still find a way to misidentify epithelial tissue. Therefore pay close attention to the following major elements that characterize this type of tissue.
Epithelial tissue covers surfaces and lines internal passage ways . As such epithelial tissue is found in 3 major places
–outer surface of the body
–surface of organs
–internal surface lining of tubules, vessels and hollow organs
The fact that Epithelial Tissue covers or lines means that most epithelial tissues have a free surface which does not contact other cells or extracellular material. This surface is called the apical surface. The opposite side is called the basal surface. On histological slides, this apical surface is the most easiest to recognize. It is at the interface where empty space (usually a vast area of white space) meets tissue.
Example of a typical epithelium layer
The picture on the right shows the epithelial layer sandwiched between the two green arrows. The obvious free empty space is located on top and the sharp point of the arrow thus points at the apical surface of the epithelium. The sharp point of the lower arrow meets up with the basal surface. The green line marks the boundary between the epithelium layer and the underlying tissue and is the site where the basement membrane can be located.
Cells of Epithelial Tissue fit closely together and form sheets of cells. There is hardly any extracellular material that separates the cells from each other.
The Basal surface of the cells are attached to a basement membrane which provides an anchor for attachment to underlying tissues such as connective tissue. NO BLOOD VESSELS PENETRATE THE BASEMENT MEMBRANE TO REACH THE EPITHELIAL LAYER.
And finally take note that most glands are composed primarily from epithelial cells.