What are the characteristics of epithelial tissues?

Regardless of shape, location or function, all epithelial tissues share a few vital characteristics. 

• Cellularity – All epithelial tissues are formed by a continuous layer of epithelial cells packed closely together with no space and very little intercellular matrix between them. 
• Presence of cell junctions – The sheets of cells that make up epithelial tissues are held together by specialized intercellular connections called cell junctions. 
• Polarity – Epithelial cells exhibit polarity with differences in structure and function between the apical or free cell surface and the basal surface that’s attached to the underlying tissue.
• High regenerative capacity – When adequately nourished, epithelial tissue is capable of rapidly regenerating and replacing damaged and dead cells after exposure to hostile substances or environments.  
• Supported by connective tissue – The basal surface of epithelial tissue is attached to a layer of connective tissue, forming a layer known as basement membrane, which separates the epithelia from the underlying connective tissues. 
• Avascular nature – Epithelial tissues are avascular. They don’t have blood vessels, which ties in with its protective nature as blood vessels are highly susceptible to rupturing and bleeding in the event of any abrasion. Epithelial cells receive essential nutrients by diffusion or absorption from capillaries present in the underlying connective tissues. 
• Absence of nerves – Epithelia do not have nerve endings except for a few axons that lay in the deeper layers.