The five distinguishing characteristics of epithelial tissues are polarity, specialized contacts, support by connective tissue, being avascular but innervated, and the ability to regenerate. Polarity means each epithelium has an apical surface and a basal surface that differ in structure and function. Specialized contacts include tight junctions and desmosomes that bind epithelial cells closely together. Epithelial sheets rest on and are supported by connective tissue, are avascular yet supplied by nerve fibers, and can regenerate rapidly through cell division.

Key points

Polarity: epithelial cells have an apical (free) surface and a basal (attached) surface that differ in structure and function.
Specialized contacts: lateral contacts such as tight junctions and desmosomes bind adjacent epithelial cells closely together.
Supported by connective tissue: every epithelium rests on connective tissue, and the basal lamina plus reticular lamina form the basement membrane.
Avascular but innervated: epithelial tissues contain no blood vessels but are supplied by nerve fibers, receiving nutrients by diffusion from underlying connective tissue.
High regenerative capacity: epithelial cells can rapidly replace lost cells by cell division when adequately nourished.

What are the five distinguishing characteristics of epithelial tissues?

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