What are the differences between epithelium, endothelium and mesothelium?

Basis of differentiation

Epithelium

Endothelium 

Mesothelium

Definition

Is the thin tissue forming the outer layer of the body’s external surface, lines body cavities and hollow organs, and is the major tissue of glands

Is a single cell layer which lines all the blood and lymphatic vessels. It modulates exchange between the bloodstream and surrounding tissues 

Is a protective membrane composed of mesothelial cells which coats the abdomen, heart, lungs and testes

Function

Its main functions are secretion, adsorption, protection, diffusion, transportation, sensory reception, and filtration

Is the key regulatory of blood fluidity, platelet aggregation, inflammation, and vascular tone 

Provides a slippery non-adhesive and protective surface to internal organs, as well as assist in the transport of fluid and cells across serosal cavities

Characteristics

Epithelial cells are closely packed and form continuous sheets, composed of an apical surface exposed to the body's exterior and a basal surface attached to a basement membrane

Endothelial cells are flat and form a single cell layer to allow for the uninterrupted flow of blood

The mesothelium forms a single cell layer of elongated, flattened, squamous-like mesothelial cells (approximately 25 μm in diameter)