Final answer:
Permeability in epithelium refers to the ability of substances to pass through or cross the tissue. Epithelial tissues act as barriers, controlling the movement of materials across them by being selectively permeable.
Step-by-step explanation:
Permeability in regard to epithelium refers to the ability of substances to pass through or cross the epithelial tissue. Epithelial tissues act as barriers, controlling the movement of materials across them. They have the ability to be selectively permeable, allowing only certain substances to pass through while blocking others. For example, the epithelial cells lining the intestine have tight junctions that prevent substances from passing between them, and instead, substances must pass through the apical surfaces of the cells to enter the bloodstream.