Final answer:
Epithelial tissues serve as boundary tissues, providing protective barriers and controlling the transport of substances into the body, highlighting their critical role in various functions such as secretion, absorption, and permeability.
Step-by-step explanation:
All functions of epithelia reflect their roles as boundary tissues. Epithelial tissues act as a barrier, providing protection and regulating the permeability and transport of substances. They form the first line of defense against physical, chemical, and biological wear and tear, with cells operating as gatekeepers controlling what enters the body.
These cells show polarity, having an apical surface facing the body's exterior or an internal space and a basal surface that attaches to underlying connective tissue via a basal lamina. Epithelial cells are bound by cell junctions and are highly cellular with little extracellular matrix. Moreover, they line body cavities, form glands, and are involved in several functions including secretion, absorption, sensation detection, and selective permeability.