barrier

Meaning of barrier: A barrier is a structure or mechanism that blocks, filters, or limits passage of substances, cells, or organisms, a concept used throughout physiology.

Definition of barrier

A barrier is a general term for any structure or mechanism that blocks, filters, separates, or otherwise limits the movement of substances, cells, or organisms from one area to another. The term is used broadly throughout biology and medicine wherever such a restriction plays a functional role.

Prominent examples include the blood brain barrier, a network of tightly joined cells lining the brain's blood vessels that restricts which substances can pass from the bloodstream into brain tissue, and the skin, which acts as a physical barrier limiting the entry of microorganisms and the loss of water from the body.

Because a barrier's function depends on its specific structure, damage or disruption to a barrier, such as a break in the skin or increased permeability of the blood brain barrier during illness, can allow substances or organisms to pass through that would ordinarily be blocked, sometimes with clinical consequences.