capillary
Meaning of capillary: Capillaries are the smallest blood vessels, forming thin walled networks where oxygen, nutrients, and waste products exchange between blood and surrounding tissue.
Definition of capillary
A capillary is the smallest type of blood vessel in the body, connecting the smallest arteries, called arterioles, to the smallest veins, called venules. Capillaries form dense, branching networks that reach into nearly every tissue, positioning blood close enough to surrounding cells to exchange substances with them directly.
The wall of a capillary is only a single layer of cells thick, thin enough to allow oxygen, nutrients, carbon dioxide, and waste products to pass between the blood and the surrounding tissue. This thin, permeable structure allows capillaries to perform their exchange function, unlike the thicker walls of arteries and veins, which are built mainly for carrying blood rather than exchanging substances.
Because capillary networks are so extensive and so thin walled, conditions that damage small blood vessels, including diabetes and certain autoimmune conditions, often affect capillaries early, sometimes producing changes detectable on specialized examination before larger vessel damage becomes apparent.
Used in a sentence
Examination of the capillaries in the retina revealed changes consistent with long standing high blood sugar.
Good to know
Capillaries are structurally distinct from arteries and veins mainly in their thin, single layer wall, a feature that allows the exchange of gases and nutrients with surrounding tissue but limits their ability to withstand the pressure that larger vessels routinely carry.
Word origin
Where “capillary” comes from
Formed from Latin capillus, meaning hair, describing the vessel's hairlike thinness.