"Capillary Permeability"

Capillaries are the tiniest blood vessels of the body, and are the vessels that exchange fluids and chemicals between the blood and the body's tissues. Capillary permeability is a property of blood capillary walls that allows for the selective exchange of substances. Small lipid-soluble molecules such as carbon dioxide and oxygen move freely by diffusion. Water and water-soluble molecules cannot pass through the endothelial walls and are dependent on microscopic pores. These pores show narrow areas (tight junctions) which may limit large molecule movement.

Capillary permeability can change in response to physiological needs as well as in a variety of disease states.