Glossary
- arteriole
- (also, resistance vessel) very small artery that leads to a capillary
- arteriovenous anastomosis
- short vessel connecting an arteriole directly to a venule and bypassing the capillary beds
- artery
- blood vessel that conducts blood away from the heart; may be a conducting or distributing vessel
- capacitance
- ability of a vein to distend and store blood
- capacitance vessels
- veins
- capillary
- smallest of blood vessels where physical exchange occurs between the blood and tissue cells surrounded by interstitial fluid
- capillary bed
- network of 10–100 capillaries connecting arterioles to venules
- continuous capillary
- most common type of capillary, found in virtually all tissues except epithelia and cartilage; contains very small gaps in the endothelial lining that permit exchange
- elastic artery
- (also, conducting artery) artery with abundant elastic fibers located closer to the heart, which maintains the pressure gradient and conducts blood to smaller branches
- external elastic membrane
- membrane composed of elastic fibers that separates the tunica media from the tunica externa; seen in larger arteries
- fenestrated capillary
- type of capillary with pores or fenestrations in the endothelium that allow for rapid passage of certain small materials
- internal elastic membrane
- membrane composed of elastic fibers that separates the tunica intima from the tunica media; seen in larger arteries
- lumen
- interior of a tubular structure such as a blood vessel or a portion of the alimentary canal through which blood, chyme, or other substances travel
- metarteriole
- short vessel arising from a terminal arteriole that branches to supply a capillary bed
- microcirculation
- blood flow through the capillaries
- muscular artery
- (also, distributing artery) artery with abundant smooth muscle in the tunica media that branches to distribute blood to the arteriole network
- nervi vasorum
- small nerve fibers found in arteries and veins that trigger contraction of the smooth muscle in their walls
- perfusion
- distribution of blood into the capillaries so the tissues can be supplied
- precapillary sphincters
- circular rings of smooth muscle that surround the entrance to a capillary and regulate blood flow into that capillary
- sinusoid capillary
- rarest type of capillary, which has extremely large intercellular gaps in the basement membrane in addition to clefts and fenestrations; found in areas such as the bone marrow and liver where passage of large molecules occurs
- thoroughfare channel
- continuation of the metarteriole that enables blood to bypass a capillary bed and flow directly into a venule, creating a vascular shunt
- tunica externa
- (also, tunica adventitia) outermost layer or tunic of a vessel (except capillaries)
- tunica intima
- (also, tunica interna) innermost lining or tunic of a vessel
- tunica media
- middle layer or tunic of a vessel (except capillaries)
- vasa vasorum
- small blood vessels located within the walls or tunics of larger vessels that supply nourishment to and remove wastes from the cells of the vessels
- vascular shunt
- continuation of the metarteriole and thoroughfare channel that allows blood to bypass the capillary beds to flow directly from the arterial to the venous circulation
- vasoconstriction
- constriction of the smooth muscle of a blood vessel, resulting in a decreased vascular diameter
- vasodilation
- relaxation of the smooth muscle in the wall of a blood vessel, resulting in an increased vascular diameter
- vasomotion
- irregular, pulsating flow of blood through capillaries and related structures
- vein
- blood vessel that conducts blood toward the heart
- venous reserve
- volume of blood contained within systemic veins in the integument, bone marrow, and liver that can be returned to the heart for circulation, if needed
- venule
- small vessel leading from the capillaries to veins