Blood vessel

A tubular structure that carries blood through the body. Arteries, veins, and capillaries form the main vessel types, differing in structure and role.

Artery: A blood vessel that carries blood away from the heart. Its thick, elastic walls withstand the high pressure of blood leaving the heart.
Blood pressure: The force exerted by circulating blood against the walls of blood vessels. Pressure drives blood through the vessel network and falls as blood moves away from the heart.
Atherosclerosis: A disease in which plaques containing lipids and inflammatory material build up inside arteries. Plaques narrow or block arteries, limiting blood supply to organs.
Lymphatic vessel: A vessel that carries lymph from tissues toward the bloodstream. Like blood vessels, it forms a network, but it carries lymph rather than circulating blood.
Vein: A blood vessel that carries blood toward the heart. Its low-pressure return flow often relies on valves and surrounding muscle contractions.
Vasoconstriction: Narrowing of blood vessels caused by contraction of smooth muscle in their walls. Changes in vessel diameter redistribute blood flow and alter resistance.
Aneurysm: A localized abnormal dilation of a blood vessel caused by weakness in its wall. A weakened vessel wall can expand and, in some cases, rupture.
Airway: A passage that conducts air between the atmosphere and the lungs. Airways are branching tubes, but they transport gas rather than blood.
Capillary: A microscopic blood vessel whose thin wall permits exchange between blood and tissues. Its narrow, permeable walls provide the main site of exchange with body cells.
Vasodilation: Widening of blood vessels caused by relaxation of smooth muscle in their walls. Wider vessels can increase local blood flow and reduce vascular resistance.

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