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What are veins?
Veins are blood vessels that transport blood back to the heart from the organs of the body (Arteries carry blood from the heart to the organs).
The blood in the veins is deoxygenated which means the oxygen has been used and replaced with carbon dioxide.
Veins have valves that ensure that blood moves in only one direction- back to the heart where it can be re-oxygenated. These valves help blood from the lower extremities of the body, such as the foot, travel against the force of gravity. Arteries do not have valves as the pressure from the heart forces the blood through them.
The blood inside the veins is actually a deep red color, but because of the way the light passes through your body, they usually look bluish in color.
Some special veins:
The jugular veins carry deoxygenated blood from the head back to the heart.
The vena cava are veins that are connected directly to the heart
The pulmonary veins carry oxygenated blood from the lungs to the left atrium of the heart (They are the only veins that carry oxygen rich blood).