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Vein - Definition


Veins are types of blood vessels, along with arteries and capillaries. While arteries carry blood from the heart to the organs, veins carry out the return journey, taking blood from the organs and peripheral tissues back to the heart. The general process consists of veins transporting oxygen-starved blood containing carbon dioxide that has passed through organs by way of arteries, supplying them with oxygen. The only exceptions are pulmonary veins, which carry oxygen-rich blood, emerging from the area of gaseous exchange through the pulmonary alveoli. Veins generally begin in the peripheral organs and tissues, to then converge and create larger veins. The superior and inferior vena cava veins are examples of very large veins, which pump their contents into the right atrium of the heart. The blood then passes through the right ventricle and pulmonary arteries towards the lungs in order to offload its carbon dioxide and take on oxygen.