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Veins (/ v eɪ n /) are blood vessels in the circulatory system of humans and most other animals that carry blood towards the heart.Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are those of the pulmonary and fetal circulations which carry oxygenated blood to the heart.
A list of veins in the human body: Veins of the heart. Coronary sinus. Great cardiac vein; Oblique vein of left atrium; Middle cardiac vein; Small cardiac vein; Pulmonary veins; Superior vena cava. Brachiocephalic vein. Inferior thyroid vein; Inferior laryngeal vein; Pericardial veins; Pericardiophrenic veins; Bronchial veins; Vertebral vein ...
In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. [1] [2] It includes the cardiovascular system, or vascular system, that consists of the heart and blood vessels (from Greek kardia meaning heart, and Latin vascula meaning vessels).
Though veins might make it appear as such, human blood is never naturally blue. [3] The blue appearance of surface veins is caused mostly by the scattering of blue light away from the outside of venous tissue if the vein is at 0.5 mm deep or more. Veins and arteries appear similar when skin is removed and are seen directly. [4] [5]
There are five types of blood vessels: the arteries, which carry the blood away from the heart; the arterioles; the capillaries, where the exchange of water and chemicals between the blood and the tissues occurs; the venules; and the veins, which carry blood from the capillaries back towards the heart.
In the smallest vessels, the vessels' own circulation nourishes the walls directly and they have no vasa vasorum at all. Vasa vasorum are more frequent in veins than arteries. [2] Some authorities hypothesize that the vasa vasorum would be more abundant in large veins, as partial oxygen pressure and osmotic pressure is lower in veins. This ...
The capillaries connect to venules, and the blood then travels back through the network of veins to the venae cavae into the right heart. The micro-circulation — the arterioles, capillaries, and venules —constitutes most of the area of the vascular system and is the site of the transfer of O 2 , glucose , and enzyme substrates into the cells.
As part of the pulmonary circulation they carry oxygenated blood back to the heart, as opposed to the veins of the systemic circulation which carry deoxygenated blood. [citation needed] By definition, a vein is a blood vessel that carries blood to the heart, whether oxygenated or deoxygenated.