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Veins have less smooth muscle and connective tissue and wider internal diameters than arteries. Because of their thinner walls and wider lumens they are able to expand and hold more blood. This greater capacity gives them the term of capacitance vessels. At any time, nearly 70% of the total volume of blood in the human body is in the veins. [3]
Veins do not have the external elastic lamina, but only an internal one. The tunica media is thicker in the arteries rather than the veins. The outer layer is the tunica adventitia and the thickest layer in veins. It is entirely made of connective tissue.
The superior vena cava is made up of three layers, starting with the innermost endothelial tunica intima. The middle layer is the tunica media , composed of smooth muscle tissue, and the outermost and thickest layer is the tunica adventitia , composed of collagen and elastic connective tissue that allow for flexibility.
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).
Post-capillary venules are the smallest of the veins with a diameter of between 10 and 30 micrometres (μm). When the post-capillary venules increase in diameter to 50μm they can incorporate smooth muscle and are known as muscular venules. [1] Veins contain approximately 70% of total blood volume, while about 25% is contained in the venules. [2]
August Krogh discovered how capillaries provide nutrients to animal tissue. For his work he was awarded the 1920 Nobel Prize in Physiology or Medicine. [38] His 1922 estimate that total length of capillaries in a human body is as long as 100,000 km, had been widely adopted by textbooks and other secondary sources.
Buoyed by promised pardons of their brethren for their Jan. 6 crimes and by Trump’s embrace of popular extremist far-right figures, those groups will likely see a resurgence after January ...
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 ...