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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.
For this reason, the blood flow velocity is the fastest in the middle of the vessel and slowest at the vessel wall. In most cases, the mean velocity is used. [18] There are many ways to measure blood flow velocity, like videocapillary microscoping with frame-to-frame analysis, or laser Doppler anemometry. [19]
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).
[3] [6] This blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. [3] [6] From the left ventricle, the blood passes through the aortic valve to the aorta. [3] [6] The blood is then distributed to the body through the systemic circulation before returning again to the pulmonary circulation. [3] [6]
Diagram showing venous blood flow from capillary beds in some specific locations including the lungs, liver, and kidneys. There are some separate parallel systemic circulatory routes that supply specific regions, and organs. [8] They include the coronary circulation, the cerebral circulation, the bronchial circulation, and the renal circulation.
Vascular resistance occurs when the vessels away from the heart oppose the flow of blood. Resistance is an accumulation of three different factors: blood viscosity, blood vessel length and vessel radius. [30] Blood viscosity is the thickness of the blood and its resistance to flow as a result of the different components of the blood.
The programmed delay at the AV node also provides time for blood volume to flow through the atria and fill the ventricular chambers—just before the return of the systole (contractions), ejecting the new blood volume and completing the cardiac cycle. [8] (See Wiggers diagram: "Ventricular volume" tracing (red), at "Systole" panel.)
Formation of interstitial fluid from blood Diagram showing the formation of lymph from interstitial fluid (labeled here as "tissue fluid"). The tissue fluid is entering the blind ends of lymph capillaries (shown as deep green arrows). The arterial blood plasma, interstitial fluid and lymph interact at the level of the blood capillaries.