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cir·cu·la·tion / ˌsərkyəˈlāshən/ (abbr.: cir. or circ.) • n. 1. movement to and fro or around something, esp. that of fluid in a closed system: an extra pump for good water circulation. ∎  the continuous motion by which the blood travels through all parts of the body under the action of the heart. ∎  the movement of sap through a plant. 2. the public availability or knowledge of something: his music has achieved wide circulation. ∎  the movement, exchange, or availability of money in a country: the new coins go into circulation today. ∎  [in sing.] the number of copies sold of a newspaper or magazine: the magazine had a large circulation. PHRASES: in (or out of) circulation available (or unavailable) to the public; in (or not in) general use: there is a huge volume of video material in circulation. ∎  used of a person who is seen (or not seen) in public: Anne had made a good recovery and was back in circulation.

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circulation The mass flow of fluid (e.g. blood or lymph) through the tissues and organs of an animal, allowing the transport and exchange of such materials as oxygen, nutrients, and waste products (see also vascular system; lymphatic system). Smaller animals (e.g. arthropods and most molluscs) have an open circulation, i.e. the blood is pumped into the body cavity, in which the internal organs are suspended. In open circulatory systems the tissues are in direct contact with the blood and materials are exchanged directly by diffusion. In a closed circulation, found in larger animals, the blood flows in vessels, which usually contain a series of one-way valves to maintain the flow in one direction. See also double circulation; haemodynamics; microcirculation; single circulation.

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circulation (ser-kew-lay-shŏn) n.
1. the movement of a fluid in a circular course, especially the passage of blood through the cardiovascular system.

2. the system of vessels effecting this passage. pulmonary c. circulation of blood between the heart and lungs. Deoxygenated blood passes to the lungs from the right ventricle via the pulmonary artery; oxygenated blood returns to the left atrium via the pulmonary vein. systemic c. circulation of blood between the heart and all parts of the body except the lungs. Oxygenated blood leaves the aorta and deoxygenated blood returns into the vena cava. See also collateral circulation.
circulatory adj.