where does blood entering the superior vena cava come from
Superior vena cava The superior vena cava (SVC) is the superior of the two venae cavae, the great venous trunks that return deoxygenated blood from the systemic circulation to the right atrium of the heart. It is a large-diameter (24Â mm), yet short, vein that receives venous return from the upper half of the body, above the diaphragm. (Venous return from the lower half, below the diaphragm, flows through the inferior vena cava.) The SVC is located in the anterior right superior mediastinum.[1] It is the typical site of central venous access (CVA) via a central venous catheter or a peripherally inserted central catheter. Mentions of "the cava" without further specification usually refer to the SVC.
Inferior vena cava The inferior vena cava (or IVC) is a large vein that carries deoxygenated blood from the lower and middle body into the right atrium of the heart. Its walls are rigid and has valves so the blood does not flow down via gravity. It is formed by the joining of the right and the left common iliac veins, usually at the level of the fifth lumbar vertebra.
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Heart The heart pumps blood with a rhythm determined by a group of pacemaking cells in the sinoatrial node. These generate a current that causes contraction of the heart, traveling through the atrioventricular node and along the conduction system of the heart. The heart receives blood low in oxygen from the systemic circulation, which enters the right atrium from the superior and inferior venae cavae and passes to the right ventricle. From here it is pumped into the pulmonary circulation, through the lungs where it receives oxygen and gives off carbon dioxide. Oxygenated blood then returns to the left atrium, passes through the left ventricle and is pumped out through the aorta to the systemic circulationâˆ’where the oxygen is used and metabolized to carbon dioxide.[8] The heart beats at a resting rate close to 72 beats per minute.[9] Exercise temporarily increases the rate, but lowers resting heart rate in the long term, and is good for heart health.[10]