The human cardiovascular system can be divided into two circuits: the circuit transports blood between the heart and lungs and the circuit transports blood between the heart and the rest of the body.

The cardiovascular system or circulatory system has following two circuits:

De-oxygenated blood begins from the right chamber of the heart into the right atrium and moves down into the right ventricle, and then is elevated into the pulmonary arteries to the pulmonary capillaries where it gets cleared of carbon dioxide and accumulates oxygen. Oxygenated blood then passes in pulmonary veins to the left chamber of the heart into the left atrium, flowing into the left ventricle, and then is pulled through systemic arteries to the systemic (body) capillaries, where it supplies oxygen to the tissue cells and accumulates up CO2. De-oxygenated blood then rotates via veins to the right chamber of the heart.

b - the respond is innate and varies over time.

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