Acountercurrent heat exchanger enables an animal to

Regulate heat throughout it's body,

Explanation:

Countercurrent Heat Exchange is a normal and varied mechanism in organisms that utilizes parallel pipes of flowing fluid in opposite directions in order to save energy, such as blood flow. For example, a whale's tongue uses this system through the blood flow to the tip of the tongue, where the countercurrent heat exchange system heats up blood returning to the body.

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.

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