Hear an exposed human heart beating

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In a circuit through the cardiovascular system, red blood cells transport oxygen from the lungs to the body tissues and carry carbon dioxide from the body tissues back to the lungs.

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In a circuit through the cardiovascular system, red blood cells transport oxygen from the lungs to the body tissues and transport carbon dioxide from the body tissues to the lungs.

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Bright swarms of Daphnia serve as the food source of many larger animals. The internal processes of Daphnia are easily studied through its transparent carapace. A single eye, sensitive to light, causes Daphnia to react in a sunlit river.

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Scientists have narrowed the answer down to a single genetic mutation.

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And how much do you really need?

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A discussion of the organ systems of the human body and their influence on one another.

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This video shows how quickly an electrical impulse is conducted from the sinoatrial node to the ventricles. The Q, R, and S waves (QRS complex) shown in the electrocardiogram represent depolarization of the ventricles.

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The heart, located between the lungs, powers the circulatory system.