Which option lists all five organs identified as requiring the most oxygen?

• A. Brain, Heart, Liver, Kidneys, Lungs
• B. Brain, Heart, Liver, Kidneys, Spleen
• C. Brain, Heart, Liver, Kidneys
• D. Brain, Heart, Lungs, Kidneys, Spleen

Answer: (A)

Oxygen use by organs tracks how active the tissue is and how much blood flows to it. The brain constantly works to process information and maintain function, so it needs a steady, rich oxygen supply. The heart is always beating, pumping blood everywhere, which requires a lot of oxygen for its muscle. The liver does a wide range of energy-intensive tasks—metabolism, detoxification, synthesis—that consume substantial oxygen. The kidneys use a lot of oxygen to power filtration and reabsorption processes that keep fluids and electrolytes in balance. The lungs themselves also consume oxygen to support the metabolism of their own cells and to maintain the tissues that enable gas exchange; they receive the entire cardiac output, which means a significant amount of oxygen is used there as well. Together, these five organs represent the regions with the highest resting oxygen demand, so listing brain, heart, liver, kidneys, and lungs best reflects the organs identified as requiring the most oxygen.