Which statement best describes the oxygen transport pathway from the atmosphere to mitochondria in muscle?

Which statement best describes the oxygen transport pathway from the atmosphere to mitochondria in muscle?

• A. Air → trachea → bronchi → alveoli → systemic circulation.
• B. Air → lungs → alveolar gas exchange → oxygenated blood via pulmonary veins → left heart → systemic circulation → muscle capillaries → mitochondria.
• C. Air → lungs → alveolar gas exchange → deoxygenated blood via pulmonary veins → left heart → systemic circulation.
• D. Air → lungs → alveolar gas exchange → oxygenated blood via pulmonary arteries → right heart → systemic circulation.

Answer: (B)

Tracing oxygen from the air to muscle mitochondria starts with getting O2 into the lungs, where it crosses the alveolar membrane into the blood. That oxygenated blood then returns to the heart through the pulmonary veins and enters the left side of the heart. From there it’s pumped into the systemic circulation, delivering oxygen to muscle capillaries. There, oxygen diffuses into muscle cells and ultimately reaches the mitochondria to drive aerobic respiration. That sequence is captured by the described option: air → lungs → alveolar gas exchange → oxygenated blood via pulmonary veins → left heart → systemic circulation → muscle capillaries → mitochondria. The pulmonary veins carry oxygenated blood to the left heart, not deoxygenated blood, and oxygenated blood does not travel via pulmonary arteries to the right heart as the body-wide supply route.

Tracing oxygen from the air to muscle mitochondria starts with getting O2 into the lungs, where it crosses the alveolar membrane into the blood. That oxygenated blood then returns to the heart through the pulmonary veins and enters the left side of the heart. From there it’s pumped into the systemic circulation, delivering oxygen to muscle capillaries. There, oxygen diffuses into muscle cells and ultimately reaches the mitochondria to drive aerobic respiration.

That sequence is captured by the described option: air → lungs → alveolar gas exchange → oxygenated blood via pulmonary veins → left heart → systemic circulation → muscle capillaries → mitochondria. The pulmonary veins carry oxygenated blood to the left heart, not deoxygenated blood, and oxygenated blood does not travel via pulmonary arteries to the right heart as the body-wide supply route.