Which of the following gases primarily binds to what in systemic capillaries to be transported?

• A. Oxygen to myoglobin
• B. Carbon dioxide to bicarbonate
• C. Nitrogen to hemoglobin
• D. Carbon dioxide to hemoglobin

Answer: (D)

In the context of gas exchange in systemic capillaries, carbon dioxide is primarily transported by binding to hemoglobin. After oxygen is delivered to tissues, hemoglobin undergoes changes that allow it to facilitate the transport of carbon dioxide, which is a byproduct of cellular metabolism.

In the bloodstream, a significant portion of carbon dioxide does dissolve in plasma, but much of it binds to hemoglobin at the amino acid sites, forming carbamino compounds. This binding is a reversible process, which allows carbon dioxide to be released in the lungs where it is expelled from the body. The relationship between carbon dioxide and hemoglobin is crucial for effective gas exchange, as it helps maintain the acid-base balance in the blood and regulate pH.

While considering the other choices, oxygen primarily binds to hemoglobin rather than myoglobin in systemic circulation; myoglobin serves more as an oxygen storage molecule in muscle tissues. Additionally, while carbon dioxide can exist in the plasma as bicarbonate, it is not primarily transported in this form during the direct exchange processes in systemic capillaries. Nitrogen has a low reactivity and does not typically bind to hemoglobin in the way that oxygen and carbon dioxide do, as it has very limited physiological roles in the respiratory process under normal