How does blood transport oxygen and carbon dioxide?

Blood transports oxygen and carbon dioxide through red blood cells, which contain a protein called haemoglobin.

In more detail, the process begins in the lungs, where oxygen from the air we breathe in diffuses across the thin walls of the alveoli and into the bloodstream. Here, it binds to the haemoglobin in red blood cells. Each haemoglobin molecule can carry up to four oxygen molecules, and the binding of oxygen to haemoglobin is a reversible process. This means that when the blood reaches tissues where the oxygen concentration is low, the oxygen will detach from the haemoglobin and diffuse into the cells.

On the other hand, carbon dioxide, a waste product of cellular respiration, diffuses out of the cells and into the bloodstream. Some of it dissolves directly into the plasma, but the majority of it is transported in the form of bicarbonate ions. This happens when carbon dioxide reacts with water in the presence of an enzyme called carbonic anhydrase, forming carbonic acid. This acid then quickly dissociates into hydrogen ions and bicarbonate ions. The bicarbonate ions are transported in the plasma back to the lungs, where the process is reversed to form carbon dioxide and water, which are then exhaled.

In addition, a small amount of carbon dioxide binds directly to haemoglobin, forming carbaminohaemoglobin. This does not interfere with oxygen transport, as carbon dioxide binds to a different part of the haemoglobin molecule than oxygen does. This dual ability of haemoglobin to carry both oxygen and carbon dioxide is crucial for the efficient functioning of our respiratory system.

In summary, the transport of oxygen and carbon dioxide in the blood is a complex process involving diffusion, reversible binding to haemoglobin, and chemical reactions facilitated by enzymes. It is a perfect example of how chemistry plays a vital role in our body's physiology.