How are respiratory gases transported in the blood?

Respiratory gases are transported in the blood through binding with haemoglobin and dissolving in plasma.

Respiratory gases, primarily oxygen and carbon dioxide, are transported in the blood in two main ways. Oxygen is carried in the blood bound to a protein called haemoglobin, found in red blood cells. When oxygen enters the bloodstream, it binds to the iron in haemoglobin, forming oxyhaemoglobin. This process occurs in the lungs, where the concentration of oxygen is high. The oxygen-rich blood is then transported to the body's tissues, where the concentration of oxygen is lower. Here, the oxygen dissociates from the haemoglobin and diffuses into the cells.

Carbon dioxide, the waste product of cellular respiration, is also transported in the blood, but in a slightly different manner. A small amount of carbon dioxide can bind to haemoglobin, but most of it is carried in the plasma, the liquid part of the blood. Carbon dioxide is converted into bicarbonate ions and hydrogen ions in the red blood cells, a reaction catalysed by the enzyme carbonic anhydrase. The bicarbonate ions then diffuse out of the red blood cells and into the plasma. This conversion is reversible, so when the blood reaches the lungs, the bicarbonate ions are converted back into carbon dioxide, which is then exhaled.

In addition to these methods, a small amount of oxygen and carbon dioxide can dissolve directly into the plasma. However, this is a less efficient method of transport, as these gases are not very soluble in water. The binding of gases to haemoglobin and their conversion into other forms in the plasma allows for a much greater amount of gas to be transported in the blood than could be achieved by dissolution alone.

In summary, the transport of respiratory gases in the blood is a complex process involving binding to haemoglobin, conversion into other forms, and dissolution in plasma. These mechanisms allow the body to efficiently deliver oxygen to its tissues and remove waste carbon dioxide.