How is carbon dioxide transported in the blood?

Carbon dioxide is transported in the blood primarily as bicarbonate ions, but also bound to haemoglobin and dissolved in plasma.

In the human body, carbon dioxide (CO2) is a waste product of cellular respiration, and its removal is crucial for maintaining the body's pH balance and preventing respiratory acidosis. The transportation of CO2 in the blood is a complex process that involves several steps and forms.

The majority of CO2, about 70%, is transported as bicarbonate ions (HCO3-). This occurs when CO2 diffuses into red blood cells and reacts with water (H2O) to form carbonic acid (H2CO3). This reaction is catalysed by the enzyme carbonic anhydrase. The carbonic acid then quickly dissociates into a hydrogen ion (H+) and a bicarbonate ion (HCO3-). The bicarbonate ions diffuse out of the red blood cells and into the plasma, where they are transported to the lungs.

Approximately 20% of CO2 is carried in the blood bound to haemoglobin, a protein found in red blood cells. This form of CO2 transport is known as carbaminohaemoglobin. The CO2 binds to the amino groups in the haemoglobin molecule, forming a stable but easily reversible compound. This allows the CO2 to be carried to the lungs, where it is released and exhaled.

The remaining 10% of CO2 is transported in the blood dissolved in plasma. This is the simplest form of CO2 transport, as the CO2 simply dissolves into the plasma and is carried to the lungs. However, because CO2 is not very soluble in water, only a small fraction of the total CO2 can be transported this way.

In summary, CO2 is transported in the blood in three main ways: as bicarbonate ions, bound to haemoglobin, and dissolved in plasma. Each method plays a crucial role in maintaining the body's pH balance and ensuring the efficient removal of this waste product.