Carbon Dioxide in Blood: Sources, Transport & Role

Carbon dioxide (CO2) is found in blood in three main forms:

1. Dissolved CO2: A small amount of CO2 is dissolved directly into the blood plasma. This dissolved CO2 is in equilibrium with the CO2 in the alveoli of the lungs and can easily diffuse across the alveolar-capillary membrane.

2. Bicarbonate Ion (HCO3-): The majority of CO2 in the blood is transported in the form of bicarbonate ions. When CO2 diffuses into the red blood cells, it reacts with water to form carbonic acid (H2CO3) through the enzyme carbonic anhydrase. Carbonic acid quickly dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-). Bicarbonate ions are the main buffer in the blood, helping to maintain the blood's pH.

3. Carbaminohemoglobin: A small amount of CO2 also binds to the amino acid side chains of hemoglobin, forming carbaminohemoglobin. This reaction is less significant compared to the transport of CO2 as dissolved CO2 and bicarbonate ions.

The transport of CO2 in the blood is essential for maintaining the body's acid-base balance and ensuring proper tissue oxygenation. The concentration of CO2 in the blood is regulated through the process of respiration, where excess CO2 is exhaled during exhalation, and fresh oxygen is taken up during inhalation.