Biology – The gas exchange system | e-Consult

Oxygen transport in the blood is primarily carried out by haemoglobin, a protein found within red blood cells (erythrocytes). Haemoglobin has a high affinity for oxygen, allowing the blood to effectively carry a large amount of oxygen from the lungs to the body's tissues.

The process of oxygen transport involves the following steps:

1. In the lungs, oxygen diffuses from the alveoli into the red blood cells and binds to haemoglobin. Each haemoglobin molecule can bind up to four oxygen molecules. This binding is reversible.
2. The oxygenated blood then travels from the lungs to the heart, where it is pumped to the rest of the body.
3. In the body's tissues, the partial pressure of oxygen is lower than in the blood. Therefore, oxygen dissociates from haemoglobin and diffuses into the tissues.
4. The oxygen released from haemoglobin diffuses into the cells, where it is used for cellular respiration.
5. Carbon dioxide, a waste product of cellular respiration, diffuses from the tissues into the blood and is transported back to the lungs.

Several factors affect the efficiency of oxygen binding to haemoglobin:

• Partial pressure of oxygen (PO₂): Higher PO₂ increases the affinity of haemoglobin for oxygen.
• pH: Lower pH (more acidic conditions) decreases the affinity of haemoglobin for oxygen (the Bohr effect). This is because acidic conditions promote the release of oxygen in tissues where it is needed.
• Carbon dioxide (CO₂): Higher CO₂ levels also decrease the affinity of haemoglobin for oxygen (the Bohr effect).
• Temperature: Higher temperature decreases the affinity of haemoglobin for oxygen.
• 2,3-bisphosphoglycerate (2,3-BPG): This molecule binds to haemoglobin and reduces its affinity for oxygen. 2,3-BPG levels increase in conditions of low oxygen availability (e.g., at high altitudes).