Transport of oxygen and

Haemoglobin, found in red blood cells, has a high affinity for oxygen. It binds oxygen in the lungs, forming oxyhaemoglobin, and transports it to tissues where oxygen is released due to lower partial pressures and higher carbon dioxide concentrations.

Haemoglobinic acid (HHb) is formed when haemoglobin accepts hydrogen ions (H⁺). This buffering action helps maintain a stable pH in the blood by binding excess H⁺ released during carbon dioxide transport and metabolic processes.

The chloride shift is the movement of chloride ions (Cl⁻) into red blood cells as bicarbonate ions (HCO₃⁻) leave, and vice versa. This maintains the electrochemical gradient and prevents the buildup of negative charge within the red blood cell during carbon dioxide transport.

Plasma transports carbon dioxide dissolved directly in it (small amount). More significantly, carbon dioxide is transported as bicarbonate ions (HCO₃⁻) within the plasma after being formed in red blood cells.

The oxygen dissociation curve for adult haemoglobin is sigmoidal (S-shaped). The shape reflects the cooperative binding of oxygen; initial binding is difficult, but subsequent binding is easier due to conformational changes in the haemoglobin molecule.

At low partial pressures of oxygen, the oxygen dissociation curve shows that haemoglobin readily releases oxygen. This ensures efficient oxygen delivery to respiring tissues where metabolic activity has lowered the pO₂.

The Bohr shift describes the decreased affinity of haemoglobin for oxygen at lower pH (higher H⁺ concentration) or higher carbon dioxide concentration. This shift promotes oxygen unloading in active tissues where carbon dioxide production and lactic acid (lowering pH) are elevated.