The Bohr Shift Explained

Full transcript

Haemoglobin carries oxygen around your body. When it's carrying oxygen, it's called oxyhaemoglobin. But how does it know when to pick oxygen up and when to let go? Partial pressure, or pO2, is just a measure of how much oxygen is around. High in the lungs, low in respiring muscle. Affinity means how strongly haemoglobin holds on to oxygen. High affinity means it grabs oxygen tightly. Low affinity means it lets go easily. This is the oxyhaemoglobin dissociation curve. Haemoglobin saturation is the percentage of binding sites holding oxygen. In the lungs, pO2 is high, so haemoglobin is nearly 100% saturated. In the tissues, pO2 drops, so saturation falls and oxygen is released. Now you exercise. Your muscles respire faster, making more CO2 and more heat, which dissolves in blood and lowers blood pH. This is the Bohr effect: more CO2, lower pH and higher temperature all change haemoglobin's shape, so its affinity for oxygen decreases, and the whole curve shifts right. This is the Bohr shift. Look at the same low pO2 in the muscle. On the shifted curve, saturation is lower, meaning more oxygen has been released. Exactly where it's needed, and exactly when. Back at the lungs, CO2 is breathed out, pH rises and haemoglobin's affinity goes back up, so it loads oxygen again, and the curve slides back left. More CO2, lower pH, higher temperature: curve shifts right, affinity falls, more oxygen unloaded. That's the Bohr shift. Always say: affinity decreases, curve shifts right, more oxygen released at the same pO2.