Most of the carbon dioxide in the body is transported in the form of the bicarbonate anion.

Carbon dioxide is offloaded at the lungs in exchange for oxygen.

The pulmonary artery carries deoxygenated blood from the heart to the lungs and the pulmonary vein carries the blood, now oxygenated, from the lungs back to the heart.

This is the only time an artery carries deoxygenated blood and the only time a vein carries oxygenated blood!

The Oxygen-hemoglobin dissociation curve is a graph that displays the amount of oxygen being carried by the hemoglobin at any given partial pressure of oxygen

If the partial pressure of oxygen is higher, the amount of oxygen carried by the hemoglobin is higher.

However, the affinity of hemoglobin for oxygen is not always the same and certain factors (like pH) can cause hemoglobin to carry more or less oxygen. This is referred to a shift in the curve.

The Bohr Effect is an important example of a “right shift” of the curve. A relatively low pH in peripheral tissues reduces the strength of the bond between hemoglobin and oxygen and makes oxygen more easily available to peripheral tissues.

The Haldane effect is a related phenomenon that enhances the offloading of carbon dioxide once the blood arrives at the lungs.