What effect does increased carbon dioxide in venous blood have on pH?

Increased carbon dioxide (CO2) in venous blood leads to a lower pH, which is a result of the physiological process known as the bicarbonate buffer system. When CO2 levels rise in the blood, it enters red blood cells and reacts with water to form carbonic acid (H2CO3). This reaction is catalyzed by the enzyme carbonic anhydrase.

Carbonic acid can then dissociate into bicarbonate ions (HCO3-) and hydrogen ions (H+). The release of hydrogen ions is what causes the pH of the blood to decrease, making it more acidic. This shift in pH is significant because it can influence various physiological processes, including the affinity of hemoglobin for oxygen (the Bohr effect), which is crucial for effective gas exchange and delivery of oxygen to tissues.

Thus, increased levels of carbon dioxide in the venous blood directly contribute to a decrease in blood pH, confirming that the correct answer is that it lowers the pH.