Final answer:
PaCO2 is indicative of lung function in the regulation of the body's acid-base balance by controlling carbon dioxide levels in the blood.
Step-by-step explanation:
The PaCO2 (partial pressure of carbon dioxide) value in arterial blood gases is primarily reflective of the effectiveness of the lungs in regulating the acid-base balance via gas exchange. When blood passes through the pulmonary capillaries in the lungs, chemical reactions regulate the levels of CO2 and carbonic acid.
Through changes in the respiratory rate, the body can modify the amount of CO2 exhaled to adjust the blood pH. Hence, the lungs play a crucial role in maintaining homeostasis of blood gases and pH, unlike the kidneys which regulate the bicarbonate level, or the liver and pancreas, which do not directly regulate the levels of carbon dioxide in the blood.