 The first is the homeostatic control of the blood partial pressure of carbon dioxide, which determines the carbonic acid concentration in the plasma, and can change the pH of the arterial plasma within a few seconds.The partial pressure of carbon dioxide in the arterial blood is monitored by the central chemoreceptors of the medulla oblongata, and so are part of the central nervous system.These chemoreceptors are sensitive to the pH and levels of carbon dioxide in the cerebrospinal fluid.