When Bufo marinus burrows, the skin becomes intimately surrounded by substrate but the nares always remain exposed to the surface air. Upon entering into a state of dormancy the animal hypoventilates and this together with the loss of the skin as a respiratory site results in a rise in arterial blood Pcoco2 despite a probable decline in metabolism. Even though lung ventilation falls, the toad regulates blood pH and the respiratory acidosis is progressively compensated for by a progressive increase in plasma [HCO3-] along the course of an elevated PCOCO2 isopleth. At steady state, the acidosis is fully compensated for by a new equilibrium ratio of HCO3- to PCOCO2 at the same pH as the non-burrowed animal. Arousal from the dormant state at this time results in a marked lung hyperventilation and a sharp decline in body CO2 stores

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