The functional morphology, nervous and hormonal control and coordination of the cardiovascular and ventilatory systems in decapodan crustaceans is reviewed. Pacemaker function reflects the reliance of crustaceans on small numbers of large, multipolar neurones. Respiratory gas exchange and transport may be limited by the potential diffusion barrier presented by chitin on the gills and by the relatively low O2 capacity of the haemolymph, though this is compensated by the relatively high O2 affinity of haemocyanin and the large volume of the haemocoel. Haemolymph buffering capacity is attributable to haemocyanin and to bicarbonate, including an internal source of fixed base, possibly the exoskeleton.
The typical hypoxic response includes a bradycardia and hyperventilation resulting in a respiratory alkalosis and resultant increase in O2 affinity of the haemocyanin. Diffusive conductance may increase. When O2 transport is limiting there is a switch to anaerobiosis with normoxic recovery including repayment of an O2 debt. Some species are facultative air-breathers and compensate for a respiratory and metabolic acidosis when in air by elevation of buffer base. Central and peripheral O2 receptors may be involved in determining respiratory and cardiovascular responses to hypoxia and airbreathers may respond to changes in haemolymph pH. Exercise induces a rapid increase in ventilation, diffusive conductance improves and O2 consumption is elevated. There is also a major anaerobic contribution causing a metabolic acidosis and recovery includes prolonged repayment of an O2 debt.