The evolution of vascularised circulatory systems facilitated the efficient and directed perfusion of tissues, and unlike open circulatory systems that lack extensive arterialisation, fluid flow within closed or heavily vascularised systems is defined by more complex laws of fluid dynamics. Control systems must be in place that allow cardiovascular responses to constantly changing demands resulting from changes in environmental factors, such as posture or heat.
Many vertebrates control blood flow between their core and periphery to alter heat transfer with the environment. In reptiles heart rates are faster during heating and slower during cooling to facilitate thermoregulation, and this process is regulated by different neural and humoral mechanisms, including prostaglandins in the case of bearded dragons (Pogona vitticeps; see Figure below). In a control treatment, heart rate was significantly faster during heating than during cooling (control)), but this difference disappeared when prostaglandins were inhibited (inhibitor).
Seebacher, F., Franklin, C. E. 2007. Redistribution of blood within the body is important for thermoregulation in an ectothermic vertebrate (Crocodylus porosus). Journal of Comparative Physiology B 177, 841-848.
Seebacher, F., and Franklin, C. E. 2005. Physiological mechanisms of thermoregulation in reptiles: A review. Journal of Comparative Physiology B 175, 533-541.
Seebacher, F., and Franklin, C. E. 2004. Integration of autonomic and local mechanisms in regulating cardiovascular responses to heating and cooling in a reptile (Crocodylus porosus). Journal of Comparative Physiology B 174, 205-210.
Seebacher, F. and Franklin, C. E. 2003.
Prostaglandins are important in thermoregulation of a lizard (Pogona
vitticeps). Proceedings of the Royal Society
Seebacher, F. and Grigg, G. C. 2001. Changes in heart rate are important for thermoregulation in the varanid lizard, Varanus varius. Journal of Comparative Physiology B 171, 395-400.
Seebacher, F. 2000. Heat transfer in a microvascular network: the effect of heart rate on heating and cooling in reptiles (Pogona barbata and Varanus varius). Journal of theoretical Biology 203, 97-109.