Heat balance and temperature regulation in complex biological systems

Abstract

The present work gives an insight into the internal heat management system of the terrestrial snail Xeropicta derbentina, which has to cope with extreme climate conditions in its habitat. The oxygen consumption of inactive animals was investigated in order to clarify if the entire metabolism is adapted to high ambient temperatures. It was found that particularly medium-sized individuals show a significant reduction in oxygen consumption when exposed to high temperatures. Additionally, the extrapolation of measured data revealed theoretical upper and lower temperature limits. These were associated with arousal of the animal and the temperature of maximum heat shock protein (Hsp70) production that serves as a molecular protection system. The metabolic scaling exponent was found to decrease for increasing temperatures. Calorimetric investigations of two size groups have shown that small individuals react more sensitive to increasing temperatures. Active and inactive metabolic energy was separated and the active share was found to decrease for both size groups as temperature increases. The comparison of mass ratio and ratio of change of time spent in activity when temperature increases from 20°C to 30°C showed an inverse proportionality indicating that mass and exposition to ambient temperature influence the behavior of the animal. NMR measurements were performed that provided data of the vein system, the lung volume and the heart volume of X. derbentina. Combining these geometrical data and the measured oxygen consumption and calorimetric data facilitated the calculation of additional physiological parameters. A surrogate model of the vein system was constructed and the active diffusive surface of capillaries and main vein was calculated and confirmed by geometrical measurements. Finally, a model was presented that is able to validate the measured oxygen consumption by the use of the Colburn analogy between mass and momentum transfer. By combining basic diffusion laws with the momentum transfer, i.e. wall shear stress, at the inner wall of capillaries and main vein the progression of oxygen mass fraction inside the hemolymph can be visualized.