A counter-current heat exchange system in the tail of the vervet monkey, Cercopithecus pygerythrus (Primata : Cercopithecidae)
Lightly anaesthetized vervet monkeys can maintain their body core-temperature by skin vasoconstriction and shivering when the environmental temperature is moderately lowered.
Under such conditions the arterial blood supplying the tail skin is several degrees cooler than the core temperature and thus heat loss from the tail is reduced.
The core-caudal artery temperature difference is most probably due to counter-current heat exchange between the median sacral and caudal artery and the median caudal veins above the sixth postsacral tail segment.
The medial caudal veins are small compared with the dorsolateral caudal veins which run a superficial course, but the arrangement of valves permits movement of blood between them. The balance of blood flow in the two systems will determine the extent of heat exchange with the arterial inflow. The properties of the dorsolateral veins and the structural arrangements increase the proportion of blood returning by the median system under cool conditions.
The functional integrity of the sympathetic nervous system is necessary for effective control of the heat exchange system.