The hunting reaction or hunting response is a process of alternating
vasoconstriction
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vesse ...
and
vasodilation
Vasodilation, also known as vasorelaxation, is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles. Blood vessel wa ...
in
extremities exposed to cold. The term Lewis reaction is used too, named after
Thomas Lewis, who first described the effect in 1930.
Vasoconstriction occurs first to reduce heat loss, but also results in strong cooling of the extremities. Approximately five to ten minutes after the start of cold exposure, the blood vessels in the extremities will suddenly vasodilate. This is probably caused by a sudden decrease in the release of
neurotransmitter
A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a Chemical synapse, synapse. The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell.
Neurotra ...
s from the
sympathetic nerves
The sympathetic nervous system (SNS or SANS, sympathetic autonomic nervous system, to differentiate it from the somatic nervous system) is one of the three divisions of the autonomic nervous system, the others being the parasympathetic nervous sy ...
to the muscular coat of the
arteriovenous anastomoses due to local cold. This cold-induced vasodilation increases blood flow and subsequently the temperature of the fingers. A new phase of vasoconstriction follows the vasodilation, after which the process repeats itself.
The hunting reaction is one out of four possible responses to immersion of the finger in cold water. The other responses observed in the fingers after immersion in cold water are a continuous state of vasoconstriction, slow steady and continuous rewarming and a proportional control form in which the blood vessel diameter remains constant after an initial phase of vasoconstriction. However, the vast majority of the vascular responses to immersion of the finger in cold water can be classified as the hunting reaction.
There are many factors which influence the strength of the response. People who live or regularly work in cold environments show an increased response. Through
acclimatization
Acclimatization or acclimatisation ( also called acclimation or acclimatation) is the process in which an individual organism adjusts to a change in its environment (such as a change in altitude, temperature, humidity, photoperiod, or pH), ...
tropical residents can develop an increased response which is indistinguishable from arctic residents. The role of genetic factors is not clear because it is difficult to differentiate between
adaptation
In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the p ...
and acclimatization.
It was thought that the hunting reaction protected the fingers against
cold injury and improved muscle function in the fingers. An experiment has shown cold acclimation minimizes the hunting reaction (reduced mean temperature of the digits and a prolonged time of cold exposure prior to initial vasodilation), thus putting the hand at a greater risk of cold injury when it is exposed to cold.
See also
*
Hypothermia
Hypothermia is defined as a body core temperature below in humans. Symptoms depend on the temperature. In mild hypothermia, there is shivering and mental confusion. In moderate hypothermia, shivering stops and confusion increases. In severe ...
*
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...
*
Axon reflex
The axon reflex (or the flare response) is the response stimulated by peripheral nerves of the body that travels away from the nerve cell body and branches to stimulate target organs. Reflexes are single reactions that respond to a stimulus making ...
*
Raynaud's syndrome
Raynaud syndrome, also known as Raynaud's phenomenon, is a medical condition in which the spasm of small arteries causes episodes of reduced blood flow to end arterioles. Typically the fingers, and, less commonly, the toes, are involved. Rare ...
References
{{Reflist, refs=
[{{cite journal, last=Daanen, first=H.A.M., year=2003, title=Finger cold-induced vasodilation: a review, journal=European Journal of Applied Physiology, volume=89, issue=5, pages=411–426, doi=10.1007/s00421-003-0818-2, pmid=12712346, s2cid=22077172 ]
[{{cite journal, last1=Geurts, first1=C. L. M., last2=Sievert, first2=G. G., last3=Cheung, first3=S. S., year=2005, title=Local cold acclimation of the hand impairs thermal responses of the finger without improving hand neuromuscular function, journal=Acta Physiologica Scandinavica, volume=183, issue=1, pages=117–124, doi=10.1111/j.1365-201X.2004.01374.x, pmid=15654925 ]
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