Convection plays a major role in the thermoregulation of the body. It characterizes heat transport in the body and heat dissipation to the outside world. Disturbances in heat exchange can be caused by disease and severely affect the body’s heat balance.
What is convection?
In convection, heat energy is transported from the heat source to all parts of the body by the flowing blood in the blood vessels. In the thermoregulation of organisms, convection represents a particular form of transport of heat during heat exchange. In this case, heat exchange takes place via a material medium. Thus, heat can be transported through a liquid such as water, transferring to a gaseous medium, the air. In the case of body temperature regulation, the liquid medium is the blood in the bloodstream and the gaseous medium is the outside air. In the context of thermoregulation, the body strives to maintain its physiological body temperature at all times, if possible. In humans, this is about 37 degrees. Heat is formed primarily by metabolic processes and secondarily by friction during muscle work. In this process, the mechanical energy of muscular work is originally also derived from metabolic activities. In convection, heat energy is transported from the heat source to all parts of the body by the flowing blood in the blood vessels. Thus, there is a constant heat transport to balance the body temperature, which, however, must be regulated by hormonal processes. In addition, heat exchange takes place between the body and the outside world, whereby the body releases heat to the environment. This heat transport is restricted via thermoregulation in the case of strong heat loss due to low external temperatures or promoted in the case of excessive heat production in the body.
Function and task
Heat exchange by convection is intended to help maintain a constant body temperature. In addition to convection, there is also heat exchange via evaporation (evaporation) or radiation (radiation). The body controls the heat exchange via regulatory mechanisms so that the body temperature is both not exceeded and not fallen below. All physiological processes are temperature-dependent and only run optimally at body temperature. If the body temperature is too low, metabolic processes are slowed down. Temperatures that are too high have a major impact on the structure of biomolecules. For example, at temperatures above 40 degrees, the denaturation of endogenous proteins begins. The secondary, tertiary and quaternary structures of the proteins are destroyed, losing their biological effectiveness. The functionality of enzymes in particular is impaired. Furthermore, the fluidity, diffusion behavior and osmosis behavior of the cell membranes change. At higher temperatures, the binding affinity of hemoglobin to oxygen also decreases, so that the oxygen supply would no longer be sufficiently guaranteed. To ensure a constant body temperature, the coordinated sequence of several processes is necessary. Among other things, this involves constant heat production, heat insulation and the body’s ability to release more heat in the event of heat overproduction. When overheating of the body occurs, the hypothalamus initiates the lowering of sympathetic tone. Peripheral vasodilation and increased sweating occur. Sweating causes an increase in heat loss by evaporation and vasodilation increases heat loss by convection. Vasodilation is the dilation of blood vessels to increase their surface area. This makes heat dissipation more effective. Convection is also necessary for the uniform heating of the body. Thus, the core of the body consisting of the abdomen and skull is warmed more than the acras and extremities by metabolism. Via the blood circulation, the differences are compensated by forced convection.
Diseases and ailments
Convection in thermoregulation is largely dependent on the functioning of blood vessels. In the case of circulatory disorders, the uniform heating of all parts of the body also no longer functions optimally. In particular, parts of the body that cool down quickly and at the same time are not heated as much remain cooler than neighboring regions. For example, cold hands or feet often occur with arteriosclerosis.Even passive heating from outside does not bring them up to body temperature so quickly. There is always a rapid cooling down. Physical activity can improve blood circulation. In severe cases, however, there is a risk of insufficient oxygen supply and, in extreme cases, necrosis of the corresponding limbs. Diabetes patients in particular often suffer from circulatory disorders that can end with the loss of certain limbs. Reduced blood flow (ischemia) also affects the extent of vasodilation. Within blood vessels, shear forces are altered by ischemia. Shear forces mediate dilation of blood vessels. However, decreased blood flow lowers shear forces, so there is also less vasodilation. Elderly people in particular often suffer from disturbed heat balance. The regulatory mechanisms no longer function optimally. On the one hand, general heat production is reduced and, on the other hand, heat transport by convection processes is restricted, since there is often a reduction in blood flow. As a result, the body cools down more, especially in areas with poor circulation. However, the regulatory mechanism can also break down if the body overheats. Overheating can be caused, among other things, by increased heat production during heavy physical exertion during muggy weather conditions. When the core temperature rises above 41 degrees, sweat production will cease at the same time. As a result, the body will attempt to dissipate heat by increasing shell blood flow to the limbs and acras, thereby lowering the core temperature. As a result, circulatory collapse may occur. This condition is called heat stroke. The body’s thermoregulation may also be overridden by a severe fever.
