Thermoregulation in Skin - Anatomy & Physiology
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Introduction
When the body's heat production is stable, the blood flowing into the dermis is regulated depending on changes in ambient temperature. The purpose of this regulation is to ensure that the difference in temperature between the skin's surface and the environment remains constant, thus regulating heat loss and maintaining an almost constant body temperature. When heat production increases, blood flow to the dermis also increases, which, in turn, increases the heat lost from the skin to the same rate as the excess heat production.
Physiology
Heat transported from the body core to the skin's surface, will pass through subcutaneous adipose tissue, dermis, and finally to the epidermis, after which, the heat passes through air trapped in fur or plumage. Adipose tissue is a poor conductor of heat, therefore, even a thin layer will confer some insulation against heat loss.
The extent of heat lost from the skin is dependent on the amount of blood flow to the dermis. As blood flow decreases due to vasoconstriction of the subcutaneous vessels, the insulating effect of the skin increases. The more vasoconstriction that occurs, the closer to environmental temperature the skin's surface will become. If blood flow to the dermis increases, however, heat loss through the skin increases as the temperature difference between the skin and the environment also increases. The insulation provided by the adipose tissue can therefore be somewhat bypassed if the blood flow to the dermis is great enough.
Blood flow to the dermis can vary by a factor of 3 to 5, depending on the requirement for heat loss or conservation. This blood flow is regulated by the sympathetic nervous system. An increase in core body temperature causes a decrease in the tone of the smooth muscle walls of the arterioles due to a reduced impulse frequency in the sympathetic nerve fibres. This casues vasodilation, which in turn, increases cutaneous blood flow and therefore heat loss. The opposite is true for a decrease in core body temperature.