Changes

Heat transported from the body core to the skin's surface, will pass through '''subcutaneous adipose tissue''', dermis, and finally to the [[Skin - Anatomy & Physiology#Epidermis|epidermis]], after which, the heat passes through air trapped in [[Hair - Anatomy & Physiology|fur]] or [[Feather - Anatomy & Physiology|plumage]].  Adipose tissue is a poor conductor of heat, therefore, even a thin layer will confer some insulation against heat loss.

Heat transported from the body core to the skin's surface, will pass through '''subcutaneous adipose tissue''', dermis, and finally to the [[Skin - Anatomy & Physiology#Epidermis|epidermis]], after which, the heat passes through air trapped in [[Hair - Anatomy & Physiology|fur]] or [[Feather - Anatomy & Physiology|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.  In theory, the more vasoconstriction that occurs, the closer to environmental temperature the skin's surface will become, although this depends greatly on the environmental temperature.  If the enviromental temperature is very low, a difference between that and the skin temperature will always exist and therefore some heat loss will invariably occur.  Similarly, if the environmental temperature is very high, there will never be a great enough difference for heat loss to occur, and therefore other ways of losing heat from the body, such as sweating and panting, must be employed.  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.

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.  In theory, the more vasoconstriction that occurs, the closer to environmental temperature the skin's surface will become, although this depends greatly on the environmental temperature.  If the enviromental temperature is very low, a difference between environmental and skin temperature will always exist and therefore some heat loss will invariably occur.  Similarly, if the environmental temperature is very high, there will never be a great enough difference for heat loss to occur, and therefore other ways of losing heat from the body, such as sweating and panting, must be employed.  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 [[Nervous System - PNS - Anatomy & Physiology|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.

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 [[Nervous System - PNS - Anatomy & Physiology|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.