Changes

In mammals with a haircoat and birds with a full plumage, a layer of air is trapped between the surface of the skin and the outer surface of the haircoat or plumage.  Air has a low heat capacity and is a poor conductor of heat, therefore it serves as an insulator.  The degree of insulation conferred by fur and feather can be altered by increasing or decreasing the thickness of the air layer.  This is acheived by the [[Hair - Anatomy & Physiology|arrector pili]] muscle in the dermis.

In mammals with a haircoat and birds with a full plumage, a layer of air is trapped between the surface of the skin and the outer surface of the haircoat or plumage.  Air has a low heat capacity and is a poor conductor of heat, therefore it serves as an insulator.  The degree of insulation conferred by fur and feather can be altered by increasing or decreasing the thickness of the air layer.  This is acheived by the [[Hair - Anatomy & Physiology|arrector pili]] muscle in the dermis.

If this insulating layer of air is replaced by water, heat is readily lost from the skin's surface, leading to a decrease in core bosy temperature and ultimately '''hypothermia'''.  The layer is protected by secretions from the skin onto the fur or feathers.  In birds, secretions from the [[The Integument of Exotic Species#Avian Skin|uropygial gland]] maintain the water repellant properties of the plumage.  In mammals that are regularly exposed to water, a thick layer of subcutaneous adipose tissue of '''blubber''' is present as the insulating air is completely lost and replaced by water.

If this insulating layer of air is replaced by water, heat is readily lost from the skin's surface, leading to a decrease in core body temperature and ultimately '''hypothermia'''.  The layer is protected by secretions from the skin onto the fur or feathers.  In birds, secretions from the [[The Integument of Exotic Species#Avian Skin|uropygial gland]] maintain the water repellant properties of the plumage.  In mammals that are regularly exposed to water, a thick layer of subcutaneous adipose tissue of '''blubber''' is present as the insulating air is completely lost and replaced by water.