Changes

===Panting===

===Panting===

Dogs, cats, ruminants and birds pant, whereas horses, pigs and most small animals cannot.  Panting requires fast, shallow breathing at the natural resonant frequency of the airways.  Little mechanical energy is required to facilitate panting, therefore, heat production in the respiratory muscles is minimised.  The main mechanism of heat loss during panting is by water evaporation from the moist '''mucous membrane''' of the nasal cavity.  The heat of evaporation is removed from the tissues of the nasal cavity, cooling its blood supply.  The cooled blood is collected in large venous sinuses and then passes through the [[Nervous System - CNS - Anatomy & Physiology|rete mirable]] which functions as a heat exchanger, cooling arterial blood to the brain.

Dogs, cats, ruminants and birds pant, whereas horses, pigs and most small animals cannot.  Panting requires fast, shallow breathing at the natural resonant frequency of the airways.  Little mechanical energy is required to facilitate panting, therefore, heat production in the respiratory muscles is minimised.  The main mechanism of heat loss during panting is by water evaporation from the moist '''mucous membrane''' of the [[Skull and Facial Muscles - Anatomy & Physiology#Ethmoid bone (os ethmoidale)|nasal cavity]].  The heat of evaporation is removed from the tissues of the nasal cavity, cooling its blood supply.  The cooled blood is collected in large venous sinuses and then passes through the [[Nervous System - CNS - Anatomy & Physiology|rete mirable]] which functions as a heat exchanger, cooling arterial blood to the brain.

Under moderate heat stress, ruminants pant with a closed mouth.  Under significant heat stress, however, all animals pant with open mouths.  This means that air with a high water content cannot condense on the mucosa of the nasal cavity, thus maximising the heat lost through evaporation.  There is also some evaporation from the oral membranes.

Under moderate heat stress, ruminants pant with a closed mouth.  Under significant heat stress, however, all animals pant with open mouths.  This means that air with a high water content cannot condense on the mucosa of the nasal cavity, thus maximising the heat lost through evaporation.  There is also some evaporation from the oral membranes.