Cutaneous circulation in animals
The skin is supplied by a dense network of cutaneous arterioles under the dermis layer. These arterioles inturn divide into metarterioles which inturn give rise to capillary loops. These capillary loops provide a greater surface area for heat exchange mechanism.
The venules form an extensive sub papillary venous plexus. Arteriovenous anastomoses communicate between the smaller arteries, arterioles and venous channels and are located in the distal parts of the extremities, nose, lips, ears etc. These vessels are wide and have low resistance connections that serve as shunts and allow blood to bypass superficial capillary tube.
The cutaneous vessels are innervated by sympathetic adrenergic vasoconstrictor fibres. Alpha and beta adrenergic receptors are found in the cutaneous arterioles and only alpha receptors in the arteriovenous anastomoses. The venous plexus have separate neural connections and undergo a marked vasoconstriction which minimizes the amount of blood to the skin.
The major function of the cutaneous vessels is the regulation of body temperature. It aids in the heat conservation and heat dissipation mechanisms. Heat conservation is brought about by vasoconstriction thereby reducing the blood flow to the skin.
Heat dissipation occurs during increased environmental temperature wherein increased blood flow to the skin occurs in order to increase the heat loss from the body.
It is brought about by vasodilatation in which increased blood temperature stimulates the hypothalamus which inturn inhibits vasoconstriction thereby increasing the blood flow and causes evaporative heat loss. Heat exchange mechanisms also occur via radiation, conduction and convection.