The Dog's Tongue and Thermoregulation
Used with permission from  Allsorts' Dog Pictures		Photographed by Robin & Harold Winter Used with permission from  Narnia Kennels

Arteriovenous Anastomoses (AVAs):  AVAs are found in many locations in many animals including in extremeties of human skin, the ears of rabbits, the mesentary and urine bladders of cats, and in the tongues of sheep, goats, and dogs.  In dogs AVAs are found most frequently on the tip and least frequently on the base of the tongue.  They can be a variety of different shapes including S-shaped, hook-shaped, bibranching, and Y-shaped and are 100-150 micrometers in length (Kishi 1988).

Blood Flow in the Tongue: Blood in the dog's tongue is carried by branchings of the profound lingual artery.  These branchings penetrate the tongue muscle before reaching the mucosal lamina propria of the dorsum of the tongue.  Under most circumstances AVAs in the tongue are open to allow arterial blood to pass directly through them to venules in the mucosal lamina propria and little arterial blood enters the superficial network of capillaries in the tongue where heat exchange with the environment occurs.

Control of Lingual Blood Flow

• AVAs: If body temperature increases, AVAs in the tongue shut down, causing blood to pass into the superficial capillary network where heat can be dissipated (Kishi 1988).
• Tongue Surface Temperature: Panting is a thermoregulatory response to heating that decreases tongue surface temperature by increasing the tongue's contact with cooler air in the environment due to the dog's open mouth and protrusion of the tongue.  Decreased tongue surface temperature causes increased total lingual blood flow which increases heat dissipation (Krönert et al. 1980).
• Hypothalamic Heating: Heating of the hypothalamus causes dilation of lingual arteries, decreased heart rate, and decreased resistance to blood flow in lingual arteries (Thomson and Pleschka 1980).

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