Functional anatomy of the footpad vasculature of dogs: scanning electron microscopy of vascular corrosion casts

Abstract

Dogs are well adapted to cold climates and they can stand, walk and run on snow and ice for long periods of time. In contrast to the body trunk, which has, dense fur, the paws are more exposed to the cold due to the lack of fur insulation. The extremities have a high surface area-to-volume ratio, so they lose heat very easily. We offer anatomical evidence for a heat-conserving structure associated with dog footpad vasculature. Methylmethacrylate vascular corrosion casts for scanning electron microscopy, Indian ink-injected whole-mount and histological specimens were each prepared, in a series of 16 limbs from four adult dogs. Vascular casts and Indian ink studies showed that abundant venules were arranged around the arteries supplying the pad surface and formed a vein-artery-vein triad, with the peri-arterial venous network intimately related to the arteries. In addition, numerous arteriovenous anastomoses and well-developed venous plexuses were found throughout the dermal vasculature. The triad forms a counter-current heat exchanger. When the footpad is exposed to a cold environment, the counter-current heat exchanger serves to prevent heat loss by recirculating heat back to the body core. Furthermore, the arteriovenous anastomoses shift blood flow, draining blood to the skin surface, and the venous plexuses retain warm blood in the pad surface. Hence, the appropriate temperature for the footpad can be maintained in cold environments.

The extracranial venous system in the heads of beaked whales, with implications on diving physiology and pathogenesis

“…In addition, most of the peripheral arteries in the head of beaked whales are accompanied on either side by paired, anastomosing veins, forming counter‐current triads. Similar peripheral triads have been noted in numerous mammalian species, including manatees and dogs (Murie, ; Fawcett, ; Ninomiya et al, ). All of the aforementioned vascular structures are strikingly similar to heat‐exchange structures described in the extremities (e.g., fins and flukes) of cetaceans (Scholander and Schevill, ; Elsner et al, ).…”

How does paw pad of canine attenuate ground impacts? A multi-layer cushion system

“…In this study, we found that the dermis layer is composed of two parts: dermal papillae, and another part that is rich in collagen fibres. The dermal papillae and the stratified epithelium layer, which have distinctive honeycomb-like structures at the micro-scale level, make up the epidermis layer; this structure is also found in the paw pad of the Beagle dog ( Ninomiya et al, 2011 ) and in the paw pad of the Clouded leopard ( Hubbard et al, 2009 ). Therefore, it appears that this special micro-structured layer is common in the paw pads of digitigrades, and to the best of our knowledge, has not been studied previously.…”

How does paw pad of Canine attenuate ground impacts: a micromechanical finite element study

“…Moreover, the material property sensitivity analysis suggests that the increasing cushioning capacity of the epidermis layer plateaus after the Young's modulus of the dermal papillae is lower than 0.04-0.004MPa. Indeed, this honeycomb micro-structures consisting of stratified epithelium and dermal papillae was also found in the paw pads of other digitigrade mammals, such as cats and leopards (Hubbard et al, 2009;Ninomiya et al, 2011), suggesting that this characteristic structure may be desirable for their quieter and faster locomotion patterns.…”

“…Dogs are well adapted to cold climates. A recent study suggested the structured epidermis layer may provide a heat conserving mechanism as well (Ninomiya et al, 2011). It is worth a further investigation to understand how this honeycomb micro-structured layer achieves multiple physical functionalities in impact attenuation, stress off-loading and heat conservation simultaneously.…”