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1 July 2012 A Special Construction of Subepidermal Capillary Loops in the Hippopotamus (Hippopotamus amphibius)
Wilfried Meyer
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Based on LM, TEM, and histochemical methods, the study describes the specific structure of subepidemal capillary loops in the integument of the hippopotamus (Hippopotamus amphibius). At 25– 60 µm, the diameter of the capillaries was more than twenty times larger than those found in other mammals, as was the diameter of the epidermal contact area of the hairpin turn, which had enlarged up to 200–400 µm2. At about 13,400, the number of loops per cm2 was three times higher than in the few other mammalian species measured to date. The remarkable sheath (thickness 2– 20 µm) of the capillary loops consists of a multitude of fine collagen IV fibres, which were in direct contact with the epidermal stratum (str.) basale, emphasizing an origin from the lamina fibroreticularis of the basement membrane. Additionally, the sheath contained many regions filled with free fatty acids. All observations confirmed the view that the walls of the subepidermal capillaries in the hippopotamus are adapted to withstand high blood pressure, permitting a high rate of blood vesselbased heat transfer from the periphery of the body. Until now this function is only known as an important thermoregulatory response in highly active mammals, e.g. dolphins. However, under hot climatic conditions but without strong exercise for cooling, such ability could be an effective and energy-saving procedure in semi-aquatic mammals.

© 2012 Zoological Society of Japan
Wilfried Meyer "A Special Construction of Subepidermal Capillary Loops in the Hippopotamus (Hippopotamus amphibius)," Zoological Science 29(7), 458-462, (1 July 2012).
Received: 16 January 2012; Accepted: 1 February 2012; Published: 1 July 2012
aquatic mammals
subepidermal capillary loop
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