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How giraffes prevent oedema

An upright giraffe, by analogy with humans, ought to suffer massive oedema in its feet; moreover, when it lowers its head to drink, the blood should rush down into it and be unable to flow up again. New pressure measurements reported on page 59 of this issue by Hargens et al. Show why neither of these things happens, and also contain some surprising observations of highly variable venous pressure (P.) in the leg and of a counter-gravitational gradient of P.

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Blood pressure and flow rate in the giraffe jugular vein

Experimental measurements in the jugular veins of upright giraffes have shown that the internal pressure is somewhat above atmospheric and increases with height above the heart. A simple model of steady viscous flow in an inverted U-tube shows that these observations are inconsistent with a model in which the blood vessels in the head and neck are effectively rigid and the system resembles a siphon. Instead, the observations indicate that the veins are collapsed and have a high resistance to

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Vascular system of giraffe

Both the discussions of the vascular system of the giraffe‚Ķmention venous valves, but both overlook the special ‘seried’ valves found at the entry of major tributaries into the axillary and brachial veins, though not into the jugular. Fewer occur in the closely-related okapi and some in jugular and femoral veins of the bactrian camel.

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The structure and function of giraffe jugular vein valves

When a giraffe (Giraffa camelopardalis) lowers its head to drink, blood could enter the jugular vein from the inferior vena cava or regurgitate from the jugular veins into the cranial veins. We investigated the anatomy of jugular valves in giraffes to establish if they could prevent either of these regurgitations. Jugular vein length and intervalve distances of 396 valves (192 left, 204 right) were measured in 60 veins from 25 adult (11 males and 14 females) and five foetal giraffes.

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Haemodynamics of the jugular vein in the giraffe

Controversy cotinues over the haemodynamics of the circulation to and from the head of the giraffe. The recent study by Hargens et al. provides new information explaining the absence of oedema in the legs of the ambulant giraffe. But in sedated, standing giraffes the pressure gradient down the jugular vein is about one-tenth of, and in the opposite direction to, that expected for a standing column of blood. Hargens et al. suggest that compartmentalization of the blood in the vein

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