The structure and function of giraffe jugular vein valves

Abstract

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. The average number of valves in the left jugular veins was 6.4 ± 2.7 (mean ± S.D.; range = 2-13) and in the right was 6.8 ± 2.1 (range = 3-12). Male giraffes had 7.3 ± 2.7, females 5.9 ± 2.1, and foetuses 7.0 ± 2.1 valves per vein. None of these differences was statistically significant (t-test; P > 0.05). Most valves (88%) were bicuspid in structure. Their position in the veins was irregular. Most (36.1%) were located in the first 500mm of vein. The relative distribution of foetal valves was not significantly different from that in adult giraffes (X2 = 0.274, P > 0.05). We concluded that the main function of the jugular vein valves is to prevent regurgitation of blood from the inferior vena cava and right atrium into the jugular vein and that the number of valves is fixed in utero.