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At last, the water hole! Copyright 1996 Corel Corporation. |
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It is common knowledge that dromedary camels can survive for many days
in the hot desert without access to water. However, the role of the camel's
hump in water preservation is not well understood by most people. Most of us, when looking at camels in the zoo, still imagine the humps to be filled with water. But
what is the truth behind the myth - what secrets are hidden beneath the
camel's skin?
First, it can be ascertained that the camel's hump is not in fact filled
with water, simply by cutting into it. Such action would reveal that the
hump is in fact composed mostly of fat. Yet, this could still suggest that
the hump acts as a water store. If a gram of fat is broken down during
metabolism, it produces more than a gram of water. However, camels cannot
use this fat for water production. Due to the arid conditions prevailing
in their habitat, they would lose too much water from their airways in obtaining
enough oxygen for fat degradation.
So, what is the role of the camel's hump? Unfortunately
the answer is relatively dull - it appears that the humps are merely food
reserves, and the fat contained within is degraded and used for nutrition
when food is scarce.
Then how exactly do camels get water? When dehydrated
camels are offered water, they drink and they drink a lot. But they just drink enough to restore the normal water content of their bodies. In other words, they do not store water for future needs.
How do camels cope without water? Camels endure long periods without water for two reasons.
First, they have an exceptional ability to minimize their water losses. They produce an exceptionally sparse and concentrated urine, as well as very dry droppings. They minimize water losses in their exhalant air by using their noses as effective water exchangers. Their prominent noses contain very large spiral protrusions, turbinates, with large surface areas. The turbinates are cooled by the inhalant air. The exhalant air is, in turn, cooled by the turbinates and becomes oversaturated with water vapour. As a result, water is saved as it condenses on the turbinates, in the same way as water droplets appear on a cold windowpane. The camels also tolerate a rise in their body temperature to well above 40 °C during the day, avoiding the need to cool themselves by evaporating body water, using sweating or panting. The excess heat is lost during the cooler desert night.
Secondly, camels have an extraordinary ability to tolerate water loss, dehydration. They may lose 30-40 per cent of their body weight as water, while still walking in the desert sun.
Although the myth that the camels' humps are filled with water has been
dispelled, this does not change the fact that, physiologically, camels are
incredible animals.
You may also read the related articles by Jenny Fredriksson (in Swedish) and Maria C Hansson) (in Swedish). Read about the regulation of body temperature in mammals on another page (in Swedish).
Note: You might ask why the fat depots of the dromedary camel are situated on the back of the animal, not all around the body as in seals and whales. An additional function of the hump is possibly to insulate the camel from solar radiation. The desert sun certainly shines mainly from above. Fat-containing adipose tissue is suitable for insulating purposes, because fat conducts heat slower than water. Also blood flow can be very low in adipose tissue, because the fatty deposits do not need oxygen. This might further contribute to the possible insulating function of the hump. The dromedary camel is also equipped with a very thick fur on its back while the fur is thinner elsewhere. The thick dorsal fur provides insulation from the heat of the sun, while the thin fur allows for heat loss from other parts of the body.
References
The text has been updated and enlarged in 2013 by Dr Anders Lundquist (senior lecturer at the Department of Biology, Lund University, Sweden).
R.W. Hill, G.A. Wyse, and M. Anderson: Animal Physiology (3rd ed, Sinauer, 2012).
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