Camels are known for their remarkable ability to go in long periods without
water, even during their long wanderings through the hot and dry deserts where
they have been known to loose up to 40% of its body weight in body water,
a loss that would be fatal in other animals. This is possible due to several
physiological adaptions, involving the animal’s metabolism, erythrocytes and
body temperature among other things.
The ancient Greek natural philosopher and author Gaius
Plinius 
Secundus(23-79), more commonly known as Pliny the Elder,
was the first to suggest that camels have an internal water-reservoir. This
theory was further developed by George Shaw in 1801, a British zoologist who
claimed that camels have, in addition to their stomach compartments, a bag
that serves for water storage. This assumption is only one of the myths that
have evolved over the years regarding the question of water storage in camels.
The fact that there actually are some pockets in the rumen of camels
doesn’t really make much difference since these hold less water than
the same pockets in other ruminants.
It has also been commonly believed that the camel store water in its
hump, but the hump is actually a reservoir of fat tissue that the animal uses
for energy source in periods when food is scarce. The camel’s diet consists
mainly of bushes, grass and leaves and if their food is rich in moisture, their
demand for water is low. Camels have actually been observed in
So how and where do the camels store this precious
water? How do their bodies cope with the large amounts of water ingested after
long periods without any? And how is it possible to loose as much as 40% body
weight in water without severe consequences? These are the questions I will try
to answer.
Camels posses a unique metabolism that enables them to
store water in the blood. The camel haemoglobin has a higher proportion of
hydrophilic amino acids compared to other mammals, and this gives the camel
haemoglobin its highly hydrophilic character. Also, the proportion of water in
the camel erythrocytes that is osmotically non-removable is almost three times
greater than in humans, which seems to lead to the extremely good resistance of
camel erythrocytes to osmotic change.
A thirsty camel can
drink as much as 27 gallons in 10 minutes. Consuming such an amount of water
after a longer period of dehydration would result in severe osmotic problems in
other animals, but in camels it doesn’t. This is because the absorption of
water from the stomach and intestines happens very slowly, allowing time for
equilibration. In addition, the erythrocytes of the camel are more stable in
order to withstand high variations in the osmotic pressure when drinking large
quantities of fluid, being able to swell to 240% of their normal size without
undergo haemolysis.
During dehydration, the food intake decreases markedly and the energy
requirements for the maintenance of camels is lower than other ruminants. When
water is available for the camels again after dehydration, they are able to
recover rapidly. This is mainly because of saliva inflow to the fore stomach
which enables a sufficient microbial digestion even when water and food intake
is low. This was the results of the experiment made by W. von Engelhardt, P.
Haarmayer and M. Lechner-Doll on water deprivation and rehydration in camels in
2005.
In 1957, the Norwegian biologist Knut Schmidt.Nielsen
explained the camel’s ability to resist great heat with low water requirements.
In mammals, as the blood is deprived of water, its consistency becomes thicker
and it’s getting harder for the heart to pump the blood to the skin where the
blood may be cooled. This is not the case in camels where the viscosity of the
blood and the blood volume remains almost constant due to fluid that migrates
from the tissues to the bloodstream so that the circulation will not be
impaired. Furthermore, the erythrocytes of camels are small and oval which
facilitates their flow in cases where there is a slight increase in the blood
viscosity. The blood viscosity and blood volume of camels has been classified
by biologists as a simple osmotic phenomenon, but why the systems of other
mammals don’t work the same way is a question that, for the time being, does
not yet have an answer.
A very important factor in the retention of water in the body of camels
is their body temperature. Camels don’t pant and their perspiration is very
low. In addition, they have a body thermostat that is unique. Camels can raise
their body temperature tolerance level up to 6°C before perspiring. Their
normal temperature at night is 34°C and at day it can reach 41°C, and it’s only
above this threshold value that they start to sweat. This way the camels are
conserving their body fluids and avoid unnecessary loss of water so that they
can preserve as much as 5 litres of water a day.
The fur of the camel is said to be one of nature’s better insulators as
it protects the camel from the direct sunshine. Professor Schmidt-Nielsen shaved
a camel to demonstrate the effectiveness of the camel hair. The shaved camel
produced 60% more sweat than the unshaved ones.
The fat layer of animals also has an insulating effect, but in camels,
also this feature is superior to the other mammals. The fat is concentrated
immediately below the hump and at this location it receives the full force of
the rays of the sun and keeps the heat out. In comparison, other animals have a
more even distribution of the fat layer over the surface of their body that
merely slows down the heat loss from the body.
Another important factor regarding water retention is the kidneys. They
are capable of concentrating the urine of the camel to a large degree to reduce
water loss. The urine can become very thick and it can have twice the salt
content of sea water. The high salt content is due to brackish well water which
is often contaminated by salts in the deserts. The camels thrive on this water
which is dangerous to humans.
In the experiment of W. von Engelhardt, P.
Haarmayer and M. Lechner-Doll mentioned earlier, they also found that the
dilution rate, the mean retention time of fluid and the fluid volume of the
fore stomach in camels that had been dehydrated for 11 days showed considerable
changes. The fluid volume decreased with 52, 2% during the days of water
deprivation. When water was available again, the fluid volume increased to 129,
7% of the volume before dehydration occurred before it rapidly decreased within
2 days to its starting value. The dilution rate decreased with 31%
during dehydration. During the first day of rehydration the dilution rate
increased to 74% of the starting value before it interestingly decreased to a
level almost as low as at the end of the dehydration period. Then, at the
second day of rehydration it returned to the original value. Mean retention
time of fluid in the fore stomach increased to 189, 3% in the time of
dehydration, and this value also returned to normal 2 days after water was
available for the camels again. All of these, the fluid volume, the dilution
rate and the mean retention time, are also involved in preventing water loss
from the camel in such periods of time when water is not available.
All these features has through evolution made
the camels uniquely adapted for a life in the desert environment where it is an
important source of transport, milk, meat, wool and hide.
Sources:
·
Feed intake, fore stomach fluid volume, dilution rate
and mean retention of fluid in the fore stomach during water deprivation and
rehydration in camels (Camelus sp.), report by W. von Engelhardt, P.
Haarmayer, M. Lechner-Doll, 2006
·
Osmotic and diffusive properties of intracellular
water in camel erythrocytes: Effect of haemoglobin crowdedness, report by Peter
Bogner, Attila Miseta, Zoltan Berente, Attila Schwarcz, Gyula Kotek and Imre
Repa, 2005
·
http://en.wikipedia.org/wiki/Camel#Adaptions_to_desert_environment
·
http://www.llamaweb.com/Camel/Info.html
·
http://en.wikipedia.org/wiki/Pliny_the_Elder
·
http://www.saudiaramcoworld.com/issue/198102/the.camel.in.retrospect.htm
Written by Nansy Tangen