Dromedaries. Those are the animals!

1987/04/01 Elhuyar Zientzia Iturria: Elhuyar aldizkaria

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If there are amazing animals, it is a dromedary certainly. In the desert you can circulate in the sun, eating little and drinking less. You can lose a quarter of your body weight without problems. Then, the dehydrated dromedary can drink 200 liters of water in a few minutes, recovering everything you have lost. In any animal a change of water balance is dangerous because it changes the blood concentration.

The organs responsible for maintaining blood concentration are the kidneys. The kidneys of the dromedary are impressive. At a given time they can produce a dense and dark urine and at an hour and a half without color. The rest of the desert animals do not behave like this and the goats and sheep need two days for the water level to pass to its normal state.

Two Israeli biologists, Z. Last morning and R. Yagils analyze the dromedary hydration system. In dehydrated mammals, the pituitary gland increases the synthesis of the antidiuretic hormone (ADH) that makes urine water reabsorbed into the blood. When an animal drinks a lot of water, the blood is diluted and as the pituary synthesizes less ADH, more water is lost in the urine. At the same time, another hormone (aldosterone) acts for blood to resist sodium, minimizing the effect of dilution.

Under normal conditions this mechanism is sufficient, but in some animals the rapid rehydration causes the collapse of the system. If the blood is too diluted (i.e. hypoonic), red blood cells absorb osmosis water and explode (hemolysis). Animals that inhabit a dry environment often have hemolysis. Desert goats and sheep, although they drink a lot of water, do not hold this type of water, as they store water in the stomach and absorb it slowly.

In dromedaries, however, water enters directly into the blood and the kidneys and other organs quickly adapt to the new situation. Although ADH production decreases and increases aldosterone production, blood is diluted. However, the dromedary red blood cells place this dilution well.

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