Camel

A camel is an even-toed ungulate within the genus Camels, bearing distinctive fatty deposits known as "humps" on its back. The two surviving species of camel are the dromedary, or one-humped camel (C. dromedarius), which inhabits the Middle East and the Horn of Africa; and the bactrian, or two-humped camel (C. bactrianus), which inhabits Central Asia. Both species have been domesticated; they providemilk, meat, hair for textiles or goods such as felted pouches, and are working animals with tasks ranging from human transport to bearing loads.

The term "camel" is derived via Latin and Greek (camelus and kamēlos respectively) from Hebrew orPhoenician gāmāl, which has later been transferred to a verb root meaning to bear or carry (in Arabicjamala). The Hebrew meaning of the word gāmālis derived from the verb root g.m.l, meaning (1) stopping, weaning, going without; or (2) repaying in kind. This refers to its ability to go without food or water, as well as the increased ability of service the animal provides when being properly cared for.

"Camel" is also used more broadly to describe any of the six camel-like mammals in the familyCamelidae: the two true camels: the dromedary and bactrian, and the four South American camelids: thellama and alpaca are called "New World camels", while the guanaco and vicuña are called "South American camels".

Biology

The average life expectancy of a camel is 40 to 50years. A full-grown adult camel stands 1.85 m (6 ft 1 in) at the shoulder and 2.15 m (7 ft 1 in) at the hump. Camels can run at up to 65 km/h (40 mph) in short bursts and sustain speeds of up to 40 km/h (25 mph).Bactrian camels weigh 300 to 1,000 kg (660 to 2,200 lb) and dromedaries 300 to 600 kg (660 to 1,300 lb).

The male dromedary camel has in its throat an organ called a dulla, a large, inflatable sac he extrudes from his mouth when in rut to assert dominance and attract females. It resembles a long, swollen, pink tongue hanging out of the side of its mouth. Camels mate by having both male and female sitting on the ground, with the male mounting from behind. The male usually ejaculatesthree or four times within a single mating session. Camelids are the only ungulates to mate in a sitting position.

         

Ecological and behavioral adaptations

Camels do not directly store water in their humps as was once commonly believed. The humps are actually reservoirs of fatty tissue: concentrating body fat in their humps minimizes the insulating effect fat would have if distributed over the rest of their bodies, helping camels survive in hot climates. When this tissue is metabolized, it yields more than one gram of water for every gram of fat processed. This fat metabolization, while releasing energy, causes water to evaporate from the lungs during respiration (as oxygen is required for the metabolic process): overall, there is a net decrease in water.

Camels have a series of physiological adaptations that allow them to withstand long periods of time without any external source of water.Unlike other mammals, their red blood cells are oval rather than circular in shape. This facilitates the flow of red blood cells during dehydration and makes them better at withstanding high osmotic variation without rupturing when drinking large amounts of water: a 600 kg (1,300 lb) camel can drink 200 L (53 US gal) of water in three minutes.

Camels are able to withstand changes in body temperature and water consumption that would kill most other animals. Their temperature ranges from 34 °C (93 °F) at dawn and steadily increases to 40 °C (104 °F) by sunset, before they cool off at night again. Maintaining the brain temperature within certain limits is critical for animals; to assist this, camels have a rete mirabile, a complex of arteries and veins lying very close to each other which utilizes countercurrent blood flow to cool blood flowing to the brain.Camels rarely sweat, even when ambient temperatures reach 49 °C (120 °F). Any sweat that does occur evaporates at the skin level rather than at the surface of their coat; the heat of vaporization therefore comes from body heat rather than ambient heat. Camels can withstand losing 25% of their body weight to sweating, whereas most other mammals can withstand only about 12–14% dehydration before cardiac failure results from circulatory disturbance.

When the camel exhales, water vapor becomes trapped in their nostrils and is reabsorbed into the body as a means to conserve water. Camels eating green herbage can ingest sufficient moisture in milder conditions to maintain their bodies' hydrated state without the need for drinking.

The camels' thick coats insulate them from the intense heat radiated from desert sand, and a shorn camel has to sweat 50% more to avoid overheating.During the summer the coat becomes lighter in color, reflecting light as well as helping avoid sunburn. The camel's long legs help by keeping its body farther from the ground, which can heat up to 70 °C (158 °F).Dromedaries have a pad of thick tissue over thesternum called the pedestal. When the animal lies down in a sternal recumbent position, the pedestal raises the body from the hot surface and allows cooling air to pass under the body.

Camels' mouths have a thick leathery lining, allowing them to chew thorny desert plants. Long eyelashes and ear hairs, together with nostrils that can close, form a barrier against sand. If sand gets lodged in their eyes, they can dislodge it using their transparent third eyelid. The camels' gait and widened feet help them move without sinking into the sand.

The kidneys and intestines of a camel are very efficient at reabsorbing water. Camel urine comes out as a thick syrup, and camel feces are so dry, that do not require drying when the Bedouinsuse them to fuel fires.

                                                    Camels' immune system differs from those of other mammals. Normally, the Y-shaped antibodymolecules consist of two heavy (or long) chains along the length of the Y, and two light (or short) chains at each tip of the Y. Camels, in addition to these, also have antibodies made of only two heavy chains, a trait that makes them smaller and more durable. These "heavy-chain-only" antibodies, discovered in 1993, are thought to have developed 50 million years ago, after camelids split from ruminants and pigs.