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Dogs come in many shapes and sizes. The smallest breeds include the toy and miniature varieties, such as the Toy Poodle, Papillon, Chihuahua, and Shih Tzu. These dogs usually weigh only 5 to 10 pounds (2.3 to 4.5 kilograms), or even less. Medium-sized dogs include many of the terriers and spaniels, which weigh in the 10 to 50 pound (4.5 to 23 kilograms) range. Larger still are the retrievers, shepherds, and setters, which often weigh 65 to 100 pounds (30 to 45 kilograms). Finally, the giant breeds, such as the Mastiff, Komondor, and Saint Bernard, can approach or exceed 200 pounds (91 kilograms). Of course, sizes vary within breeds, with males usually being larger than females. Mixed-breed dogs include all size ranges.
Dogs are generally much better at conserving heat than at cooling themselves. In sled dogs, who can survive outdoors even in bitterly cold temperatures, the fur acts as an insulating “blanket” that retains the heat generated by the dog’s high metabolism. However, in hot or humid weather, most dogs have difficulty. Dogs cannot sweat, which is an effective form of evaporative cooling. Instead, dogs lose heat primarily by panting. During the short, shallow breaths in panting, little air can be exchanged in the lungs. In fact, dogs must stop panting periodically to take a good respiratory breath. Drinking water also helps dogs cool down, and the canine hair coat helps insulate from the sun.
Dogs can see movement and light much better than people. In the retina of the eye, dogs have more of a specific type of cell called a rod, which is good at collecting dim light, so they have better night vision. A reflective layer in the dog’s eye, called the tapetum lucidum, magnifies incoming light. This reflective layer lends a characteristic blue or greenish glint to dogs’ eyes when light (for example, headlights of passing cars) shines into them at night. However, dogs do not have as much visual acuity as people, meaning that they cannot distinguish fine details as well. They also cannot differentiate colors as well because they have fewer of the cells in the retina called cones, which are responsible for color vision. Contrary to popular belief, however, dogs are not completely colorblind.
The ear canal of the dog is much deeper than that of people and creates a better funnel to carry sound to the ear drum. The average dog can hear about 4 times better than the average person, including sounds at higher frequencies than can be detected by the human ear. Dogs are also better at distinguishing the direction of a sound, which is an adaptation useful for hunting. Unfortunately, this deeper ear canal predisposes dogs to ear problems. Grease, wax, and moisture can build up in the ear, leading to inflammation and infection. Floppy ears or hair within the ears further limit ventilation, making matters worse. This is why many dogs need frequent preventive ear cleaning.Dogs have an extraordinarily acute sense of smell; it is about a million times more sensitive than that of people. They can detect odors at extremely low levels and can distinguish odors that are subtly different. This is why dogs are able to sniff out drugs and explosives at airports, search for human victims at disaster sites (including victims deep under water), and follow the scent track of criminals.
Dogs also have an organ on the roof of the mouth that allows them to “taste” certain smells. As in people, taste and smell in dogs are closely linked. However, dogs gain much more information about food from smell than from taste. Dogs have only about one sixth the number of taste buds that people do, and their distinct sense of taste is actually quite poor.
(Espero que esto te sirva, porque yo tengo cuatro perros, XD)