Dogs are related to wolves and have been companions to people for thousands of years. At first, they were used as helpers for work and to protect people. Today, they do many jobs, such as helping people with disabilities, finding illegal drugs, looking for survivors after disasters, and even detecting illnesses like cancer. But the most important job dogs have is being loyal companions to people.
Even though dogs look very different from people, they have some of the same body features. They have hearts to pump blood, lungs to help them breathe, and stomachs to process food.
Dogs are wonderful companions and have unique needs and characteristics that make them special friends to people.
What Size Are Most Dogs?
Dogs come in all sizes and shapes:
The smallest breeds, like the Toy Poodle and Chihuahua, weigh only about 5–10 pounds (about 2½–4½ kilograms).
Medium-sized dogs include many terriers and spaniels, which weigh 10–50 pounds (about 4½–23 kilograms).
Larger dogs, like retrievers and shepherds, can weigh 65–100 pounds (about 30–45 kilograms).
Giant breeds, such as the Mastiff and Great Dane, can weigh over 200 pounds (more than about 90 kilograms)!
Sizes can vary within the same breed, and males are often bigger than females. Mixed-breed dogs can be any size.
Dog breeds and sizes
How Long Do Dogs Live?
Dogs grow up quickly and live shorter lives. Most dogs are considered puppies for about a year, but they often stay playful longer.
A common way to think about dog years is that each of the first 2 years of a dog's life equal about 10–12 human years. After that, each dog year equals about 4 human years.
In general, smaller dogs tend to live longer than larger ones.
Dog Years Versus Human Years
Dog Years | Human Years |
|---|---|
6–12 months | 10–15 years |
12–18 months | 15–20 years |
18–24 months | 20–24 years |
4 years | 32 years |
6 years | 40 years |
8 years | 48 years |
10–12 years | 56–64 years |
13–14 years | 68–72 years |
15–20 years | 76–96 years |
Normal Physiological Values for Dogs
Body temperature (average) | 101–102.5°F (38.3–39.2°C) |
Heart rate | 70–120 beats per minute (small dogs have faster heart rates than larger dogs have) |
Respiratory rate (at rest) | 18–34 breaths per minute |
Average lifespan | 8–16 years (depends on the breed) |
How Do Dogs Stay Warm or Cool?
Dogs are generally better at keeping warm than cooling down. Some dogs, like sled dogs, can survive in really cold weather because their fur keeps them warm. But they struggle to cool off in hot weather.
Dogs can't sweat like humans, so they cool down by panting. When they pant, they take quick breaths to help release heat, but they need to pause sometimes to take deeper breaths.
Because dogs don’t cool themselves well, hot weather can be dangerous for them. Dogs can suffer from heatstroke if left in a hot environment. For example, a parked car can quickly heat up to over 150°F (about 66°C), which can be deadly.
It’s important to keep dogs cool by providing shade, fresh water, and a cool space indoors. On hot days, you can also use air-conditioning, water misters, or even a small swimming pool to help keep them cool.
The best way to prevent heatstroke is to keep your dog indoors on hot days.
Do Dogs Have the Same Senses as People?
Dogs have the same five senses as people, but these senses have developed a little differently to help them survive:
Sight: Dogs are better than people at seeing movement and low light, which helps them see well at night. However, they don’t see fine details as clearly, and they can’t distinguish colors as well as people do.
Hearing: Dogs can hear sounds, especially high-pitched sounds, about 4 times better than people do. They also have a deeper ear canal, which helps them figure out the direction of a sound. This combination helps them in hunting. Their ear structure can also lead to ear problems, though, so they often need their ears cleaned.
Smell: Dogs have an amazing sense of smell, about a million times stronger than the human sense of smell. They can detect very faint odors, which is why they are used for many sniffing jobs, like finding drugs or searching for missing people.
How Do Dogs Walk and Run?
Like people, dogs have muscles and joints that help them walk and run. They can move in different ways, such as walking, trotting, cantering, and galloping, kind of like horses.
Most dogs can swim, but some, like retrievers, are much better at it than others, like bulldogs.
Will a Dog’s Nails Scratch Me?
Dogs have special pads on their paws that help them grip different surfaces. Their toenails have the same structure as human nails but are much thicker, which helps them run and dig.
Dogs must have their nails trimmed so that they don’t get hurt while playing. When you are trimming dog nails, it's important not to cut into the "quick," a blood vessel in the nail that bleeds and is painful to the dog when it's nicked. The quick is hard to see in dogs that have black nails.
Some dogs also have an extra toe, called a "dewclaw," a little above the foot on the back of the leg. Dewclaws have no purpose, but they have nails that need to be trimmed just like other nails. Dewclaws can get caught on things and are easily injured, so veterinarians often recommend surgically removing them.
Nails, dog
Is Dog Hair Like Human Hair?
Dog hair grows into a coat that protects dogs' skin and helps keep them warm. Each strand of a dog's hair is thicker than most human hair.
Different breeds have different types of coats for various climates:
Dogs that come from cold climates have a soft, thick undercoat for warmth.
Water dogs have longer, stiffer coats and oil glands to add some waterproofing.
Dogs from warm climates have shorter coats.
Some dogs shed their hair throughout the year but more during spring and autumn. Others, like poodles, shed less or not at all.
Dog skin is thinner and more sensitive than human skin. Dogs should be washed only with shampoos made for them, because human products can irritate their skin.
How Many Teeth Does a Dog Have?
Dogs' teeth are similar to those of their wolf ancestors. They have 28 baby teeth that fall out and are replaced by 42 adult teeth. This happens between 2 and 7 months of age.
Dogs can get tartar on their teeth just like humans. Brushing your dog's teeth regularly and feeding your dog harder food can help prevent tartar buildup on its teeth, just like with human teeth.
Dog teeth
How Do Dogs Digest Food?
Dogs digest food in their stomach and intestines, absorbing nutrients and getting rid of waste in their pee and poop. A dog with a digestive problem might vomit or have diarrhea for many reasons, like having an infection or eating something it shouldn’t have eaten.
The urinary system helps filter and remove waste from a dog's body. Female dogs can get urinary infections more easily, often causing them to have blood in their urine. If your dog has difficulty pooping or peeing, it’s essential to monitor the dog closely, and consult a veterinarian if the symptoms don't go away.
Why Do Dogs Sometimes "Scoot" on the Ground?
Dogs have anal glands on their rear ends that contain oils that get released as they poop. This helps dogs mark their territories.
Sometimes anal glands get backed up with oils, and dogs will try to empty them by dragging, or "scooting," their rear ands across the ground. If the glands are not emptied, they can cause pain and can even become infected.
Many dogs that have problems emptying their anal glands on their own need the glands cleaned out regularly by a vet.
