Like dogs, cats look very different from people but share many of our body’s characteristics, such as a circulatory system, lungs, a digestive tract, a nervous system, and so on.
There are many different breeds of cats, including Abyssinian, Himalayan, Maine Coon, Manx, Persian, Scottish Fold, and Siamese, to name a few. The Cat Fanciers’ Association, which is the world’s largest registry of pedigreed cats, recognizes about 40 distinct breeds. The most familiar cats are the domestic shorthair and the domestic longhair, which are really mixtures of different breeds. Cat breeds differ in looks, coat length, and other characteristics but vary relatively little in size. On average, only 5 to 10 pounds separate the smallest and largest domestic breeds of cats.
Cats also share the rapid metabolism that dogs have, which results in a higher heart rate, respiratory rate, and temperature than those of people (see Table: Normal Feline Physiologic Values). Cats generally live longer than dogs, and many live to be 20 years old or older.
Cats are better at conserving heat than at cooling themselves, although their small size relative to their large surface area makes for more effective cooling than in dogs. Cats lose heat through external radiation. They have some sweat glands that aid in evaporative cooling, and licking their fur further improves this process. Heat is also lost through panting, although this is not as effective a method of cooling as it is in dogs. Cats typically also seek dark, cool places to shelter themselves from the heat of the day. As with all animals, cats should never be shut in cars or other hot, confined spaces. This can lead to heat stroke and death.
Cats have the same 5 senses as people do but to very different degrees. Some senses are much better developed than in people.
Cats have keen vision; they can see much more detail than dogs. Concentrated in the center of the retina of the eye, a specific type of cell called a cone gives cats excellent visual acuity and binocular vision. This allows them to judge speed and distance very well, an ability that helped them survive as hunters. However, although the cone cells are also responsible for color vision, it is uncertain whether cats can see colors. Like dogs, cats also have a lot of the retinal cells called rods, which are good at collecting dim light. In fact, cats can see 6 times better in dim light than people, giving rise to the myth that cats can see in the dark. Cats also have a reflective layer called the tapetum lucidum, which magnifies incoming light and lends a characteristic blue or greenish glint to their eyes at night.
A unique feature of both canine and feline eyes is the nictitating membrane, which is also called the third eyelid. This additional eyelid is a whitish pink color and is found under the other eyelids in the inside corner (near the nose) of the eye. The third eyelid extends up when needed to protect the eyeball from scratches (such as while traveling through brush) or in response to inflammation.
Cats are very sensitive to sound, with a range of hearing both above and below the range of frequencies that can be detected by people. They can hear better than people and even better than most dogs. Feline hearing also acts as a direction finder, which is useful for hunting purposes. Cats generally turn their heads toward the direction of the sound while listening to pinpoint the location. The ear canal of cats is deeper and more tapered than in people. This deeper canal is subject to buildup of dirt and wax that can lead to inflammation and secondary infection, although to a lesser degree than in dogs.
The semicircular canals, which are found within the inner ear, are filled with fluid and are important for maintaining balance. These are highly developed in cats, accounting for their agility and excellent sense of balance. Cats can usually determine their body position at all times and can rapidly right themselves when falling, which explains the origin of the phrase, “Cats always land on their feet.”
Cats do not rely as much on the sense of smell as some other animals. The sense of smell is less developed in cats than in dogs. Like people, cats are finicky about odors and try to cover disagreeable smells. Also like people, odor is an extremely important part of taste and enjoyment of food for cats. Cats that have lost their sense of smell due to illness (such as nasal or severe respiratory infection, nerve damage, or certain cancers) often stop eating completely.
Most cats are excited by the smell of catnip, a plant that is a member of the mint family. However, not all cats react in the same way. Some become manic, others roll and purr, others are minimally affected. This herb is harmless and can be given to your cat either directly or as part of a catnip toy or ball.
The muscles, tendons, joints, ligaments, and spine of cats are extremely flexible, making them agile hunters. Cats can walk, run, leap, twist, and even roll into a ball. They can leap long distances and twist in mid-air to obtain a better angle of attack. The feline bones that are comparable to the long bones of our hands and feet are located in the cat’s lower legs. The angular hock in the hind legs is comparable to the ankle in people. Their normal gait is a “pace,” in which both legs on one side move together.
As in dogs, the bottom of the paw in cats is covered by thick, resilient pads that cushion the foot and help provide a secure grip on many types of surfaces. Cats have claws that are much more highly adapted and complex than in the dog. Feline claws are very sharp and curved, which makes it easier to grasp prey while hunting or to slash during fights over territory. The claws are retractable, so that they do not get in the way or make noise when walking or running.
Many cats frequently scratch or knead furniture, bedding, drapes, and other types of material as a way of removing the outer layers of the front claws and keeping them sharp. Obviously, this habit can be very destructive. Solutions include providing a scratching post as an alternative and periodically clipping the nails. Nail clipping is usually easier in cats than in dogs, although caution must be used to avoid cutting the central “quick,” which is the blood supply to the growing nail. A more permanent solution is a “declaw” surgery, in which the front claws are completely removed, including the dew claw, which has no function but can potentially snag and break. Although the surgery is controversial and prohibited in some areas, there is no evidence that it increases behavioral problems such as biting or failure to use a litter box. If you choose to declaw your cat, this procedure should be done before the cat is around 6 months of age. It is not recommended for adult or older cats. Declawed cats can have trouble climbing and defending themselves and should not be let outdoors.
Feline skin, like that of people and dogs, has an outer layer called the epidermis that is constantly being replaced, and an inner layer called the dermis that contains nerves and blood vessels, oil glands, and hair follicles. The oil glands secrete sebum that coats and protects the fur, giving it a glossy sheen. Feline skin is more sensitive than human skin, which is why it is important to use topical preparations that are specifically formulated for pets. Shampoos and other topical products for people can irritate your cat’s skin and should be avoided.
Cat fur protects the skin from sun, cold, scratches, and insect bites; helps regulate body temperature; and supports the sense of touch. Cat fur consists of several types of hairs. Cats also have whiskers that are attached to nerve cells in the face. These sensitive hairs can be used to judge the size of an opening, such as a rodent hole. As in dogs, cats have small muscles attached to hair follicles, which can make hair stand erect for temperature control or as a warning sign (that is, “raised hackles”) in response to danger.
Different breeds of cats have different types of hair coats. Some have long hair (for example, the Persian, the domestic longhair), some have short hair (the Abyssinian, domestic shorthair), and some have “-mutant” hair. The mutant hair types on Rex or wire-haired breeds are shorter and curlier than the hair of most other cats. Some breeds even lack hair on certain areas of the body, usually the chest and belly.
Cats shed hair naturally year round, although the rate of shedding depends on climate, nutrition, and general overall health. Outdoor cats shed more in fall and spring. Shedding may increase in all cats due to stress, such as a trip to the veterinarian. Excessive shedding and bald patches can be a sign of illness that should be investigated.
Cats are carnivores with teeth designed for piercing and tearing meat. They have 26 deciduous (baby) teeth that are replaced by 30 permanent (adult) teeth that erupt between 5 and 7 months of age (see Table: Feline Adult Dentition). The different types of teeth have specialized functions, depending on their position in the mouth. The front teeth, which include the 12 incisors and 4 large canine teeth (also known as eye teeth), are designed for grasping and tearing. The rearward premolar and molar teeth grind food into smaller pieces so that it can be swallowed.
The mouth contains the salivary glands, which lubricate food and begin digestion. The tongue helps guide food to the back of the throat and is important for licking up small food pieces and lapping up water. The feline tongue is covered with tiny, thornlike structures that give it a rough, sandpapery texture. The rough tongue aids in grooming and can be used to scrape meat away from bones.
The gastrointestinal tract includes the stomach, the small intestine, and the large intestine (colon). This system digests food into useful nutrients, absorbs water, and eliminates waste. Digestive problems often show up as vomiting or diarrhea, which can have many causes, including viral infections; worms; stress; or ingestion of bones, string, hair, or other foreign material.
The urinary system eliminates wastes from protein breakdown and helps control fluid levels. Waste products are filtered by the kidneys and then sent through the ureters to the urinary bladder for storage. Urine is passed out of the body through the urethra. In males, the urethra doubles as a channel for sperm during copulation. The feline penis is small and “hidden” within the scrotal pouch that holds the testicles. This can sometimes make it difficult for pet owners to determine whether their cat is male or female.
Urinary infections usually show up as frequent dribbles of urine that may be tinged with blood. Cats commonly develop a condition called feline lower urinary tract disease, which is also called feline urologic syndrome. Signs can be similar to signs of infection. Feline lower urinary tract disease is caused by a buildup of crystals in the urine, which develop into a sludge that irritates the urinary tract. This is particularly dangerous in male cats, because their urethra, which carries urine from the bladder out of the body, is narrow and bends and turns. If the tract becomes blocked and the cat is unable to pass urine, kidney failure and death can ultimately result without prompt treatment.
Both urinary and digestive problems are often associated with straining while urinating or defecating. At first glance, it may be difficult for cat owners to tell the source of the problem. Therefore, it is important to watch your cat while it eliminates and to check the litter for the character and color of the urine and feces. Diarrhea usually consists of frequent, soft or runny feces that may be a different color (often yellow, gray, or black) than usual. Any sign of blood in the feces calls for veterinary attention. Repeated, unproductive attempts to pass a bowel movement can be a sign of serious constipation or obstruction. Male cats that strain, dribble blood, howl, or have a painful abdomen are likely to have feline lower urinary tract disease. Blockage of either the urinary or gastrointestinal tract is an emergency, and your pet should be seen by a veterinarian immediately.