A Healthy Cat’s Body - A Healthy Cat - The Veterinarians' Guide to Your Cat's Symptoms - Michael S. Garvey, Anne E. Hohenhaus

The Veterinarians' Guide to Your Cat's Symptoms - Michael S. Garvey, Anne E. Hohenhaus (1999)

Part I. A Healthy Cat

A Healthy Cat’s Body

In this chapter is a short description of the various systems in normal, healthy cat’s bodies, touching on the differences between cats and humans and among cat breeds. The primary purpose of this chapter is to provide cat owners with a basis of comparison in case a cat’s body seems not to be functioning correctly.

In general, cat’s bodies work in much the same way as those of all other mammals, humans included. However, cats are apt to develop different diseases and illnesses than other species do. These specific problems and diseases will be covered in the symptoms section of this book. Cats have also evolved over the ages to have particular abilities that meet their particular needs. For example, they have a very highly developed ability to see and “sense” in the dark; they are able to jump very high, turn their paws inward, and retract and extend their claws. We will learn more about these special skills in this chapter.

Although breeds of cats have been developed with a variety of body, face, and ear shapes, tail lengths, and hair coats, all cats are alike physiologically. There are, however, some differences among cat breeds. For example, manx cats, which are tailless, often suffer from congenital abnormalities of their hindquarters.

Skin and Hair

One of the most noticeable differences among cat breeds is the length of their hair, or coat. Cat’s coats form an insulating layer between their skin and the external environment and protect them from the cold in winter and the sun in summer. Cats have three basic types of hair. Fine hairs make up a soft undercoat, while the outercoat is longer and coarser. There are also the stiff vibrissae, or whiskers, which project from a cat’s body. These tactile, or sinus, hairs are unique to cat’s bodies and include not only the whiskers but the eyelashes and sinus hairs on the insides of the middle forearms. Exceptions are rex cats, both Cornish and Devon. Cornish rex cat’s coats have no guard hairs at all, and Devon rex cats have uneven coats and few whiskers. Both have short, curly coats that lie close to their bodies. Cat’s whiskers are enervated by the fifth cranial nerve of the brain, and are able to act like radar, allowing cats to “feel” air currents and movements. Cat’s hair can stand on end all over their bodies when they are afraid or angry because of tiny muscles that react in an action called piloerection.

All cats shed all year long. Outdoor cats shed more in the spring, as days begin to become longer. Different coat lengths and types of hair determine the amount of shedding, although all cats will shed excessively when they are under stress. It is especially important to groom longhaired cats regularly or the shed hairs will become matted and tangled instead of falling out.

Cat’s skin plays many important roles. Not only does it protect a cat’s body from loss of fluids, electrolytes, and proteins but it also serves as a barrier against infections. Cats do not perspire through their skin, but the skin does help maintain body temperature. The blood vessels in the skin either dilate to cool the body or constrict to retain body heat when it’s cold. One of the skin’s most important functions is as a sensory perceptor, conveying things like heat, cold, and pain to the brain.

A healthy cat’s coat is shiny and full and her skin is clear and free of sores, scabs, redness, or scaly patches. If a cat is born with brown or black spots on her skin it is probably normal pigmentation, but if dark skin spots or discoloration suddenly occur they should be evaluated by a veterinarian.

Eyes and Vision

Although cat’s eyes have essentially the same parts as humans and other mammals, they differ from all other animals’in several ways, enabling cats to have the best night vision of all domestic animals. Cat’s eyes have a great many more rods than cones, while human eyes have more cones than rods. Because rods respond to very low light, cats can see extremely well in dim light. Also, their pupils are oblong instead of round, which enables them to dilate widely in low light, and thereby let in more light. In bright light cat’s pupils become a very thin slit, protecting their eyes, which are sensitive to light.

Owners are sometimes concerned when a cat’s eyes seem to have a bluish or yellowish glare if the animal is looking toward the light; blueeyed cat’s eyes will have a reddish glare. This is the reflection from a region around the retina called the tapetum. The tapetum reflects light back to the retina, further enhancing a cat’s night vision. Older cats sometimes develop a condition called lenticular sclerosis, in which the lens fibers become dense and refract light differently, making the eyes look bluish. This condition does not affect a cat’s vision but should be observed by a veterinarian to distinguish it from cataracts.

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Another cause for possible owner concern is a pinkish membrane that sometimes appears in the inside corner of a cat’s eye, partially covering the eyeball. This membrane is called a third eyelid (nictitating membrane) and is present in all mammals except humans. The third eyelid pops up automatically when a cat retracts her eyes (pulls them back into the eye sockets). It protects and cleans the eyeball, and may become more noticeable if a cat’s eye is irritated or if she is suffering from an illness. Burmese cats occasionally develop an eversion (outward turning) of the gland-, of the third eyelid, which can be surgically corrected. Cats with prominent eyes and flat faces (brachycephalic breeds) such as Persians and Himalayans are more susceptible to eye damage because their eyes are not set deep in their sockets.

Ears and Hearing

Cat’s internal ears have the same parts as humans’. All cats have pointed, upright ear flaps, or pinnae. Variations occur in Scottish Folds, whose ear tips are flipped forward, and American Curls, whose ears flip backward at the tips. Cat’s upright ears help capture sounds and direct them down the ear canal to the eardrum, from where they are transmitted to the brain.

Cat’s hearing is estimated to be at least three times more acute than humans’and they are able to hear high-pitched sounds much better than people. It is common for white cats with two blue eyes to suffer from congenital deafness.

Noses and a Sense of Smell

Cat noses come in variations of two basic shapes; pointed and flat-faced, or brachycephalic Longhaired cats, such as Persians and Himalayans, have been bred to have extremely flat faces. Some shorthaired cat breeds such as British Shorthairs and Scottish Folds have somewhat flattened faces and protuberant eyes, but are not truly brachycephalic Extremely brachycephalic cats may have upper respiratory problems due to their very small nasal openings (nares).

Cat’s sense of smell is very acute because the olfactory (smell-sensing) areas of their brains are highly developed. Their appetite is mostly controlled by smell. Therefore, if a cat’s nose is stuffed up, she will not be very interested in eating.

Mouth and Teeth

Cat’s teeth serve two purposes. They are both offensive and defensive weapons, and also are designed to fit cat’s particular style of eating. Cats grasp and then shred or tear their food before swallowing. Adult cat’s canine teeth are slanted inward in order to trap prey better.

Kittens have twenty-six teeth, which are replaced by thirty adult teeth by the time a kitten is six months old. The teeth are evenly divided between the upper and lower jaws.

Cat tongues are very rough and serve primarily as grooming tools, smoothing fur and removing loose hair like a comb. If too much loose hair is swallowed, a cat will develop hair balls in the stomach.

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Cardiovascular System

Cat’s cardiovascular systems are similar to those of humans and other mammals. Cats have a four-chambered heart with two atria and two ventricles. A cat’s heart is primarily responsible for pumping and circulating blood through an elaborate network of arteries, which deliver oxygenated blood to tissues, and veins, which drain deoxygenated blood from tissues and return it to the heart. It is then pumped into the lungs for reoxygenation during respiration.

In general, cats do not suffer from the types of cardiovascular disease that humans do. For example, arteriosclerosis, or plaques on the inside of arteries caused by an excess of cholesterol, is virtually nonexistent in cats. Nor do they suffer from heart attacks brought on by clogged arteries. Cats do, however, have other types of heart problems, which we will discuss later.

Digestive System

The digestive system of the cat is made up of components that transport food and fluids into and through the body. On the way through the digestive system, nutrients and fluid are absorbed and utilized by the body tissues. The remaining waste products are eventually eliminated.

The mouth and teeth grab and grind food until it can be swallowed and passed via the esophagus, a long muscular tube running from the back of the throat, to the stomach. In the stomach, food is further ground and churned. Stomach acids and small amounts of enzymes begin the digestive process. The resulting gruel then moves into the small intestine, where pancreatic enzymes, intestinal enzymes, and bile (produced by the liver) break it down into absorbable components. Fluids and these nutrients are absorbed through the lining of the small intestines. Remaining nonabsorbed material, including wastes for excretion, then move into the large intestine or colon. Most fluid is removed from this waste, and firm stool is produced and excreted via the rectum.

The liver is the largest organ in a cat’s body. It is responsible for a myriad of important functions. In addition to producing bile to aid digestion, it acts to metabolize and detoxify any drugs, chemicals, or poisons that enter a cat’s body. It manufactures the major blood-clotting factors, and stores sugar to provide energy between meals.

Endocrine System

The endocrine glands axe located throughout a cat’s body. They manufacture and release hormones into the bloodstream, which then travel to other organs and attach themselves, causing necessary functions to occur.

Some of the endocrine glands that are important are the thyroid glands, which exert a major impact on a cat’s metabolism and regulate how rapidly the body’s metabolic functions occur. The parathyroid glands are located near the thyroid glands and are important in regulating levels of calcium and phosphorous in the animal’s bloodstream. Adrenal glands, which are near the kidneys, secrete a variety of important hormones, such as cortisol and others that regulate blood pressure and electrolyte balance.

Part of the endocrine system also includes a network of cells in the pancreas that secretes insulin and other hormones that help utilize and assimilate sugars and other nutrients.

There are also a variety of reproductive hormonesthat a cat’s glands secrete. These are responsible for normal heat cycles, egg production, and uterine health in female cats, and normal sperm production in males.

If a particular endocrine organ oversecretes or undersecretes hormones, diseases occur in a cat’s body, which will be discussed later in this book.

Musculoskeletal System

Like humans, cats have clavicles (collarbones), which dogs do not. Cats have a more flexible skeletal system than dogs do. A cat can compress her body, or “coil,” allowing her to spring high from a standing or crouching position.

Cats have specialized muscles in their forearms that enable them to turn their front pawsinward (pronate them) so they can bat or grasp prey or toys.

Nervous System

Just as in humans, cat’s nervous systems are basically broken up into two different areas, the central nervous system and the peripheral nervous system. The central nervous system includes the brain and the spinal cord, which runs from the back of the brain through small bones or vertebrae in the spine along almost the entire length of a cat’s body.

The brain is responsible for thinking, memory, cognitive function, and many other things. The spinal cord accepts impulses from nerves located everywhere on a cat’s body, especially the legs and feet, and brings important information from peripheral nerves to the brain such as sensations of cold, heat, pain, and touch. It also transmits conscious and unconscious commands to the periphery of the body.

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The peripheral nervous system includes the twelve cranial nerves that come out of the brain and are responsible for all of the things that occur from the neck up, including vision, smell, and hearing. Peripheral nerves branch out of the brain and the spinal cord also transmit messages to the muscles, telling them either to expand or contract so the cat can stand, walk, jump, and move normally. There is also a sensory component of peripheral nerves that relays sensations up the spinal cord.

Reproductive System

Cat’s reproductive systems have the same components as those of all other mammals.

The age when a female cat enters puberty depends on when she was born and can vary from five to twelve months of age. This is because cats are what is called seasonally polyestrus, that is, their estrus (heat) cycle depends on the amount of daylight (photoperiod) in a day In the Northern Hemisphere most cats begin to cycle in February or March and continue to cycle every two to three weeks until fall, unless a cat is mated and becomes pregnant. Approximately twelve to fourteen hours of light a day is the normal measure used. Persian cats are the exception; they enter puberty as late as one and a half years of age. Indoor cats that live in nothing but bright artificial light, on the other hand, may cycle all year long. Signs of estrus in female cats are mostly behavioral. Cats in estrus will become very affectionate, vocalize a lot, become agitated, and walk with their backs arched and tails extended. They also roll around on the floor; this behavior can be so dramatic owners may confuse it with seizures.

Female cats have a total of eight mammary glands, four on each side of the body. In young cats these glands are not very prominent and look like little specks. In older females, particularly those who have had a litter of nursing kittens, the breasts may be more prominent and pendulous. In older, unspayed female cats the mammary glands may develop tumors. Cat breast tumors, while less common than in dogs, are often highly malignant. If an owner detects a lump in the area of the mammary glands, a veterinarian should be consulted immediately.

Surgical neutering prevents many health problems in both male and female cats and protects females from unwanted pregnancies. Unneutered male (torn) cats usually spray foulsmelling urine markers all around their territories, which makes them most unpleasant house pets. For the greatest health benefits females should be spayed (have an overiohysterectomy) before their first heat, at anywhere between six and seven months of age; males should be castrated by the time they’re eight months old so that spraying urine doesn’t become a habit. In recent years many shelters have found that both male and female kittens can be neutered at much earlier ages with no ill side effects. This earlier neutering has been effective in preventing unwanted kittens. For more about this, see “Spaying and Neutering” in the following chapter.

Respiratory System

A cat’s respiratory system brings oxygen into her body to be carried into the bloodstream, and eliminates carbon dioxide (the waste product of organ metabolism) from her body. The respiratory system starts with the nose or mouth, which brings air to the trachea, or windpipe, a long hollow tube that begins at the back of the throat. Air is brought through the trachea to the lungs through a branching network of smaller tubes called bronchi and bronchioles. The lungs are an elaborate network of membranes with very small blood vessels through which oxygen can pass and enter the bloodstream. Anything that interrupts this process of oxygenation, such as lung or bronchial disease, will cause difficulties because a cat’s body will not get its required oxygen supply. Cats who exhibit difficulty breathing should be handled very carefully. Any stress can cause hypoxia (low blood oxygen), which causes cats to become wild and uncontrollable and often leads to death.

Urinary System

The urinary system of all mammals, including cats, is primarily responsible for maintaining body water balance, i.e., assuring that the body has the proper amount of water at all times. The kidneys regulate this by removing water from urine before it is excreted, or by allowing water to be passed in urine when it is excreted. Two very long, thin tubes, called ureters, connect the kidneys to the bladder. The bladder is a hollow, muscular organ that stores urine and then contracts to excrete it. Kidneys also provide an important function in removing toxins and waste products from a cat’s body.

Unlike all other mammals, male cats do not have a discrete large prostate gland. Instead, they have several very small, scattered prostate glands. Therefore, they are able to avoid the prostate gland problems many other species often have.

Other Systems

Paws and claws: Cats usually have five toes on each front foot, and four on each back foot, but they sometimes have extra toes on their front feet and occasionally on their hind feet. This is an inherited trait called polydactyly.

Cat footpads are thick and smooth. Sweat glands are located between their footpads.

Cats are able to extend and retract their claws by using specialized muscles, tendons, and ligaments. Cat claws serve several purposes. They are used as weapons, as an aid in climbing, for catching prey, and for digging to bury waste. If a cat’s claws do not wear down naturally, they must be clipped to prevent them from catching on things and damaging people and other pets.

Anal glands: Cats have anal glands, or sacs, on either side of the rectum that contain a foul-smelling secretion. The secreted matter in the anal glands is forced out when a cat defecates. Unlike dogs, cats rarely suffer from impacted anal glands, but anal gland abscesses have been seen occasionally in cats.