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The Cat Body

The Cat Body

By Arnold Plotnick, DVM

If you want a cat who will be as healthy as possible inside and out, from the first day you bring her home to last day of her long, happy life, then you need to learn all about every square inch of her body. It is not enough to just admire the long, flowing locks of a Persian's coat or the striking color of a Siamese's eyes. You need to understand what each part of the cat's body does to keep her safe and you need to know what can go wrong with each part. In this chapter, we begin by taking a look at the different parts of the fascinating feline body from the outside in.

Skin and Coat

Skin and Coat

The hair coat and skin make up the outer covering of the body. The coat is the first barrier to mechanical trauma. The thick coat and orientation of the hairs of some cats repel water, so that it doesn't reach the skin surface. Certain breeds, such as the Norwegian Forest cat, have coats that are very repellant to water. In fact, some show judges will let several drops of water fall onto the hair coat to see if the drops roll off without wetting the cat. The hair coat also is an effective barrier to visible light and ultraviolet light. (White cats and those with very light coats are at increased risk for some types of cancers that are known to be induced by frequent exposure to the sun.) The skin is the largest and one of the most important organs of the body. It forms an essential barrier between the cat and her environment, protecting her from infections, parasites, and the elements. The skin consists of an outer layer (epidermis) and an inner layer (the dermis). The epidermis consists of tough cells containing a protective protein called keratin. As keratinized cells are shed from the skin surface, new ones are continuously formed. The dermis, located beneath the epidermis, contains blood vessels, nerves, connective tissue, hair follicles, and various glands. The skin also prevents dehydration and protects against infection by microorganisms and harmful chemicals. The skin is also where vitamin D is synthesized.

The coat and skin play a significant role in thermoregulation. The thick hair coat and subcutaneous fat cells protect the cat during cold weather. Blood vessels in the dermis also play a role in temperature regulation. Vasodilation (expansion of the blood vessels in the skin) allows for heat loss, whereas vasoconstriction (contraction of the blood vessels in the skin) prevents heat loss from the circulation. The skin also plays a sensory role through free nerve endings in the skin that recognize such sensations as heat, cold, pain, and itchiness. Specialized structures contained within the skin allow for recognition of pressure and touch. The skin and coat are often a good reflection of the general state of a cat's health.

A cat's fur is her first barrier to injury, and it also protects her skin from ultraviolet light.

Although they can't see in total darkness, cats require only one-sixth the amount of light to see as a human does.

Ears and Eyes

Ears and Eyes

The cat's ear is divided into three parts: the external (outer) ear, the middle ear, and the inner ear. The outer part of the ear-the part you can see when you glance at your cat-is called the pinna. The pinna acts like a funnel that catches sound vibrations and transmits them to the eardrum, via the ear canal. The eardrum separates the external ear from the middle ear. Vibrations from the eardrum are transmitted through small bones in the middle ear to the vestibular window. From the vestibular window, vibrations enter the inner ear, where the cochlea turns them into nerve impulses that travel to the brain via the auditory nerve. Within the inner ear, too, is the vestibular system, which is responsible for maintaining the sense of balance. Cats can distinguish among sounds better than can dogs or humans. They can also hear sounds at a higher pitch (up to 65 kHz) than can humans. The eye is made up of three layers. The outer layer is the fibrous layer, the middle layer is the vascular layer, the inner layer is the nervous layer. The outer fibrous layer consists of the sclera (the white of the eye) and the cornea (the clear part of the eye). The thick middle layer is called the uvea, and it is composed of the choroid (the blood-vessel containing layer behind the retina), the ciliary body (a structure that produces the fluid in the front chamber of the eye), and the iris (the colored part of the eye that surrounds the pupil). The muscles in the iris that surround the pupils are able to narrow the pupil into a vertical slit in bright light and open fully in dim light, allowing maximum illumination to enter the eye.

In humans as well as in animals, the role of the visual system is to collect light and focus it onto the retina, where specialized cells convert this light energy into nerve impulses. The amount of light that passes through the cornea is controlled by the pupil. Similar to the aperture of a camera, the pupil adjusts to different light levels by dilating to let in more light during dim conditions or by constricting to limit the amount of light in bright conditions. The lens, located just behind the pupil, focuses the light coming through the pupil onto the retina. The retina at the back of the eye acts like the film in a camera. When light strikes the retina, lightsensitive photoreceptor cells (rods and cones) are stimulated, causing them to produce impulses that travel to the brain via the optic nerve. Rods are sensitive to dim light; cones are sensitive to bright light and colors. As nocturnal creatures, cats are more sensitive to light than humans. Although they can't see in total darkness, cats require only one-sixth the amount of light as a human to see. Their pupils can dilate three times larger than a human's, and the feline cornea is bigger, allowing more light in. The feline retina also contains reflective cells that amplify the light coming into the eye. These reflective cells (the tapetum) are responsible for the glowing appearance of the eyes when light strikes them.

Eyesight in cats is geared to assist in hunting. Being predators, their eyes are placed on the front of the head. This results in a larger area of binocular vision, allowing for more accurate depth perception and coordination of body movements with visual events. Cats, however, cannot see detail very well. Visual acuity is the ability to see the detail of an object separately and clearly. A person with 20/20 vision can discern the details of an image (such as letters on a chart) perfectly from 20 feet away. Applied to animals, dogs are said to have a visual acuity of 20/75. The average cat is believed to have a visual acuity between 20/100 and 20/200. Simply put, cats are nearsighted. Cats can see color, but they do not have as many color-sensitive photoreceptors as humans do. Colors that would appear to be very rich to us are more pastel-like to the cat. Cats respond to the blue and yellow wavelengths best, having trouble with green and red. What appears to us as red is simply dark to cats. A fraction Bibleof the green spectrum in cats is indistinguishable from white. Cats would see a green, grassy lawn as a whitish lawn, and a green rosebush with red roses would appear as a whitish bush with dark flowers. Cats, however, are very good at distinguishing many different shades of gray.

Cats start losing their baby teeth at about four months of age and have all their adult teeth by six months.

Teeth

Teeth

Kittens are born with no teeth. At one to two weeks of age, the deciduous teeth (baby teeth) erupt. At six weeks of age, all twenty-six baby teeth should be present. At four to five months of age, the baby teeth are shed, and the permanent teeth erupt. By six months of age, all thirty adult teeth will have erupted. The thirty teeth include twelve little incisors in front, four canine teeth (the two upper and two lower fangs), ten premolars, and four molars. The periodontium consists of the structures around the teeth, namely, the periodontal ligaments that attach the gums to the teeth, the alveolar bone (the "tooth socket"), and the gingiva (the gums).

Cats start losing their baby teeth at about four months of age and have all their adult teeth by six months.

Paws

Paws

A cat's front paws differ slightly from the back paws. Front paws normally have five toes; back paws normally have four toes. Some cats have a harmless genetic trait that causes them to have extra toes on the front feet, back feet, or both. This is called polydactyly. Each feline toe has a pad and a claw associated with it. In the center of each paw is a large paw pad. Some cats have pink paw pads. Others have black paw pads. Some cats have both colors, sometimes within the same pad. The skin of the paw pads is thicker than the skin on the rest of the body, providing the toughness necessary for walking and jumping. Despite the added thickness, the skin on the paws is capable of sensing vibrations and temperature changes. Paw pads also contain sweat glands, making them the only places on a cat's body that sweats. Longhaired cats can have tufts of hair growing between the toes. Cats' claws, like the claws and nails of all animals, are made of the protein keratin. Beneath the claw is a pink structure, the quick, which contains blood vessels, nerves, and cells that give rise to the keratin that makes the nail. Cats use their claws for climbing, for killing prey, and for defense.

The Declawing Debate

Perhaps no topic involving feline welfare is more controversial and ignites more passion than the topic of declawing. Declawing is the surgical removal of the cat's claws. In most cases, only the front feet are declawed. The surgery involves the amputation of the last digit of each toe with the cat under general anesthesia. There are several techniques for removal of the claws. Traditionally, the individual claws are dissected out using a scalpel blade or similar instrument. In recent years, laser declaw surgery has become more readily available and may offer quicker recovery times and less discomfort. If declawing is to be performed, it is best done in kittenhood. Because of their small size, kittens bear less weight on their feet after the procedure and recover more quickly. Because the claws are a major method of defense, declawed cats should never be let outdoors.There are several reasons why cat owners choose to have their cat declawed. They range from a desire to protect furniture and furnishings from destruction to preventing or reducing the chance of a cat's scratching children or others to protecting the health of household members who are immunocompromised.

Those who are against declawing believe that the surgery is unnecessary and that cats can be trained not to scratch the furniture or people and to use appropriate items like scratching posts instead. They argue that the procedure is painful and can lead to behavioral and health problems for the cat later on. Many people feel that the procedure is cruel and amounts to mutilation, and they point to the fact that many countries outlaw the procedure for this reason. Yet even some who are against declawing in general might feel that declawing is acceptable as a last resort if it prevents a cat from being relinquished to a shelter. Destructive behavior is a common reason for pets to be relinquished to shelters.There are alternatives to declawing. One is a surgical procedure wherein the tendon attached to each nail is severed, resulting in the inability of a cat or kitten to extend the nails. This is known as a digital flexor tendonectomy. However, because the nails are still present, cat owners opting for this alternative to declawing must trim their cat's nails regularly. If they don't, the nails can overgrow and penetrate the skin and pads of the feet, causing pain and infection. Another alternative to declawing, one which might appeal more to those who are against any surgical procedures, is to apply soft plastic nail caps to the claws. These nail caps are available under the brand name Soft Paws. The nail caps are glued into place. Cat owners utilizing this product need to be aware that the nail caps have to be replaced periodically, usually once every four to six weeks. The application of Soft Paws is not painful and can usually be performed without sedation. (Exceptionally grumpy cats, however, may need a sedative or tranquilizer.)

Nail caps.

Musculoskeletal System

Musculoskeletal System

Making up a large part of the cat's weight, the musculoskeletal system comprises all of the bones and muscles in the cat's body. The skeleton supports the body and provides the framework for the muscles. The bones have other functions as well, such as mineral storage and the formation of blood cells, which occurs in the marrow within the bones. Cats have approximately 230 bones in their body, approximately twenty-five more than humans have. Most of those extra bones are found in the tail. The skeleton can be divided into two parts: the axial skeleton-the skull, spine, ribs, and sternum- and the appendicular skeleton, which comprises the front and hind legs. Although cats are very limber and coordinated, their bones are fairly fragile and orthopedic injuries such as broken bones are common. Muscles can be divided into three basic types: skeletal, smooth, and cardiac. Skeletal muscle is responsible for voluntary movement such as running, jumping, and walking. Smooth muscle is found in internal organs such as the intestines and bladder and is involved in involuntary actions within the body. Cardiac muscle, found only in the heart, is a specialized type of muscle that is capable of contracting rhythmically and spontaneously. Tendons are strong bands of connective tissue that attach the skeletal muscles to the bones. When a muscle contracts, it pulls on the tendons, which pull on the bones and result in movement. Ligaments are strong pieces of connective tissue that connect bones to other bones. Tendon and ligament injuries are not as common in cats as in dogs, but they do occur.

The cat skeleton. Cats have approximately 230 bones.

Cardiovascular System and Respiratory System

Cardiovascular System and Respiratory System

The cardiovascular system of the cat is similar to our own. A heart, consisting of four chambers-the left atrium, left ventricle, right atrium, and right ventricle-pumps the blood through arteries that carry blood away from the heart, through smaller vessels and capillaries where oxygen is exchanged, and then through veins that return the blood back to the heart. The heart rate in the cat can vary, but is generally between 160 and 240 beats per minute-much faster than the human heart. Heart disease can occur in any age cat. Fortunately, unlike in humans, diseases of the blood vessels that supply the heart itself, such as atherosclerosis, are very rare in cats. The heart and the respiratory system are intimately connected (hence the familiar term cardiopulmonary, which refers to both the heart and the lungs). The heart pumps blood to every inch of the body. The lungs make sure that blood is properly oxygenated and remove carbon dioxide at the same time.

The respiratory system of the cat consists of the nasal cavity and mouth, the pharynx (back of the throat) and larynx (voice box or "Adam's apple"), the trachea, bronchi and lungs, the diaphragm, and the muscles of the chest. Cats, like humans, have two lungs. The lungs are divided into smaller sections, called lobes. Within the lobes, the large air passages (bronchi) divide into smaller branches called bronchioles. These split into progressively smaller tubes, in much the same way that a tree divides into smaller and smaller branches. At the end of the smallest bronchioles are the alveoli. It is here that gas exchange occurs; carbon dioxide is removed and oxygen is delivered. The respiratory system, working together with the tongue and mucous membranes of the mouth, serves another important function: heat regulation. This is important, because cats have a poorly developed mechanism for sweating. The cat's upper respiratory system begins at the nostrils. Occupying the space from the nostrils to the back of the throat is the nasal passage. The nasal passage is divided into the right and left side by the septum, which runs down the middle and is composed partly of bone and partly of cartilage. The nose and mouth are responsible for taking air into the body. Fine hairs that line the nasal cavity and mucus produced by the cells in the nasal cavity help to filter debris from the air before it enters the body. The nasal cavity also warms and moistens the air. At the back of the nasal cavity is the olfactory region; as air passes over this region, the sense of smell is activated. Further along, beyond the end of the nasal cavity is the pharynx (the throat). The lower part of the pharynx that is part of the oral cavity is the oropharynx. The upper part of the pharynx that is part of the respiratory system is called the nasopharynx. The nasopharynx connects the back of the nasal cavity to the larynx (voice box or "Adam's apple"). The larynx is composed of muscle and cartilage. The cartilages at the front of the larynx act as a valve or doorway to the trachea (windpipe), closing and covering it during swallowing so that food does not enter the trachea. When open, it allows air to pass from the nose to the trachea. The larynx also contains the vocal folds, which are necessary for vocalization, such as meowing or growling. Cats use their voices to communicate and have a vocabulary of several types of meows, such as the demand meow ("feed me," "I want to go outside"), the pleading meow, the hunting meow, the trilling meow that mother cats use with their kittens, and caterwauling-an aggressive call between two males.

The Immune System: Ready for Battle

The immune system can be thought of as an "army" whose job is to defend the body against "invaders." These invaders come in the form of bacteria, viruses, parasites, toxins, and other foreign materials.The immune system comprises various organs and cells located throughout the body. The main organs of the immune system are the lymph nodes. They are small structures located throughout the body in areas such as the neck, armpits, groin, chest, and abdominal cavity. As blood flows through the lymph nodes, antigens (proteins found on invading viruses, bacteria, and so on) are filtered and trapped by the lymph node. The nodes contain large numbers of lymphocytes, the white blood cells that are the key players in the immune response. Other organs involved in the immune response are the lungs, the liver, the intestine, the thymus, and the blood. The spleen is an important component of the immune system; it filters and traps antigens directly from the blood stream. The bone marrow is another major component of the immune system and is the site where most of the infection-fighting white blood cells are produced. A variety of white blood cells participate in the immune response. Some white cells attack and kill invading bacteria and viruses directly. Others produce antibodies (also called immunoglobulins), specialized proteins that play an important role in the immune response, especially against viruses.

The organs of the immune system connect and communicate with each other via the lymphatic system, a network of vessels that is very similar to the circulatory system. The cells of the immune system and the materials that they produce (antibodies, for example) circulate through the lymphatic system so that they can be deployed to those areas of the body that are most in need. The immune system is programmed so that it recognizes self (the cat's own body) and nonself (bacteria, viruses, parasites, and so on). Occasionally, the immune system goes awry and directs itself against the body's own components, resulting in immune-mediated disorders. The cat is susceptible to a number of these disorders, such as pemphigus, lupus, and immune-mediated hemolytic anemia. Some viruses, such as the feline immunodeficiency virus (FIV), attack the immune system itself, leaving the cat susceptible to other infectious diseases. Cancer of the immune system can also develop in the form of a solid tumor (for example, as lymphoma of the lymph nodes) or as a circulating leukemia of the white blood cells.

Digestive System

Digestive System

Although we don't usually think of it this way, the gastrointestinal (GI) tract is basically a long hollow tube lined by different types of cells. Within the walls of this tube are a variety of glands, muscles, and nerves. These structures, as well as the diameter and shape of the tube, vary depending on which region of the GI tract one is observing. The gastrointestinal system is responsible for digesting food and absorbing nutrients. It is also responsible for collecting waste material and expelling it from the body. The GI tract starts at the mouth, where food is taken in. As food is swallowed, it passes through the pharynx and enters the esophagus, which is located in the cat's neck and chest. The esophagus contains muscles that rhythmically propel food down its length toward the stomach. Food then enters the stomach. The stomach contains glands that produce enzymes and acids that help digest the food. The walls of the stomach also contain muscles that mix and grind the food. From here, the partly digested food moves into the longest part of the tube, the small intestine. It is in the small intestine that most of the absorption of nutrients occurs.

The first part of the small intestine is called the duodenum. Digestive enzymes from the pancreas and gall bladder enter the small intestine through ducts that lead into the duodenum. The next section of the small intestine is the jejunum. In this portion, food continues to be digested and nutrients are absorbed. The short, final section of the small intestine is the ileum. From here, digested food moves into the large intestine. The large intestine participates in the last phase of digestion, absorbing water and electrolytes from the food. It also forms and stores feces, and it produces enzymes that further help break down difficult to digest material. The large intestine is composed of the cecum, colon, and rectum. The cecum is a small pouch located at the junction between the ileum and the large intestine. The colon consists of three sections. The first portion is the ascending colon. Beyond that is the transverse colon. The last portion is the descending colon. The descending colon leads into the rectum, which receives undigested food and expels it through the anus.

Cats are carnivores, so they need very little fiber in their diet.

Urinary System

Urinary System

The feline urinary system consists of two kidneys, two ureters, the bladder, and the urethra. These organs work together to eliminate waste materials from the body. The urinary system also regulates the amount of water and the levels of electrolytes in the body. The kidneys filter toxins from the bloodstream. Urine that is produced in the kidneys flows through the ureters, which connect the kidney to the bladder. The bladder stores the urine until it is eliminated through the urethra, the tube that connects the bladder to the exterior, during urination. Typically, feline urine is yellow and clear and has a mild smell. It may be cloudy or bloody, however, if a urinary tract infection is present. Urine from tomcats (unneutered males) has a particularly strong odor.

Reproductive System

Reproductive System

The major parts of the male reproductive system are the testes, the scrotum, and the penis. The testes are located in the scrotum. The testes (also called testicles) produce sperm. Sperm production is influenced by testosterone, a hormone produced by the testicles. Testosterone also influences some male behaviors, such as territorial aggression. Normally, there are two testes present, which an examiner should be able to feel in the scrotum of a kitten by six weeks of age. However, sometimes neither testicle, or only one testicle, can be seen or felt in the scrotum. This condition is called cryptorchidism (crypt = hidden; orchid = testicle). If neither testicle is present, it is called bilateral cryptorchidism. This is very rare. More common is unilateral cryptorchidism, when only one testicle is present. When removing the testes during neutering, it is imperative that the veterinarian locate and remove the retained testicle(s) or else the cat will develop (or continue to exhibit) behaviors such as mounting and/or spraying. The urine will also continue to retain its characteristic pungent tomcat odor. Retained testicles also have an increased probability of becoming cancerous. Rough little spines called papillae protrude from the penis’s surface in intact male cats. These rough projections are responsible for stimulating the female cat to ovulate during mating. Neutering the cat causes the spines to disappear.

The major organs of the female reproductive tract are the ovaries, the fallopian tubes, the uterus, the vagina, and the mammary glands. The mammary glands run in two rows along the outside of the abdomen, from the groin to the chest. Cats typically have four or five pairs of mammary glands, which store and secrete milk. The ovaries, fallopian tubes, and uterus are located inside the abdomen. The right and left ovaries are situated just behind the kidneys. Ovaries produce eggs, as well as important hormones (estrogen and progesterone). The ovaries are connected to the uterus by small ducts called fallopian tubes (also called oviducts). The uterus is shaped like the letter Y, with the arms of the Y representing each uterine horn. The uterine horns extend from each ovary. The uterus is the site where fertilized eggs develop into fetuses. The uterus houses the fetuses until they are ready to be delivered. The base or stem of the Y represents the body of the uterus. The very tip at the base of the Y is the cervix. The cervix is a muscular tube that remains closed during pregnancy to prevent infection occurring in the uterus. During fertilization and birth, the cervix is relaxes and opens. The cervix separates the uterus from the vagina. The vagina provides a passage way from the outside of the body to the uterus. It also provides a protected passageway for the fetuses as they travel from the uterus to the outside during birth.

The kittens in a single litter can have different fathers.

Reproductive System
From The Cat Bible, Copyright by Sandy Robins, licensed through ContentOro, Inc and used by arrangement with I-5 Press

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