Within the bodies of all mammals, a complex network of glands (the endocrine system) is responsible for the production and secretion of special proteins and lipids (fats) called hormones. In turn, these hormones serve to regulate many vital functions within the body, from growth and development to digestion and utilization of nutrients. Like the nervous …

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The nervous system involves a complex interaction between special elements designed to originate or carry unique electrochemical charges to and from the various organs within the body. Like its endocrine counterpart, the nervous system initiates and regulates bodily functions and ensures its owner of an awareness to the surrounding environment. Anatomy and Physiology The smallest …

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The musculoskeletal system in mammals is responsible for locomotion, plus support and protection of vital internal organs. The components of this system include muscles, bones, and a variety of supportive structures, including ligaments, tendons, and cartilage. Disorders of the musculoskeletal system can be quite debilitating to a dog or cat and be accompanied by a …

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The sense of hearing in the average cat is much more fine-tuned than that of a human, allowing it to detect much higher sound pitches. The upper range of hearing is thought to be around 60,000 kilohertz for cats, well above the 20,000-kilohertz norm for people. Anatomy and Physiology The feline hearing apparatus can be …

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The skin, or integument, functions to protect the body from outside foreign invaders and from water loss. It provides a focus for the sense of touch and assists in the regulation of the temperature within the body. In addition, special modifications of the skin, such as claws and pads, provide a means of traction and …

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The question about what to do with the female cat that is accidentally bred is not an easy one to answer. In the old days, all that a pet owner needed to do was to take her in to the veterinarian for a “mismating” shot or pill. What these treatments consisted of were formulations of …

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Diseases and conditions involving the reproductive tract tend to be either infectious or anatomical in nature. Prompt medical attention is warranted in any disorder involving the reproductive tract. Anatomy and Physiology The Male Reproductive System Starting with the male cat, the major parts of the reproductive system include the testicles (with associated epididymis and ductus …

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In the normal, day-to-day functioning of the body, lots of waste material is formed as a result of metabolic activity. It is the function of the urinary system to handle and to rid the body of these waste products. In addition, through its ability to dilute or concentrate the urine, it serves to regulate fluid …

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The digestive system of the cat is made up of a collective network of organs designed to supply the body with the nutrition it needs for growth, maintenance, and repair. It also functions to rid the body of waste. Because of this, diseases involving the digestive system can have a profound effect not only on …

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Nasopharyngeal polyps are benign, pendulous masses that are associated with chronic ear infections in cats. These polyps normally arise within the throat region and extend into the latter part of the nasal cavity. They may grow to significant sizes and actually interfere with the normal flow of air into the trachea and respiratory airways, causing …

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Preventing the growth of cancer cells and tumors is also in its job description. Although the immune system serves a rough and rugged function, a delicate balance does exist as far as its activity is concerned.

Stress, poor nutrition, and hormone fluctuations are only some of the many factors which can deleteriously alter this activity, leading to a  weakened defense system. As if this weren’t enough, certain viruses, such as the canine parvovirus and the feline leukemia virus, have the ability to suppress the immune system.

Such an overwhelming upset of the body’s natural defense mechanisms can only lead to one outcome, and it isn’t good. This balance can be thrown the other way as well. There are certain disease conditions that can be caused by an overactive, overworking immune system. Allergies are a good example of this.

Allergic reactions can even turn deadly if the response is exaggerated enough. At other times the immune system, in carrying out its duties, will destroy or damage normal healthy tissue in the process.

These autoimmune diseases usually result from the body’s inability to turn off the immune response, with disastrous consequences.

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As a result, the function of all body systems, including the respiratory system itself, depends first on the ability of this system to deliver its product. In addition to this vital function, the respiratory system also serves as a means of thermoregulation.

Anatomy and Physiology

The respiratory system begins with the mouth and nose, which, under the influence of the breathing mechanism, facilitate the passage of air into the trachea. The wall of this cylindrical structure is lined with rings of tough cartilage which prevent it from collapsing during normal breathing activity.

The trachea enters the thorax, or chest cavity, and eventually branches into bronchi and smaller bronchioles within the lungs themselves. Thin membranes called pleura line the lungs and inner wall of the thorax.

Pleuritis is the term used to describe inflammation of these membranes, which can make normal respiration difficult and painful. The smallest unit of the respiratory system is the alveolus, located at the terminus of the bronchioles.

It is within these alveoli that gas exchange occurs between the lungs and the circulatory system. Surfactant (surface-active agent) is a special substance found lining the insides of normal alveoli. It is responsible for preventing alveolar collapse during the breathing cycle.

The major blood supply to the lungs and alveoli comes from the pulmonary artery originating from the right ventricle of the heart. In dogs and cats, heartworms reside in the right side of the heart and can effectively clog this artery and its branches supplying the lungs.

The resulting disruption of blood flow and increase in pulmonary blood pressure can have devastating consequences on respiratory function. The only air within the thorax, or chest cavity, is contained within the lungs.

As a result, a negative pressure system exists that facilitates normal breathing. Intake or inspiration of air occurs as the diaphragm, the large muscular band separating the thorax from the abdominal cavity, flattens and lowers itself, and the ribcage expands.

The resulting negative pressure caused by the increased thoracic size actively draws air through the trachea and into the lungs. On exhalation, or expiration, the diaphragm and ribcage are returned to their normal size, forcing air out of the lungs.

Pneumothorax is a life-threatening condition in which air is allowed into the thoracic cavity, either through a penetrating wound through the skin and ribcage or through a tear in the lung tissue.

Either way, the loss of negative pressure within the thorax quickly collapses the lungs, and renders the normal breathing mechanisms inoperable. Because of its direct exposure to a hostile environment, the respiratory system contains several defense mechanisms to help keep foreign invaders and particulate matter out of the lungs.

The sticky substance called mucus, produced by cells lining the trachea and bronchi, serves to trap contaminants and foreign debris that might gain external access to the respiratory system.

In addition, tiny, movable, fingerlike projections called cilia line the surface of airways and function to mechanically maneuver trapped contaminants in a direction away from the lungs. Any significant buildup of respiratory mucus or irritation to the respiratory lining results in a cough, and (hopefully) the forceful expulsion of any offending substance.

The airways are also lined with surface antibodies that provide a first line of defense against infectious organisms.

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The heart pumps blood around the body in two separate circuits. The pulmonary circuit takes stale, or deoxygenated, blood to the lungs to pick up oxygen. This freshly oxygenated blood then returns to the heart to be pumped around the body to all its organs and tissues in the larger circuit. Arteries have muscular walls that expand and contract as bright-red oxygenated blood surges through them with each heartbeat.

This creates a pulse that can be felt at various points of the cat’s body. Darker deoxygenated blood returns to the heart in thin-walled veins, which contain valves to maintain blood flow in one direction only.

A network of microscopic blood vessels called capillaries lies between the arteries and veins. Here, oxygen and other molecules, such as glucose, pass from the blood into surrounding cells and tissues. Wastes, such as carbon dioxide, pass in the opposite direction.

The brain makes up only 0.9 percent of a cat’s weight, but it receives up to 20 percent of blood flow. Muscles at rest receive 40 percent of blood flow, but this amount can rapidly increase to up to 90 percent during short bursts of exercise.

An averaged-sized cat of 11lb (5kg) has about 11fl oz (330ml) of blood in its body. By volume, blood is about 54 percent plasma, a watery liquid that carries food molecules such as glucose, salts, wastes, hormones, and other chemicals around the body.

Biconcave, disk-shaped red blood cells, which carry oxygen picked up from the lungs, account for another 46 percent of volume. The remaining 1 percent contains white blood cells, which fight infection, and cell fragments called platelets, which help blood clot at sites of injury.

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The highly flexible spine and maneuverable limbs allow a cat to reach most parts of its body when grooming with its paws, tongue, or teeth. Variances occur in body form among different breeds in cats but nowhere near the extent seen in dogs.

Skeleton

A cat skeleton, like that of all mammals, is a collection of bones connected by joints that allow different amounts of movement and are modified to suit its lifestyle as a carnivore. It provides a framework for the muscles that move the bones and also gives the cat its characteristic shape.

Other functions include the protection of delicate internal organs such as the heart and lungs. The skull contains the brain and houses the sense organs—eyes, ears, and nose—that, among other things, help the cat to detect prey effectively. The orbits are very large and often open posteriorly to allow for the powerful jaw muscles that attach to the skull just behind them.

The cat’s head can turn 180° to groom the back. The hyoid bone sits in the throat where it supports the tongue and voice box (larynx) and is thought to be involved in purring.  A cat has seven neck, or cervical, vertebrae—the same number as is seen in nearly all mammals, but it has a long back for its size, with 13 thoracic vertebrae to which the ribs are attached.

The number of vertebrae and their structure increases spinal flexibility, as does the size of the intervertebral spaces, which are occupied with pads of gristly cartilage and allow some movement between adjacent bones.

The tail, an extension of the spine, is made up of about 23 bones in most cat breeds and aids balance when climbing. The rib cage, connected to the spine in the chest region, protects the heart, lungs, stomach, liver, and kidneys.

The cat’s forelimbs are “floating”: the clavicle is greatly reduced in size and the shoulder blade is supported only by muscles and ligaments. This arrangement gives the shoulders a great range of movements and allows a cat to squeeze effortlessly through gaps wide enough to accommodate its head.

Like all carnivores, three of the wrist bones are fused into what is known as the scapholunar bone. It is thought to be an adaptation for climbing that appeared in the early ancestors of the group. Powerful, long hind limbs are attached to the pelvis with ball-and-socket joints and provide drive when running and pouncing.

A domestic cat’s skull is broad with a short nose. It is made up of 29 bones that fuse together as a cat matures and stops growing. The eye sockets, or orbits, are very large and face forward, which allow hunters to judge distance accurately when pouncing on prey.

The lower jaw of the cat is relatively short compared to their wild relatives, especially big cats such as the leopard and lion. It is connected to the skull by a hinge joint that limits movement to the vertical plane and is controlled by strong masseter muscles that provide a powerful bite so that a cat can maintain its hold on struggling prey.

Body form

The body form of different types of cat is remarkably uniform when you consider the range of shapes and sizes in dogs. This is partly due to the fact that their function was solely pest control, whereas dogs were used for many different purposes, such as hunting and herding; and partly due to the fact that the genes that control size are not as easy to manipulate.

There are, however, some feline exceptions, such as the tailless Manx and the short-legged Munchkin. The smallest cats, such as the Singapura, reach an adult weight of 4–9lb (2–4kg) and the largest breeds, such as the Highlander, range from 10–25lb (4.5–11kg). The adult weight among dog breeds, on the other hand, can range from 3–175lb (1–79kg).

The relatively large size of some of the new hybrid breeds may be influenced by the genes from their wild cat ancestors. For example, the Savannah is derived from a serval-domestic cat cross and the Chausie from a jungle cat-domestic cat cross. Some variety does occur, however, within the head and body shapes of domestic cats. Oriental breeds, such as the Siamese, tend to have a slender, highly sinuous build, long, thin limbs and tail, and a wedge-shaped head.

Western breeds, such as the British Shorthair, have a stocky shape, with a compact, muscular body, relatively short legs, a thicker tail, and a rounder head. Of course, many breeds, such as the Ragdoll, fall between these two extremes of body shape, and the head and body forms can be combined in different ways by the different cat breeders. Body forms also tend to vary around the world, depending on the climate of a region.

Most cats have a long tail, which they use for balance and communication. A few breeds, such as the Bobtail, have a short, stumpy tail or no tail at all.

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Disorders of the musculoskeletal system can be quite debilitating to a dog or cat and be accompanied by a lot of pain.

Anatomy and Physiology

The type of muscle involved in skeletal locomotion is termed striated muscle. This type of muscle is in contrast to the cardiac muscle found in the heart, and the smooth muscle found in many of the internal organs, both of which are under involuntary control by the nervous system.

Striated muscle consists of interlocking bands of cells capable of contracting with great force, thereby achieving movement. Tendons are those tough, fibrous bands that anchor the striated muscle to bone and allow this movement to occur. A strain is said to have occurred on injury to a muscle or a tendon.

The axial skeleton of the cat consists of the skull, the vertebrae, and the ribcage. The appendicular skeleton consists of the bones making up the front and hind limbs, as well as the pelvis.

Each type is made up of a hard mineralized matrix with bone cells interspersed within. The centers of most bones are hollow and filled with soft bone marrow. This substance is an important component of the host immune system as the location for white blood cell production.

Red blood cells and platelets, those structures involved in the blood- clotting scheme, are also produced exclusively within the bone marrow.

Bone is a dynamic tissue, constantly being reabsorbed and regenerated throughout the life of the individual. Long bones grow in length by means of a special structure called an epiphyseal plate, located at the ends of the bones.

It is interesting to note that overall health and growth patterns of bony tissue are very dependent on proper nutrition; malnutrition and vitamin or mineral deficiencies can wreak havoc on the development and/or integrity of the skeletal system.

A ligament is different from a tendon in that it connects bone to bone, not muscle to bone. Injuries involving ligaments are properly termed sprains.

A joint is the site at which two bones meet. Not all joints are movable, such as those making up the skull. However, for purposes of discussion, the types of joints referred to most often are called synovial joints.

These joints, found throughout the body, allow for free movement between bones and also serve a shock-absorbing capacity.

Each synovial joint consists of ligaments, cartilage on which the ends of the bones move or articulate, joint fluid designed to lubricate the joint and provide nutrition to the articular cartilage, and a tough, fibrous capsule surrounding it all.

In addition, some synovial joints contain special pads of cartilage, called menisci, which act as super shock absorbers. The knee joint, or stifle, is a good example of such a joint.

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The brain analyses information from stimuli gathered by the sensory organs, such as the cat’s eyes and ears, and from inside a cat’s body, too. It then makes changes by stimulating muscle activity or causing the release of chemical messengers called hormones that can alter body chemistry.

The anatomical structure of a cat’s brain is similar to that of other mammals. Its largest part, the cerebrum, governs behavior, learning, memory, and the interpretation of sensory information. It is divided into two halves, or cerebral hemispheres, each made up of lobes with their own functions.

The cerebellum, at the back of the brain, fine-tunes body and limb movements. Other structures within the brain include the pineal gland, hypothalamus, and pituitary body, which are also part of the endocrine system. The brainstem connects the brain to the spinal cord, which runs inside the vertebral column, or spine.

Cortical folding

A cat’s brain weighs up to about 1oz (30g), which is just under 1 percent of its total body weight. That’s relatively small compared to a human brain (2 percent of body weight) or even that of a dog (1.2 percent). The domestic cat’s brain is also about 25 percent smaller than that of its closest relative, the wildcat.

This reduction in size is mainly because the regions of a wildcat’s brain used to map an extensive hunting territory are no longer needed in the domestic cat, which gradually came to depend on humans for most of its food. The cerebrum of a cat’s brain has a higher degree of folding in its outer layer (cortex) than that of a dog.

Cortical folding significantly increases the amount of the cerebral cortex, which contains the cell bodies of neurons (also known as “gray matter”), allowing many more cells to be packed into the confined space of the skull.

A cat’s cerebral cortex contains about 300 million neurons. That is almost double the number in a dog’s cerebral cortex. A high degree of cortical folding is linked to increased brain processing and what we humans think of as intelligence.

Highly developed regions

The areas of the brain involved in interpreting sensory information are particularly well developed in cats. For example, the feline visual cortex, which receives input from the eyes, contains more neurons than the equivalent area of a human brain. Vision is a cat’s key sense when it hunts.

The regions that control paw movements and grip are also intricate, allowing cats to be surprisingly dextrous with their paws. They can use their paws almost like human hands when seizing and manipulating objects, such as items of prey and toys. This skill and other hunting behaviors, such as stalking, pouncing, and biting, appear to be hardwired into a cat’s brain.

Kittens instinctively begin to practice hunting when playing with their littermates, and indoor cats without access to wild prey will continue to hone their predatory skills on toys.

A cat’s brain has a built-in directional compass. A frontal area of the brain contains iron salts that are sensitive to the Earth’s magnetic fields. This compass helps cats navigate their territory and may also explain how some cats have managed to travel hundreds of miles back to their home after being moved away.

The cat’s brain also registers the different times of the day from the movement of the sun. From this internal clock, a cat soon learns when to appear each day for its dinner.

CNS and PNS

Together, the brain and spinal cord (which contains bundles of nerve fibers) are known as the central nervous system (CNS). The rest of the nervous system—nerve fibers branching off from the CNS and associated groups of cells called ganglia—is known as the peripheral nervous system (PNS).

The PNS connects the CNS with the limbs and body organs. Some nerve fibers of the PNS transmit electrical signals to the CNS for analysis; others carry signals in the opposite direction to cause a change in the body.

Some parts of the PNS are under voluntary, or conscious, control, such as the nerves that allow a cat to wave its tail to show annoyance or to pounce on a mouse; other parts of the PNS are involuntary, subconsciously affecting internal processes such as regulation of heartbeat or digestion.

Hormones

The nervous system works closely with the endocrine system. Hormones made by the pituitary gland in the brain control the production of many other hormones, including those regulating metabolism, response to stress, and sexual behavior.

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This energy is then used to power biochemical activities in cells. As air travels to and from the lungs, it passes through the larynx, the source of a cat’s vocalizations, including its purr.

The airways and lungs comprise the respiratory system. Air inhaled through a cat’s nose is humidified in the nasal passages and drawn along the trachea (windpipe), which branches into two air passages called bronchi, one for each lung.

Within the lungs, the bronchi divide into smaller tubes called bronchioles, which end in tiny air sacs called alveoli. Gas exchange occurs inside the alveoli. Oxygen diffuses across the thin walls of the millions of alveoli into tiny blood vessels called capillaries, where it is picked up by red blood cells. The waste gas carbon dioxide travels in the opposite direction, out of the blood and into the alveoli, to be exhaled.

At rest, cats breathe in and out about 20–30 times a minute. During exercise, when the muscles need more oxygen, the rate increases. Muscles between the ribs and a sheet of muscle below the rib cage, called the diaphragm, power breathing.

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The kidneys clean the blood, removing wastes and eliminating them from the body. Queens tend to give birth in spring and summer when food is likely to be plentiful for the kittens once they are weaned.

Cats have one of the narrowest diets of all carnivorous mammals. Their diet must include certain vitamins, fatty acids, and amino acids, as well as a chemical called taurine, which is found only in meat.

Cats cannot make these nutrients, or taurine, themselves nor get them from other sources of food, such as plants, and they cannot survive without them. Unlike vegetable matter, meat is relatively easy to break down into nutrients in the intestines.

Cats, therefore, have a relatively short, simple digestive tract compared to that of herbivores such as sheep and horses.

Digestion

The domestic cat’s digestive tract is a little longer than that of its wildcat ancestor. This suggests that the cat’s digestive system has been adapting to the increased plant matter in its diet (probably from scavenged scraps of human food containing both meat and cereal) since it first began to associate with humans several thousand years ago.

Kittens have 26 milk teeth, which erupt before 2 weeks of age and begin to fall out at about 14 weeks. Cats have 30 permanent teeth. Small incisors at the front of the jaws are used for grasping prey, while the canines, or fangs, kill prey by severing the spinal cord.

Cats cannot chew very well; instead, their back teeth chop up food into smaller pieces before it is swallowed. The carnassial teeth (the upper jaw’s back premolars and the lower jaw’s molars) are especially effective in slicing through food with a scissorlike action. When eating, the cat’s rough tongue—which is covered in little barbs—can rasp meat from the bones of prey animals.

Cats eat little and often. The transit of food—from eating to defecating—takes about 20 hours. The first stage of digestion is the physical breakup of food in the mouth by the teeth. The mouth produces saliva to lubricate the food, which, on being swallowed, passes down the esophagus into the stomach, where further physical digestion as well as some chemical breakdown by enzymes occurs.

The strong acid in a cat’s stomach is powerful enough to soften swallowed bones. (Any bones, hair, and feathers that cannot be digested are usually regurgitated later.)

Partly digested food leaves the stomach through the pyloric sphincter and enters the first section of the small intestine, the duodenum, where most of the chemical digestion takes place. Bile, produced by the liver and stored in the gall bladder, and a mix of enzymes from the pancreas enter this small loop of intestine and digest fats, proteins, and carbohydrates.

Nutrients are then absorbed across the wall of the small intestine into the bloodstream. They travel to the liver to be processed into useful molecules. Water is absorbed in the colon, and waste matter is passed out through the anus as feces.

Elimination of wastes

Besides solid feces, waste from the liver is processed by the kidneys. Their major role is to cleanse the blood, removing potentially harmful metabolic wastes, such as urea. The kidneys also control the composition and volume of fluids in a cat’s body.

Waste substances leave the kidneys, dissolved in water as urine. The urine flows along narrow ureters—one from each kidney—to be stored in the bladder. This balloon like organ holds up to 3½fl oz (100ml) of urine, which exits the bladder through the urethra. The urine of unneutered cats can be especially pungent and is used to mark territory and advertise sexual status.

Reproduction

Cats usually become sexually mature between 6–9 months, although in some Oriental breeds it may be earlier. As daylight hours increase during spring, hormonal changes in an unaltered female, or queen, make her receptive to finding a mate. She is then said to be “in heat” or “in season.”

She produces scents that attract intact males, or toms, and she may also call to them. Sexual intercourse is painful for the female. A tom’s penis has a band of 120–150 backward-pointing hooks that abrade the female’s vagina as he withdraws, causing her to yowl loudly and lash out. However, this does not seem to have a lasting effect because she mates many times while in heat, often with several toms.

The pain also triggers the release of eggs from the ovaries about 25–35 hours after the first mating. The eggs travel along the two “horns” of the uterus. The period of heat then eases off. If no pregnancy occurs, the queen will go into heat again a couple of weeks later. If mating is successful, pregnancy lasts for about 63 days. The average litter size is 3–5 kittens and can be as many as 10.

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The clinical signs of otitis media are essentially the same as those for otitis externa, with a few notable additions. Pets so afflicted will usually exhibit a head tilt toward the side of the affected ear. In severe cases, paralysis of the facial muscles on the side of the lesion might be seen as the nerves passing through the middle ear become involved.

This can result in a characteristic drooping of the eyelids, cheeks, and lips. In addition, a decreased tear production, pinpoint pupil, and protrusion of the third eyelid might be noted in the eye on the affected side.

If the infection extends from the middle ear into the inner-ear apparatus, the signs become even more pronounced.

Since the inner ear functions in maintaining balance and equilibrium as well as hearing, pets suffering from otitis interna tend to become very uncoordinated and might fall down frequently or move in circles toward the affected side.

A characteristic twitching of the eyeball, called nystagmus, also becomes more noticeable. Although the clinical signs seen are often diagnostic, radiographs of the skull are quite helpful at confirming a diagnosis of otitis media or interna and determining the extent of the disorder.

Therapy for otitis media or interna must be instituted promptly to prevent permanent damage to the hearing apparatus. Oral antibiotics should be started immediately. In cases of otitis interna, continued treatment with antibiotics might be required for up to 30 days to afford a complete cure.

In select cases, anti-inflammatory medications have been used to reduce signs associated with inflammation. If not already ruptured, the eardrum on the affected side is usually punctured to allow for thorough drainage of the middle-ear cavity and for the direct infusion of medications.

Of course, such treatment steps must be carried out in a veterinary hospital under heavy sedation or anesthesia. In tough, refractory cases, surgical placement of a drain in the bony tympanic bulla affords excellent exposure to the middle- and inner-ear spaces.

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