The respiratory system of dogs and cats

Breathing is an essential function of life, but it is just one function of the respiratory system in our pets. The respiratory system brings air into your dog or cat’s body, humidifies that life-giving air, heats it up and filters it, and then uses the components of that air to energise cells and balance the body’s pH levels. It then removes the resultant waste products. All of this is done involuntarily – your pet doesn’t have to think about breathing; it just happens.

In this article, we’ll explore the organs of the respiratory system, its specific functions, and how the respiratory system works. We’ll also look at what happens when parts of the respiratory system don’t work as they should – the signs and symptoms of respiratory disorder and diseases – and how the vet will diagnose and treat the most common respiratory disorders in pets. Lastly, what can you do to protect your pet’s respiratory system?

Organs of the respiratory system

The respiratory system comprises the upper and lower respiratory systems.

The upper respiratory system includes the:

nose
sinuses
pharynx (throat)

The lower respiratory system includes the:

larynx
trachea
bronchi
bronchioles
alveoli
lung tissue

What are the functions of the respiratory system?

In order to play its part, every cell in the dog or cat’s body requires oxygen. When the oxygen is used up, the cells produce carbon dioxide as a waste product. The function of the respiratory system, then, is to bring oxygen into the body (inhalation) and to remove carbon dioxide from the body (exhalation). This gas exchange occurs in the alveoli – sac-like structures in the lungs.

The respiratory system also has a number of secondary functions:

Producing sound – when air is pushed through the vocal cords, the result is sound, which the dog or cat uses to communicate.
Balancing the pH of the body – carbon dioxide binds to water and is circulated in the body as carbonic acid. The lungs help to expire (breathe out) enough CO2 to balance the body’s pH levels.
Thermoregulation – when dogs (and sometimes cats) overheat, they pant to cool down: exhaling warm air and inhaling cool air into the body to bring their body temperature down.
Sense of smell – chemicals in the air are inhaled, triggering the olfactory fibres lining the dog or cat’s nasal passages. The olfactory (smell) nerves are stimulated, sending sensory signals to the brain, which then interprets the source of the chemicals – i.e. it tells them whether they are sniffing roast chicken or picking up the scent of an intruder.

How does the respiratory system work?

There are three types of respiration that take place, as part of the function of the respiratory system:

External respiration involves air (containing oxygen) being inhaled into the lungs, which then transport the oxygen into the bloodstream where it is circulated in the body.
Internal respiration occurs when the oxygen and carbon dioxide are exchanged on a molecular level – the oxygen going into and being used up by cells and body tissues, and carbon dioxide being produced and migrating back into the bloodstream to be exhaled by the lungs.
Cellular respiration is the process that happens when oxygen and glucose are converted into energy at the cellular level.

The automatic or involuntary behaviour of breathing occurs thanks to the autonomic nervous system, whose function helps to regulate all systems in the body. Every cell in the body needs oxygen. This need for oxygen triggers an inhalation, in which air is taken into the lungs via the nose. It travels down the trachea (windpipe), is split between left and right bronchi, pulled into the bronchioles, and eventually reaches the alveoli – sac-like structures within the lungs. It is in the alveoli where the oxygen in the inhaled air passes into the one-cell-thick epithelial membrane and is transported in the bloodstream to the rest of the body. At the same time, carbon dioxide from the bloodstream crosses the alveolar membranes into the lungs, to be exhaled into the outside air.

During the physical process of breathing, air particles, dust, pollen, chemicals and other matter gets trapped in the nasal passages. Tiny finger-like structures called cilia, with the help of mucous, move these particles down into the pharynx to either be sneezed out, coughed out or swallowed. Any microorganisms that make their way into the lungs are blitzed by the immune response, to ensure the most efficient process of gas exchange takes place.

Common respiratory issues in pets

Dogs and cats can be particularly susceptible to upper and lower respiratory disorders, especially because they explore the world with their noses, sniffing and inhaling many things that are potentially harmful to them. Their respiratory system can be compromised by viruses, bacteria, fungi, trauma, overheating, tumours, inflammation, obstruction in the airways, and even secondary effects from other diseases in the body – such as pulmonary oedema or congestive heart failure.

Symptoms such as eye and nasal discharge, sneezing or congestion are typical of respiratory disorders in the upper airways, and are common in diseased cats, as well as in dogs in the early stages of distemper. Lower respiratory diseases are more common in sick dogs, although young and old dogs are particularly vulnerable to infection. Puppies are born with their respiratory system and immune systems only partially developed, making them susceptible to pathogens entering and compromising their lungs. Older dogs’ respiratory and immune systems are not as efficient as they were in filtering out harmful intruders and infection, also rendering them vulnerable to lung diseases.

Diseases and disorders of the respiratory system that pets present with in the veterinarian’s office can include:

Upper airway obstruction: If something gets stuck in your dog or cat’s nasal cavities, throat or trachea, it’s imperative to get it out as soon as possible, as this directly impacts the animal’s ability to breathe. Partial or complete obstruction both constitute a medical emergency and the vet must see to them as soon as possible.
Pneumonia: This disease occurs in dogs and cats infected by bacteria, viruses, parasites or fungi, which cause inflammation in the lungs. They can also aspirate (inhale) vomit or food particles, which should not be introduced to the lungs. Fatigue, lack of appetite, dry or wet cough, fever and breathing distress may all present.
Allergic pneumonitis: This is like pneumonia, except it’s caused by the pet’s immune system overreacting to an allergen, which affects and can even injure the lungs. This immune reaction causes white blood cells build up in the highly sensitive airway ‘branches’ in the lungs – the bronchioles and alveoli – which interrupt their ability to function properly.
Pulmonary oedema: Excessive fluid in or around the lungs of dogs and cats can make it very difficult for them to breathe and poses the risk of respiratory failure – a medical emergency. Pulmonary oedema is usually a symptom of a chronic condition such as congestive heart failure, trauma, infection (such as in pneumonia) or cancer. Its symptoms will all involve signs of difficulty breathing (like wheezing, open-mouthed breathing, coughing, noisy breathing) as well as lethargy, increased heartrate and ultimately, collapse. Treatment will depend on the cause, but if it’s caused by a chronic condition, careful, long-term management with medication, diuretics and a low-salt diet will be necessary.
Brachycephalic airway syndrome: Short-snouted dogs are at risk of experiencing any number of upper airway problems related to their anatomical characteristics. Stenotic nares are narrowed nostrils that affect how much air is inhaled. An elongated soft palate can partially block the tracheal opening and cause breathing difficulty. Hypoplastic trachea refers to a narrower trachea than is normal, and everted laryngeal saccules refer to pouches of the larynx that can also block the airway. Laryngeal collapse and extended nasopharyngeal turbinates also affect airflow in and out of the lungs. When brachycephalic dogs present with more than one of these conditions, it can make breathing exceptionally laboured for them and they may need surgery to fix these anatomical abnormalities and help them to breathe better.
Tracheal collapse: A genetic condition most common in older small and toy breed dogs, collapsed trachea involves the cartilaginous rings of the trachea becoming weak, and flattening when air is pulled into the trachea on inhalation. The most prevalent symptom is the goose-honk sound when the dog coughs; and a lack of exercise tolerance due to an insufficient intake of oxygen.
Bronchitis in dogs: Acute or chronic, bronchitis in dogs occurs when the trachea and bronchial airways become inflamed. In the long term, the inflammation can progress into the lungs and even cause pneumonia – the two diseases are often difficult to differentiate. The symptom most often seen in canine bronchitis is intense spasms of coughing. When bronchitis is caused by viruses or bacteria and is easily communicable in large populations of dogs in close confines, it is likely to be infectious tracheobronchitis – or kennel cough.
Canine influenza: Despite its name, canine influenza can be found in dogs and cats. It’s caused by the H3N8 or H3N2 viruses, and presents as a persistent cough, high temperature (fever), eye and nasal discharge, lack of appetite, and fatigue. Cats will present with the additional symptoms of sneezing, lip smacking, and excessive salivation. Some pets will show no symptoms, some will show mild symptoms and some will go on to develop pneumonia. The vet will offer supportive treatment and pets will need to be isolated from other healthy pets for up to four weeks after recovery.
Laryngitis: Inflammation of the larynx (vocal cords) can be caused by infection in the upper airways, dust, foreign material, excessive barking, and even from the placement of a breathing tube during a surgical procedure. Other health issues like cancer, heart disease or hypothyroidism can also cause swelling in the larynx. The most obvious symptom is a hoarse voice; accompanied by other symptoms such as a persistent cough, halitosis, raspy breathing, fever, and loss of appetite. If laryngitis is mild, the pet can recover at home with rest and water. For more severe symptoms, the vet may treat the disease with antibiotics, anti-inflammatories, cough suppressants and pain medication. Where swelling from the laryngitis poses a threat to the animal’s ability to breathe, the vet may need to place a tracheotomy tube through the neck to enable the animal to breathe while the laryngitis is being treated.
Rhinitis and sinusitis: Inflammation of the mucous membranes (rhinitis) and nasal and sinus cavity membranes (sinusitis) in dogs and cats are most often caused by viral, bacterial or fungal infection. Sinusitis can also be caused by a dental abscess in the upper fourth premolar; while the inflammation in both conditions can also be caused by an allergic response. The symptoms include sneezing, eye and nasal discharge, reduced appetite, facial swelling, noisy breathing, halitosis, pain when moving their head, and lethargy. Treating sinusitis and rhinitis will involve finding and treating the underlying cause, and managing the symptoms.

When should you see a vet about your pet’s respiratory system?

It is painful and uncomfortable and potentially life-threatening for pets to contend with diseases and disorders of the respiratory system, or obstruction in any of their respiratory organs. If you notice your dog or cat develops a discharge from their nose or eyes, a persistent cough, laboured breathing or a rapid heartrate, take them to the vet as soon as possible.

If your pet has recurring infections or something just doesn’t seem quite right with their breathing, sleeping, exercise ability or appetite – all of these symptoms warrant quick action to treat your pet’s respiratory trouble.

How do you take care of your pet’s respiratory system?

Pets can’t be taught to breathe more efficiently, not sniff the ground, or keep a distance from other animals in order to protect their respiratory system. However, there is a lot you can do to ensure your pets don’t contract respiratory diseases.

Vaccinate your pets

Many bacterial and viral infections attack the respiratory system, are highly contagious and can cause severe illness and death in dogs and cats. Vaccination is the quickest, easiest and cheapest method that all pet owners can (and should) use to protect your pets from respiratory diseases. Make sure puppies and kittens get vaccinated at the correct intervals in their first two years, and top up their schedule with annual or triennial boosters.

Notice the symptoms

If your dog or cat gets sniffly or sneezy, or they develop a cough, don’t wait to see if it resolves itself. Take your pet to the vet as soon as possible to get an accurate diagnosis and timeous treatment for any respiratory illness.

Be cautious of large groups of dogs, or stray cats

Whether your dog attends doggy daycare, puppy school, or needs to be boarded from time to time, be aware that there may be an unvaccinated or infectious member/s of the furry friend group that could put the other dogs at risk. If yours is the pup with the sniffles, rather keep your dog isolated until the vet gives you the all-clear. Similarly, keep your cats safe from exposure to unvaccinated and sick stray cats.

Know your pet’s health status

As mentioned above, it’s not just pets with respiratory diseases who need to be protected. If your dog or cat is brachycephalic (with a short snout), know the breed’s risks for health conditions and monitor them very closely; don’t exercise them in the heat of the day, and keep them away from any risks that could cause inflammation and swelling in organs of the respiratory system. Reduce their exposure to allergens, and train them not to chew on or swallow foreign objects. Always supervise their play sessions to prevent the possibility of swallowing something that could end up causing a tracheal or respiratory blockage.

Similarly, pets who are prone to heart disease, hypothyroidism, cancer, etc. can develop respiratory disorders as a symptom of their chronic disease. Keep an eye on their symptoms and notify the vet of any changes in their breathing.

If you have any questions or concerns about your pet’s respiratory health, don’t hesitate to contact the vet for clarity and help.