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Although most of us learn how mammals breathe at school, I still get emails asking me to write an article, so here it is.

All mammals use a pair of lungs for breathing oxygen. Mammals need oxygen to survive, which is contained in the air. Marine mammals breathe air at the surface of the water, and the sperm whale can hold their breath the longest, allowing them to dive for up to 90 minutes. 

There are around 4500 species of mammals globally, with approximately 457 mammals living in the continent of North America.  Although mammals breathe differently, they all use lungs. Please read on to learn more about how mammals breathe on land and in the sea.

Respiratory system of the dog

Do All Mammals Have Lungs?

One of the crucial characteristics of mammals is that they breathe oxygen using their lungs. All mammals have lungs, including those living in the sea.

Lungs are used to inhale fresh air filled with oxygen to fuel the mammals’ bodies.  This air exhaled is filled with carbon dioxide. 

Though lungs come in different sizes and shapes for various mammals, all mammals have lungs, which are crucial for breathing. Whales, dolphins, and other underwater mammals use lungs as their breathing organ, not gills, which fish use to breathe.

Despite having the same use, the lungs of different kinds of mammals work differently and are designed to survive in their particular environment. 

Seals have lungs, which help them to stay underwater for long periods.  Predatory mammals like wolves and jaguars have lungs that help them run long distances to chase prey.  Bats have lungs designed to help them fly efficiently.

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Do All Mammals Breathe Through the Lungs?

All mammals breathe through their lungs. No matter how big or small the mammal is, they always use its lungs to inhale oxygen before exhaling carbon dioxide. 

Though their ability to take deep breaths or hold their breath differs from one mammal to another, all mammals use their lungs for breathing. Some mammals store oxygen more efficiently than others, despite breathing the same way as other mammals.

Seals are semi-aquatic marine mammals and store oxygen in their muscles and blood instead of in their lungs. This adaptation helps them to stay underwater for long periods. 

Seals breathe out when they dive into the water instead of holding their breath like other mammals. 

When underwater, seals rely on the stored oxygen in their muscles and blood, which helps them to sustain themselves underwater for a very long time. 

Not all mammals breathe in the same way. While some mammals breathe through their nose, some breathe through their mouth, and some use both.

There are four different groups of marine mammals.  Find out what they are in this article I wrote.

Breathing apparatus

How Does a Mammal’s Respiratory System Work?

All mammals need oxygen to survive, which can be found in the air around them.  The respiratory system helps mammals exchange crucial gases such as oxygen and carbon dioxide.  With the constant expulsion of carbon dioxide and oxygen intake, mammals take the necessary gases from the air, allowing them to live. 

Breathing system of the cat

While animals like fish and amphibians use their gills and moist skin to exchange gases, mammals use their lungs for breathing.

Mammals either breathe through the nose or the mouth.  The air is inhaled into the nose or mouth before passing into the pharynx.

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The pharynx is commonly known as the throat.  As part of the respiratory system, the air is inhaled through the mouth or nose and passed down through the animal’s throat.  The atmosphere is then passed to the trachea in the process.


The trachea, also known as the windpipe, is a tube that carries the air down from the pharynx to the lungs.  The trachea functions as a passage for air, warm and moistening, to protect the lungs from foreign particles.  This is achieved with the help of cilia.  The cilia are hairlike and run throughout the trachea, collecting the particles. This tube branches into two bronchi, where the air will be passed into the lungs.


Mammals possess two lungs, and the bronchi split the air to reach either of the two lungs.  The bronchi are made of muscle and cartilage to help prevent the trachea from collapsing.  The bronchi are lined with mucus that covers the rest of the respiratory system.  Most mammals, including humans, have a larger right bronchus than the left.  

The bronchus inside the lungs is divided further into five smaller bronchi.  These then provide air to the bronchioles.


While bronchi are passages for the air to enter the lungs, bronchioles are tiny branches into which the bronchus divides. Whereas the bronchi are made up of cartilage and muscle, the bronchioles are muscles and tissues lined with epithelium. 

The bronchioles are smaller airways carrying the air to the alveoli.  


Once the air moves from the bronchioles, it is passed to the alveoli.  Alveoli are at the end of the respiratory system, where the gas exchange occurs.  Blood, rich with carbon dioxide, is pumped into the alveoli, where oxygen is absorbed, and carbon dioxide is expelled. 

In the alveoli, the gases, oxygen, and carbon dioxide diffuse between blood and air.

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Ribcage during breathing


The respiratory system of almost all mammals works similarly to the way of a human’s respiratory system.  The air is moved with the help of the diaphragm.

The lungs of mammals are powered by a thin skeletal muscle called the diaphragm. The diaphragm pulls and pushes the lungs downwards and upwards.  The diaphragm pulls the lungs downwards to increase the volume of air in the lungs.  To expel the air, the diaphragm pushes upwards, and the lung’s capacity becomes smaller.  

The pressure between the chest cavity and the atmosphere determines the movement of gases inside and out of the lungs. 

Depending on factors like altitude and environment, mammals may breathe only through their mouth or nose occasionally. 

How do Mammals Breathe in Extreme Temperatures?

Many mammals live in environments with extreme temperatures.  These can range from extremely cold to scorching temperatures.  

Some mammals hibernate in the winter, with the arctic ground squirrel being an example of one of the few arctic animals that hibernate.  They live in Alaska and Canada, and their body temperature decreases to -3 degrees centigrade during hibernation.  

The heart rate drops to 1 bpm, and the blood reaches subzero temperatures.  The blood does not freeze as they cleanse their bodies of the particles that act as a nucleus for forming ice crystals.

Reindeer have adapted to cold environments where they live.  Reindeer breathe through their nose, adapted to warm the air as they breathe in.  This allows them to breathe in without hurting their lungs.  

Mammals have different adaptations in warm climates, such as in America’s plains and deserts.  

Mammals tend to be smaller in warmer climates and larger in colder climates.  As the animals are smaller, they lose their heat quickly and cool down faster.  In warm-blooded mammals, the heat loss is in proportion to their size.  The mammals in these environments are generally smaller, so the heat is lost quicker.

Want to know how wolverines survive?  Please find out more in this article I wrote. 

How Do Mammals Breathe Underwater?

No mammal can breathe underwater.  Mammals that live underwater have to expose their nostrils, usually on top of their heads, while resting at the top of the ocean to get oxygen from the air.

Dolphins, whales, and other sea mammals have complex respiratory systems like humans. As they use their lungs to breathe in oxygen from the air, they come to the ocean’s surface to inhale air and exhale carbon dioxide.

In the air around us, twenty percent is oxygen; In water, the oxygen concentration is less than one percent. The oxygen concentration in water depends on the depth, the temperature, and the amount of salt in the water. 

Fish breathe underwater with the help of gills, which helps pull the oxygen from water instead of from the air. However, unlike fish and other creatures that live and breathe underwater, ocean mammals cannot breathe the same way. 

Fish have gills that are high oxygen-catching membranes.  As mammals have lungs, the amount of oxygen in the water is insufficient, and they need to reach the surface to breathe through their lungs effectively.

Mammals living underwater exhale before breathing in to ensure no water gets into their lungs. 

To boost the oxygen in the lungs, the mammals living underwater hyperventilate intentionally, which helps increase the rate of losing carbon dioxide.

Marine mammals like dolphins and whales are voluntary breathers. This means they must remember to breathe, unlike other land mammals who automatically breathe. 

It doesn’t take long for marine mammals to come to the water’s surface and fill their lungs with oxygen.

Many marine mammals feed underwater.  Find out how here

Why do Whales and Dolphins Have Blowholes?

Marine mammals such as whales and dolphins do not have noses like humans. Instead of a nose to breathe in and out of, whales and dolphins have a blowhole on the top of their heads. They take the required oxygen from the air through the blowhole and exhale carbon dioxide. 

The muscles surrounding the blowhole ensure that it remains closed every time they go underwater.  The closure ensures that water can never get inside the lungs. 

Whenever they reach the surface and require oxygen, the muscles surrounding the blowhole open the hole again. Whales breathe warm air out of their blowhole, and a mist or spray can often be seen. The mist seen when a whale exhales comes not from its lungs but from the water collected on the top of its head.

When a whale exhales, the air is forced up, causing the water to be forced into the air.  This action ensures that no water gets into their lungs.

When dolphins inhale air through their blowholes, around 80% of the gas inside their lungs is exchanged with fresh air, which helps them hold their breath and stay underwater for up to 7 minutes.  

Humans can only exchange 17% of the air in their lungs with each breath. The speed at which dolphins can exhale air can be up to 100 mph, making it extremely quick for them to breathe at the surface. 

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Whale with 2 blowholes

Why do Some Whales Have Two Blowholes?

Some aquatic mammals, such as dolphins, killer whales, and beluga whales, have one blowhole on top of their heads.

However, baleen whales (whales without teeth), including blue whales, humpback whales, and mink whales, have two blowholes.

Due to their vast size, these whales need to absorb more surface oxygen than smaller, faster whales. The extra passageway allows them to breathe more air and hold their breath for much longer.

Baleen whales scoop up large amounts of food in one gulp rather than chasing their prey, so they need to stay underwater longer.

The sperm whale is the exception. The sperm whale can hold its breath for more than an hour and only has one blowhole.

Aquatic mammals have two passages to their lungs, as do humans. The lungs’ location is the same in both whales and humans.

Mammals, humans, and aquatic mammals have diaphragms in their respiratory systems. The ocean mammals’ blowhole functions similarly to a human’s mouth.

Which Mammals Can Hold Their Breath the Longest?

While humans and whales share similarities, it takes much longer for the marine mammals’ respiratory system to complete one cycle. 

An average human in good health can hold their breath for approximately two minutes, although the Guinness World Record was set in 2011 at over twenty minutes. Marine mammals can hold their breath the longest.

As they use their lungs to breathe oxygen, they have to surface above the water and collect enough oxygen for diving.

Unlike other mammals, marine mammals can hold their breath underwater for an extended period, despite not breathing underwater. 

Seals primarily live in the water and only come to the land to mate, give birth, or escape from natural predators such as sharks or killer whales. Seals can spend months at sea and can sleep underwater with the capability of holding their breath for around 2 hours.

While an elephant seal can hold its breath underwater for around two hours, dolphins can do this for about 7 minutes.  Fin whales can hold their breath for approximately 20 minutes, while sperm whales hold their breath for 90 minutes.

In 2014, a Cuvier-beaked whale held its breath underwater for around 2 hours and 17 minutes, breaking the previous record held by elephant seals.

Ever wondered how whales breastfeed underwater? Find out here in this article I have written.

Common Respiratory Issues

Several things can go wrong with the respiratory system of mammals. Just like humans, other mammals may also suffer from various breathing issues. 

The respiratory system of any mammal is vulnerable to both diseases and toxins. Just as humans are affected by pneumonia and asthma, mammals like horses and cats are prone to develop respiratory issues.

Which Mammals Have the Smallest and Largest Lungs? 

The blue whale has the largest lungs, holding up to five thousand liters.  The tiny little bumblebee bat, weighing only 2 grams, has the smallest lungs in a mammal.

Sea otters’ lungs are three times bigger than other mammals of the same body mass.

If you would like to know why mammals have hair, I have written an article you may find interesting. You can find it here.

References and Further Reading

“Respiratory Physiology: The Essentials” by John B. West

“Comparative Mammalian Respiratory Systems” by Mark Westneat

“Functional Anatomy of the Mammalian Respiratory System” by Michael J. Sanderson

“Respiratory Physiology of Newborn Mammals: A Comparative Perspective” by Richard G. Barratt

“Breathing and Respiration in Vertebrates” by Peter W. Hochachka and George N. Somero

“Mammalian Respiration: From Molecular to Integrative Physiology” edited by John R. West

“Control of Breathing in Mammals” by Michael T. Harris and Brian J. Whipp