Respiratory System: Function, Parts, and Main Organs

2.11.2025 0 comments

Author: Trisha Houghton, CNS, ASIST

Every single cell in the human body needs oxygen to function, which makes your respiratory system one of the most crucial of your body systems.

The primary respiratory system function is to absorb oxygen from the air you breathe and expel carbon dioxide to get rid of waste gases released by your cells. However, you’ll find it also plays a number of other crucial roles in your body function overall.

In this post, we’ll take a deep dive into the respiratory system as a whole. We’ll look at which respiratory system organs get involved in the process, what the various parts of the respiratory system are, and how your respiratory system works to maintain homeostasis.

We’ll also look at a few of the more common disorders that impact your respiratory system and learn how to maintain good respiratory system health through a few simple daily practices.

Introduction to the Respiratory System

What is the respiratory system? It’s the system responsible for absorbing oxygen from the air you breathe.

Earth’s atmosphere is roughly 21% oxygen (along with argon, nitrogen, helium, methane, and many other gases). The respiratory system  facilitates gas exchange. 

It takes in the air we breathe out of that atmosphere, removes the carbon dioxide and disperses the pure oxygen into your bloodstream so your circulatory system can deliver it to your body’s cells.

Oxygen is needed by every cell in the human body. It’s crucial for the majority of cellular processes.

At the same time, the respiratory system eradicates carbon dioxide, a waste product that could become toxic to your body if not expelled.

It’s safe to say your respiratory system’s job is absolutely essential for not only optimal function, but basic survival.

Primary Functions of the Respiratory System

Here is what your lungs and respiratory system organs do:

• Gas Exchange: “Gas exchange” refers to the body’s process of exchanging oxygen and carbon dioxide. Oxygen is absorbed via inhalation and transported to the cells, while carbon dioxide “waste gas” is transported back to the lungs to be expelled via exhalation. This simple exchange facilitates cellular function and maintains homeostasis.
• Oxygen Supply: One of the main respiratory system functions is to absorb oxygen from the air you breathe and pass it on to the circulatory system to be delivered to the cells.
• Waste Elimination: Carbon dioxide is the natural byproduct of many cellular processes. If not expelled, the accumulation of carbon dioxide can be toxic to the human body. The respiratory system prevents toxicity by eliminating this waste gas.
• Sound Production: The respiratory system is also responsible for producing sound, both the words we speak and the other non-specific sounds that are crucial for communication. Air passing over your larynx (called your vocal cords) is what produces sound.
• Olfaction: The respiratory system also plays a role in olfaction, your sense of smell. As air moves through your nasal passages, it passes olfactory receptors that detect smells and transmit specific scent signals via the olfactory nerve to your brain to register.
• pH Balance: As mentioned above, too much carbon dioxide (CO2) in your blood can be toxic. The respiratory system prevents toxicity and regulates your blood pH levels by ensuring efficient elimination of the carbon dioxide that is a waste byproduct of cellular functions.

Given these vital functions, your respiratory condition is of primary importance for your overall well-being.

Main Respiratory System Parts

In order to understand the respiratory system work and principles, let’s first take a look at its primary parts and organs.

Nasal Cavity

Your nasal cavity is one of two openings of your upper respiratory tract through which air enters your body (the other being your mouth). The nasal cavity is connected to your sinuses, hollow spaces in your head that play a role in both the tone of your voice and regulating the temperature and humidity level of the air you breathe.

Your nasal cavity filters toxins from the air, and provides a hollow space where air can be warmed up before it passes on into your body. Cold air can be painful to the lungs and can cause bronchoconstriction in those who have respiratory conditions like asthma. By warming the air, it ensures your lungs can properly process it and absorb the oxygen.

Your nasal cavity is also lined with tiny hairs called cilia and mucus that traps particles to filter them from the air. The nasal cavity even regulates the amount of moisture present in the air that passes into your lungs to make breathing easier.

Finally, the olfactory receptors in your nasal cavity detect smells and pass electrical signals on to the brain.

Oral Cavity

Air can also enter the body through the mouth, especially for those who prefer mouth-breathing over nose-breathing. Mouth-breathing allows larger volumes of air to enter more quickly. This can be helpful during physical exertion or when nasal passages are blocked.

However, it bypasses the nose’s natural filtration and humidification processes. As a result, cooler, drier air and more irritants can reach the lower respiratory tract, including the trachea, bronchi, and lungs. This can affect how much air reaches the lungs efficiently and may increase the risk of respiratory irritation or infection.

Pharynx (Throat)

The pharynx (more commonly called the throat) is a passageway that allows air to flow from the nasal cavity and oral cavity into your trachea on its journey toward your lungs.

The pharynx is made up of three parts: 

• The nasopharynx, located behind your nose;
• The oropharynx, located behind your oral cavity (and which contains your tonsils);
• The laryngopharynx, also called the hypopharynx, located below your hyoid bone.

The pharynx connects your two air intakes into a single passage that ensures the filtered, warmed, properly humid air can reach your lungs efficiently.

Larynx (Voice Box)

The larynx, or voice box, is what produces sound. Air flowing over your vocal cords as you inhale and exhale causes the vocal cords to vibrate—a vibration you control—thereby producing what you know as sounds and forming words.

The top of the larynx is protected by the epiglottis, a flap of cartilage that keeps food and liquid from entering your airway, instead sending it down the esophagus (food tube to your stomach).

Trachea (Windpipe)

The trachea runs from the pharynx to your lungs. It provides a protected passage to pull air from your nose and mouth to pass into your lower respiratory system, and for air expelled from your lungs to leave your body via your nose and mouth.

The trachea is supported by cartilage rings that provide stability and structure.

Bronchi and Bronchioles

At the bottom, your trachea divides into the two bronchi, bronchial tubes that deliver air into each of your lungs.

The bronchi branch into smaller tubes, called bronchioles. The bronchioles end in air sacs called alveoli, which are the final destination of inhaled air.

Lungs and Alveoli

Your lungs are the primary organs of respiration. It’s here in the lungs that gas exchange takes place—where oxygen is extracted from the oxygen rich air you breathe in and carbon dioxide is infused into the air you breathe out.

The lungs are divided into lobes:

• The right lung has three lobes, the right upper lobe, right middle lobe, and right lower lobe.
• The left lung has only two lobes, the left upper lobe and left lower lobe. The left lung also contains the lingula, a small, tongue-shaped projection that functions similarly to one of the lobes.

These lobes are sponge-like tissue structures that absorb oxygen and expel carbon dioxide.

Thousands of tiny air sacs in the lungs called alveoli pull oxygen from the air into the bloodstream because your blood has less oxygen. Simultaneously, the alveoli takes the carbon dioxide that the body needs to get rid of which we then expel as we exhale.

Capillaries (tiny blood vessels) feed blood to the alveoli, where the carbon dioxide passes across a thin moisture film and into your alveoli. The waste gases are expelled, while the oxygen moves across the moisture film to be absorbed into your capillaries.

The circulatory system transports oxygen rich blood, in which oxygen is bound to hemoglobin in red blood cells and delivered to tissues throughout the body.

Diaphragm 

While the lungs work as the main organ of respiration, the diaphragm is the main muscle of respiration.

The diaphragm is a muscle sheet that passes beneath the lungs. When we exhale, the diaphragm relaxes and moves upward to reduce volume in the thoracic cavity. It then increases pressure to expel air out of the lungs. When we inhale, the diaphragm contracts to allow the lungs to expand and fill.

When we breathe, the respiratory system creates a pressure gradient that allows air to flow in and out of the lungs. It’s only because the diaphragm muscles contract and expand that we are able to inhale and exhale.

Intercostal Muscles

The intercostal muscles play a crucial role in respiration by elevating and depressing the ribs which helps the thoracic cavity expand and contract. 

Our rib cages are like protective bone shields that protect the lungs from impact and damage. They provide support for your chest wall and keep your various organs (including your lungs) in place.

However, because your lungs expand when you inhale, your rib cage needs some mobility to move and expand, too. The intercostal muscles located between the ribs facilitate this expansion when you inhale, and cause your rib cage to contract when you exhale.

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How the Respiratory System Works

Inhalation is triggered by a contraction of the diaphragm. This creates a negative pressure in the vacuum in your lungs that pulls air into your body, beginning at your oral and nasal cavities and passing through your pharynx, larynx, and down your trachea. The air fills your lungs, which expand to accommodate it.

Blood enters your lungs via the pulmonary arteries, carrying oxygen-poor blood from the heart to the lungs. These arteries branch into tiny capillaries that surround your alveoli allowing for gas exchange.

In the alveoli, carbon dioxide is extracted from the blood and oxygen is absorbed. The oxygenated blood exits your lungs via the pulmonary veins, transporting it back to the heart. Then the heart pumps it through the aorta to be delivered to your entire body.

Exhalation is triggered by the relaxation of the diaphragm muscles, which moves the diaphragm upward to reduce space in the chest cavity. This increases pressure in the lungs to propel the carbon dioxide-rich air back out your respiratory tract.

Regulation of Breathing

While most of the activity of respiration (what we call “breathing”) takes place in the lungs, there are other body parts that get involved in regulating the breathing process.

The respiratory center of your brain, located in the medulla oblongata (or brainstem), regulates your breathing rate, rhythm, and depth. It also triggers the protective responses intended to prevent damage to your lungs.

Chemoreceptors in both your brainstem and major blood vessels detect changes in your oxygen, carbon dioxide, and pH levels. When carbon dioxide levels rise or pH drops, they signal the brain to adjust the rate of your breathing to maintain homeostasis.

The cerebral cortex controls voluntary breathing, such as holding your breath, taking a deep breath, blowing, or speaking. It also works together with your brain stem to regulate involuntary breathing (though its role isn’t fully understood).

Common Respiratory System Disorders

Below you can find some of the most common diseases of the human respiratory system.

Asthma

Asthma is a chronic inflammatory condition that causes narrowing, swelling, and (sometimes) excess mucus production in the airways which leads to difficulty breathing.

It is usually triggered by allergens such as pollen, dust mites, pet dander, or mold spores. Other triggers include cold air, physical exercise, air pollutants, strong emotions, stress, sulfites, and preservatives. GERD and the common cold can also cause asthmatic attacks.

Asthmatic attacks can range from mild, causing shortness of breath or wheezing, to severe and life-threatening.

Chronic Obstructive Pulmonary Disease (COPD)

Chronic Obstructive Pulmonary Disease (also called COPD) is a progressive lung disease in which damage to the lungs causes swelling and irritation in the bronchi. This causes irreversible lung damage, chronic inflammation, which can limit airflow in and out of the lungs.

Symptoms may include wheezing and trouble catching your breath. You may also experience chest heaviness or tightness. An ongoing cough, which may produce mucus, is common. Lung infections may occur more frequently.

The most common cause of COPD is long-term exposure to cigarette smoke, chemicals, dust, or smoke fumes. Emphysema and chronic bronchitis are two types of COPD.

Pneumonia

Pneumonia is an infection caused by bacteria, fungi, or viruses which creates inflammation in the alveoli.

The infection in your alveoli may cause the air sacs to fill with pus or fluid, which may cause you to cough up phlegm or trigger chills, fever, and breathing difficulties.

Pneumonia can be caused by viral, bacterial, or fungal infections. These infections are typically contracted through community exposure, in hospitals, or in long-term care facilities. Pneumonia can also occur when you aspirate food, saliva, drinks, or vomit into your lungs.

Tuberculosis (TB)

Tuberculosis is an airborne bacterial infection that affects the lungs.

A primary TB infection is typically a low-symptom minor infection that the immune system is able to defeat, though some germs may still survive.

A latent TB infection is an infection that has been neutralized (the immune system builds a “wall” around the lung tissue that contains the TB germs). However, the germs survive and may cause infections in the future.

An active TB infection is an infection that has spread beyond the immune system’s ability to control. It can occur in the lungs or in other parts of the body because the germ-infected tissue has spread. It may happen immediately after a primary infection, but can sometimes happen months or years after latent infection.

Tuberculosis is dangerous because it can be not only highly contagious (germs spread in particles coughed up), but drug-resistant forms of the infection have emerged and spread in recent years. The good news is, it doesn’t spread as easily as viral infections like the flu, it typically requires prolonged close contact to contract, and not all forms are drug resistant.

Lung Cancer

Lung cancer is malignant cellular growth in the lung tissue. Changes to the lungs’ DNA alter the cellular reproduction and growth rate, causing cells to multiply out of control. This can lead to the formation of tumors (masses of cells) which invade and break down healthy body tissue.

Lung cancer is most commonly caused by smoking, though many people who are exposed to a lot of secondhand smoke also develop lung cancer. However, there are those who have never smoked or been seriously exposed to secondhand smoke that also develop lung cancer.

Other causes of lung cancer include exposure to radon gas, air pollution, workplace toxins, and genetic factors.

Sleep Apnea

Sleep apnea is a sleep disorder in which your breathing stops and starts frequently throughout the night, during sleep.

Obstructive sleep apnea (OSA) is when your throat muscles relax excessively and your airways are blocked.

Central sleep apnea (CSA) is when your brain fails to send proper signals to your lungs to regulate breathing. Treatment-emergent sleep apnea is when OSA turns into CSA over the course of treatment.

Sleep apnea is characterized by loud snoring and gasping for air during sleep. Other symptoms include morning headaches, excessive daytime sleepiness, difficulty concentrating, and episodes of stopped breathing while asleep.

Men are 2-3 times more likely to develop sleep apnea than women, although overweight women or women who have gone through menopause may also be at risk. Obesity, neck circumference, age, alcohol consumption, and family history all also play a role in the probability of developing sleep apnea.

Tips For Maintaining Respiratory Health

To keep your respiratory system healthy and well-functioning, keep in mind the tips provided in the paragraphs below.

Avoid Smoking

Smoking is the primary contributor to many different respiratory diseases, including lung cancer, COPD, and asthma. It may even put you at greater risk of bacterial infection.

If you smoke, quit now for your lungs’ sake. If you don’t smoke, try to avoid exposure to secondhand smoke as much as possible.

Exercise

Exercise strengthens the muscles in your respiratory system that support breathing, enhances the body’s ability to use oxygen, and aids in removal of carbon dioxide. It can also boost your immune system so you’re more protected against infection and respiratory conditions.

Try to exercise regularly, at least 4-6 times per week, for your respiratory health’s sake.

Mind Air Quality

If you live in a big city, try to live in an area with less exposure to air pollution.

Even if you live in the heart of dense urban areas, you can minimize your exposure to pollutants and allergens by cleaning up the air quality in your home (using an air filter).

Provide Hydration

Proper hydration facilitates the production of the mucus that lines your throat and lungs.

Drinking enough water will help your body keep the mucus in your respiratory tract thin and effective in protecting against infections. Aim for 2-3 liters of water per day.

Have Regular Check-Ups

Schedule regular check-ups and see your doctor if you notice common respiratory symptoms such as wheezing, breathing difficulties, coughing, or shortness of breath.

High-risk individuals should prioritize their respiratory health even more.

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Conclusion

It’s amazing just how important the respiratory system is for our overall health!

From absorbing oxygen to expelling wastes, producing sound to maintaining a proper chemical balance in our bodies, it’s one of the most crucial systems for efficient function.

To keep your respiratory system healthy and strong, adopt the lifestyle habits we shared above. Make it a goal to prioritize exercise, clean air, proper hydration, and frequent checkups to make sure your lungs are getting the protection they need against the threats they face every day.

FAQs

What is the difference between breathing and respiration?

Breathing is the involuntary mechanical process of inhaling and exhaling air, initiated by the diaphragm and intercostal muscles. Respiration is the biochemical process by which oxygen absorbed into the cells is used to break down glucose to produce cellular energy (ATP).

What is quiet breathing?

Quiet breathing, or eupnea, is a breathing mode that happens when your body is at rest, and doesn’t require cognitive thought but just happens on its own as controlled by your brain.

What muscles are used when coughing?

A lot of muscles get involved when we cough: the primary muscles used include the diaphragm, abdominal muscles, intercostal muscles, and laryngeal muscles..

How does air travel through the respiratory system to reach the lungs?

Air enters the body through the nose or mouth and passes through the pharynx and larynx, and down the trachea. The trachea splits into the left and right bronchi, which further branch into smaller tubes called bronchioles, making up the small airways. These bronchioles continue to divide and lead into tiny air sacs called alveoli, where gas exchange occurs. The entire process is regulated by pressure changes within the thoracic cavity, which houses and protects the lungs.

How does the respiratory system protect the lungs and maintain efficient breathing?

The diaphragm and intercostal muscles help expand and contract the chest for breathing, while the lungs elastic tissue allows them to stretch and recoil. Macrophages in the alveoli remove pathogens, and dry air is humidified in the nasal cavity and upper air way to protect lung tissue. The respiratory system uses mucus and cilia to trap and remove particles, keeping the airways clear.

Resources

Respiratory System

The Respiratory System

Respiratory system

Respiratory system

Respiratory System

human respiratory system

Introduction to the Respiratory System

Asthma

COPD

Pneumonia

Tuberculosis

Lung cancer

Sleep apnea

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