The Respiratory System

Respiratory System

The respiratory system is made up of organs and tissues that help you breathe. The main parts of this system are the airways, the lungs, linked blood vessels, and the muscles that enable breathing.

When the respiratory system is mentioned, people generally think of breathing, but breathing is only one of the activities of the respiratory system.

The body cells need a continuous supply of oxygen for the metabolic processes that are necessary to maintain life.

The respiratory system works with the circulatory system to provide this oxygen and to remove the waste products of metabolism. It also helps to regulate the pH of the blood.

Respiration is the sequence of events that results in the exchange of oxygen and carbon dioxide between the atmosphere and the body cells.

Every 3 to 5 seconds, nerve impulses stimulate the breathing process, or ventilation, which moves air through a series of passages into and out of the lungs.

After this, there is an exchange of gases between the lungs and the blood. This is called external respiration. The blood transports the gases to and from the tissue cells. The exchange of gases between the blood and tissue cells is internal respiration.

Finally, the cells utilize the oxygen for their specific activities: this is called cellular metabolism, or cellular respiration. Together, these activities constitute respiration.

Airway Components

The Upper Respiratory Tract

  • Airways
  • Frontal Sinus
  • Sphenoid Sinus
  • Nose and Mouth
  • Pharynx (Throat)
  • Larynx (Voice Box)
  • Epiglottis
  • Cilia

The Lower Respiratory Tract

  • Trachea (Windpipe)
  • Bronchus (plural is Bronchi)
  • Bronchi
  • Bronchioles
  • Alveolar Ducts
  • Alveoli
  • Lobes
  • Fissures
  • Pleura
  • Bronchial Tree
  • Lungs

The Upper Respiratory Tract


Within the respiratory system are pipes that carry oxygen-rich air to the lungs. They also carry carbon dioxide, a waste gas, out of the lungs.

Frontal Sinus

A type of paranasal sinus (a hollow space in the bones around the nose). There are two, large frontal sinuses in the frontal bone, which forms the lower part of the forehead and reaches over the eye sockets and eyebrows.

The frontal sinuses are lined with cells that make mucus to keep the nose from drying out.

Sphenoid Sinus

A type of paranasal sinus (a hollow space in the bones around the nose). There are two large sphenoid sinuses in the sphenoid bone, which is behind the nose between the eyes.

The sphenoid sinuses are lined with cells that make mucus to keep the nose from drying out.

Nose and Mouth

Air first enters your body through your nose or mouth, which wet and warm the air (because cold, dry air can irritate your lungs).

Pharynx (Throat)

The hollow tube inside the neck that starts behind the nose and ends at the top of the trachea (windpipe) and esophagus (the tube that goes to the stomach). The pharynx is about five inches long, depending on body size.

Larynx (Voice Box) and Trachea (Windpipe)

From the pharynx, the air then travels through your larynx (or voice box) and down your trachea (windpipe).

Epiglottis (Adam’s Apple)

A thin flap of tissue called the epiglottis covers your windpipe when you swallow. This prevents food and drinks from entering the air passages that lead to your lungs.


Except for the mouth and some parts of the nose, all the airways have special hairs called cilia that are coated with sticky mucus.

The cilia trap germs and other foreign particles that enter your airways when you breathe in air. These fine hairs then sweep the particles up to the nose or mouth.

From there, they’re swallowed, coughed, or sneezed out of the body. Nose hairs and mouth saliva also trap particles and germs.

The Lower Respiratory Tract


The trachea, commonly called the windpipe, is the main airway to the lungs. It divides into the right and left bronchi at the level of the fifth thoracic vertebra, channelling air to the right or left lung.


The trachea splits into two bronchi (a left and a right).

Bronchi (Plural of Bronchus)

Each main bronchus subdivides into smaller airway passages referred to as bronchi.


Within the lungs, the bronchi branch into thousands of smaller, thinner tubes called bronchioles.

Alveolar Ducts

As the bronchioles proceed further into the lungs, they become thinner and develop into alveolar ducts.


The alveolar ducts end in tiny round air sacs that contain clusters of cup-shaped alveoli. Each of these air sacs is covered in a mesh of tiny blood vessels called capillaries.

The alveoli are the centre of the respiratory function of the lungs. The pulmonary artery and its branches deliver blood rich in carbon dioxide (and lacking in oxygen) to the capillaries that surround the air sacs.

Inside the air sacs, carbon dioxide moves from the blood into the air. At the same time, oxygen moves from the air into the blood in the capillaries. The oxygen-rich blood then travels to the heart through the pulmonary vein and its branches. The heart pumps the oxygen-rich blood out to the body.


The lungs consist of five lobes. Each lung receives air from its own bronchus. The right lung has three lobes and the left has two. The left lung has a superior and inferior lobe. The right lung has superior, middle, and inferior lobes.

Each lobe is separated from the other by fissures (partitions) to protect against disease or mechanical injury.

Though some people need to have a diseased lung lobe removed, they can still breathe well using the rest of their lung lobes.


The thin walls of tissue that separate the different lobes.


A double-layered membrane that encloses each lung. It also lines the chest cavity. The small space between the layers of the pleura is called the pleural cavity. It contains a thin film of fluid that is produced by the pleura.

The fluid acts as a lubricant to reduce friction as the two layers slide against each other, and it helps to hold the two layers together as the lungs expand during inhalation, and contract during exhalation. The pleura also provides protection against disease.

Bronchial Tree

  • The combination of:
  • the trachea
  • the two primary bronchi
  • the alveolar ducts
  • the alveolar sacs
  • the alveoli, located at the end of the bronchial tree.
  • The entire bronchial tree has a covering of veins and arteries that go into and out of the lungs.


  • The lungs and linked blood vessels deliver oxygen to and remove carbon dioxide from your body.
  • They are the major organs of the respiratory system and are divided into two sections called lobes. The right lung is slightly larger than the left lung and has three lobes. The left lung has two lobes.
  • The lungs are soft and spongy because they are mostly air spaces surrounded by the alveolar cells and elastic connective tissue.
  • They are separated from each other by the mediastinum (the area that contains the heart, trachea, esophagus, and many lymph nodes).
  • The trachea, which begins at the edge of the larynx, divides into two bronchi and continues into the lungs.
  • The bronchi divide into smaller bronchioles, which branch out in the lungs forming passageways for air.
  • The terminal parts of the bronchi are the alveoli. 
  • The alveoli are the functional units of the lungs and they form the site of gaseous exchange (delivering oxygen to, and removing carbon dioxide from your body).

Pulmonary Blood Vessels

Pulmonary Artery

The pulmonary artery and its branches deliver blood rich in carbon dioxide (and lacking in oxygen) to the capillaries that surround the alveoli.

Inside the alveoli, carbon dioxide moves from the blood into the air. At the same time, oxygen moves from the air into the blood in the capillaries.

Pulmonary Vein

The oxygen-rich blood then travels to the heart through the pulmonary vein and its branches. The heart pumps the oxygen-rich blood out to the body.

Muscles Used for Breathing

Muscles near the lungs help expand and contract the lungs to allow breathing. Muscles in your neck and collarbone area help you breathe in when other muscles involved in breathing don’t work well, or when lung disease impairs your breathing.


A dome-shaped muscle located below your lungs separates the chest cavity from the abdominal cavity. The diaphragm is the main muscle used for breathing.

Intercostal Muscles

Located between your ribs, they also play a major role in helping you breathe.

Abdominal Muscles

Beneath your diaphragm, they help you breathe out when you’re breathing fast (for example, during physical activity).

Upon Inhalation

When you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. This increases the space in your chest cavity into which your lungs expand.

The intercostal muscles between your ribs also help enlarge the chest cavity. They contract to pull your rib cage both upward and outward when you inhale.

As your lungs expand, the air is sucked in through your nose or mouth. The air travels down your windpipe and into your lungs. After passing through your bronchial tubes, the air finally reaches and enters the alveoli (air sacs).

Through the very thin walls of the alveoli, oxygen from the air passes to the surrounding capillaries (blood vessels). A red blood cell protein called haemoglobin helps move oxygen from the air sacs to the blood.

At the same time, carbon dioxide moves from the capillaries into the air sacs. The gas has travelled in the bloodstream from the right side of the heart through the pulmonary artery.

Oxygen-rich blood from the lungs is carried through a network of capillaries to the pulmonary vein. This vein delivers oxygen-rich blood to the left side of the heart.

The left side of the heart pumps the blood to the rest of the body. There, the oxygen in the blood moves from blood vessels into surrounding tissues.

Upon Exhalation

When you breathe out or exhale, your diaphragm relaxes and moves upward into the chest cavity. The intercostal muscles between the ribs also relax to reduce the space in the chest cavity.

As the space in the chest cavity gets smaller, air rich in carbon dioxide is forced out of your lungs and windpipe, and then out of your nose or mouth.

Breathing out requires no effort from your body unless you have a lung disease or are doing physical activity. When you’re physically active, your abdominal muscles contract and push your diaphragm against your lungs even more than usual. This rapidly pushes air out of your lungs.

Respiratory System Injuries and Conditions

Respiratory Conditions


Struggling for air, difficulty breathing, laboured breathing.


A lack of air going into the lungs due to blockage of the air passage.


Acute or chronic inflammation of the bronchial tubes, which are the airways that lead to the alveoli in the lungs. Results in reduced airflow, mucus build-up, and persistent coughing.

Asthma (Bronchial Asthma)

Episodes of breathing difficulty and wheezing while breathing out. The condition is more accurately referred to as bronchial asthma because it differentiates the condition from the wheezing that is associated with heart failure.

When wheezing is associated with heart failure, it is more accurately referred to as cardiac asthma.

Exercise-Induced Asthma

For the asthma sufferer, exercise may trigger an asthma attack due to the body’s increased demand for oxygen.


In cases where an asthma attack is very severe, the individual may suffer from a very low amount of oxygen in the blood, which causes a blue-purple discoloration of the face, especially the lips. This discoloration is referred to as cyanosis.

Additionally, the individual may also suffer from pale and clammy skin.

Chronic Obstructive Pulmonary Disease (COPD)

Asthma, bronchitis, and emphysema are examples of chronic obstruction of airflow.


A serious chronic disease of the lungs in which there is damage to, or loss of, the air sacs (alveoli), which results in a shortness of breath.

In more severe cases, this condition can lead to respiratory failure or heart failure, which can lead to death.

Breathing Abnormalities

Valsalva Maneuver

A condition caused by holding one’s breath while straining during the performance of an exercise. It is a phenomenon that increases pressure within the chest region and also raises blood pressure.

It is especially dangerous for people with high blood pressure. Always exhale through the mouth during exertion.


Excessive swallowing of air.


Abnormally rapid breathing usually resulting from an anxiety or panic attack. Other causes of hyperventilation can occur from diabetes mellitus, pulmonary edema, emphysema, or renal failure.

Hyperventilation results in an abnormal loss of carbon dioxide in the blood and may also cause alkalosis, which is an increase in the alkalinity level in the blood. The typical symptoms are dizziness, feeling faint, numbness or tingling in the extremities, and feeling that breathing is difficult.

The alkalosis associated with hyperventilation worsens the existing condition of anxiety to such a level that the individual has a sense of impending doom.

To counter the effects of hyperventilation, it is recommended that an individual breathe into a paper bag so as to increase the level of carbon dioxide in the blood and also to prevent the risk of alkalosis.

Leave a Comment