Discovering the Site of External Respiration: Where Does it Happen?

Discovering the Site of External Respiration: Where Does it Happen?

External respiration is an essential process for human beings to survive. We breathe in oxygen and breathe out carbon dioxide constantly, but have you ever wondered where this process takes place? In this article, we will explore the different sites where external respiration occurs in the body, as well as the mechanisms involved.

The Respiratory System: An Overview

Before we dive into the specific sites of external respiration, let’s take a look at the respiratory system as a whole. The respiratory system is responsible for the exchange of gases between the body and the environment. It consists of several organs, including the nose, pharynx, larynx, trachea, bronchi, lungs, and diaphragm. Each of these organs plays a crucial role in the respiratory process.

The Nasal Cavity: Where it All Begins

The respiratory process starts in the nasal cavity. The nasal cavity is lined with tiny hairs called cilia and mucus-producing cells. When we breathe in, the air is filtered by the cilia and mucus, trapping any dust, dirt, or other foreign particles. Additionally, the nose warms and humidifies the air before it reaches the lungs.

The Pharynx and Larynx: The Path to the Lungs

As the air leaves the nasal cavity, it enters the pharynx and then the larynx. The pharynx is a cone-shaped passageway located at the back of the nose and mouth that connects to both the esophagus and trachea. The larynx, also known as the voice box, is located at the top of the trachea and is responsible for producing sound.

The Trachea: A Tube Connecting the Larynx and Lungs

The trachea, or windpipe, is a tube that connects the larynx to the lungs. It is made up of cartilage rings and is lined with cilia and mucus-producing cells, just like the nasal cavity. The trachea branches off into two bronchi, one for each lung.

The Bronchi and Bronchioles: Bringing Air to the Alveoli

As the bronchi enter the lungs, they branch off into smaller and smaller tubes called bronchioles. The bronchioles end in small air sacs called alveoli. The alveoli are the primary site of gas exchange in the lungs, and where external respiration occurs.

The Alveoli: Where Gas Exchange Happens

The alveoli are small sacs located at the end of the bronchioles. They are surrounded by a network of tiny blood vessels called capillaries. When we breathe in, oxygen passes through the alveolar walls and into the capillaries, where it binds to hemoglobin in red blood cells. At the same time, carbon dioxide from our blood diffuses into the alveoli, ready to be breathed out.

The Diaphragm: The Muscle that Controls Breathing

The diaphragm is a large, dome-shaped muscle that separates the chest cavity from the abdominal cavity. It is the primary muscle used in breathing, contracting and relaxing to change the volume of the chest cavity and allow air to flow in and out of the lungs.

Respiratory System Disorders: What Can Go Wrong?

There are several disorders that can affect the respiratory system, including asthma, bronchitis, emphysema, and pneumonia. These conditions can affect the different organs involved in the respiratory process, making it difficult to breathe and reducing the efficiency of external respiration.

Asthma: A Chronic Inflammatory Disorder

Asthma is a chronic inflammatory disorder that affects the airways, causing them to become narrow and inflamed. This can result in difficulty breathing, wheezing, coughing, and chest tightness. Asthma can be triggered by various factors, including allergens, exercise, and stress. Treatment usually involves inhalers to open up the airways and reduce inflammation.

Bronchitis: Inflammation of the Bronchial Tubes

Bronchitis is an inflammation of the bronchial tubes, which can cause coughing, chest discomfort, and shortness of breath. It can be caused by viruses, bacteria, or environmental factors like smoking. Treatment usually involves rest, fluids, and in some cases, antibiotics.

Emphysema: Damage to the Alveoli

Emphysema is a condition in which the walls of the alveoli become damaged, leading to shortness of breath and difficulty breathing. It is usually caused by smoking or exposure to other harmful substances. Treatment may involve medication, oxygen therapy, and pulmonary rehabilitation.

Pneumonia: Infection of the Lungs

Pneumonia is an infection of the lungs that can cause coughing, fever, and difficulty breathing. It can be caused by viruses, bacteria, or fungi. Treatment usually involves antibiotics or antiviral drugs, and rest.


In conclusion, external respiration occurs primarily in the alveoli, which are located at the end of the bronchioles in the lungs. However, each organ in the respiratory system plays a crucial role in the respiratory process, from filtering out foreign particles in the nasal cavity to controlling breathing with the diaphragm. Understanding how the respiratory system works is essential for maintaining good respiratory health and preventing respiratory disorders.


  • Bailey, B. (2017). Anatomy and Physiology of the Respiratory System. Retrieved from
  • National Heart, Lung, and Blood Institute. (n.d.). How the Lungs Work. Retrieved from
  • Porth, C. (2015). Essentials of Pathophysiology. Wolters Kluwer.

Frequently Asked Questions

  • Q: Why is external respiration important?
  • A: External respiration is important because it is the process by which our bodies obtain oxygen and get rid of carbon dioxide, which are essential for proper cell function.
  • Q: What causes respiratory disorders?
  • A: Respiratory disorders can be caused by a variety of factors, including infections, allergies, environmental pollutants, and genetics.
  • Q: What is the difference between external and internal respiration?
  • A: External respiration is the exchange of gases between the body and the environment, while internal respiration is the exchange of gases between the blood and body tissues.

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