Respiratory system

Introduction
The gases in the environment
Basic types of respiratory structures
- Respiratory organs of invertebrates
  - Trachea
  - Gills of invertebrates
- Respiratory organs of vertebrates
  - The gills
  - The lung
Dynamics of vertebrate respiratory mechanisms
- Fishes
- Amphibians
- Reptiles
- Birds
- Mammals

References & Edit History Quick Facts & Related Topics

Images & Videos

Illustration showing different animals and their respiratory organs: a spider with book lungs, a chicken with lungs, a sponge with labeled inflow and outflow pores, a fish with gills, and a caterpillar with spiracles.

A swimmer wearing goggles and a swim cap turns their head to breathe while swimming in open water, emphasizing the act of breathing during exercise.

Diagram of a grasshopper with its respiratory system highlighted, showing labeled spiracles and internal tracheal tubes that deliver air throughout the insect's body.

Observe ciliated cells throughout the human respiratory system

At a Glance

respiration summary

Quizzes

3d illustration human heart. Adult Anatomy Aorta Black Blood Vessel Cardiovascular System Coronary Artery Coronary Sinus Front View Glowing Human Artery Human Heart Human Internal Organ Medical X-ray Myocardium

Human Organs

Superficial arteries and veins of face and scalp, cardiovascular system, human anatomy, (Netter replacement project - SSC)

The Human Body

Related Questions

How do bronchi branch into bronchioles inside the lungs?
How do bronchi warm, moisten, clean, and distribute inhaled air?
How do cilia and mucus protect the trachea from dust and other particles?
How do elastic and collagen fibres support the walls of alveoli?
How do mucus and cilia in the nasal cavity trap inhaled particles?
How do the auditory tubes connect the nasopharynx to the middle ears?
How do the cartilage rings keep the trachea open?
How do the diaphragm and ribs support the lungs during breathing?
How do the external intercostal muscles move the ribs during inhalation?
How do the nasal conchae, also called turbinates, shape airflow in the nasal cavity?
How do the paranasal sinuses reduce skull weight and affect the voice?
How do the pleural membranes cover the lungs and chest wall?
How do the right and left main bronchi differ in size, length, and direction?
How do the vocal cords in the larynx produce sound?
How do thin alveolar walls help oxygen and carbon dioxide move between air and blood?
How does an enlarged pharyngeal tonsil interfere with nasal breathing?
How does carbon dioxide move from the blood into the alveoli?
How does coughing help remove foreign material from the trachea?
How does oxygen move from the alveoli into the blood?
How does pleural fluid help the lungs move during breathing?
How does pulmonary surfactant prevent alveoli from collapsing?
How does smooth muscle in the bronchial walls change airway diameter?
How does the diaphragm change the size of the chest cavity during inhalation?
How does the epiglottis direct food toward the esophagus during swallowing?
How does the nasal septum divide the nasal cavity?
How does the nose filter, warm, and moisten inhaled air?
How does the olfactory region in the roof of the nose detect smells?
How does the pharynx serve both the respiratory and digestive systems?
How does the soft palate separate the nasopharynx from the oropharynx?
How many alveoli are found in an adult human lung?
How many major lobes does the right lung have?
What are the three sections of the pharynx?
What enters and leaves each lung at the hilum?
What role do nasal hairs called vibrissae play in the nose?
What roles do type I and type II pneumocytes play in the alveoli?
What route does air follow from the nostrils to the alveoli?
Where are the lungs located within the thoracic cavity?
Where are the paranasal sinuses located in the skull?
Where does the trachea divide into the two main bronchi?
Where is the larynx located in relation to the pharynx and trachea?
Which organs make up the human respiratory system?
Why are inhaled foreign objects more likely to enter the right main bronchus?
Why are the cartilage rings of the trachea incomplete at the back?
Why does swallowing help equalize pressure in the middle ears?
Why does the left lung have fewer lobes than the right lung?

Health & Medicine Anatomy & Physiology

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External Websites

National Heart, Lung, and Blood Institute - The Respiratory System
Cleveland Clinic - Respiratory System
Nemours KidsHealth - For Parents - Lungs and Respiratory System

Britannica Websites

Articles from Britannica Encyclopedias for elementary and high school students.

respiration - Children's Encyclopedia (Ages 8-11)

Respiratory system

anatomy

Also known as: airway, respiratory tract

Written by

Warren W. Burggren

Professor of Biological Sciences, University of Nevada, Las Vegas. Editor, Physiological Zoology. Coeditor of New Directions in Ecological Physiology.

Warren W. BurggrenAll

Fact-checked by

Britannica Editors

Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....

Britannica Editors

Last updated

Nov. 6, 2026 •History

Respiratory system, the system in living organisms that takes up oxygen and discharges carbon dioxide in order to satisfy energy requirements. In the living organism, energy is liberated, along with carbon dioxide, through the oxidation of molecules containing carbon. The term respiration denotes the exchange of the respiratory gases (oxygen and carbon dioxide) between the organism and the medium in which it lives and between the cells of the body and the tissue fluid that...

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