• supplies oxygen to cells and removes carbon dioxide
  • defending the body against invasion of microorganisms
  • control the body’s blood pH


Ventilation (breathing) > inhalation and exhalation; take in oxygen and dispose of carbon dioxide

External Respiration > the exchange of gases between the alveoli and the blood

Internal Respiration > exchange of gases between the blood and tissue cells

Nasal cavity– lined with capillaries; warm air to 37°C- secrete mucus; moisten and filter air


– lined with cilia; filter out debris in the air

– warms, moistens and filters air entering the respiratory system
Pharynx – path that connects nasal cavity to the trachea
Epiglottis– a tiny flap of connective tissue– prevents food from entering the trachea during swallowing- prevents air from entering the stomach when breathing in
Larynx– made up of cartilage- contains the vocal cords; two highly elastic folds– to produce sound for communication
Trachea– a hollow tube surrounded by tough, flexible C-shaped cartilage rings- lined with cilia


– lined with mucus secreting cells

– allows air to pass from the pharynx into the lungs- cartilage rings prevent the trachea from collapsing and provide it with support
Lung– composed of the bronchi, bronchioles and alveoli– the main organs of the respiratory system
Bronchi– branch out of the trachea- hollow tubes surrounded by cartilage rings


– lined with cilia and mucus secreting cells

– to carry the air into the lungs
Bronchioles– branch out of the bronchi- large bronchioles secrete mucous and are lined with cilia– to decrease in size and carry air to the alveoli
Alveoli– clusters of tiny hollow air sacs; the ends of the smallest bronchioles- surrounded by an extensive network of capillaries


– very small structures with very high surface area

– are the sites of gas exchange

Respiratory Membrane

  • wall of alveoli and wall of capillaries come together for form a respiratory membrane
  • gas exchange occurs across the respiratory membrane

Gas Exchange

  • exchange of gases (O2 & CO2) between the alveoli & the blood occurs by simple diffusion
  • diffusion requires a concentration gradient
  • the surface of the alveoli must be moist so that diffusion can occur
author avatar
William Anderson (Schoolworkhelper Editorial Team)
William completed his Bachelor of Science and Master of Arts in 2013. He current serves as a lecturer, tutor and freelance writer. In his spare time, he enjoys reading, walking his dog and parasailing. Article last reviewed: 2022 | St. Rosemary Institution © 2010-2024 | Creative Commons 4.0


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