• 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

Organ Structure Function
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

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