Human Gas Exchange
Applied Science: BTEC Level 3 National Extended Diploma, topic 4.6.1
Structure
Human gas exchange takes place in specialised organs called the lungs. The lungs are specialised for the quick exchange of oxygen and carbon dioxide with the bloodstream.
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Structure
Trachea
- The trachea is the entrance to the human gas exchange system.
- When you breathe in, air flows through the trachea.
- Ridges of cartilage surround the front of the trachea to provide protection and structure.
- There is no cartilage at the back of the trachea so that the oesophagus (the tube where food travels) is not constricted.
Bronchi
- The trachea divides into two bronchi.
- Air flows along each bronchus to a lung.
- The bronchi are made from cartilage and smooth muscle.
Bronchioles
- Each bronchus divides into many smaller bronchioles.
- The many bronchioles branch throughout the the lungs into small air-sacs called alveoli.
Alveoli
- The alveoli are sacs that fill with air when you breathe in.
- Oxygen in the alveoli diffuses into the bloodstream and carbon dioxide in the bloodstream diffuses into the alveoli.
- There are millions of alveoli in the lungs
- The alveoli provide a large surface area for gas exchange.
Control of ventilation
- Ventilation is controlled by the ribcage, intercostal muscles and the diaphragm.
- When you breathe in, these structures move to allow the lungs to fill with air.
- When you breathe out, these structures move to allow air to leave the lungs.
Alveoli
Alveoli are the millions of air sacs within the lungs where gases are exchanged with the bloodstream. They provide a large surface area for gas exchange.
Capillaries
- Each alveolus is surrounded by a network of capillaries.
- The many capillaries provide a large surface area for gas exchange between the alveoli and the bloodstream.
Alveolar epithelium
- The epithelium is made up of a single layer of epithelial cells that line the walls of the alveoli.
- The epithelium provides a very short diffusion distance from the alveoli to the capillaries which maximises the rate of gas exchange.
Concentration gradient
- The capillaries supply carbon dioxide to the alveoli and oxygen is rapidly carried away from the alveoli.
- The quick transport of gases in the bloodstream maintains a steep concentration gradient of oxygen and carbon dioxide.
- The steep concentration gradient allows quick diffusion of gases into and out of the bloodstream.
Test yourself on Human Gas Exchange
Which of these is NOT a structure in the lungs?
Which of the following statements about the lungs are true?
Which of the following statements about alveoli are true?
What is the benefit of the single layer of epithelial cells in the alveoli for gas exchange?