The Breathing System (Cambridge (CIE) O Level Biology): Revision Note
The Breathing System
The Human Breathing System Diagram
Structures in the human breathing system
Organs of the breathing system table
Structure | Description |
|---|---|
Ribs | The bone structure that protects internal organs such as the lungs |
Intercostal muscles | Muscles between the ribs control their movement causing inhalation and exhalation |
Diaphragm | Sheet of connective tissue and muscle at the bottom of the thorax that helps change the volume of the thorax to allow inhalation and exhalation |
Trachea | The windpipe that connects the facial airways (mouth and nose) to the lungs. It is supported by C-shaped rings of cartilage |
Larynx | Also known as the voice box, when air passes across here we are able to make sounds |
Bronchus (plural: bronchi) | Large tubes branching off the trachea with one bronchus supplying each lung |
Bronchioles | Bronchi split to form smaller tubes called bronchioles in the lungs connected to alveoli |
Alveolus (plural: alveoli) | Tiny air sacs where gas exchange takes place |
Capillaries | Blood vessels surround each capillary supplying deoxygenated blood and leaving with oxygenated blood |
The Role of the Alveoli
The lungs are the gas exchange surface in humans and so are adapted to maximise the exchange of gas by diffusion
Inside the lungs, there are many rounded alveolar sacs which give a very large surface area to volume ratio
These alveoli are highly specialised structures
They (and the capillaries around them) have thin, single layers of cells to minimise diffusion distance
Ventilation maintains high levels of oxygen and low levels of carbon dioxide in the alveolar air space
A good blood supply ensures a constant supply of blood high in carbon dioxide and low in oxygen
A layer of moisture on the surface of the alveoli helps diffusion as gases need to dissolve before taking part in metabolic reactions
The Role of the Alveoli Diagram
Alveoli are specifically adapted to maximise gas exchange
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