Respiratory System
Functions
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Oversees gas exchanges (oxygen and carbon dioxide) between the blood and external environment.
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Exchange of gases takes place within the lungs in the alveoli.
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Passageways to the lungs purify, warm and humidify the incoming air.
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Shares responsibility with the cardiovascular system.
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Structure
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Gas Exchange
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Gas crosses the respiratory membrane by diffusion
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Oxygen enters the blood
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Carbon dioxide enters the alveoli
Mechanics of breathing
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Completely mechanical process
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Depends on volume changes in the thoracic cavity
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Volume changes lead to pressure changes, which lead to the flow of gases to equalise pressure.
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Two phases
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Inspiration – flow of air into lung
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Expiration – air leaving lung
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Inspiration
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Active process where muscles create movement to increase cavity volume so air pulled in.
Expiration
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Largely a passive process which depends on natural lung elasticity.
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As muscles relax, air is pushed out of the lungs.
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Forced expiration can occur mostly by contracting internal intercostal muscles to depress the rib cage.
Respiratory capacities
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Gas transport in the blood
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Oxygen transport
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Inside red blood cells attached to haemoglobin
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Small amount is carried dissolved in the plasma
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Carbon dioxide transport
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Most is transported in the plasma as bicarbonate ions
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Small amount is carried inside red blood cells on haemoglobin but at different binding sites to oxygen.
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