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Gas exchanges

Topic 6
...
4

Biology SL

➢ The abdominal and intercostal muscles can achieve a greater initial thoracic
volume leading to deeper breathing
➢ Muscles only perform work when contracting, thus different muscles are needed to
breathe in and out
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Each muscle pair is said to have an antagonistic muscle action

➢ The intercostal muscles are the muscles that are found between the ribs
○

There are two antagonistic sets of these muscles
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External intercostal muscles, which are used when breathing in

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Internal intercostal muscles, which are used when breathing out

Gas exchange
➢ Air enters through the mouth or nasal passages
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Passes the pharynx

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Passes the larynx (production of sound)

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Goes down through the trachea

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Goes to the right and left primary bronchi

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Then to smaller and smaller branches of the bronchi
■

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The smallest are called bronchioles

Reaches the small air sacs in the lungs called alveoli

➢ Alveoli are found in the lungs as clusters at the ends of the smallest bronchioles
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Approximately 300 million alveoli in each lung

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Each cluster of alveoli has one or more surrounding capillary bed(s)

➢ The blood entering these capillary beds comes from the right ventricle via the
pulmonary arteries
➢ While the blood is in the capillary bed, oxygen diffuses from the air in each alveolus
cell through the 2 cells thich membrane
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One is the single cell making up the alveolus

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One is the single cell making up the wall of the capillary

➢ Carbon dioxide diffuses in the opposite direction through the same 2 cells
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The gas exchange is ensured by different concentration gradients

Alveoli
➢ Alveoli are composed of specialized cells called pneumocytes
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2 types of cells

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The single layer of cells facilitates oxygen and carbon dioxide diffusion

➢ Type I pneumocytes
2

Gas exchanges

Topic 6
...
4

Biology SL

Examples of carcinogens
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Tobacco

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Asbestos

If you stop smoking…
➢ After 20 minutes, your blood pressure and pulse are back to normal
➢ After 8 hours, the carbon dioxide levels in the blood decrease and you feel less tired
➢ After 24 hours, the risk of a heart attack decreases
➢ After 2-12 weeks, the circulation is enhanced which makes you feel more alert

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