Structure and function of the gas exchange system

 

Breathing, respiration and gas exchange

 

• Breathing or ventilation moves air in and out of your lungs.
• Respiration is a chemical process in all your cells that releases energy from glucose.
• Gas exchange swaps gases between air and blood at the alveoli in your lungs.
• Gas exchange lets oxygen go into your cells for respiration and removes carbon dioxide, a waste product of respiration. All living things need respiration to stay alive.

 

Structure of the gas exchange system

The gas exchange system is made from key parts, each with a different function:

 

• Trachea
• Alveoli
• Bronchi (Left & right bronchus)
• Intercostal muscles
• Pleural membranes
• Diaphragm

Part of the gas exchange system	Function
Trachea	Windpipe that carries air from mouth to lungs. Has cartilage rings to keep it open.
Alveoli	Tiny air sacs at the end of bronchioles where gas exchange happens.
Bronchus	Left and right branches of trachea that lead to each lung.
Bronchiole	Smaller tubes that split from bronchi and take air deeper into lungs.
Intercostal muscles	Muscles between ribs that form chest wall. They move with diaphragm during breathing.
Diaphragm	Flat muscle under lungs that changes shape with intercostal muscles during breathing.

 

• The trachea splits into two bronchi (one leads to the left lung and the other to the right).
• Pleural membranes surround each lung.
• Cartilage rings in the walls of the trachea help to keep it open.
• The bronchioles end in small sacs called alveoli. This is where the gas exchange takes place.

 

 

How does oxygen travel into blood?

 

• Air goes through the trachea (windpipe) to the lungs.
• The trachea splits into two bronchi, which split into many bronchioles.
• The bronchioles end in alveoli, tiny air sacs with millions in the lungs.
• Alveoli are surrounded by capillaries, where oxygen and carbon dioxide are swapped between air and blood. Oxygen is carried by red blood cells.
• This gas swap happens by diffusion.

 

Alveoli

 

• Alveoli are tiny air sacs in the lungs where air and blood swap gases.
• The alveoli are an exchange surface adapted for gas exchange. This means:
• Oxygen from the air goes into the blood for respiration.
• Carbon dioxide from respiration goes from the blood to the air.

 

Note: Deoxygenated blood appears blue in this diagram for explanation purposes only.

 

Exchange of gases in the Lungs

Breathing is a gas exchange mechanism.  Your Lungs help to do just that!  They contain millions of  tiny air pockets called ALVEOLI (air sacs)  which are adapted to maximise the diffusion of carbon dioxide and oxygen (see diagram below).  Alveoli are good at gas exchange because they have:

 

• a large surface area.  If all the air sacs were flattened out, they would cover an area of 100m2.
• moist surface which speed up diffusion.
• very thin walls (just one cell thick) which speeds up diffusion.
• lots of blood capillaries to carry the gasses.
• many blood capillaries which help the diffusion O2 and CO2 as their walls are only one cell thick.

 

In the alveolus (single air sac) oxygen passes from a high concentration (loads of oxygen) through the thin wall into the blood capillary where there is a low concentration (very little oxygen) .  This is called diffusion, because oxygen is moving from high concentration to low concentration.  When blood returns to lungs it has high concentration of carbon dioxide, so CO2 diffuses out of the blood into the alveolus.

 

Summary:

 

• Air has three main gases: oxygen, nitrogen and carbon dioxide.
• Gas exchange swaps oxygen and carbon dioxide between blood and air.
• Diffusion moves oxygen from air sacs into the blood.