The human gas exchange system
Aerobic respiration needs oxygen, and it produces carbon dioxide as a waste product. The human respiratory system contains the organs that allow us to get the oxygen we need and to remove the waste carbon dioxide we do not need. It contains these parts:
- two lungs
- tubes leading from the mouth and nose to the lungs
- various structures in the chest that allow air to move in and out of the lungs
Connecting the outside to the inside
Air passes from the mouth into the trachea, often called the windpipe. The trachea divides into two bronchi, with one bronchus for each lung.
Each bronchus divides further in the lungs into smaller tubes called bronchioles. At the end of each bronchiole, there is a group of tiny air sacs. These air sacs have bulges called alveoli to increase their surface area.
Ventilation
Ventilation or breathing involves movements of the ribs, intercostal muscles and diaphragm to move air into and out of the lungs:
- when we breathe in, we inhale
- when we breathe out, we exhale
The table describes the changes involved:
| Inhaling | Exhaling | |
| Diaphragm | Contracts and moves downwards | Relaxes and moves upwards |
| Intercostal muscles | Contract, moving the ribs upwards and outwards | Relax, letting the ribs move downwards and inwards |
| Volume of ribcage | Increases | Decreases |
| Pressure inside the chest | Decreases below atmospheric pressure | Increases above atmospheric pressure |
| Movement of air | Moves into the lungs | Moves out of the lungs |
| Diaphragm | |
|---|---|
| Inhaling | Contracts and moves downwards |
| Exhaling | Relaxes and moves upwards |
| Intercostal muscles | |
|---|---|
| Inhaling | Contract, moving the ribs upwards and outwards |
| Exhaling | Relax, letting the ribs move downwards and inwards |
| Volume of ribcage | |
|---|---|
| Inhaling | Increases |
| Exhaling | Decreases |
| Pressure inside the chest | |
|---|---|
| Inhaling | Decreases below atmospheric pressure |
| Exhaling | Increases above atmospheric pressure |
| Movement of air | |
|---|---|
| Inhaling | Moves into the lungs |
| Exhaling | Moves out of the lungs |
Image caption, Inhaling
When we inhale, changes in the diaphragm and ribcage reduce the pressure in the chest, and air moves into the lungs
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A recap of respiration and an explanation of why we need glucose and oxygen