Oxygen is inhaled from the surrounding
The inhaled air which is rich in oxygen is found inside the alveolus
The oxygen dissolves in the moist lining of the alveolus and then diffuses into the blood cappilaries
The blood inside the cappilaries contains red blood cells which are rich in a substance called haemoglobin.
The oxygen combines with the haemoglobin to form oxyhaemoglobin.
The blood rich in oxygen is then carried away from the lungs to the heart.
When the heart pumps, oxygenated blood is distributed to all parts of the body.
When blood reaches the cells or tissues with insufficient amout of oxygen, the oxyhaemoglobin is broken down and oxygen is released.
Oxygen then diffuses into the cells and simultaneously carbon dioxide from the cell diffuses into the capillaries to be carried back into the lungs.
CHARACTERISTICS OF ALVEOLI WHICH MAKES DIFFUSION OF GASES EASIER
- Consists of million of alveoli
- Alveolus has one cell wall thick
- Moist cell wall
- Large surface area
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