The diffusion of oxygen from the alveoliinto the blood capillaries•During inhalation, air is taken into the lungsthrough the nasal cavity, passing through thetrachea, bronchi, bronchioles and finally alveoli.•The air that reaches the alveoli is called alveolarair. It is rich in oxygen and poor in carbon dioxide.•The blood that reaches the capillariessurrounding the alveoli is poor in oxygen and richin carbon dioxide.
•Gas exchange takes place in the lungs bydiffusion.•Oxygen diffuses from the alveoli into thered blood cells in the capillaries.•At the same time, the red blood cells in thecapillaries release carbon dioxide whichdiffuses into the alveoli.
•Red blood cells contain the oxygen –carrying pigment called hemoglobin.•Oxygen combines with hemoglobinto form oxyhaemoglobin.•The blood cells are transportedaround the body.
•Gas exchange also takes place between thecapillaries and the body cells.•Capillaries have a higher concentration ofoxygen than the body cells.•Body cells have a higher concentration ofcarbon dioxide than the capillaries.•Oxyhaemoglobin releases oxygen whichdiffuses into the body cells.•Carbon dioxide diffuses into the blood at thesame time.