Describe how oxygen enters the blood in lungs with the help of a block diagram.
- Gaseous exchange takes place within the lungs by diffusion from the alveoli to blood capillaries and vice versa. Alveoli in lungs are numerous and only one cell thick.
- Alveoli are surrounded by capillaries that are also one cell thick.
- Blood, dark red in colour flows from the heart through these capillaries and collects oxygen from the alveoli.
- At the same time, carbon diox¬ide passes out of the capillaries and into the alveoli.
- When we breathe out, we get rid of carbon dioxide.
- The bright red, oxygen rich blood is returned to the heart and pumped out to all parts of the body.