The respiratory system

2. The Respiratory system
• Our cells need oxygen to combine
with nutrients and to produce energy.
During this process, the cells produce
carbon dioxide that has to be expelled
from the body. To obtain oxygen and
get rid of carbon dioxide we use our
respiratory system.

3. Respiration
When we take a breath, air enters through the
nose and mouth. It passes down the pharynx
and then to the trachea (or windpipe).
The trachea divides into two tubes called
bronchi. Each bronchus then subdivides into
smaller and smaller bronchi. The smallest are
bronchioles.
Bronchus (singular) Bronchi (plural)

4. • At the end of each bronchiole is a cluster of tiny
air sacks called alveoli. Lungs have about 600
million alveoli. Lungs have about 600 million
alveoli.
• Alveolus (singular) Alveoli (plural)
• The alveoli are covered with a network of
capillaries. Gas exchange takes place in the
alveoli. Oxygen passes from the alveoli to the
capillaries and into the blood.

5. • At the same time carbon dioxide
leaves the blood and enters the alveoli.
The air carrying carbon dioxide goes
through the bronchioles to the
bronchi and the trachea and finally
out through the moth and nose.

6. Inhalation and Exhalation
• Inhalation: when we take a breath, our
diaphragm, the big muscle under the lungs,
contracts and flattens to allow the lungs to
inflate. The ribs expand and move up to
make more room.
• Exhalation: When we breath out, the ribs
relax and move back in. The diaphragm
relaxes and moves up, pushing the carbon
dioxide out of the lungs and back up the
trachea, out of the nose and mouth.