The respiratory system has three main functions: (1) to provide oxygen to cells, (2) to remove carbon dioxide from cells, and (3) to remove water from cells. Air passes through the nose, pharynx, trachea, bronchi, and into tiny sacs called alveoli in the lungs where gas exchange occurs between the blood and air. The diaphragm and rib muscles expand the chest during inhalation, allowing air to rush into the lungs due to the created vacuum. During exhalation, the muscles relax and the chest contracts, pushing air back out.

1. Section 3: The Respiratory System
What are the functions of the respiratory system?
What structures does air pass through as it travels
to the lungs?
What happens during gas exchange and
breathing?
• 7.5.a Students know plants and animals have levels
of organization for structure and function,
including cells, tissues, organs, organ systems, and
the whole organisms.
• 7.5.b Students know organ systems function
because of the contributions of individual organs,
tissues, and cells. The failure of any part can affect
the entire system.

2. Respiratory System Functions
• Your body cells need oxygen
and they get it from the air
you breathe.
• The respiratory system
moves oxygen from the
outside environment into
the body.
• It also removes carbon
dioxide and water from the
body.

3. Taking in Oxygen
• Like a fire: Your cells cannot “burn” the “fuel”
that you eat without oxygen.
• Respiration = the process by which cells
break down simple food molecules such as
glucose to release the energy they contain
– AKA cellular respiration
– Respiration ≠ Breathing

4. Removing Carbon Dioxide and Water
• Released through lungs

5. The Air You Breathe
The air you breathe in
contains several
different gases, shown
in the circle graph on
the left. The air you
breathe out contains
the same gases, but in
the amounts shown in
the circle graph on the
right.

6. The Air You Breathe
Percent of a gas breathed in
or out
•Reading Graphs:
What does each wedge of
the graphs represent?

7. The Air You Breathe
Oxygen; less oxygen is
breathed out than breathed
in—meaning that some must
have been used by the body.
•Interpreting Data:
Based on the data, which gas
is used by the body? Explain.

8. The Air You Breathe
There is a higher percentage
of carbon dioxide in exhaled
air. Carbon dioxide is a waste
product of cellular activity.
•Drawing Conclusions:
Compare the percentage of
carbon dioxide in inhaled air
with the percentage in
exhaled air. How can you
account for the difference?

9. The Air You Breathe
Nitrogen is not used by the
body and is not a waste
product.
–Inferring:
Explain why the percentage
of nitrogen is the same in
both inhaled air and exhaled
air.

10. Systems Working Together
Oxygen from the air and glucose from digested food are
both carried to the cells by the blood. During respiration,
oxygen reacts with glucose to release energy.

11. Path of Air
• Particles in the air
must be filtered out.
• As air travels from the
outside environment
to the lungs, it passes
through the following
structures: nose,
pharynx, trachea, and
bronchia.
• Air is also warmed and
moistened.

13. The Nose (1)
• Air enters into the body through the nose and then into nasal
cavities. Some of the cells lining the nasal cavities produce
mucus.
• Mucus = A thick, sticky liquid produced by the body.
– moistens the air, keeps lining from drying out, traps particles
• Cilia = The hairlike projections on the outside of cells that
move in wavelike manner.
– Swept into your stomach.
• Sneeze

14. The Pharynx (2)
• Pharynx = The throat.
• Both the nose and the mouth connect to the
pharynx.
• Shared with digestive system.

15. WHAT IS THE ROLE OF CILIA?
Reading Checkpoint

16. The Trachea (3)
• Trachea = The windpipe; a
passage which air moves in
the respiratory system.
• Continue cleaning and
moistening of air.
– Cough
– Choking
• Epiglottis - seals off the
trachea during swallowing

17. The Bronchi (4) and Lungs (5)
• Bronchi = The passages that direct air into the
lungs.
• Lungs = An organ found in air-breathing
vertebrates that exchanges oxygen and carbon
dioxide with the blood.
• Alveoli = Tiny sacs of lung tissue specialized for
the movement of gases between air and blood.
– surrounded by capillaries
– blood picks up oxygen from the air

18. HOW IS FOOD PREVENTED FROM
ENTERING THE TRACHEA?
Reading Checkpoint

20. Gas Exchange
• The walls of both the alveoli and the capillaries are very
thin!
• After air enters an alveolus, oxygen passes though the
wall of the alveolus and then through the capillary wall
into the blood.
• Carbon dioxide and water pass from the blood into the
alveoli.
• This whole process is known as gas exchange.

21. How Gas Exchange Occurs
• Circulatory and respiratory systems work
together
• Pulmonary circulation – carries blood from the
heart to the lungs and back
After air enters an alveolus,
oxygen passes through the wall of
the alveolus and then through the
capillary wall into the blood.
Carbon dioxide and water pass
from the blood into the alveoli.

23. Surface Area For Gas Exchange
• 300 million alveoli, 70 square meters

24. WHAT GASES ARE EXCHANGED
ACROSS THE ALVEOLI?
Reading Checkpoint

25. Surface Area
Surface area refers to the total area of all the surfaces of a three-
dimensional object. Consider a cube, which has six equal sides. Each
side measures 2 cm by 2 cm.
1. To find the surface area of the cube, first calculate the area of one
of the six sides:
Area = length x width = 2 cm x 2 cm = 4 cm2
Each side has an area of 4 cm2.
2. Then, add the areas of the six sides together:
4 cm2 + 4 cm2 + 4 cm2 + 4 cm2 + 4 cm2 + 4 cm2 = 24 cm2
The surface area of the cube is 24 cm2.

26. How You Breathe
When you breathe, the actions
of your rib muscles and
diaphragm expand or contract
your chest. As a result, air flows
in or out.
The more oxygen you need, the
faster you breathe.

27. Muscle for Breathing
• Diaphragm = A large
muscle located at the
bottom of a
mammal’s rib cage
that functions in
breathing.

28. The Process of Breathing
• When you breathe, the actions of your rib muscles
and diaphragm cause your chest to expand or contact.
• As a result, air flows in or out.
• Vacuum – causes air to rush into your lungs

29. WHAT MUSCLES CAUSE THE CHEST
TO EXPAND DURING BREATHING?
Reading Checkpoint

30. Relating Breathing and Speaking
• Larynx = The voice box.
• Vocal chords = Folds of
connective tissue that
stretch across the
opening of the larynx and
produce a persons voice.
• Air moving over the vocal
cords causes them to
vibrate and produce
sound.