About gas exchange

1. Gas Exchange
IB BIOLOGY Year 1
Human Health and Physiology
Topic 6.4 Gas Exchange

2. Overview of the Respiratory
System

3. UNDERSTANDINGS
U1. Ventilation maintains concentration gradients of oxygen and carbon
dioxide between air in the alveoli and blood flowing in adjacent capillaries.
U2. Type 1 pneumocytes are extremely thin alveolar cells that are adapted to
carry out gas exchange.
U3. Type II pneumocytes secrete a solution containing surfactant that creates
a moist surface inside the alveoli to prevent the sides of the alveolus
adhering to each other by reducing surface tension.
U4.Air is carried to the lungs in the trachea and bronchi and then to the
alveoli in bronchioles.
U5. Muscle Contractions cause the pressure changes inside the thorax that
force air in and out of lungs to ventilate them.
U6.Different muscles are requires for inspiration and expiration because
muscles only do work when they contract.

4. APPLICATIONS
A1. External and internal intercostal muscles, and the diaphragm and
abdominal muscles are examples of antagonistic muscle action.
A2. Causes and consequences of lung cancer.
A3. Causes and consequences of emphysema.
SKILLS
Monitoring of ventilation in humans at rest and after mild and vigorous
exercise.
NATURE OF SCIENCE
Obtain evidence from theories: epidemiological studies have contributed to
our understanding of the causes of lung cancer.

5. • I. The Human Respiratory System
Why do we breath?
– A. The Functions of the Respiratory System
• 1. The respiratory system provides the body’s cells
with the means of obtaining oxygen and
eliminating carbon dioxide for our cells to produce
ENERGY.

7. – a. CELLULAR RESPIRATION occurs in the
cytoplasm and mitochondria of cells to release
the energy from food (oxidize organic
compounds) into the form of ATP.

8. • 2. Gas exchange - or the swapping of oxygen for
carbon dioxide in the alveoli of the lungs.
– a. Oxygen from the air taken into the alveoli of
the lungs diffuses (H L) into the blood of the
surrounding capillaries while high
concentrations of carbon dioxide in the blood of
the capillaries diffuse into the alveoli to be
expelled by the lungs.
– b. Diffusion and gas exchange also occurs in
the tissues of the body with the blood.
alveoli tissue
alveoli

10. • 3. Ventilation- otherwise known as breathing,
involves the physical movement of air into and out
of the lungs.
– a. Breathing helps to maintain the
concentration gradients in the alveoli of the
lungs.
» INHALATION replaces the diffused O2
maintaining a HIGH oxygen concentration
inside the alveoli and EXHALATION
removes CO2 keeping carbon dioxide
concentrations LOW.

11. • This means oxygen can always diffuse down its
concentration gradient (HL) from the air to the
blood, while at the same time carbon dioxide
can diffuse down its concentration gradient
(HL) from the blood to the air.
HIGH
HIGH
LOW
LOW
* Add the
HIGH’s and
LOW’s

12. U4.Air is carried to the lungs in the trachea and
bronchi and then to the alveoli in bronchioles.

13. B. Alveoli Air Sac Adaptations for Gas
Exchange
• 1. Type 1 pneumocytes: flattened cells
that make up a very thin single layer of
epithelial cells for ease of diffusion (
less than .15 m across)
• * majority of cells in the alveoli
• 2. Type 2 pneumocytes: are rounded
cells in the alveoli that secretes an oily
fluid called a surfactant.
• The surfactant coats the inner
surface of the alveoli in a film of
moisture.
• -Prevents alveoli from sticking.
- Allows for gases to dissolve for
exchange.
• Surfactant acts as a detergent to
lower the surface tension.

14. – 3. Very large surface area because of large
number of air sacs. (140 square meters- about half
of a tennis court)
– 4. Surrounded by dense capillary network.
– 5. Small distance for gas exchange with
pulmonary capillaries, which are just large enough
for a RBC to get through. ( distance as little as
.5µm)

17. C. The Ventilation System

18. – 1. Air enters the
ventilation system through
the nose or mouth and
then passes down the
trachea.
• Nasal passage is lined
with a ciliated mucus
membrane.
• The cilia and mucus
filter, warm and
moisten the air.
– 2. The TRACHEA (wind
pipe) has cartilage rings
to keep it open .

19. –3. Trachea
divides into two
smaller tubes
into each of the
LUNGS called
BRONCHI (walls
strengthened
with cartilage)
which further
branch into
smaller and
narrower
BRONCHIOLES
.

20. •Bronchioles
have smooth
muscle that
can control
the amount
of air flow in
the lungs.

21. –4. At the end of
the narrowest
bronchioles are
clusters of tiny
air sacs or
ALVEOLI.

24. • D. The Mechanism of Ventilation

25. – 1. LUNGS are large spongy organs encased by
the ribs and DIAPHRAGM.
• a. DIAPHRAGM- muscle that forms the floor of
the chest cavity and aids in the breathing process.
– Relaxed- dome shaped and projects upward.
– Contracted- flattened
– 2. Lungs have a double membrane. (Pleura)
• a. One layer covers lung while outer layer is
attached to the diaphragm and chest cavity
allowing their movement to influence the pressure
in the chest cavity.

27. • 3. Muscles only do “work” when they contract
and shorten creating a pulling force or tension
causing movement in one direction.
– Muscles lengthen when they relax. This is often
caused by the contraction of another “opposite”
muscle.
• Muscles that work together in this “opposite” way are called
ANTAGONISTIC MUSCLES.

28. • 4. The internal and external intercostal
muscles and the diaphragm and the
abdominal muscles are antagonistic
muscles used in ventilation.
– When one is contracted and doing work the
other is relaxed.

29. • INSPIRATION
(INHALATION)
• External intercostal
muscles contract,
moving ribs up and
out (Internal –relax)
• Diaphragm contracts,
Flattening and
moving down.
• Increased volume in
thorax (chest cavity)
lowers the pressure
• Air flows in from
environment (HIGH
PRESSURE) into the
lungs (LOW
PRESSURE) to
balance the pressure
change
• EXPIRATION
(EXHALATION)
• Internal intercostal
muscles contract,
moving ribcage down
and in (External relax)
• Abdominal muscles
contract pushing the
relaxed diaphragm up
into a dome shape
• Decrease in volume of
thorax increases the
air pressure
• Air flows out from the
lungs (HIGH
PRESSURE) to the
environment (LOW
PRESSURE)