6.4 Gas exchange
• The as exchange is passive, as oxygen and
carbon dioxide move from areas of high
concentration to low concentration.
• The process of ventilating the lungs in requires
energy.
• Exchange of gas in the lungs is passive
transport as it takes place as a result of
diffusion.
• 6.4U1: Ventilation maintains concentration
gradients of oxygen and carbon dioxide
between air in alveoli and blood flowing in
adjacent capillaries.
• The lungs are the respiratory surface that is
being ventilated. Other respiratory surfaces
include gills for fish, skin for worms, leaves for
plants, cell membranes for bacteria… Lungs
are the specialized structure some animals
use.
• 6.4U2: Type I pneumocytes are extremely thin
alveolar cells that are adapted to carry out gas
exchange.
• 6.4U3: Type II pneumocytes secrete a solution
containing surfactant that creates moist
surface inside the alveoli to prevent the sides
of the alveolus adhering to each other by
reducing surface tension.
• How are Type I pneumocytes adapted to carry
out gas exchange?
• What would happen if Type II pneumocytes
stopped functioning?
• Capillary
• https://www.youtube.com/watch?v=Q530H1
WxtOw
• Blood in capillaries
• https://www.youtube.com/watch?v=4yBMY9
Wj7z0
• 6.4U4: Air is carried to the lungs in the
trachea and bronchi and then to the alveoli in
bronchioles
• 6.4U5: Muscle contractions cause the pressure
changes inside the thorax that force air in and
out of the lungs to ventilate them.
• 6.4U6: Different muscles are required for
inspiration and expiration because muscles
only do work when they contract.
• 6.4A1 External and internal intercostal
muscles, and diaphragm and abdominal
muscles as examples of antagonistic muscle
action.
The table on page 315-316 nicely summarizes this:
Inhalation: Sucking air in!
• External intercostal muscles contract pulling the ribs up
and out.
• The diaphragm contracts and pulls down.
• As a result the thoracic cavity around the lungs
expands increasing the volume of the lungs.
• This causes the pressure inside the lungs to decrease
relative to the environment.
• Gas moves from higher pressure to lower pressure and
moves into the lungs.
• Exhalation: Blowing air out!
• The external intercostal muscles and diaphragm
relax.
• this moves the ribs down and in and the
diaphragm up decreasing the volume of the
thoracic cavity around the lungs.
• This decreases the volume and increases pressure
inside the lungs.
• Gas moves from high pressure to low pressure,
and moves out of the lungs.
• The internal intercostal muscles may also contract
to force air out when coughing for example.
• 6.4A2: Causes and consequences of lung
cancer. Page 316
• Since it is cancer it is a set of mutations in cells
that therefore miss checkpoints and divide too
fast.
• Smoking (87%) Second hand smoke (3%), air
pollution (5%), Radon gas, Asbestos, and other
particles.
• 85% 5 year mortality (and survival often
means loss of part of your lungs).
• 6.4A3: Causes and consequences of
emphysema. Page 317
• Phagocytes prevent infections by engulfing
bacteria and digesting them with a protease
called ELASTASE inside vesicles called
endocysts.
• This breaks down proteins including the
protein elastin which serves important
functions in the body.
Elastin
• Usually there is an enzyme inhibitor that
prevents elastase from digesting lung tissue.
Elastase vs alpha 1-antitrypsin
• Genetic factors can lead to too little of the
inhibitor being produced.
• More importantly, in 30% of smokers, there is
an elevated level of the protease elastase such
that it degrades the alveoli walls and so lung
volume decreases.
• In addition to tobacco and marijuana smoke,
air pollution and other inhaled fumes can be
causes.
• 6.4S1: Monitoring of ventilation in humans at
rest and after mild and vigorous exercise
(PRACTICAL 6)
• Look at page 312
• 6.4:NOS: Obtain evidence for theories:
epidemiological studies have contributed to
our understanding of the causes of lung
cancer.
• See page 316
• What is the association between being thin
and lung cancer?