Download 6.4 Gas Exchange - hrsbstaff.ednet.ns.ca

OUTCOMES
•
•
•
•
6.4 GAS EXCHANGE
IB Biology
•
6.4.1 Distinguish between ventilation, gas
exchange and cell respiration.
6.4.2 Explain the need for a ventilation system.
6.4.3 Describe the features of alveoli that adapt
them to gas exchange.
6.4.4 Draw and label a diagram of the ventilation
system, including trachea, lungs, bronchi,
bronchioles and alveoli.
6.4.5 Explain the mechanism of ventilation of the
lungs in terms of volume and pressure changes
caused by the internal and external intercostal
muscles, the diaphragm and abdominal muscles.
VENTILATION
GAS EXCHANGE
Ventilation can be defined as any method of
increasing contact between the respiratory
medium and the respiratory surface.
In humans, ventilation
involves bringing fresh
air to the alveoli and
removing stale air.
GAS EXCHANGE ANIMATION!
CELL RESPIRATION
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter
25/animation__gas_exchange_during_respiration.
html
Gas exchange can be defined as the uptake of
oxygen molecules from the environment and the
discharge of carbon dioxide into the environment.
This happens in the
alveoli of human lungs
and the exchange
occurs with the blood
in the capillaries.
Cell respiration occurs at the cellular level in
the mitochondria and cytoplasm of cells.
The mitochondria produce and release energy in
the form of ATP which can be used inside the cell.
Cell respiration uses
oxygen to produce
ATP and releases
carbon dioxide as a
waste product.
THE VENTILATION SYSTEM
Humans need a ventilation system because the
exchange of gases and cell respiration depend on
the concentration of gases.
Exchange of gases occurs inside the human body
as a result of concentration gradients.
Gases will diffuse from
areas of higher
concentration to those
of lower concentration.
The ventilation process ensures that the
concentration gradients are maintained by bringing
in fresh air (more oxygen) and breathing out stale
air (expelling carbon dioxide).
THE ALVEOLI
The alveoli are clusters of small air sacs located
at the tips of the bronchioles.
Gas exchange occurs across the thin walls in the
alveoli with the matrix of capillaries surrounding
the alveoli.
The first feature that adapts the alveoli to gas
exchange is their total surface area.
In humans the alveoli have a surface area of about
100 m2 which provides enough area to carry out gas
exchange for the entire body.
The second feature of the alveoli is its surrounding
wall that consists of a single layer of flattened cells.
This layer of thin cells allows for efficient exchange
of materials via diffusion due to the short distance
the materials have to travel.
The third feature of the alveoli that adapts them to
gas exchange is their moist lining.
The cells in the walls of the alveoli secrete a fluid
which the gases to be exchanged may then dissolve
into.
The fluid also contains
a natural detergent that
helps to prevent the sides
of the alveoli from
sticking together.
The fourth feature
of the alveoli is the
dense network of
capillaries which
surround them and
allow for exchange
of carbon dioxide
and oxygen.
YOU MUST...
Draw and label a diagram of the ventilation
system, including trachea, lungs, bronchi,
bronchioles and alveoli – use the diagram in
the green study guide as a model.
THE MECHANISM OF VENTILATION
INHALING
Air is inhaled in the human body through the
trachea and it travels down the bronchi to the
bronchioles and into the alveoli.
Air is exhaled through the same route and both
inhalation and exhalation are achieved with the
help of muscles such as the diaphragm,
intercostals and abdominals.
During inhalation the external intercostals
contract and this moves the rib cage up and out.
At the same time the
diaphragm is contracting
which causes it to move
down and flatten out.
Both of these muscle contractions increase the
volume of the thorax (chest) which in turn results
in a decrease in pressure inside the chest.
EXHALING
During exhalation the internal intercostal
muscles contract which move the rib cage down
and in.
At the same time the abdominal muscles contract
and the diaphragm is pushed upward into a dome
shape.
The increased pressure in the chest cavity causes
the air to flow out of the lungs until pressure inside
the lungs falls back to atmospheric pressure.
The decrease in pressure in the chest cavity causes
air to rush in from outside until the pressure inside
the lungs rises to match the atmospheric pressure
outside.
The result of these muscles contractions is a
decreased volume in the thorax and pressure rises
above atmospheric pressure.
A VIDEO...
http://www.youtube.com/watch?v=HiT621PrrO0