Download 6.4 Gas Exchange

6.4 Gas Exchange
Some basic ideas:
We have to breathe so that we can exchange the
carbon dioxide that our cells produce during cell
respiration for the oxygen that our cells need for cell
respiration
• ventilation – the exchange of air between our lungs
and the atmosphere
• Gas exchange – the back and forth diffusion of
gases
– Occurs in our lungs (exchange with bloodstream)
– Occurs in capillary beds (exchange with surrounding
cells)
Why do we need a Ventilation System?
• To maintain the concentration gradients of oxygen and carbon
dioxide in the alveoli.
• The body needs oxygen to make ATP via cell respiration.
• The body needs to get rid of carbon dioxide which is a product of
cell respiration.
• Oxygen needs to diffuse from the alveoli into the blood. Carbon
dioxide needs to diffuse from the blood into the alveoli.
• To do so there must be a high oxygen concentration and a low
carbon dioxide concentration in the alveoli.
• A ventilation system makes this possible by getting rid of the carbon
dioxide in the alveoli and bringing in more oxygen.
Tim & Moby: Respiratory System
Anatomy of the Respiratory System
1. Nose/Mouth – brings in/removes gases
2. Pharynx – back of your throat where air and food
will be separated so that food goes down
esophagus and air down trachea
3. Trachea – transports air to and from lungs
4. Bronchi – the branching airway to each lung
5. Bronchioles – smaller branches in lungs leading to
alveoli
6. Alveoli – air sacks where the diffusion of gases
takes place
Ventilation Process
The alveoli
• Alveoli are found in clusters at the ends of the
smallest bronchioles (think about a bunch of grapes)
• Surrounding each cluster of alveoli is a capillary bed
• Blood entering the capillary beds is from the
pulmonary arteries (CO2-rich/O2-poor) and here the
exchange takes place; now the blood (O2-rich/CO2poor) can return to the heart via the pulmonary
veins
• The gases must each diffuse through two
membranes (phospholipid bilayers)
– The cell membrane of the alveoli
– The cell membrane of the capillary
• As long as you continue breathing then you will
maintain the proper concentration gradients of O2
and CO2
Summary of Features of Alveoli that allow for Efficient Gas
Exchange:
• Great numbers increase the surface area for gas
exchange.
• Wall made up of single layer of cells and so are the
walls of the capillaries so diffusion distance is small
allowing rapid gas exchange.
• Covered by a dense network of capillaries which have
low oxygen and high carbon dioxide concentrations.
This allows oxygen to diffuse into the blood and carbon
dioxide to diffuse out of the blood.
• Some cells in the walls secret fluid allowing gases to
dissolve. Fluid also prevents the sides of alveoli from
sticking together.
This process works like Boyle’s Law :
P1 x V1 = P2 x V2
Process of Breathing: Volume/Pressure
Relationship


Inspiration (air in)/Expiration (air out):
Cycle:
 Relaxed state: diaphragm and intercostal muscles relaxed
 Inspiration: diaphragm contracts (pulling muscle down),
intercostal muscles contract elevating chest wall and
expanding volume of chest which lowers pressure in
lungs therefore pulling in air
 Expiration: muscles relax, diaphragm resumes dome
shape, intercostal muscles allow chest to lower resulting
in increase of pressure in chest and expulsion of air
Video Clip
Review Video