Chapter 20
Gas exchange
Objectives:
• Understand gas exchange across taxa
• Learn how gas exchange occurs
• Understand Fick’s Law
• Be able to explain where gas exchange occurs.
• Organisms need oxygen
- for metabolism + catabolism
- for ATP production
Food
O2
Chemical
Reactions
tissues
cells
Digest
CO2
• Organisms need to get O2 into tissues (cells)
and CO 2 out of the tissues (cells )
• Four main types of respiratory systems for gas
exchange
Considerations - • Diffusion is passive (no ATP required)
• Higher the concentration gradient the faster
the diffusion will occur
- body surface
- tracheal tubes
Facilitate gas
exchange
- gills
ATP
• Larger the surface area - the more gas can
be exchanged
- lungs
Important!!!! Gases enter and leave tissues
as a result of diffusion
• Sponges, Cnidarians , Annelids
- diffusion
• Fish
- Gills provide a large surface area
- Counter current exchange maintains
a strong concentration gradient
CO2
O2
1
What about terrestrial critters?
- evolution of internal passages instead
of gills
- Why?
1. Gills would collapse
2. Water diffuses into air by evaporation
- gills would provide large surface
area for water loss
So Tracheae + lungs
Counter current exchange
2
44.5
One way airflow
In higher vertebrates
Larynx
Trachea
Bronchi
Bronchioles
Alveoli
44.5
From bronchiole
44.6
44.7
3
Now that oxygen has entered the lungs
or gills, or air sacs - how does it
travel to the tissues????
Alveolus
T
I
s
s
u
e
Oxygenated blood
Respiratory
pigments
Dude!
• An overview of gas
exchange
Gases move in and out
of the lungs by breathing
Deoxygenated blood
CO2
O2
O2
O2
CO2
O2 and
CO2 are
exchanged
in the lungs
by diffusion
O2
O2
Gases
dissolved in
blood are
transported
by the
circulatory
system
alveoli
(air sacs)
left
atrium
right
atrium
Hemaglobin
right
ventricle
left ventricle
O2
CO2
CO2
CO2
CO2
CO2
O2 and CO2
are exchanged
in the tissues
by diffusion
Fig. 20-22
- What about CO2 transport??
Bicarbonate
ion
1. Dissolved in plasma (7-10%)
2. Combines w/ hemaglobin (20%)
3. Most CO2 transported back to lungs as
Bicarbonate ions (70%)
Carbonic acid
Decrease
in pH
4
• Breathing is regulated by respiratory
centers (brain stem)
• Chemoreceptors (CO2, pH):
- medulla oblongata, aorta, corotid
arteries
So, How do we breath?
Where does the oxygen come from??
Air moves in
Rib cage
expands
Air moves out
Lungs
expand
Rib cage
contracts
Lungs
compress
Atmosphere : 21% Oxygen
78% nitrogen
1% other (smog?)
Weight of these gases provides barometric
pressure
Diaphragm
contracts downward
(a) Inhalation
Diaphragm
relaxes upward
(b) Exhalation
5