Gas Exchange
Week 4
Daltons Law
The partial pressures of the 4 gases add
up to 760mm Hg.
Dalton’s Law; in a mixture if gases, the
total pressure equals the sum of the
partial pressures exerted by each gas.
Important Point
• Gases in our bodies are dissolved in
fluids, such as blood plasma.
• According to Henry’s law,
– gases dissolve in liquids in proportion to their
partial pressures, depending also on their
solubilities in the specific fluids and on the
temperature.
The Site of Gas Exchange
• External Respiration
• CO2 diffuses from pulmonary
capillaries into alveoli
• O2 Diffuses from alveoli into
pulmonary capillaries
•Internal respiration
•O2 diffuses from systemic capillaries into
cells
•CO2 diffuses from cells into systemic
capillaries
Factors Influencing External
Respiration
•
Efficient external
respiration depends on
3 main factors
1) Surface area and
structure of the
respiratory membrane
2) Partial Pressure
gradients
3) Matching alveolar
airflow to pulmonary
capillary blood flow.
Important Point
• Partial pressure gradients affect gas
exchange between the alveoli and
pulmonary capillaries.
External respiration: Partial
Pressures
•
The Partial pressures of
gases in the alveoli differ
from those in the
atmosphere.
1) Humidification of inhaled
air
2) Gas exchange between
alveoli and pulmonary
capillaries
3) Mixing of new and old air
Oxygen Loading
• Oxygen diffuses
along its partial
pressure gradient,
from the alveolus into
the blood, until
equilibrium is reached
• Equilibrium is reached
within the first third of
the capillary.
Oxygen Loading
Carbon Dioxide Uploading
• Carbon dioxide
diffuses along its
partial pressure
gradient, from the
blood into the
alveolus, until
equilibrium is reached
• Equilibrium is reached
within the first 4
4/10’s of the capillary
This Occurs Simultaneously
•Carbon dioxide is very
soluble in blood, allowing
many molecules to diffuse
along this small pressure
gradient.
•Oxygen is less soluble,
requiring a larger
concentration gradient.
Other Factors Affecting External
Respiration
1) Matching alveolar airflow to pulmonary
capillary blood flow.
2) Watch the following clip.
3) This is Know as the Ventilation-Perfusion
Coupling
Internal Respiration
• Internal Respiration
• O2 diffuses from
systemic capillaries
into cells
• CO2 diffuses from
cells into systemic
capillaries.
Internal Respiration Depends on:
1) Available surface
area, which varies in
different tissues.
2) Partial Pressure
gradients
3) Rate of blood flow
varies (e.g.
metabolic rate of
tissue)
Internal Respiration CO2 and O2
Exchange
Summary