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Physiology Term 2 #8 - Gas Exchange
1. CO2 O2
Alveoli of lungs
Airways
CO2
CO2
O2
O2
Pulmonary
circulation
CO2 O2
Cellular
respiration
ATP
Nutrients
Cells
Systemic
circulation
CO2 O2
Oxygen exchange
at cells
Oxygen transport
CO2 exchange
at alveolar-capillary
interface
Oxygen exchange
at alveolar-capillary
interface
CO2 exchange
at cells
CO2 transport
1
2
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5
6
Overview
Overview of oxygen and carbon dioxide exchange
and transport
2. Diffusion and Solubility
These are factors that affect diffusion if membrane permeability
remains the same
• Surface area- diffusion rate is proportional to available surface
area
– Constant- remains the same over a long period of time
• Concentration gradient- diffusion rate is proportional to
concentration gradient
– Most important factor- O2 and CO2 gradients will be present at lung
and tissue capillaries
• Membrane thickness – diffusion rate is inversely proportional
which is why walls are so thin
– Constant- number of cells in walls should not change
• Diffusion distance- diffusion rate is inversely proportional, another
reason why walls are thin
– Constant
3. Movement of Gases
These are factors that influence the movement of gasses from
air into a liquid
• Pressure gradient- drives gas flow
• Solubility- the gas must be able to dissolve in the liquid,
diffusion will continue until it reaches equilibrium,
increased pressure may dissolve some gas if solubility is
low.
• Temperature- temperature is constant so it doesn’t play a
role in the body unless there is pathology
4. Behavior of Gases in Solution
PO2 = 100 mm Hg
PO2 = 0 mm Hg
PO2 =
100 mm Hg
[O2] =
5.20 mmol/L
PO2 =
100 mm Hg
[O2] =
0.15 mmol/L
(a) (b) (c)Initial state:
no O2 in solution
Oxygen dissolves. At equilibrium, PO2 in air and water
is equal. Low O2 solubility means
concentrations are not equal.
The pressure equilibrium is not the same as the concentration dissolved.
5. Behavior of Gases in Solution
Oxygen is less soluble in water than carbon dioxide
7. Gas Exchange at the Alveoli and Cells
Gases move
from areas of
high partial
presssures to
areas of low
partial pressure
Venous blood
has the same Po2
as tissues
8. Gas Exchange
Oxygen diffuses across alveolar epithelial cells and
capillary endothelial cells to enter the plasma
Gas exchange is rapid
and blood flow is slow
which allows for
equilibrium in 1 second!
9. Gas Exchange
Hypoxia is not a disease, it is caused by something that decreases
diffusion or oxygen deliver, that can cause disease
10. O2
O2 dissolved in plasma (~ PO2) < 2%
O2 + Hb
ARTERIAL BLOOD
Alveolar
membrane
Alveolus
Capillary
endothelium
Red blood cell
Cells
Oxygen Transport
98% of oxygen is
bound to
hemoglobin and
the other 2% is
dissolved in plasma
11. O2
O2 dissolved in plasma (~ PO2) < 2%
O2 + Hb Hb•O2
> 98%
ARTERIAL BLOOD
Alveolar
membrane
Alveolus
Capillary
endothelium
Red blood cell
Cells
Oxygen Transport
Because oxygen is not
easily dissolve in water,
hemoglobin is a protein
that binds O2 and
dramatically increased the
amount of blood in the
plasma
12. O2
O2 dissolved in plasma (~ PO2) < 2%
O2 + Hb Hb•O2
> 98%
ARTERIAL BLOOD
Alveolar
membrane
Alveolus
Capillary
endothelium
Transport
to cells
Red blood cell
Cells
Hb•O2
Oxygen Transport
One reason why blood
transfussions are used is to
provide hemoglobin for
efficient O2 transport.
Researcher are working on
carrier proteins
13. Oxygen Transport
O2
O2
O2 dissolved in plasma (~ PO2) < 2%
O2 dissolved in plasma
O2 + Hb Hb•O2
> 98%
Hb + O2Hb•O2
ARTERIAL BLOOD
Alveolar
membrane
Alveolus
Capillary
endothelium
Transport
to cells
Red blood cell
Cells
Used in
cellular
respiration
Oxygen can travel
bound to hemoglobin
or to be dissolved in
plasma
14. Oxygen Transport
The role of hemoglobin in oxygen transport
This shows that without hemoglobin
very little oxygen would dissolve into
the plasma- an amount that is not
sufficient for cell demand
15. Oxygen Transport
In the presence of hemoglobin a
higher concentration can be
dissolved in blood when pressure
equilibrium is reached
16. Oxygen Transport
If there are no problems with
hemoblogin binding oxygen,
then low blood oxygen levels
could be due to a problem
with ventilation
17. The Hemoglobin Molecule
The amount of oxygen bound to hemoglobin depends on the PO2 of plasma-
each hemoglobin can carry 4 oxygen molecules, the % saturation tells
how much is carried.
18. Oxygen-Hemoglobin Dissociation
Curve
In vitro testing reveals a
varying amount of O2
saturation dependent on
O2 partial pressure- it
doesn’t reach 100% within
physiological conditions
19. Oxygen Binding
Physical factors alter hemoglobin’s affinity for oxygen
Changes can alter the
hemoglobin
conformation which
influence delivery at
tissues more than
obtaining oxygen in the
lungs.
Release more O2 at pH
7.2 (during exercise)
than pH7.4
25. Carbon Dioxide Transport
• Dissolved: 7% - although CO2 is more soluble in
plasma than oxygen only a small amount is dissolved in
it.
• Converted to bicarbonate ion: 70% - an enzyme
converts of the CO2 in RBCs into bicarbonate
• Bound to hemoglobin: 23% -
– Hemoglobin also binds H+ - hemoblogin acts as a buffer
binding H+ to resists pH changes
– Hb and CO2: carbaminohemoglobin – formed with CO2
and hemoglobin bind, it decreases affinity for O2
26. Carbon Dioxide Transport in the Blood
CO2 Dissolved CO2
(7%)
CO2
Cellular
respiration
in
peripheral
tissues
VENOUS BLOOD
Alveoli
Red blood cell
Capillary
endothelium
Cell membrane
27. Carbon Dioxide Transport in the Blood
CO2 Dissolved CO2
(7%)
CO2 + Hb Hb•CO2 (23%)
CO2 + H2O
HCO3
–
H+ + Hb Hb•H
Cellular
respiration
in
peripheral
tissues
VENOUS BLOOD
Alveoli
Red blood cell
Capillary
endothelium
Cell membrane
H2CO3
CA
28. Carbon Dioxide Transport in the Blood
CO2
CO2
Dissolved CO2
(7%)
Dissolved CO2 Dissolved CO2
CO2 + Hb
Hb + CO2
Hb•CO2 (23%)
Hb•CO2
CO2 + H2O
HCO3
– HCO3
– in
plasma (70%)
H+ + Hb Hb•H
Cl–
Cellular
respiration
in
peripheral
tissues
VENOUS BLOOD
Alveoli
Transport
to lungs
Red blood cell
Capillary
endothelium
Cell membrane
H2CO3
CA
29. Carbon Dioxide Transport in the Blood
CO2
CO2
Dissolved CO2
(7%)
Dissolved CO2 Dissolved CO2
CO2 + Hb
Hb + CO2
Hb•CO2 (23%)
Hb•CO2
CO2 + H2O
H2CO3
HCO3
–
HCO3
–
HCO3
– in
plasma (70%)
HCO3
–
in
plasma
H+ + Hb Hb•H
H+ + HbHb•H
Cl–
Cl–
Cellular
respiration
in
peripheral
tissues
VENOUS BLOOD
Alveoli
Transport
to lungs
Red blood cell
Capillary
endothelium
Cell membrane
H2CO3
CA
Reverse
chloride shift
H+
disassociate
H+ combine to
form carbonic
acid
30. Carbon Dioxide Transport in the Blood
CO2
CO2
Dissolved CO2
(7%)
Dissolved CO2 Dissolved CO2
CO2 + Hb
Hb + CO2
Hb•CO2 (23%)
Hb•CO2
CO2 + H2O
H2O + CO2H2CO3
HCO3
–
HCO3
–
HCO3
– in
plasma (70%)
HCO3
–
in
plasma
H+ + Hb Hb•H
H+ + HbHb•H
Cl–
Cl–
Cellular
respiration
in
peripheral
tissues
VENOUS BLOOD
Alveoli
Transport
to lungs
Red blood cell
Capillary
endothelium
Cell membrane
H2CO3
CA
CA