Embed Size (px)
Citation preview
CHAPTER 22:
RESPIRATORY SYSTEM
(3): GAS EXCHANGE
Human Anatomy and Physiology II –
BIOL153
Processes of Respiration
Pulmonary
ventilation
External
respiration
Transport
Internal
respiration
Respiratory
system
Circulatory
system
Goals/Objectives
State Dalton’s law of partial pressures and Henry’s law
Describe how atmospheric and alveolar air differ in composition, and explain these differences
Relate Dalton’s law and Henry’s laws to events of external and internal respiration
Describe how oxygen is transported in blood, and explain how temperature, pH, BPG, and PCO2
affect oxygen loading and unloading
Describe carbon dioxide transport in blood
Basic Properties of Gases: Dalton's
Law of Partial Pressures
Total pressure exerted by mixture of gases =
sum of pressures exerted by each gas
Partial pressure
Pressure exerted by each gas in mixture
Directly proportional to its percentage in mixture
Basic Properties of Gases: Henry's
Law
Gas mixtures in contact with liquid
Each gas dissolves in proportion to its partial
pressure
At equilibrium, partial pressures in two phases
will be equal
Amount of each gas that will dissolve
depends on
Solubility–CO2 20 times more soluble in water
than O2; little N2 dissolves in water
Temperature–as temperature rises, solubility
decreases (higher temp = gas state)
External Respiration
Influenced by:
• Thickness and surface
area of respiratory
membrane
• Partial pressure gradients
and gas solubilities
• Ventilation-perfusion
coupling
Steep partial pressure
gradient for O2 in lungs
• Drives oxygen flow to
blood
Ventilation-Perfusion Coupling
Perfusion-blood flow reaching alveoli
Ventilation-amount of gas reaching alveoli
Ventilation and perfusion matched (coupled) for efficient gas exchange
Never balanced for all alveoli due to
Regional variations due to effect of gravity on blood and air flow
Some alveolar ducts plugged with mucus
Ventilation-Perfusion Coupling
Ventilation less than perfusion Ventilation greater than perfusion
Mismatch of ventilation and perfusion
ventilation and/or perfusion of alveoli
causes local P and PCO2 O2
Mismatch of ventilation and perfusion
ventilation and/or perfusion of alveoli
causes local P and PCO2 O2
O2 autoregulates
arteriolar diameter
O2 autoregulates
arteriolar diameter
Pulmonary arterioles
serving these alveoli
constricts
Pulmonary arterioles
serving these alveoli
dilate
Match of ventilation
and perfusion
ventilation, perfusion
Match of ventilation
and perfusion
ventilation, perfusion
Transport of Respiratory Gases by
Blood
Pulmonary
ventilation
External
respiration
Transport
Internal
respiration
Respiratory
system
Circulatory
system
Internal Respiration
Clicker Question
The pressure exerted by each gas in a mixture is
proportional to its percentage. This is _______.
a) Dalton's law of partial pressures
b) Boyle's law of partial pressures
c) Henry's law of gas percentages
d) the law of gas proportionality
Clicker Question
Why is the rate of CO2 exchange roughly
equivalent to that of O2 despite its less steep
pressure gradient?
a) CO2 diffuses much more rapidly out of the
cells.
b) CO2 binds to O2 and moves across the
respiratory membrane simultaneously.
c) CO2 is more soluble in water than is O2.
d) CO2 is actively transported into the alveoli.
Goals/Objectives
State Dalton’s law of partial pressures and Henry’s law
Describe how atmospheric and alveolar air differ in composition, and explain these differences
Relate Dalton’s law and Henry’s laws to events of external and internal respiration
Describe how oxygen is transported in blood, and explain how temperature, pH, BPG, and PCO2
affect oxygen loading and unloading
Describe carbon dioxide transport in blood
O2 Transport
Molecular O2 carried in blood 1.5% dissolved in plasma
98.5% loosely bound to each Fe of hemoglobin (Hb) in RBCs
Clicker Question
The maximum molecule(s) of O2 that can be
transported by one hemoglobin molecule is:
a) one
b) two
c) three
d) four
Globin chains
Hemegroup
Globin chains
Hemoglobin consists of globin (two alpha and two beta
polypeptide chains) and four heme groups.
Iron-containing heme pigment.
Hemoglobin (Hb) - Structure
oxyhemoglobindeoxyhemoglobin
Hemoglobin attached to carbon
dioxide = carbaminohemoglobin
O2 and Hemoglobin
Loading and unloading of O2 facilitated by change in shape of Hb
As O2 binds, Hb affinity for O2 increases
As O2 is released, Hb affinity for O2 decreases
Fully saturated (100%) if all four hemegroups carry O2
Partially saturated when one to three hemes carry O2
O2 and Hemoglobin
In the lungs, here
PO2is high (100
mm Hg), Hb is
almost fully
saturated (98%)
with O2.
If more O2 is present,
more O2 is bound.
However, because of Hb’s
properties (O2 binding
strength changes with
saturation), this is an S-
shaped curve, not a
straight line.
In the tissues of other
organs, Where PO2is
low (40 mm Hg), Hb is
less saturated (75%)
with O2.
This axis tells you how much
O2 is bound to Hb. At 100%,
each Hb molecule has 4 bound
oxygen molecules.
Hemoglobin
Oxygen
100
80
60
40
20
0
0 20 40 60 80 100
Pe
rc
en
t O
2sa
tu
ra
tio
n o
f h
em
og
lo
bin
P (mm Hg)
This axis tells you the relative
Amount (partial pressure) of
O2 dissolved in the fluid
Surrounding the Hb.
•
•
O2
O2 and Hemoglobin
In the lungs
100
80
60
40
20
00 20 40 60 80
Perc
ent O
2sa
tu
ra
tio
n o
f h
em
oglo
bin
100
PO
2
(mm Hg)
At high PO2
, large changes in PO2
cause only
small changes in Hb saturation. Notice that the
curve is relatively flat here. Hb’s properties produce a
safety margin that ensures that Hb is almost fully
saturated even with a substantial PO2
decrease. As a
result, Hb remains saturated even at high altitude or with
lung disease.
At high altitude, there is less O2.
At a PO2in the lungs of only 80
mm Hg, Hb is still 95% saturated.
At sea level, there is lots of O2.
At a PO2in the lungs of 100 mm Hg,
Hb is 98% saturated.
98%
95%
O2 and Hemoglobin
In the tissues
100
80
60
40
20
0
Per
cent O
2sa
tura
tion o
f hem
oglo
bin
0 20 40 60 80 100PO2
(mm Hg)
At low PO2, large changes in PO2
cause large
changes in Hb saturation. Tissues other than
lungs have a low PO2because they consume O2.
Notice that the curve is relatively steep at low PO2.
Hb’s properties ensure that oxygen is delivered
where it is most needed—when tissues need more,
they get more.
In metabolically active tissues (e.g.,
exercising muscle), the PO2is even lower.
At a PO2of 20 mm Hg, Hb is only 40%
saturated—an additional 35% of O2 has
been unloaded for tissue use.
In resting tissues, at a PO2of 40 mm Hg,
Hb is 75% saturated—only 23% of O2
carried by Hb is released.
75%
40%
Other Factors Influencing
Hemoglobin Saturation
Increases in temperature, H+, Pco2, and BPG
Modify structure of hemoglobin; decrease its affinity for O2
Occur in systemic capillaries
Enhance O2 unloading from blood
Shift O2-hemoglobin dissociation curve to right
Decreases in these factors shift curve to left
Other Factors That Effect
Hemoglobin Saturation
Perc
ent O
2sa
tu
ra
tio
n o
f h
em
og
lo
bin 10ºC
20ºC
38ºC
43ºC
0
20
40
60
80
100
Normal body
temperatureP
erc
ent O
2satu
ration of hem
oglobin
0
20
40
60
80
100
Decreased carbon dioxide(PCO2
20 mm Hg) or H+ (pH 7.6)
Normal arterial
carbon dioxide
(PCO
2
40 mm Hg)
or H+
(pH 7.4)
Increased carbon dioxide
(PCO280 mm Hg)
or H+ (pH 7.2)
20 40 60 80 100
P (mm Hg)O
2
Factors that Increase Release of
O2 by Hemoglobin
As cells metabolize glucose and use
O2
Pco2 and H+ increase in capillary blood
Declining blood pH and increasing Pco2
Bohr effect - Hb-O2 bond weakens
oxygen unloading where needed most
Heat production increases directly
and indirectly decreases Hb affinity for
Transport and Exchange of CO2
Globin chains
Hemegroup
Globin chains
Hemoglobin consists of globin (two alpha and two beta
polypeptide chains) and four heme groups.
Iron-containing heme pigment.
CO2+Hb↔HbCO2
CO2 transported in
blood in three forms
7 to 10% dissolved in
plasma
20% bound to globin of
hemoglobin
(carbaminohemoglobi
n)
70% transported as
bicarbonate ions
(HCO3–) in plasma
Transport and Exchange of CO2
CO+HbHbCO
