Lecture 4 slides
Transport of oxygen and carbon dioxide in
blood and body fluids
July 13th, 2011
Ann Raddant, B.S.
Email: ann-raddant@uiowa.edu
Phone: 335-7873
Pressures of gases in water and tissues
• Henry’s Law
• Solubility coefficient depends on physical and chemical
attraction or repulsion to water molecules
Molecule
Oxygen
Carbon dioxide
Solubility coefficient
0.024
0.57
More soluble = lower partial pressure
Blood PO2: 100mmHg
Blood CO2: 40mmHg
Today’s Topics
• Diffusion of respiratory gases from the alveolus to the
level of the systemic capillary and back to the lung
• The two mechanisms by which oxygen in carried in the
blood: dissolved and bound to hemoglobin
• Oxygen-hemoglobin dissociation curve
• The three forms by which carbon dioxide is carried in the
blood
• The basics of acid-base control using the HendersonHasselbach equation and Davenport diagrams for
analysis
Uptake of oxygen by pulmonary blood
• PO2 gradient between alveolus
and pulmonary capillary
• RBC transit time
– Safety factor
• Increased flow during exercise is
easily accommodated
• Pathological thickening of
membranes can limit O2 transfer
– Fick’s Law (increased surface area)
– Decreased rate of diffusion
Safety factor
PO2 in arterial blood
Of blood entering the left heart:
• 98% oxygenated in pulmonary capillaries
• 2% shunted blood from bronchial circulation
Arterial PO2 in systemic circuit is about 95 mmHg
Oxygen: from blood to cell: 2 step process
Diffusion of oxygen from capillaries to the interstitial fluid
• PO2 capillary = 95
• PO2 interstitial fluid = 40
Increased blood flow will increase interstitial fluid P O2
Increased metabolic rate will decrease interstitial fluid P O2
Oxygen: from blood to cell: 2 step process
Diffusion of oxygen from interstitial fluid to cells
• PO2 interstitial fluid = 40
• PO2 intracellular = 5 – 40 (shown as 23 here)
Metabolic functions of cell can be supported with as little as 1-3 mmHg
Large safety factor
CO2 diffusion from peripheral tissues back to alveoli
CO2 is a waste product of many metabolic reactions
• PCO2 intracellular = 46
• PCO2 interstitial = 45
• PCO2 capillary = 45
CO2 diffusion from peripheral tissues back to alveoli
• ΔP can be lower for CO2 than O2 because it
diffuses so much faster than O2
• Increased blood flow will reduce venous PCO2
• Increased metabolic rate will increase venous PC O2
Diffusion of CO2 from blood to alveolar air
Transport of O2 in the blood
1. Dissolved oxygen – 3%
–
Low solubility limits the concentration of O2 that can
be transported dissolved in blood
2. Hemoglobin (Hb) – 97%
–
–
Contained within red blood cells (RBC’s)
Each Hb molecule contains 4 chains
• Can bind 4 O2 molecules
Oxygen capacity
• ~ 20 ml O2/100ml blood
• O2 capacity is affected in diseases such as anemia
and polycythemia
– anemia: decreased number of RBC’s or
decreased amount of Hb in blood
– polycythemia: increased blood volume occupied
by RBC’s
Oxygen saturation: percent of maximal O2
combined with hemoglobin
Volumes per cent: common expression of
a solution’s concentration
Vodka: 40% EtOH
Saturated blood: 20% O2
Volumes per cent: common expression of
a solution’s concentration
Saturated blood: 20% O2
15 grams Hb per 100ml blood
1.34 ml O2 per 1g Hb
20ml in 100ml blood = 20%
Oxygen-Hemoglobin Dissociation Curve
Small change in PO2 here
won’t impair Hb loading
Small change in PO2 here
allows O2 release
Utilization coefficient
• Percentage of blood that gives up its
oxygen as it passes through the tissue
capillaries
• Compare O2 content (using % volume) of
arterial blood and venous blood
Utilization coefficient
5ml O2
per 100ml
blood
Venous
blood
5ml O2 per 100ml of blood used
20ml O2 = starting amount
5/20 = 25%
Arterial
blood
Utilization coefficient
Arterial
blood
Venous blood
during exercise
15ml O2 per 100ml of blood used
20ml O2 = starting amount
15/20 = 75%
15ml O2
per 100ml
blood
Factors that shift the OxygenHemoglobin dissociation curve
The Bohr Effect: CO2 and H+ ions interact with Hb
and reduce its affinity for O2
• Shifting the curve to the right enhances the release of O2
– Lower saturation at the same PO2
• Shifting the curve to the left enhances loading of O2
% Hb
Saturation
– Higher saturation at the same PO2
PO2
R: release
L: loading
Shift to the right: hemoglobin is less saturated at same blood PO2 values
R: release
L: loading
Shift to the left: hemoglobin is more saturated at same blood P O2 values
Factors which can shift the curve to the right
• Decreased pH
– Increased [H+]
•
•
•
•
Increased CO2
Increased temp
Increased DPG
Exercise
Enhanced release allows for more O2 to reach tissues
DGP: 2,3-diphosphoglycerate
Conditions of low tissue O2 lead
to generation of more DGP
• High altitude
• Airway obstruction
• Congestive heart failure
Factors which can shift the curve to the left
• Increased pH
– Decreased [H+]
• Decreased CO2
Transport of CO2 in the blood
1. Dissolved carbon dioxide – 7%
–
Obeys Henry’s law, by CO2 is 20x more soluble than O2
2. Bicarbonate (HCO3-) – 70%
–
carbonic anhydrase - CA
3. Carbamino compounds – 23%
–
CO2 reacts with Hb to form carbaminohemoglobin (HbCO2)
The chloride shift
• HCO3- diffuses out of RBC down its
concentration gradient
• Cl- moves into RBC in order to balance total
charge
Transport of CO2 in the blood
CO2 dissociation curve
Summary of CO2 dynamics for all forms
The Haldane Effect
• Binding of O2 with hemoglobin tends to displace
CO2 from the blood
– Opposite of Bohr effect
• Reduced Hb is a better proton and CO2 acceptor
The Haldane Effect
In peripheral tissues (top):
• Reduced Hb (no O2) is a
better proton acceptor –
binds H+, shifts CO2 bicarb rxn (below) to right
and allows blood to carry
more CO2
The Haldane Effect
In the lungs (bottom):
• O2 -Hb is a bad proton
acceptor – promotes H+
release, shifts CO2 bicarb rxn (below) to left
and promotes release of
CO2
Displacement of O2 by CO
• Hemoglobin has a
much higher binding
affinity for CO then
oxygen – small
amounts of this gas
can be lethal
Respiratory exchange ratio
Transported in every 100ml of blood:
• 5ml O2
• 4ml CO2
R changes in response to metabolism
• Carbs: R = 1.0
• Fat: R = 0.7
• Mixed (normal) R ~ 0.8
Acid Base Balance
Lung excretes 10,000 mEq/day of carbonic acid every day
Bicarb buffer is critical for maintenance of blood pH
pH = 6.1 + log [HCO3-]/[CO2]
Acid Base Balance
Physiological response to acidosis or
alkalosis
Take home points
• Oxygen and carbon dioxide move
between blood to tissue based on partial
pressure gradients
• Most oxygen is transported bound to
hemoglobin, while most carbon dioxide is
transported as bicarbonate
• Many factors can affect the binding of
oxygen to hemoglobin
• Carbon dioxide carried in the blood as
bicarbonate contributes to physiological
buffering of blood pH
blood and body fluids
July 13th, 2011
Ann Raddant, B.S.
Email: ann-raddant@uiowa.edu
Phone: 335-7873
Pressures of gases in water and tissues
• Henry’s Law
• Solubility coefficient depends on physical and chemical
attraction or repulsion to water molecules
Molecule
Oxygen
Carbon dioxide
Solubility coefficient
0.024
0.57
More soluble = lower partial pressure
Blood PO2: 100mmHg
Blood CO2: 40mmHg
Today’s Topics
• Diffusion of respiratory gases from the alveolus to the
level of the systemic capillary and back to the lung
• The two mechanisms by which oxygen in carried in the
blood: dissolved and bound to hemoglobin
• Oxygen-hemoglobin dissociation curve
• The three forms by which carbon dioxide is carried in the
blood
• The basics of acid-base control using the HendersonHasselbach equation and Davenport diagrams for
analysis
Uptake of oxygen by pulmonary blood
• PO2 gradient between alveolus
and pulmonary capillary
• RBC transit time
– Safety factor
• Increased flow during exercise is
easily accommodated
• Pathological thickening of
membranes can limit O2 transfer
– Fick’s Law (increased surface area)
– Decreased rate of diffusion
Safety factor
PO2 in arterial blood
Of blood entering the left heart:
• 98% oxygenated in pulmonary capillaries
• 2% shunted blood from bronchial circulation
Arterial PO2 in systemic circuit is about 95 mmHg
Oxygen: from blood to cell: 2 step process
Diffusion of oxygen from capillaries to the interstitial fluid
• PO2 capillary = 95
• PO2 interstitial fluid = 40
Increased blood flow will increase interstitial fluid P O2
Increased metabolic rate will decrease interstitial fluid P O2
Oxygen: from blood to cell: 2 step process
Diffusion of oxygen from interstitial fluid to cells
• PO2 interstitial fluid = 40
• PO2 intracellular = 5 – 40 (shown as 23 here)
Metabolic functions of cell can be supported with as little as 1-3 mmHg
Large safety factor
CO2 diffusion from peripheral tissues back to alveoli
CO2 is a waste product of many metabolic reactions
• PCO2 intracellular = 46
• PCO2 interstitial = 45
• PCO2 capillary = 45
CO2 diffusion from peripheral tissues back to alveoli
• ΔP can be lower for CO2 than O2 because it
diffuses so much faster than O2
• Increased blood flow will reduce venous PCO2
• Increased metabolic rate will increase venous PC O2
Diffusion of CO2 from blood to alveolar air
Transport of O2 in the blood
1. Dissolved oxygen – 3%
–
Low solubility limits the concentration of O2 that can
be transported dissolved in blood
2. Hemoglobin (Hb) – 97%
–
–
Contained within red blood cells (RBC’s)
Each Hb molecule contains 4 chains
• Can bind 4 O2 molecules
Oxygen capacity
• ~ 20 ml O2/100ml blood
• O2 capacity is affected in diseases such as anemia
and polycythemia
– anemia: decreased number of RBC’s or
decreased amount of Hb in blood
– polycythemia: increased blood volume occupied
by RBC’s
Oxygen saturation: percent of maximal O2
combined with hemoglobin
Volumes per cent: common expression of
a solution’s concentration
Vodka: 40% EtOH
Saturated blood: 20% O2
Volumes per cent: common expression of
a solution’s concentration
Saturated blood: 20% O2
15 grams Hb per 100ml blood
1.34 ml O2 per 1g Hb
20ml in 100ml blood = 20%
Oxygen-Hemoglobin Dissociation Curve
Small change in PO2 here
won’t impair Hb loading
Small change in PO2 here
allows O2 release
Utilization coefficient
• Percentage of blood that gives up its
oxygen as it passes through the tissue
capillaries
• Compare O2 content (using % volume) of
arterial blood and venous blood
Utilization coefficient
5ml O2
per 100ml
blood
Venous
blood
5ml O2 per 100ml of blood used
20ml O2 = starting amount
5/20 = 25%
Arterial
blood
Utilization coefficient
Arterial
blood
Venous blood
during exercise
15ml O2 per 100ml of blood used
20ml O2 = starting amount
15/20 = 75%
15ml O2
per 100ml
blood
Factors that shift the OxygenHemoglobin dissociation curve
The Bohr Effect: CO2 and H+ ions interact with Hb
and reduce its affinity for O2
• Shifting the curve to the right enhances the release of O2
– Lower saturation at the same PO2
• Shifting the curve to the left enhances loading of O2
% Hb
Saturation
– Higher saturation at the same PO2
PO2
R: release
L: loading
Shift to the right: hemoglobin is less saturated at same blood PO2 values
R: release
L: loading
Shift to the left: hemoglobin is more saturated at same blood P O2 values
Factors which can shift the curve to the right
• Decreased pH
– Increased [H+]
•
•
•
•
Increased CO2
Increased temp
Increased DPG
Exercise
Enhanced release allows for more O2 to reach tissues
DGP: 2,3-diphosphoglycerate
Conditions of low tissue O2 lead
to generation of more DGP
• High altitude
• Airway obstruction
• Congestive heart failure
Factors which can shift the curve to the left
• Increased pH
– Decreased [H+]
• Decreased CO2
Transport of CO2 in the blood
1. Dissolved carbon dioxide – 7%
–
Obeys Henry’s law, by CO2 is 20x more soluble than O2
2. Bicarbonate (HCO3-) – 70%
–
carbonic anhydrase - CA
3. Carbamino compounds – 23%
–
CO2 reacts with Hb to form carbaminohemoglobin (HbCO2)
The chloride shift
• HCO3- diffuses out of RBC down its
concentration gradient
• Cl- moves into RBC in order to balance total
charge
Transport of CO2 in the blood
CO2 dissociation curve
Summary of CO2 dynamics for all forms
The Haldane Effect
• Binding of O2 with hemoglobin tends to displace
CO2 from the blood
– Opposite of Bohr effect
• Reduced Hb is a better proton and CO2 acceptor
The Haldane Effect
In peripheral tissues (top):
• Reduced Hb (no O2) is a
better proton acceptor –
binds H+, shifts CO2 bicarb rxn (below) to right
and allows blood to carry
more CO2
The Haldane Effect
In the lungs (bottom):
• O2 -Hb is a bad proton
acceptor – promotes H+
release, shifts CO2 bicarb rxn (below) to left
and promotes release of
CO2
Displacement of O2 by CO
• Hemoglobin has a
much higher binding
affinity for CO then
oxygen – small
amounts of this gas
can be lethal
Respiratory exchange ratio
Transported in every 100ml of blood:
• 5ml O2
• 4ml CO2
R changes in response to metabolism
• Carbs: R = 1.0
• Fat: R = 0.7
• Mixed (normal) R ~ 0.8
Acid Base Balance
Lung excretes 10,000 mEq/day of carbonic acid every day
Bicarb buffer is critical for maintenance of blood pH
pH = 6.1 + log [HCO3-]/[CO2]
Acid Base Balance
Physiological response to acidosis or
alkalosis
Take home points
• Oxygen and carbon dioxide move
between blood to tissue based on partial
pressure gradients
• Most oxygen is transported bound to
hemoglobin, while most carbon dioxide is
transported as bicarbonate
• Many factors can affect the binding of
oxygen to hemoglobin
• Carbon dioxide carried in the blood as
bicarbonate contributes to physiological
buffering of blood pH