Transcript hemoglobin - SHMD 339: Exercise Physiology 3

Oxygen and Carbon
Dioxide transport in
the blood
Majority of O2 and CO2 is transported
in the blood by:
 O2 combing with hemoglobin
 CO2 transformed into bicarbonate
(HCO3¯)

Hemoglobin and O2 transport

±99% of O2 transported in blood is
chemically bound to hemoglobin

Hemoglobin is a protein found in red
blood cells (erythrocytes)

Each hemoglobin molecule can hold up to
4 O2 molecules

O2 combined with hemoglobin =
oxyhemoglobin

O2 that is NOT combined with
hemoglobin = deoxyhemoglobin
Oxyhemoglobin

The amount of O2 that can be transported
depends on the concentration of hemoglobin
Normal, healthy men = 150g/L of blood
 Normal, healthy women = 130g/L of blood


When a hemoglobin molecule is completely
saturated with O2  it can transport 1.34ml
of O2

Therefore if hemoglobin if full (100% saturated
with O2):
Healthy male can transport 200ml of O2
 Healthy female can transport 174ml of O2


100% saturation occurs at sea level (low
altitude)
Partial Pressure

The amount of O2 bound to hemoglobin is directly
related to the partial pressure of O2.

PO2:
All gases exert pressure on the walls of their container
because the molecules of gas bounce off the walls.

Partial pressure is used to describe a mixture of gases.

Defined as the pressure that any one gas would exert
on the walls of the container if it were the only gas
present
In the lungs, where the alveoli and capillaries
exchange gases, PO2 is high
 Therefore O2 binds instantly to hemoglobin.


As the blood circulates to other body tissue
 the PO2 becomes lower

Therefore hemoglobin releases O2 into the
tissue because the hemoglobin cant maintain
its full capacity of O2
Oxyhemoglobin Dissociation Curve

In the alveolar capillaries in the lungs:

O2 binding with hemoglobin is called loading

Release of O2 from hemoglobin is called
unloading

Loading & unloading are reversible actions:
Deoxyhemoglobin + O2
Oxyhemoglobin
Oxyhemoglobin Dissociation Curve

An important tool for understanding how our blood carries
and releases oxygen.

Relates oxygen saturation (SO2) and partial pressure of
oxygen in the blood (PO2)

Determined by what is called "hemoglobin's affinity for
oxygen“
how readily hemoglobin acquires and releases oxygen
molecules from its surrounding tissue.
Oxygen hemoglobin dissociation curve
Oxygen Dissociation Curve

Shows the percentage of O2 that is bound to hemoglobin
at each O2 pressure.

The curve is S-shaped with a steep slope between 10 and
60 mmHg and a flat portion between 70 and 100 mmHg.

At rest the body’s O2 requirement is low & only ±25% is
unloaded into muscles

At intense exercise, PO2 can reach 20mmHg and 90% of
O2 is unloaded into muscles
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Significance of the Flat Portion

The flat portion of the curve shows that the PO2 can fall from 100
to 60 mmHg and the hemoglobin will still be 90% saturated with
O2

At pressures above 60mm Hg, the dissociation curve is relatively
flat.

This means the O2 content does not change much (even with large
changes in the partial pressure of oxygen)

E.g. PO2 can fluctuate between 90 – 100mmHg without a large
drop in the percentage of hemoglobin that is saturated with O2

*This is important because there is a drop in PO2 with aging and
with climbing high altitudes
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Haemoglobin Saturation at High Values
Lungs at sea level: PO2
of 100mmHg
haemoglobin is 98%
SATURATED
When the PO2 in the lungs
declines below typical sea
level values, haemoglobin
still has a high affinity for
O2 and remains almost
fully saturated.
Lungs at high
elevations: PO2 of
80mmHg,
haemoglobin 95
% saturated
Even though PO2
differs by 20 mmHg
there is almost no
difference in
haemoglobin
saturation.
Significance of Steep Portion

PO2 reductions below 40 mm Hg produce a rapid
decrease in the amount of O2 bound to hemoglobin.

When the PO2 falls below 40 mm Hg, the quantity of O2
delivered to the tissue cells may be significantly reduced.

As PO2decrease in this steep area of the curve, the O2
is unloaded to peripheral tissue as hemoglobin’s affinity
for O2 diminishes.

Therefore, small changes in PO2 will release large
amounts of O2 from hemoglobin.

* This is critical during exercise when O2 consumption
is high.
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Haemoglobin Saturation at Low Values
Factors that affect the O2
Dissociation
◦ pH - Change in the blood pH
◦ Temperature- temp increases = the curve
moves to the right
◦ Carbon Dioxide – increased PCO2
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Factors Altering Haemoglobin
Saturation
Factors Altering Haemoglobin
Saturation (Exercise)
Example

During exercise, the oxyhemoglobin
dissociation curve will shift to the RIGHT

This is because the pH in the body is
decreased (from increased lactic acid)
AND

Temperature increases during exercise
O2 Transport in muscle

Myoglobin:
- Protein that binds with O2
- Found in Skeletal and Cardiac muscle fibers (not in blood)
- Acts as a shuttle to transport O2 from muscle cell
membrane to the mitochondria
- Found in large quantities in slow-twitch fibers (high aerobic
capacity)
- Smaller amounts in intermediate fibers
- Limited quantity in fast twitch fibers

Myoglobin has a similar structure to hemoglobin, but is ¼
weight

Difference in structure = difference in affinity for O2

Myoglobin has a greater affinity for O2:
Therefore the myoglobin-O2 dissociation curve is much
steeper
= myoglobin releases O2 at very
low PO2 values

NB because PO2 in mitochondria
of contracting skeletal muscle
can be as low as 1mmHg.

Myoglobin stores O2 = reserve O2 for transition
from rest to exercise

At the start of exercise there is a lag time from
the onset of muscular contraction and increased
O2 delivery to the muscles

Therefore O2 bound to myoglobin before
exercise acts as a buffer
so that muscles can receive O2 until the
cardiopulmonary system can meet the new O2
demand

At the end of exercise:
- myoglobin- O2 stores must be replenished to
ensure O2 is available for the next time exercise
begins

Therefore O2 consumption above rest
contributes to the O2 debt

i.e. O2 consumption continues after exercise has
stopped  leading to an O2 debt (O2 deficit)
(Anaerobic metabolism of lactate – also called
EPOC  Post Exercise Oxygen Consumption)
Carbon Dioxide Transport in Blood

CO2 transported in the blood by:
1. Dissolved CO2 (±10%)
2. CO2 bound to hemoglobin (±20%)
3. Bicarbonate (HCO3¯)(±70%)
Dissolved
bound to Hb
HCO3-

CO2 is converted to bicarbonate in red blood cells:

A high PCO2 causes CO2 to combine with water, forming
carbonic acid.

This reaction is rapidly catalyzed by the enzyme Carbonic
Anhydrase

The carbonic acid then dissociates into bicarbonate ion and
hydrogen ion.

The hydrogen ion then binds with hemoglobin

The bicarbonate ion diffuses out of the red blood cell into
the blood plasma
Carbon Dioxide
Transport of CO2
Transport
CO2 + H2O
CA
H2 CO3
Carbonic Acid
H2 CO3
H+ + H-CO3
Bicarbonate ion
Bicarbonate Ion Exchange

Because bicarbonate carries a negative charge
(anion), removal of a negatively charged molecule
from a cell = electrochemical imbalance

Therefore the negative charge must be replaced

Bicarbonate is replaced by chloride (Cl¯) which
diffuses from the plasma into the red blood cell

This is called chloride shift
 the shift of anions into red blood cells as
blood moves through tissue capillaries

When blood reaches the pulmonary capillaries:
PCO2 of the blood is greater than that of the alveolus
= CO2 diffuses out of the blood across the blood-gas
interface

At the lungs:
Binding of O2 to hemoglobin causes a release of the
hydrogen ions (which are bound to hemoglobin) to
promote the formation of carbonic acid

H+ + HCO3¯
H2CO3

In conditions where PCO2 is low (at the
alveolus), carbonic acid then dissociates into
CO2 and H2O
H2CO3

CO2 +H2O
The release of CO2 from the blood into the
alveoli is removed from the body in expired
gas (CO2 we breathe out)
Revision Questions

1. What is the amount of hemoglobin found in a
normal male and female? (2)

2. What is the amount of oxygen carried in a
normal male and female? (2)

3. What is partial pressure? (2)
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4. Explain the oxghemoglobin dissociation curve,
focusing on the use, flat and steep portions (10)

5. What factors affect the oxghemoglobin
dissociation curve? (3)
Revision Questions

6. How does exercise affect the oxghemoglobin dissociation
curve? (3)
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7. What is myoglobin and where is it found? (4)
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8. How is myoglobin different to hemoglobin? (4)

9. What are the differences in myoglobin and oxygen at the
start and end of exercise? Why does this happen? (8)
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10. What are the way in which carbon dioxide is
transported? (3)
11. How is carbon dioxide converted to bicarbonate? (5)
 12. Explain bicarbonate exchange. (8)
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