3. Goals For Learning
• To explore how O2 is
transported in the
blood.
• To explore how Co2 is
transported in the
blood.
• This will include
understanding the
oxygen dissociation
curve.
• What you need to
know
• Definition of partial
pressure
• Processes of external
respiration and
internal respiration.
4. Oxygen Transport
• O2 is transported by the blood either,
– Combined with haemoglobin (Hb) in the red blood
cells (>98%) or,
– Dissolved in the blood plasma (<2%).
5. Oxygen Transport
• The resting body requires 250ml of O2 per
minute.
• We have four to six billion haemoglobin
containing red blood cells.
• The haemoglobin allows nearly 70 times
more O2 than dissolved in plasma.
6. Haemoglobin
Haemoglobin molecules can
transport up to four O2’s
When 4 O2’s are bound to
haemoglobin, it is 100% saturated,
with fewer O2’s it is partially
saturated.
Oxygen binding occurs in
response to the high PO2 in the
lungs
Co-operative binding:
haemoglobin’s affinity for
O2 increases as its
saturation increases.
7. Lets Now Look at Haemoglobin
Saturation
• Haemoglobin saturation is the
amount of oxygen bound by
each molecule of haemoglobin
• Each molecule of haemoglobin can carry four
molecules of O2.
• When oxygen binds to haemoglobin, it forms
OXYHAEMOGLOBIN;
• Haemoglobin that is not bound to oxygen is
referred to as DEOXYHAEMOGLOBIN.
8. Haemoglobin Saturation
• The binding of O2 to haemoglobin
depends on the PO2 in the blood and
the bonding strength, or affinity,
between haemoglobin and oxygen.
• The graph on the following page shows an
oxygen dissociation curve, which reveals
the amount of haemoglobin saturation at
different PO2 values.
9. The Oxygen Dissociation Curve
•Reveals the amount of
haemoglobin saturation
at different PO2 values.
10. The Oxygen Disassociation Curve
Haemoglobin saturation is
determined by the partial pressure of
oxygen. When these values are
graphed they produce the Oxygen
Disassociation Curve
In the lungs the partial
pressure is approximately
100mm Hg at this Partial
Pressure haemoglobin has
a high affinity to 02 and is
98% saturated.
In the tissues of other
organs a typical PO2 is 40
mmHg here haemoglobin
has a lower affinity for O2
and releases some but not
all of its O2 to the tissues.
When haemoglobin leaves
the tissues it is still 75%
saturated.
11. Haemoglobin Saturation at High Values
Lungs at sea level:
PO2 of 100mmHg
haemoglobin is 98%
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.
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.
16. Factors affecting Disassociation
BLOOD TEMPERATURE
• increased blood temperature
• reduces haemoglobin affinity for O2
• hence more O2 is delivered to warmed-up
tissue
Respiratory Response to Exercise
BLOOD Ph
• lowering of blood pH (making blood
more acidic)
• caused by presence of H+ ions from lactic
acid or carbonic acid
• reduces affinity of Hb for O2
• and more O2 is delivered to acidic sites
which are working harder
CARBON DIOXIDE CONCENTRATION
• the higher CO2 concentration in tissue
• the less the affinity of Hb for O2
• so the harder the tissue is working, the
more O2 is released
17. Key Point
• Increased temperature and hydrogen ion
(H+) (pH) concentration in exercising
muscle affect the oxygen dissociation
curve, allowing more oxygen to be
uploaded to supply the active muscles.
18. Carbon Dioxide Transport
• Carbon dioxide also relies on the blood fro
transportation. Once carbon dioxide is
released from the cells, it is carried in the
blood primarily in three ways…
• Dissolved in plasma,
• As bicarbonate ions resulting from the
dissociation of carbonic acid,
• Bound to haemoglobin.
19. Dissolved Carbon Dioxide
• Part of the carbon dioxide released from the
tissues is dissolved in plasma. But only a small
amount, typically just 7 – 10%, is transported
this way.
• This dissolved carbon dioxide comes out of
solution where the PCO2 is low, such as in the
lungs.
• There it diffuses out of the capillaries into the
alveoli to be exhaled.
20. In Review
1) Oxygen is transported in the blood primarily
bound to haemoglobin though a small amount
is dissolved in blood plasma.
2) Haemoglobin oxygen saturation decreases.
1) When PO2 decreases.
2) When pH decreases.
3) When temperature increases.
21. In Review
Each of these conditions can reflect increased
local oxygen demand. They increase oxygen
uploading in the needy area.
3) Haemoglobin is usually about 98% saturated
with oxygen. This reflects a much higher
oxygen content than our body requires, so the
blood’s oxygen-carrying capacity seldom limits
performance.
22. In Review
4) Carbon dioxide is transported in the blood
primarily as bicarbonate ion. This
prevents the formation of carbonic acid,
which can cause H+ to accumulate,
decreasing the pH. Smaller amounts of
carbon dioxide are carried either
dissolved in the plasma or bound to
haemoglobin
Editor's Notes
Only about 3 ml of O 2 are dissolved in each litre of plasma. Assuming we have a total plasma volume of 3 to 5 litres, only about 9 – 15 ml of O 2 can be carried in the dissolved state.
This is not enough to supply even the resting body, which requires 250ml per minute. Fortunately we have four to six billion haemoglobin containing red blood cells. The haemoglobin allows nearly 70 times more O 2 than dissolved in plasma.
Factors Affecting Haemoglobin Saturation – Blood Acidity If the blood becomes more acidic the dissociation curve shifts right. This means that more oxygen is being uploaded from the haemoglobin at tissue level. See overhead. Factors Affecting Haemoglobin Saturation – Blood Acidity The rightward shift of the curve is due to a decline in pH. This is referred to as the BOHR effect. Factors Affecting Haemoglobin Saturation – Blood Acidity The pH in the lungs is generally high. So haemoglobin passing through the lungs has a strong affinity for oxygen, encouraging high saturation. At the tissue level, however the pH is lower, causing oxygen to dissociate from haemoglobin, thereby supplying oxygen to the tissues. Factors Affecting Haemoglobin Saturation – Blood Acidity With exercise, the ability to upload oxygen to the muscles increases as the muscle ph decreases. Factors Affecting Haemoglobin Saturation – Blood Temperature Increased blood temperature shifts the dissociation curve to the right, indicating that oxygen is uploaded more efficiently. Factors Affecting Haemoglobin Saturation – Blood Temperature Because of this, the haemoglobin will upload more oxygen when blood circulates through the metabolically heated active muscles. In the lungs, where the blood might be a bit cooler, haemoglobin’s affinity for oxygen is increased. This encourages oxygen binding.
Dissolved Carbon Dioxide Part of the carbon dioxide released from the tissues is dissolved in plasma. But only a small amount, typically just 7 – 10%, is transported this way. This dissolved carbon dioxide comes out of solution where the PCO2 is low, such as in the lungs. There it diffuses out of the capillaries into the alveoli to be exhaled. Bicarbonate Ions The majority of carbon dioxide ions is carried in the form of bicarbonate ion. 60 - 70% of all carbon dioxide in the blood. The following bit is quite heavy just listen hard. Bicarbonate Ions Carbon Dioxide and water molecules combine to form carbonic acid (H 2 CO 3 ). This acid is unstable and quickly dissociates, freeing a hydrogen ion (H + ) and forming a bicarbonate ion (HCO 3 - ): CO 2 + H 2 O H 2 CO 3 CO 2 + H 2 O Bicarbonate Ions The H + subsequently binds to haemoglobin and this binding triggers the BOHR effect (mentioned earlier). This shifts the oxygen-haemoglobin dissociation curve to the right. Thus formation of bicarbonate ion enhances oxygen uploading. Bicarbonate Ions This also plays a buffering as the H+ is neutralised therefore preventing any acidification of the blood. When blood enters the lungs, where the PCO 2 is lower, the H+ and bicarbonate ions rejoin to form carbonic acid, which then splits into carbon dioxide and water. In other words the carbon dioxide is re-formed and can enter the alveoli and then be exhaled. Key Point The majority of carbon dioxide produced by the active muscles is transported back to the lungs in the form of bicarbonate ions. Carbaminohaemoglobin CO 2 transport also can occur when the gas binds with haemoglobin, forming a compound called Carbaminohaemoglobin. It is named so because CO 2 binds with the amino acids in the globin part of the haemoglobin, rather than the haeme group oxygen does.
Dissolved Carbon Dioxide Part of the carbon dioxide released from the tissues is dissolved in plasma. But only a small amount, typically just 7 – 10%, is transported this way. This dissolved carbon dioxide comes out of solution where the PCO2 is low, such as in the lungs. There it diffuses out of the capillaries into the alveoli to be exhaled.
