Download 3. SJW Bohr effect

The transport of oxygen
• When oxygen from the alveoli diffuses across the
alveolar capillary membrane, it enters the
bloodstream. It is the function of the blood to
transport oxygen and does it in two ways:
• 1. 97% is carried in haemoglobin
• 2. 3% is dissolved in the blood plasma
• When oxygen combines with haemoglobin, it forms
oxy-haemoglobin
o Hb(haemoglobin) + O2 (oxygen) = HbO2 (oxy-haemoglobin)
GAS TRANSPORT
• GAS TRANSPORT ACROSS THE RESPIRATORY MEMBRANE
• oxygen diffuses from alveolus across the alveolar wall,
respiratory membrane, and capillary wall towards red blood cells
• carbon dioxide diffuses in the opposite direction from the red
blood cell and from blood plasma to the alveolus
What happens when
we exercise?
• Task: complete flow diagram
• Page 74 Fig. 4.20 Putting it all together
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•
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Increases in Lactic Acid
Increases in CO2
Increases in blood and muscle temperature
Decreases in pH thus acidity levels increase.
These changes mean that the body needs oxygen
quickly.
Haemoglobin
• Haemoglobin has a very high affinity for oxygen
• The most important factor that determines how
much oxygen combines with haemoglobin is the
partial pressure of oxygen.
• When the pO2 of blood is high, such as in the
alveolar capillaries of the lungs, haemoglobin
readily combines with large amounts of oxygen until
it becomes almost fully saturated.
• When the pO2 of blood is low, such as in the
capillaries of the contracting muscles, oxygen is
released by the haemoglobin. This O2 can now be
used by the muscle tissues.
• This is represented by the oxy-haemoglobin
dissociation curve.
The Bohr Effect
During exercise muscles
need more oxygen so the
dissociation (release) of
oxygen from Hb happens
more readily
Dissociation
curve shifts to
the RIGHT
This is known as the Bohr
effect and frees up more
oxygen = used by working
muscles
Animation
• http://www.getbodysmart.com/ap/respiratorysyste
m/physiology/gases/hbsaturation/animation.html
Factors shifting the dissociation curve to the right are:
•1. Increase in blood and muscle temperature
•2. Decreases in PP oxygen within muscle
increasing the oxygen diffusion gradient.
•3. Increase in PP of carbon dioxide increasing
carbon dioxide gradient.
•4. Bohr effect – increase in acidity (lower pH)
• The effect is that the working muscles:
• Generate more heat when working
• Use more oxygen to provide energy, lowering the PP
oxygen
• Produce greater carbon dioxide as a by-product
• Increase lactic acid levels which increase muscle/blood
acidity
• Collectively all four factors increases the dissociation of
oxygen from haemoglobin that increases the supply of
oxygen to the working muscles.
Transport of oxygen
3% dissolves in plasma. 97% combines with haemoglobin to
form oxyhaemoglobin
One further method the body has of ensuring the muscles
are constantly supplied with adequate amounts of oxygen
is through myoglobin. It is only found in the skeletal
muscles.
Iron based protein
Similar to Hb
•In the muscle oxygen is transported by myoglobin.
•Myoglobin has a high affinity for oxygen.
•It stores oxygen and transports it from the capillaries to
the mitochondria.
•Mitochondria are the centres in the muscle where aerobic
respiration takes place.
Much
higher
affinity
For 02 than
Hb
(a-vo2 diff)
This represents how much oxygen is actually
extracted and used by the muscles
Measured by:
Analysing the difference in oxygen content of the blood in
the arteries leaving the lungs and that in the mixed venous
blood returning to the lungs
Exam Questions
1. Explain how oxygen is taken up by haemoglobin
from the lungs and released at the muscle site.
(3 marks)
2. Explain why aerobic training improves the
performer’s ability to transport oxygen.
(2 marks)
Mark scheme
1. A. Forms oxyhaemoglobin/Hb O2
• B. At lungs - high partial pressure of O2/ blood – low
partial pressure of O2;
• C. Haemoglobin becomes saturated;
• D. At muscles - low partial pressure of Oxygen/ O2/
blood - high partial
• pressure of O2;
• E. Hence oxygen dissociates from haemoglobin;
• F. Mention of myoglobin.
Mark scheme
2. A. More blood volume/haemoglobin/Hb/red blood
cells;
• B. Increased a-VO2 diff/more oxygen extracted by
muscles;
• C. Increased capilliarisation/more capillaries.