Allied Science Physiology 09-10. Respiratory System. Lecture 4.
Allied Science Physiology. Respiratory System. Lecture 4.
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•
Transported in 2 modes:
a)  1.5% dissolved in plasma
–  At rest we consume 250 mlO2/min
–  CO = 5 l/min
–  O2 breathed per min: 1 liter
–  In arterial blood: 200ml O2 / 1 l of blood
–  3 ml of O2 / 1l blood dissolves
b)  98.5% bound to haemoglobin (Hb)
–  Hemoglobin located in red blood cells
–  4 globins (structural; CO2 binding site)
–  4 heme groups per haemoglobin (each with an iron atom)
–  Oxygen binds reversibly to heme group (iron) in Hb
–  Thus each hemoglobin can bind 4 O2 molecules
–  Amount of O2 bound to Hb is a function of the PO2
Allied Science Physiology. Respiratory System. Lecture 4.
oxyhemoglobin
deoxyhemoglobin
Hb.O2
Hb + O2
Figure 17.6
Allied Science Physiology. Respiratory System. Lecture 4.
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•
Binding of oxygen to hemoglobin follows
Law of Mass Action
–  More oxygen  more binds to hemoglobin
–  Non-linear relationship
•  Positive cooperativity
•
Saturation of hemoglobin is a measure of how much oxygen
bound to hemoglobin
–  100% saturation  all 4 binding sites on hemoglobin have
oxygen bound to them
•
98.5 % saturated in arterial blood (arterial PO2=100mmHg)
•
75% saturated in mixed venous blood (venous PO2 = 40mmHg)
•
Summarised by: Hemoglobin-Oxygen dissociation curve
Allied Science Physiology. Respiratory System. Lecture 4.
Figure 17.7
Allied Science Physiology. Respiratory System. Lecture 4.
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Figure 17.8
Allied Science Physiology. Respiratory System. Lecture 4.
•  Rightward shift (unloading,
decreased affinity):
–  Tissue level
–  H+ ( pH, Bohr effect)
–  PCO2
–  Temperature
–  2,3 DPG
•  Leftward shift (loading,
increased affinity):
–  Lung level
–  H+ ( pH, Bohr effect)
–  PCO2
–  Temperature
Figure 17.9
Allied Science Physiology. Respiratory System. Lecture 4.
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•  Increase in metabolic
activity increases
temperature
•  Increase in temperature
decrease Hb
affinity for O2
•  Decrease affinity
increases oxygen
unloading in tissue
Opposite effect at lung level
Figure 17.10a
Allied Science Physiology. Respiratory System. Lecture 4.
•  When oxygen binds to
hemoglobin, hydrogen
ions are released
•  Hb + O2  Hb.O2 + H+
•  Active tissue produces H+
This increases oxygen
unloading in tissue
(equation to the left)
Opposite effect at lung level
Figure 17.10b
Allied Science Physiology. Respiratory System. Lecture 4.
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•  CO2 reacts with Hb to form
carbaminohemoglobin
Hb + CO2  HbCO2
PCO2
PCO2
•  Increased metabolic activity
 increases CO2  reaction
to the right  change in Hb
conformation and decreases
Hb affinity for O2
•  Increases oxygen unloading in
active tissue
Opposite effect at lung level
Figure 17.9
Allied Science Physiology. Respiratory System. Lecture 4.
•  2,3-DPG = 2,3-diphosphoglycerate
•  Produced in red blood cells under
conditions of low oxygen such as
anemia and high altitude
2,3-DPG
•  High HbO2: inhibit DPG synthesis;
Low HbO2: stim. DPG synthesis
•  In tissue: 2,3-DPG decreases
affinity of hemoglobin for O2
enhancing O2 unloading
At lung level: decreases affinity of Hb
for O2 (negative side)
Figure 17.9
Allied Science Physiology. Respiratory System. Lecture 4.
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•  Hemoglobin has greater affinity for carbon
monoxide (CO) than for oxygen (24 times!)
•  Prevents oxygen from binding to hemoglobin
•  Toxic, can be fatal
Allied Science Physiology. Respiratory System. Lecture 4.
•  3 modes of transport:
–  5 – 6% transported dissolved in plasma
–  5-8% transported bound to hemoglobin
–  86-90% transported dissolved in the plasma as
bicarbonate ions
Carbonic Anhydrase
CO2 + H2O  -----------------  H2CO3  H+ + HCO3Law of Mass Action:
An increase in CO2 causes an increase in bicarbonate and
hydrogen ions (note that bicarbonate is transported out of the
erythrocyte into the plasma)
Allied Science Physiology. Respiratory System. Lecture 4.
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Figure 17.11
Allied Science Physiology. Respiratory System. Lecture 4.
Oxygen decreases affinity of hemoglobin
for carbon dioxide
Figure 17.12
Allied Science Physiology. Respiratory System. Lecture 4.
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Remember:
-Haldane effect: O2 decreases affinity of Hb for CO2
-Bohr effect: Hb + O2  Hb.O2 + H+
-Carbomino effect: Hb + CO2  HbCO2
Figure 17.13
Allied Science Physiology. Respiratory System. Lecture 4.
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