3rd hour

1
3rd hour

• By the end of the lesson, student should be able
  to
• explain characteristics of oxygen dissociation
  curve
• compare oxygen dissociation curves of
  haemoglobin in foetus and adult
• explain Bohr effect due to partial pressure of
  CO2

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2
Oxygen dissociation curve of haemoglobin

• an S- shaped curve obtained when the percentage
  oxygen saturation of blood is plotted against the
  partial pressure of oxygen
• an S-shaped curve is obtained due to the way that
  Hb binds to oxygen
• When the first oxygen bind with the Hb with
  difficulty
• it alters the shape of the Hb molecule
• subsequently it is easier for the next O2
  molecule to be taken up easily

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3
Oxygen dissociation Curve

• at pO2 of approximately 30 mm Hg, 50 of the Hb
  is present as HbO8
• this is caused by the high affinity Hb to O2 at
  partial pressure of 73 mm Hg, the Hb is
  completely saturated with O2 this point is called
  loading tension
• at higher partial pressures of O2, further uptake
  of O2 can occur, but 100 saturation of Hb is
  rarely achieved

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4
Oxygen dissociation Curve
100
Amount of O2 unloaded to tissues at rest
80
Amount of O2 unloaded to tissues during exercise
60
Percent saturation
40
Veins (exercised)
20
Veins (at rest)
Arteries
0
0
20
40
60
80
100
PO2 (mm Hg)
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5
Oxygen dissociation Curve
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6
Oxygen dissociation curves of haemoglobin and
myoglobin in comparison

• Myoglobin molecule is widely distributed in
  animals and is particularly common in skeletal
  muscle tissues of mammals
• very similar to the Hb subunits with respect to
  both amino acid sequence and three dimensional
  structure
• This pigment may also bind to O2, but since there
  is only one haem group there can be no
  cooperative binding

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7
Oxygen dissociation curvesHemoglobin and
Myoglobin Compared
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8
Effect of partial pressure of carbon dioxide
towards O2 dissociation

• Once blood has travelled to the body tissues, O2
  is released
• this is due to the drop in the partial pressure
  of the O2 and a rise in the partial pressure of
  carbon dioxide in respiring cells
• A rise in the partial pressure of the carbon
  dioxide lowers the affinity of Hb for O2 which is
  therefore released

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9
Bohr effect

• Bohr effect or the Bohr shift
• an increase in the partial pressure of carbon
  dioxide shifts the oxygen dissociation curve to
  the right
• Tissue pH affects Oxygen delivery
• The Bohr effect
• Hemoglobin binds oxygen less strongly at lower pH
  values
• Ensures more efficient O2 delivery in working
  tissues
• Greater CO2 production in working tissues
• therefore lowers pH
• Greater O2 demand in working tissues

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10
Bohr effect
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11
Bohr effect explained
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12
Thank you for your attention

• Next lecture
• Explain the role of chemoreceptors in
  controlling rate of breathing
• Describe structure and functions of guard cells

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