Review exam questions
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XxwY
Starter - Key Word Revision
 Erythrocyte (RBC)
 Dissociation
 Partial pressure
 Oxyhaemoglobin (Hb + 4O2  HbO8)
 Biconcave
 Oxygen Dissociation Curve
 Diffusion
 Plasma
 Saturated
 Platelets
 Bone Marrow
 Blood
 Oxygen
 Association
 Carbon Dioxide
 Bohr Effect
 Leukocyte (WBC)
 Alveoli
 Haemoglobin
Transport of carbon dioxide
H+
OBJECTIVES
 Describe the 3 ways in which carbon dioxide is carried in
the blood
 Describe the importance of the formation of hydrogen
carbonate in the carrying of carbon dioxide in the blood.
 Describe and explain the Chloride shift.
KEY TERMS
 Haemoglobin
 Carbamino-haemoglobin
 Carbonic Acid
 Carbonic anhydrase
 Haemoglobinic acid (HHb)
 Buffer
 Chloride Shift
•
Carbon dioxide is transported through
the circulatory system in 3 ways:
1.
Dissolved in plasma (5%)
2.
Associated with Hb to form
carbaminohaemoglobin (10%)
(Changes shape of haemoglobin
and encourages oxygen
dissociation)
Sequence of events in which hydrogen carbonate is formed is significant
for a number of reasons
85% of CO2 is transported as
hydrogen carbonate ions
•
CO2 dissolves in water to form
carbonic acid (via carbonic
anhydrase catalyst in RBC)
CO2 + H2O  H2CO3
•
Carbonic acid releases H+ protons
(acid dissociation – chemistry)
H2CO3  HCO3- + H+
Question 1:
What will happen to the nvironment
within the erythrocyte?
•
H+ ions bind to Hb to form
haemoglobinic acid
Question 2:
If Hb is absorbing H+ ions, what can
we say Hb is acting as?
Sequence of events in which hydrogen carbonate is formed is significant
for a number of reasons
85% of CO2 is transported as hydrogen
carbonate ions
•
H+ ions lower blood pH and combine with
Hb to make haemoglobinic acid (HHb)
decreasing Hb O2 affinity (Bohr)
H+ + HB  HHb
•
HCO3- ions diffuse out of erythrocyte.
•
Cl- diffuse into the cell to balance the
charge  CHLORIDE SHIFT
Conclusion:
•
In a CO2-rich environment (i.e. at
respiring tissue), more oxygen
dissociates from oxyhaemoglobin
•
Oxygen dissociation curve shifts
to the right
(requires higher pO2 to saturate Hb due to
H+ competition)
•
This is known as the Bohr effect
Sequence of events in which hydrogen carbonate is formed is significant
for a number of reasons
85% of CO2 is transported as hydrogen
carbonate ions
•
CO2 dissolves in water to form carbonic acid
(via carbonic anhydrase catalyst in RBC)
CO2 + H2O  H2CO3
•
Carbonic acid releases H+ protons (acid
dissociation – chemistry)
H2CO3  HCO3- + H+
•
H+ lower blood pH and combine with Hb to
make haemoglobinic acid decreasing
Hb O2 affinity (Bohr)
H+ + HB  HHb
HCO3- ions diffuse out of the erythrocyte.
•
•
•
Cl- diffuse into the cell to balance the charge
 CHLORIDE SHIFT
TASK:
Write equations for the following steps
CO2 dissolves in water to form carbonic acid (via
carbonic anhydrase catalyst in RBC)
2. Carbonic acid releases H+ protons (acid dissociation
– chemistry)
3. H+ lower blood pH and combine with Hb to make
haemoglobinic acid decreasing Hb O2 affinity (Bohr)
4. HCO3- ions diffuse out of the erythrocyte & Cldiffuse into the cell to balance the charge 
CHLORIDE SHIFT
1.
EXT – Link these equations into a sequence (in a red blood
cell so you can show what is & isn't inside the cell)
CO2
CO2 + H2OH2CO3H+ + HCO3Carbonic anhydrase
Conformational change
Decreased affintiy for O2
We know that oxygen dissociates from
oxyhaemoglobin where the pO2 is low
(i.e. in respiring tissue).
•
If H+ ions can bind with Hb, they
must compete with oxygen
•
In respiring tissue:
- More CO2 produced
- More Carbonic acid formed
- More H+ dissociated
- More competition for Hb
- More oxygen dissociation
Formation of hydrogen carbonate
 Build up of hydrogen carbonate ions causes them to diffuse out of RBC
leaving inside of RBC positively charged.
 To balance electric charge Cl- ions diffuse into the RBC from plasma –
this is known as the chloride shift.
In this reaction Hb is acting as a buffer
http://www.youtube.com/watch?feature=player_embedded&v=x26TWL3VKMg
http://www.youtube.com/watch?feature=player_embedded&v=bklrcFuiH-8
Breakdown of hydrogen carbonate
 When blood gets to the
lungs, all the reactions are
reversed
 The hydrogen carbonate and
hydrogen ions recombine
releasing CO2
 The chloride shift is reversed
 Carbamino-haemoglobin
breaks down to release CO2
CO2 + H2OH2CO3H+ + HCO3H+ + HCO3-  H2CO3  CO2 + H2O
Transport of carbon dioxide
 In tissue :
plasma
CO2 + H2O
enzyme
H+ + HCO3-