Transport of carbon dioxide
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Transcript Transport of carbon dioxide
Review exam questions
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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 + H2OH2CO3H+ + 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 + H2OH2CO3H+ + HCO3H+ + HCO3- H2CO3 CO2 + H2O
Transport of carbon dioxide
In tissue :
plasma
CO2 + H2O
enzyme
H+ + HCO3-