Review exam questions

http://www.youtube.com/watch?v=Qrvrs6RXxwY

Starter - Key Word RevisionErythrocyte (RBC)DissociationPartial pressureOxyhaemoglobin (Hb + 4O2 HbO8)BiconcaveOxygen Dissociation CurveDiffusionPlasmaSaturatedPlatelets

Bone MarrowBloodOxygenAssociationCarbon DioxideBohr EffectLeukocyte (WBC)AlveoliHaemoglobin

Transport of carbon dioxide

H+

OBJECTIVESDescribe 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 TERMSHaemoglobin Carbamino-haemoglobinCarbonic Acid Carbonic anhydraseHaemoglobinic acid (HHb)BufferChloride 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)

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+

Sequence of events in which hydrogen carbonate is formed is significant for a number of reasons

Question 1:What will happen to the nvironmentwithin the erythrocyte?

• H+ ions bind to Hb to form haemoglobinic acid

Question 2:If Hb is absorbing H+ ions, what canwe say Hb is acting as?

85% of CO2 is transported as hydrogencarbonate 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

Sequence of events in which hydrogen carbonate is formed is significant for a number of reasons

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

85% of CO2 is transported as hydrogencarbonate 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

Sequence of events in which hydrogen carbonate is formed is significant for a number of reasons

TASK: Write equations for the following steps

1. 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 & Cl- diffuse

into the cell to balance the charge CHLORIDE SHIFT

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+ + HCO3-

Conformational change

Carbonic anhydrase

Decreased affintiy for O2

We know that oxygen dissociates fromoxyhaemoglobin 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 carbonateBuild 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 carbonateWhen 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+ + HCO3-

H+ + HCO3- H2CO3 CO2 + H2O

Transport of carbon dioxideIn tissue :

+ H2O H++HCO3-

plasma

enzyme

CO2