Physiology - CO2 transport

Question 1

How does CO2 enter the cell?

6

Answer 1

1- CO2 diffuses in
2-CO2 + H2O —> H2CO3
Catalysed by Carbonic anhydrase
3-H2CO3 dissociates to get rid of 1 H+ ion into HCO3- and H+, HCO3- diffuses into plasma down its concentration gradient
4- H+ added to haemoglobin makes HHb ( haemoglobin acid )
5-chloride ions move in to maintain charge
6- Oxyhaemaglobin dissociates at low pO2 to release O2 at respiring tissue ( Bohr shift)
the low pH causes the affinity of Hb and O2 to reduce, hence why it dissociates at respiring tissue!

Question 2

How is co2 transported in blood?

3

Answer 2

1- Carbaminocompounds
2-Dissolved CO2
3-HCO3-

Question 3

What is the differences in the co2 dissociation curve for arterial and venous blood?
(2)

Answer 3

venous blood is shifted to the right+ higher because it can carry more CO2
there is NO PLATEAUX in co2 dissociation curves because there is NO LIMIT to the number of h2o molecules that co2 can bind to.

Question 4

what is Ficks principal and the respiratory exchange ratio ?

Answer 4

1- Ficks principle:
CO2 OUTPUT = (arteriolar-venous diff ) xCO
RER= CO2 OUTPUT /O2 CONSUMPTION

Question 5

how does the Haldane effect work?

4

Answer 5

increased co2 hence reduced pH causes :

• more co2 to bind to Hb at lower pO2
• more H+ and low Ph causes a change in haemoglobins tertiary structure reducing the affinity for O2, so more co2 is picked up at respiring tissue .

-Bound Co2 is released from Hb when it becomes oxygenated at the lungs = reverse Haldane effect

the buffering capacity of the deoxyhaemoglobin is increased because :
1-when CO2 Binds to Hb = reduced Hb, this is more basic which means it is willing to accept more H+ ions, so more H2co3 dissociates causing increased co2 carriage.

Question 6

how is oxygen transported case study summary 
1-curve and plateaux
2-Bohr
3-fetal 
4-anemia 

(5)

Answer 6

Oxyhemoglobin
1-ox dissociation curve has plateaux which Are called O2 capacity = due to the limited number of HB sites

2-Bohr shift= to the right =, increase pco2 = more H+ = more 2,3,BPG( less affinity for O2) = more co2 binding and o2 off loading

3-Myoglobin = shifts to LHS = can pick up O2 in Low pO2 so baby gets O2

4-anaemia = shift curve down as Hb is reduced

Question 7

outline the acidosis and alkalosis ranges
-metabolic acidosis and alkalosis EXPLANATION
(5)

Answer 7

Acute respiratory Acidosis = due to increase PCO2= ph<7.35

acute respiratory alkalosis = pCO2 decreases =pH>7.45

EXPLANATION
Metabolic acidosis = due to the other metabolites INCREASING which cause CO2 to be blow off to compensate at the lungs = hence reduce PCO2 & HCO3-

Metabolic alkalosis = due to other metabolites decreasing in number = more CO2 kept in, and it dissociates to HCO3-, pCO2 increases to try and compensate.