carbon dioxide transport

Question 1

different ways carbon dioxide is transported in the blood + percentages

Answer 1

dissolved carbon dioxide 5% art 10% ven

carbamino carbon dioxide 5% art 30% ven

and carriage in blood as bicarbonate ions 90% of CO2 carriage art 60% ven

Question 2

where is carbon dioxide transported to and from?

Answer 2

from the tissues to the lungs

Question 3

explain dissolved CO2

Answer 3

carbon dioxide becomes dissolved obeying Henry’s Law, where the amount dissolved is proportional to partial pressure

Question 4

PaCO2

Answer 4

between 35mmHg and 45mmHg

Question 5

What happens when the carbon dioxide diffuses into the RBCs?

Answer 5

it is hydrated to form carbonic acid, catalysed by the enzyme carbonic anhydrase

Question 6

why is the hydration slow in plasma but rapid in erythrocytes?

Answer 6

the cells contain the enzyme whereas plasma doesn’t

Question 7

what then happens to the carbonic acid?

Answer 7

spontaneously dissociates into H+ ions and HCO3- ions

CO2+H20 H2CO3 H+ + HCO3-

Question 8

what happens next?

Answer 8

the concentration of HCO3- ions increases within the RBC and then diffuses out down the concentration gradient into the blood plasma

Question 9

explain chloride shift

Answer 9

to maintain electrical neutrality, Cl- diffuses into the erythrocytes from the plasma

occurs via the anion exchanger isoform 1

shifts the equilibrium of dissociation to the right, so more carbon dioxide can be absorbed by the red blood cells

Question 10

What happens to the H+ ions?

Answer 10

the intracellular of hydrogen ions begins to rise and can’t easily diffuse out of the cell

they bind to intracellular buffers, primarily haemoglobin

bind to reduced haemoglobin, as it is less acidic and thus a better proton acceptor

presence of reduced Hb in the peripheral blood helps with the loading of CO2

Question 11

what does haemoglobin therefore act as?

Answer 11

a buffer

Question 12

where is there more chloride ions + why?

Answer 12

intercellular higher for venous erythrocytes than arterial, as more carbon dioxide is taken up in the tissues than near the lungs

Question 13

Haldane effect explained

Answer 13

describes the fact that deoxygenation of the blood increases its ability to carry oxygen. The binding of oxygen to Hb promotes the release of carbon dioxide.

oxygenation of blood in the lungs displaces carbon dioxide from haemoglobin which increases the removal of carbon dioxide.

Question 14

what is the Henderson-Hasselbalch equation?

Answer 14

pH= pKa + log10(concentration of A-/HA)

Question 15

what is the equation used for?

Answer 15

can be used to estimate the pH of a buffer solution

Question 16

explain shape of carbon dioxide dissociation curve

Answer 16

almost linear in the physiological range

carbon dioxide dissociates more readily from oxygenated Hb resulting in a rightward shift of the dissociation for oxygenated blood

curve is steeper than oxygen dissociation, explaining why there is a smaller difference in arterial and venous PCO2 compared to PO2

Question 17

explain carbamino compound transport

Answer 17

co2 can bind to the terminal amine groups of proteins in the blood cells and plasma

can combine to the globing of haemoglobin, to produce carbaminohaemoglobin

Hb.NH2 + CO2 ↔ Hb.NH.COOH

Question 18

how does the carbon dioxide dissociate from the amine groups?

Answer 18

oxygen loading in the lungs forms oxygenated Hb which changes the conformation and loses H+ ions so cannot bind to carbon dioxide