carbon dioxide transport Flashcards
different ways carbon dioxide is transported in the blood + percentages
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
where is carbon dioxide transported to and from?
from the tissues to the lungs
explain dissolved CO2
carbon dioxide becomes dissolved obeying Henry’s Law, where the amount dissolved is proportional to partial pressure
PaCO2
between 35mmHg and 45mmHg
What happens when the carbon dioxide diffuses into the RBCs?
it is hydrated to form carbonic acid, catalysed by the enzyme carbonic anhydrase
why is the hydration slow in plasma but rapid in erythrocytes?
the cells contain the enzyme whereas plasma doesn’t
what then happens to the carbonic acid?
spontaneously dissociates into H+ ions and HCO3- ions
CO2+H20 H2CO3 H+ + HCO3-
what happens next?
the concentration of HCO3- ions increases within the RBC and then diffuses out down the concentration gradient into the blood plasma
explain chloride shift
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
What happens to the H+ ions?
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
what does haemoglobin therefore act as?
a buffer
where is there more chloride ions + why?
intercellular higher for venous erythrocytes than arterial, as more carbon dioxide is taken up in the tissues than near the lungs
Haldane effect explained
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.
what is the Henderson-Hasselbalch equation?
pH= pKa + log10(concentration of A-/HA)
what is the equation used for?
can be used to estimate the pH of a buffer solution
explain shape of carbon dioxide dissociation curve
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
explain carbamino compound transport
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
how does the carbon dioxide dissociate from the amine groups?
oxygen loading in the lungs forms oxygenated Hb which changes the conformation and loses H+ ions so cannot bind to carbon dioxide
