CO2 Transport and pH homeostasis

Question 1

forms of CO2 in blood that make up partial pressure

Answer 1

dissolved CO2 - 5%
bicarbonate (HCO3-) - 90%
carbamino Hb (bound to N terminus of Hb) - 5%
carbonic acid (H2CO3) and carbonate (CO3-2) are negligible

Question 2

what is the pH “window of life” and what are its usual values?

Answer 2

WoL - 6.8 to 8.0

usual - 7.4 +/- 0.03

Question 3

rate of production of CO2

Answer 3

0.234 L/min = 0.01 mol/min = 14 moles/day

Question 4

Jacobs-Stewart cycle in regular tissues and lungs

-what does this do to osmolarity?

Answer 4

1. CO2 from tissues diffuse to RBC, and either bind to Hb or convert to H2CO3 (via carbonic anhydrase)
2. H2O3 –> HCO3- + H+; the HCO3 can leave the cell (via an anionic exchanger with Cl- that doesn’t need ATP) while the H+ can displace O2 on Hb
3. O2 leaves RBC to tissues
   since CO2 and Cl- enter, but only HCO3- leaves (don’t count O2), osmolarity increases so H2O increases too

all reactions are reversed in the lungs

Question 5

imidazole buffer

Answer 5

a secondary blood buffer

histidine-Hb + H+ –> histidine+-Hb

Question 6

what is the major blood buffer?

Answer 6

carbonid acid/bicarbonate buffer

Question 7

what does increased PCO2 do to hemoglobin affinity for O2?

Answer 7

it weakens affinity for O2 (Bohr effect)

Question 8

what does decreased pH do to hemoglobin affinity for O2?

Answer 8

it weakens affinity for O2 (Bohr effect)

Question 9

what does increased temp do to hemoglobin affinity for O2?

Answer 9

it weakens affinity for O2

Question 10

what 2 things does deoxygenation promote?

Answer 10

1. carbamino-Hb formation

2. H+ binding and formation of HCO3-

Question 11

Haldane effect and Bohr effect and what they both mean

Answer 11

H: at any given PCO2, the CO2 content increases if blood is deoxygenated (PO2 decreases)
B: at any given PO2, O2 saturation decreases as PCO2 increases
-this minimizes acidification of venous blood, b/c deoxyhemoglobin is a weaker acid, and binds H+ more tightly, than oxyhemoglobin
-upon deoxygenation, more bicarbonate is formed, resulting in an upward shift in CO2 absorption curve
-upon binding to H+, Hb has reduced binding affinity for O2

Question 12

what would isovolemic anemia do to total CO2 in the blood

Answer 12

nothing, b/c of Haldane effect

• RBC decreases, so less Hb, and H+ binding activity is reduced
• also PO2 decreases

Question 13

Henderson-Hasselbach equation for carbonic acid

Answer 13

pH = pKa + log [HCO3-]/[CO2]

Question 14

what does the bicarbonate titration curve tell you? why is this not so in real life?

Answer 14

at pKa, large fluctuations in acid/base would have little change in pH

• but at physiological pH, small fluctuations would cause large changes in pH
• if CO2 built up, pH would decrease and cause acedemia
• this doesn’t happen in the body, because CO2 is constantly leaving the system, so pH changes little