CO2 Transport/ pH Homeostasis Flashcards
Give the equation for CO2 + H2O & state the 3 areas where CO2 is in the body (& their percentages).
CO2 + H2O H2CO3 H+ + HCO3-
HCO3- = bicarbonate
H2CO3 = carbonic acid
1) Dissolved CO2 = 5%,
2) Carbamino CO2Hb (in hemoglobin) = 5%
3) *Bicarbonate (HCO3) CO2 = 90%
1, 2, & 3 constitute total CO2
This rxn occurs naturally in the blood
According to Guyton & Hall:
1) Dissolved CO2 = 7%,
2) Carbamino CO2Hb (in hemoglobin) = 23%
3) *Bicarbonate (HCO3) CO2 = 70%
Most of the carbon dioxide (70%) is transported in the blood in the form of bicarbonate ion. Dissolved carbon dioxide reacts with water to form carbonic acid (mostly in red blood cells), which dissociates into bicarbonate and hydrogen ions. Carbon dioxide also reacts with amine radicals of the hemoglobin molecule to form the compound carbaminohemoglobin, which accounts for about 23% of the carbon dioxide transported in the blood. The remaining carbon dioxide (7%) is transported in the the dissolved state.
_____ CO2 is the only one that contributes to the partial pressure of CO2 in the blood.
Dissolved CO2 is the only one that contributes to the partial pressure of CO2 in the blood.
Dissolved CO2 = 5%,
The source of CO2 in the body is in the ____, where _____ occurs. This CO2 is taken up by the _____ circulation & that’s why PCO2 is higher there @ ____mmHg. After this, some CO2 diffuses into the alveoli & is ______, the majority of CO2, however goes into the _____ blood where PCO2 is 40mmHg. We produce more than 1 lb of CO2/day.
tissues
metabolism
venous
46mmHg, 55 volume%
exhaled
arterial
Blood is normally maintained at an alkaline pH of ___ +/- ___; the “window of life” is from about pH ___ to ___.
Blood is normally maintained at an alkaline pH of 7.40 +/- 0.03; the “window of life” is from about pH 6.8 to 8.0.
Abnormal functioning of the blood buffers, or of the systems to which the blood is interfaced, can lead to metabolic acidosis, metabolic alkalosis, respiratory acidosis, or respiratory alkalosis.
The pH of the venous blood is only slightly lower than the arterial blood, why?
Because hemoglobin serves as a buffer.
Normal arterial pH = 7.4
Normal venous pH = 7.38
Describe the Jacob Stewart Cycle & describe Isohydric shift.
See pg. 278-280
The pH ______ as PCO2 increases.
The pH decreases as PCO2 increases.
See the CO2 adsorption curve on pg. 281.
How would the CO2 Adsorption curve change with completely deoxygenated blood?
The curve would shift up since the pH increases since the deoxyHB would bind the proton; therefore more CO2 would be converted to bicarbonate. The total CO2 content increases in deoxygenated blood (via bicarbonate). Therefore, more CO2 is carried for a given partial pressure. This is the Haldane effect. Deoxygenating the blood, allows more CO2 to be carried in the blood @ a given partial pressure since dexy-Hb is a weaker acid than Oxy-Hb so it holds on to the proton tighter (neutralizes it) & more CO2 is converted to bicarbonate. Therefore, there is minimization of acidification of the venous blood (lower O2) in the Haldane effect.
Haldane effect has 2 net effects:
1) Allows deoxygenated blood to carry more CO2
2) Decreases acidity of the venous blood or minimizes the effect of acidification
See pg. 282
Describe the Haldane effect
Deoxygenation of the blood increases its ability to carry carbon dioxide; this property is the Haldane effect. Conversely, oxygenated blood has a reduced capacity for carbon dioxide. his is a consequence of the fact that reduced (deoxygenated) hemoglobin is a better proton acceptor than the oxygenated form. Therefore, pH in the blood increases (less H+).
CO2 + H2O H2CO3 -> H+ + HCO3-
By Le Chatelier’s principle, anything that stabilizes the proton produced will cause the reaction to shift to the right, thus the enhanced affinity of deoxyhemoglobin for protons enhances synthesis of bicarbonate and accordingly increases capacity of deoxygenated blood for carbon dioxide. The majority of carbon dioxide in the blood is in the form of bicarbonate.
In other words, as CO2 content increases as PO2 decreases.
Describe the Bohr effect
O2 saturation decreases as CO2 increases. This is because Deoxy-Hb binds the proton tighter & Hb thus has a lower affinity for O2. Right shift on curve.
Bohr & Haldane effect are both explained by the fact that deoxy-Hb is a weaker acid than Oxy-Hb.
Haldane refers to CO2 while Bohr effect refers to O2
See pg. 282-283
Would isovulemic anemia cause changes in the total CO2 concentration in the blood?
The amount of Hb is reduced, but reduced Hb in the arterial blood O2 content is reduced but extraction is the same so O2 saturation in the blood would be more reduced than normal & deoxy-Hb would increase. Therefore, CO2 increases, giving a greater Haldane effect since the Hb is more deoxygenated than normal blood.
Also, in anemia the CO2 is increased.
1) What is the equation for pH =
2) What is the concentration of H+ for pH 7
1) -log[H+]
2) 10^-7mol/L
Give the Henderson Hasselbach equation. When is it used?
The pH at equilibrium is given by the HENDERSON-HASSELBALCH EQUATION, it serves as a buffer to keep blood pH in the normal range. It is the most important & significant biological buffer:
pH = pK + log [HCO3-]/[CO2]
pH = pK + log [HCO3-]/(0.03 • PCO2)
Remember that the buffer capacity is maximal when this ratio is one, @ the pK. Therefore, better buffers have pH very close to pK. In other words, @ the pK, large changes in acid or base, correspond in small changes in pH = buffer.
The bicarbonate buffer system, is not a very good buffer system since its pK & pH are not close to eachother. However, it is still a good buffer because of the actions of the lung removing CO2 making its job easier.
See pg. 287
Do problem on pg. 286 & 288-291
Note that kidneys regulates bicarbonate concentration & lungs regulate CO2 concentration; therefore, together, the regulate pH of the blood.
Discuss how adding acid to open systems does not lead to fatal acidemia.
If the body were a closed system, we would get fatal acidemia after eating (even with the buffer).
We still get acidemia after eating, but our open system allows CO2 to be exhaled & acidemia is minimized with help of the buffer system.
CO2 (exhale) + H2O H2CO3 H+ + HCO3-
The carbonic acid formed is effectively exhaled as carbon dioxide in the lung. By this mechanism blood pH is normally held within limits compatible with life. Therefore the ventilatory response to acidemia maintains pH homeostasis.
