ABGs Flashcards
What is the main buffer in blood?
bicarb/CO2
What is the role of Hb in the maintenance of blood pH
Hb can donate or accept electrons
What is meant by the term “positive cooperativity”?
Hb becomes more efficient at binding oxygen as oxygen levels increase
What is the T state of Hb? What is the chemical change that allows for this?
“tense” state, where Hb has a low affinity for oxygen
Beta subunits are blocked by a Valine residue
What is the R state of Hb?
High oxygen affinity state.
What is the change that occurs going from the T state to the R state?
Oxygen binding to the alpha subunits in the T state, cause the valine residue in the beta subunit to move away from the binding site of oxygen
What stabilizes the R form, factors that increase the strength of bonds between subunits, or factors that decrease? Why?
Decrease, since stronger bonding means less likely to move Valine residue out of the way in the beta chain
What is the role of 2,3 BPG?
The negatively charged 2,3 BOG interacts with the positively-charged amino-termini of the beta chains, and also with specific K and H residues within the beta chains
What is the Bohr effect?
Increased H+ formed from metabolizing tissues is absorbed by Hb Histidine residue, stabilizing the T state
What happens with the Bohr effect in the lungs?
H+ leaves the Hb d/t need to form CO2 from bicarb, stabilizing the R state
What is the interaction between CO2 and Hb besides the Bohr effect?
CO2 binds to the N terminal end of the subunit, forming a carbamate and salt bridge formation, thus stabilizing the T state
What are the three forms in which CO2 is transported?
- Dissolved CO2 gas
- Combined to N terminal Hb
- Bicarb
What percent of CO2 is transported as bicarb?
80-90%
What is the only form CO2 can take that does not contribute a H+ to the serum?
Dissolved CO2
What form of CO2 is the only form that can pass through the alveolar capillaries?
CO2 gas
What is the Haldane effect?
At any given partial pressure of CO2, oxygenated blood contains less total CO2 than deoxygenated blood at the same partial pressure of CO2
Which is a stronger base: deoxyhemoglobin, or oxyhemoglobin? What is the consequence of this?
Deoxyhemoglobin, meaning that deoxygenated blood more readily accepts H+ from the solvation of CO2 than oxygenated blood
Why is it that the amount of oxygen dissolved in the blood is very low, but is extremely important?
Since this is the form that:
- Diffuses from lungs into blood
- enters erythrocytes
- binds Hb
Anything that increases what type of bond will reduce the oxygen affinity of Hb (stabilize the T form)?
Salt bridge formation
What is the effect on the PO2 vs hemoglobin saturation curve with increases in [H]? PCO2? 2,3 BPG?
All shift the curve to the right (lower the % oxygen saturation at every level of PCO2)
What is the enzyme in RBCs that takes CO2 from the blood and turns it into H2CO3?
Carbonic anhydrase
What ion in the serum is exchanged for HCO3 in the RBC?
Cl-
What is the Henderson-Hasselbach equation?
pH = pKa + log(base/acid)
What is the simplification made for the henderson-hasselbach equation when calculating the pH of the bicarb buffer?
Very little H2CO3 present (almost all is either dissolved CO2, or HCO3) Thus the [CO2] is substituted for the “acid” in the equation
What is the equation for the CO2 buffer in the blood?
pH = 6.1 + log ([HCO3]/0.03pCO2)
What is the normal PCO2 in the blood?
40 torr
What is the normal [HCO3] in the blood?
24 mM
What is the normal [HCO3]/[CO2]?
20/1
What is the normal pH of the blood?
7.4
What are respiratory acid/base imbalances?
Blood pH changes that are the result of changes in PCO2
What are metabolic acid/base imbalances?
Blood pH changes that are the result from changes in [HCO3]
Why is it that pH can be normal despite having abnormal [CO2] and [HCO3]?
It’s the ratio of the two that matter, not the absolute value of one
How is hypoventilation reflected on the pH vs [HCO3-] graph?
Shifs to the right
How is hyperventilation reflected on the pH vs [HCO3-] graph?
Shifts to the left
What is the normal buffer slope in the pH vs [HCO3] graph? What determines the slope?
Represents the effect of other blood buffers on [HCO] and pH as PCO2 varies
Mostly represents the effect or [Hb]
Why is it that the pH values predicted by the henderson hasselbach equation are not always precise?
Does not take into account other buffers in the blood, namely the Hb buffer
How are metabolic disturbances reflected in the pH vs [HCO3] graph?
Shifts along the curve of a PCO2 isobar
How are respiratory disturbances reflected in the pH vs [HCO3] graph?
Shifts of the PCO2 isobar
How does the body compensate for acidosis/alkalosis?
Will shift the non-affected variable to maintain the ratio of [HCO3]/PCO2
What are the two major organ systems that regulate the pH of the blood?
Lungs and kidneys
What is the compensatory reaction for metabolic acidosis, and how is this reflected in the pH vs [HCO3] graph?
Initial shift down the isobar, but then shift to the right of the curve
What is the compensatory reaction for respiratory acidosis, and how is this reflected in the pH vs [HCO3] graph?
Shift of the curve to the left, followed by a slow increase in the | slope | of the compensatory curve
What is the compensatory reaction for respiratory alkalosis, and how is this reflected in the pH vs [HCO3] graph?
Shift of the curve to the right, followed by a decrease in the compensatory curve | slope |
What is the compensatory reaction for metabolic alkalosis, and how is this reflected in the pH vs [HCO3] graph?
Initial change along the curve, then change in the slope of the curve to the left
