EXAM #1: ABG Flashcards
What are the two ways in which oxygen is transported in the blood?
1) Bound to Hb (majority, called “oxyhemoglobin”)
2) Dissolved in blood (minority)
What is the impact of decreased pH on oxygen binding by Hb? What physiologic effect does this facilitate?
Reduced oxygen affinity (right shift) , which facilitates unloading of oxygen in the tissues
- H+ binds Hb and generates salt bridges
- Salt bridges stabilize the T-form of Hb
What is the impact of increased PCO2 on oxygen binding by Hb? What physiologic effect does this facilitate?
Reduced oxygen affinity (right shift) , which facilitates unloading of oxygen in the tissues
- CO2 binds N-terminal ends of Hb subunits
- Induces negative charge that facilitates salt bridge formation
- Salt bridges stabilize the T-form of Hb
What is the impact of increased 2,3-BPG on oxygen binding by Hb? What physiologic effect does this facilitate?
Reduced oxygen affinity (right shift) , which facilitates unloading of oxygen in the tissues
- 2,3 BPG is negative charged
- Beta-globin subunits are positive charged
*Thus, 2,3 BPG stabilizes the T-form of Hb
What are the three ways that carbon dioxide is transported in the blood?
1) Bicarbonate (Majority)
2) Dissolved in blood (much more soluble than O2)
3) Combined to Hb, forming “Carboyxhemoglobin”
What is the Haldane effect?
This effect describe the manner in which CO2 concentration in blood varies as a function of blood oxygenation
- Oxygenated blood= less CO2
- Deoxygenated blood= more CO2
*Deoxyhemoglobin is a stronger base than oxyhemoglobin; it accepts more H+, which increases the HCO3- that can be generated in deoxygenated blood
What are the three ways that the body regulates pH and the time frame involved?
1) Buffer
2) Respiratory (hours)
- Hyper or hypoventilation
3) Renal (days)
- Bicarboante
- H+
What are the special features of the carbonic acid - bicarbonate buffer system? Why is this buffer so effective?
- Recall, a buffer is a solution of a weak acid and conjugate base–resist changes in pH
What is the normal values for blood pH?
- 4
* Note that the ratio of HCO3-/dissolved CO2 is what maintains pH despite changes in absolute values
What is the normal values for blood PCO2?
40 torr
What is the normal values for blood HCO3-?
24 mM
What is the normal blood value for [HCO3-][CO2(d)]?
20/1
What is the effect of hypoventilation on the bicarbonate buffer?
- PCO2 increases
- Increased dissolved CO2
- Increased H2CO3
- Increased H+
Decreased pH (respiratory acidosis)
What is the effect of hyperventilation on the bicarbonate buffer?
- PCO2 decreased
- Decreased dissolved CO2
- Decreased H2CO3
- Decreased H+
Increased pH (respiratory alkalosis)
How does an increase of PCO2 effect blood pH?
Decreased pH
How does a decrease of PCO2 effect blood pH?
Increased pH
How does an increase in HCO3- effect blood pH?
Increased pH
How does a decrease in HCO3- effect blood pH?
Decreased pH
Define PCO2 isobar.
This is the line that illustrates how pH changes as a function of HCO3-
What is the normal buffer slope.
This is the effect of other blood buffers e.g. Hb
*Could be changed by anemia for example.
What is respiratory acidosis?
Acidosis resulting from increased PCO2
What is respiratory alkalosis?
Alkalosis resulting from decreased PCO2
What is metabolic acidosis?
Acidosis from decreased HCO3-
What is metabolic alkalosis?
Alkalosis from increased HCO3-
Draw a graph of pH vs [HCO3-]. Label metabolic acidosis and metabolic alkalosis on the normal PCO2 isobar at 40 torr.
See pdf.
12 mM HCO3-= pH 7.2 (metabolic acidosis)
26 mM HCO3-= pH 7.6 (metabolic alkalosis)
Draw a graph of pH vs [HCO3-]. Add 2x PCO2 isobars, one for 20 torr, and one for 80 torr PCO2. What do these correspond with?
See pdf.
20 torr= hyperventilation (thus, decreased PCO2)
80 torr= hypoventilation (thus, increased PCO2)
What is the T-form of Hb?
“Tight-binding” i.e.
- Deoxygenated Hb
- Low O2 affinity
What is the effect of stabilizing the T-form of Hb? Describe the biochemical forces at play in the T-form of Hb?
Stabilization of the T-form of Hb= reduced oxygen affinity, which is maintained by:
- Valine residues partially blocking B-globin subunit oxygen binding sites
What is the effect of stabilizing the R-form of Hb? Describe the biochemical forces at play in the R-form of Hb?
Stabilization of the R-form of Hb= increased oxygen affinity, which is maintained by
- O2 binding to alpha-globin, which rotates valine out of beta-globin binding sites
- O2 can bind beta subunits in R-from
What is the equation for the Henderson-Hasselbalch equation for the bicarbonte buffer system?
pH= 6.1 + log [HCO3-]/(0.03)(PCO2)
How does the body compensate for metabolic acidosis?
1) Increased ventilation
2) Secretion of H+ in the urine and increased HCO3-
How does the body compensate for respiratory acidosis?
Kidney increases HCO3- production
How does the body compensate for respiratory alkalosis?
Kidney excreted HCO3-
How does the body compensate for metabolic alkalosis?
1) Hypoventilation
2) Kidney excretes HCO3-
1) Draw a graph of pH vs [HCO3-].
2) Add 2x PCO2 isobars, one for 20 torr, and one for 80 torr PCO2.
3) Add the normal buffer slope. What does this line represent?
Normal buffer slope= effect of other blood buffers on pH and HCO3- as PCO2 changes (i.e. Hb)
1) Draw a graph of pH vs [HCO3-].
2) Label the regions of:
- Metabolic alkalosis
- Respiratory acidosis
- Respiratory alkalosis
- Metabolic acidosis
Metabolic= vertical
- Alkalosis= top
- Acidosis= bottom
Respiratory= horizontal
- Acidosis= left
- Alkalosis= right
Draw the graphs for compensation of the following:
- Metabolic alkalosis
- Respiratory acidosis
- Respiratory alkalosis
- Metabolic acidosis
See pdf.
