EXAM #1: ABG

Question 1

What are the two ways in which oxygen is transported in the blood?

Answer 1

1) Bound to Hb (majority, called “oxyhemoglobin”)

2) Dissolved in blood (minority)

Question 2

What is the impact of decreased pH on oxygen binding by Hb? What physiologic effect does this facilitate?

Answer 2

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

Question 3

What is the impact of increased PCO2 on oxygen binding by Hb? What physiologic effect does this facilitate?

Answer 3

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

Question 4

What is the impact of increased 2,3-BPG on oxygen binding by Hb? What physiologic effect does this facilitate?

Answer 4

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

Question 5

What are the three ways that carbon dioxide is transported in the blood?

Answer 5

1) Bicarbonate (Majority)
2) Dissolved in blood (much more soluble than O2)
3) Combined to Hb, forming “Carboyxhemoglobin”

Question 6

What is the Haldane effect?

Answer 6

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

Question 7

What are the three ways that the body regulates pH and the time frame involved?

Answer 7

1) Buffer
2) Respiratory (hours)
- Hyper or hypoventilation
3) Renal (days)
- Bicarboante
- H+

Question 8

What are the special features of the carbonic acid - bicarbonate buffer system? Why is this buffer so effective?

Answer 8

• Recall, a buffer is a solution of a weak acid and conjugate base–resist changes in pH

Question 9

What is the normal values for blood pH?

Answer 9

7. 4

* Note that the ratio of HCO3-/dissolved CO2 is what maintains pH despite changes in absolute values

Question 10

What is the normal values for blood PCO2?

Answer 10

40 torr

Question 11

What is the normal values for blood HCO3-?

Answer 11

24 mM

Question 12

What is the normal blood value for [HCO3-][CO2(d)]?

Answer 12

20/1

Question 13

What is the effect of hypoventilation on the bicarbonate buffer?

Answer 13

• PCO2 increases
• Increased dissolved CO2
• Increased H2CO3
• Increased H+

Decreased pH (respiratory acidosis)

Question 14

What is the effect of hyperventilation on the bicarbonate buffer?

Answer 14

• PCO2 decreased
• Decreased dissolved CO2
• Decreased H2CO3
• Decreased H+

Increased pH (respiratory alkalosis)

Question 15

How does an increase of PCO2 effect blood pH?

Answer 15

Decreased pH

Question 16

How does a decrease of PCO2 effect blood pH?

Answer 16

Increased pH

Question 17

How does an increase in HCO3- effect blood pH?

Answer 17

Increased pH

Question 18

How does a decrease in HCO3- effect blood pH?

Answer 18

Decreased pH

Question 19

Define PCO2 isobar.

Answer 19

This is the line that illustrates how pH changes as a function of HCO3-

Question 20

What is the normal buffer slope.

Answer 20

This is the effect of other blood buffers e.g. Hb

*Could be changed by anemia for example.

Question 21

What is respiratory acidosis?

Answer 21

Acidosis resulting from increased PCO2

Question 22

What is respiratory alkalosis?

Answer 22

Alkalosis resulting from decreased PCO2

Question 23

What is metabolic acidosis?

Answer 23

Acidosis from decreased HCO3-

Question 24

What is metabolic alkalosis?

Answer 24

Alkalosis from increased HCO3-

Question 25

Draw a graph of pH vs [HCO3-]. Label metabolic acidosis and metabolic alkalosis on the normal PCO2 isobar at 40 torr.

Answer 25

See pdf. 12 mM HCO3-= pH 7.2 (metabolic acidosis) 26 mM HCO3-= pH 7.6 (metabolic alkalosis)

Question 26

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?

Answer 26

See pdf. 20 torr= hyperventilation (thus, decreased PCO2) 80 torr= hypoventilation (thus, increased PCO2)

Question 27

What is the T-form of Hb?

Answer 27

"Tight-binding" i.e. - Deoxygenated Hb - Low O2 affinity

Question 28

What is the effect of stabilizing the T-form of Hb? Describe the biochemical forces at play in the T-form of Hb?

Answer 28

Stabilization of the T-form of Hb= reduced oxygen affinity, which is maintained by: - Valine residues partially blocking B-globin subunit oxygen binding sites

Question 29

What is the effect of stabilizing the R-form of Hb? Describe the biochemical forces at play in the R-form of Hb?

Answer 29

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

Question 30

What is the equation for the Henderson-Hasselbalch equation for the bicarbonte buffer system?

Answer 30

pH= 6.1 + log [HCO3-]/(0.03)(PCO2)

Question 31

How does the body compensate for metabolic acidosis?

Answer 31

1) Increased ventilation | 2) Secretion of H+ in the urine and increased HCO3-

Question 32

How does the body compensate for respiratory acidosis?

Answer 32

Kidney increases HCO3- production

Question 33

How does the body compensate for respiratory alkalosis?

Answer 33

Kidney excreted HCO3-

Question 34

How does the body compensate for metabolic alkalosis?

Answer 34

1) Hypoventilation | 2) Kidney excretes HCO3-

Question 35

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?

Answer 35

Normal buffer slope= effect of other blood buffers on pH and HCO3- as PCO2 changes (i.e. Hb)

Question 36

1) Draw a graph of pH vs [HCO3-]. 2) Label the regions of: - Metabolic alkalosis - Respiratory acidosis - Respiratory alkalosis - Metabolic acidosis

Answer 36

Metabolic= vertical - Alkalosis= top - Acidosis= bottom Respiratory= horizontal - Acidosis= left - Alkalosis= right

Question 37

Draw the graphs for compensation of the following: - Metabolic alkalosis - Respiratory acidosis - Respiratory alkalosis - Metabolic acidosis

Answer 37

See pdf.