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Respiratory > EXAM #1: ABG > Flashcards

EXAM #1: ABG Flashcards

1
Q

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

A

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

2) Dissolved in blood (minority)

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2
Q

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

A

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
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3
Q

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

A

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
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4
Q

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

A

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

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5
Q

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

A

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

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6
Q

What is the Haldane effect?

A

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

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7
Q

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

A

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

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8
Q

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

A
  • Recall, a buffer is a solution of a weak acid and conjugate base–resist changes in pH
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9
Q

What is the normal values for blood pH?

A
  1. 4

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

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10
Q

What is the normal values for blood PCO2?

A

40 torr

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11
Q

What is the normal values for blood HCO3-?

A

24 mM

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12
Q

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

A

20/1

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13
Q

What is the effect of hypoventilation on the bicarbonate buffer?

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

Decreased pH (respiratory acidosis)

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14
Q

What is the effect of hyperventilation on the bicarbonate buffer?

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

Increased pH (respiratory alkalosis)

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15
Q

How does an increase of PCO2 effect blood pH?

A

Decreased pH

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16
Q

How does a decrease of PCO2 effect blood pH?

A

Increased pH

17
Q

How does an increase in HCO3- effect blood pH?

A

Increased pH

18
Q

How does a decrease in HCO3- effect blood pH?

A

Decreased pH

19
Q

Define PCO2 isobar.

A

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

20
Q

What is the normal buffer slope.

A

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

*Could be changed by anemia for example.

21
Q

What is respiratory acidosis?

A

Acidosis resulting from increased PCO2

22
Q

What is respiratory alkalosis?

A

Alkalosis resulting from decreased PCO2

23
Q

What is metabolic acidosis?

A

Acidosis from decreased HCO3-

24
Q

What is metabolic alkalosis?

A

Alkalosis from increased HCO3-

25
Q

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

A

See pdf.

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

26
Q

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?

A

See pdf.

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

27
Q

What is the T-form of Hb?

A

“Tight-binding” i.e.

  • Deoxygenated Hb
  • Low O2 affinity
28
Q

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

A

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

29
Q

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

A

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
30
Q

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

A

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

31
Q

How does the body compensate for metabolic acidosis?

A

1) Increased ventilation

2) Secretion of H+ in the urine and increased HCO3-

32
Q

How does the body compensate for respiratory acidosis?

A

Kidney increases HCO3- production

33
Q

How does the body compensate for respiratory alkalosis?

A

Kidney excreted HCO3-

34
Q

How does the body compensate for metabolic alkalosis?

A

1) Hypoventilation

2) Kidney excretes HCO3-

35
Q

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?

A

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

36
Q

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

A

Metabolic= vertical

  • Alkalosis= top
  • Acidosis= bottom

Respiratory= horizontal

  • Acidosis= left
  • Alkalosis= right
37
Q

Draw the graphs for compensation of the following:

  • Metabolic alkalosis
  • Respiratory acidosis
  • Respiratory alkalosis
  • Metabolic acidosis
A

See pdf.

Respiratory (35 decks)

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