5B - Gas Transport and Ventilation/Perfusion Ratios Flashcards

1
Q

What are the two forms that oxygen is carried in the blood?

A
  1. Bound to hemoglobin (~98.5% - most important)

2. Dissolved in plasma (~1.5%)

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2
Q

Normal adult hemoglobin is comprised of what subunits?

What state is iron in to bind O2?

A

a2b2

Ferrous state (Fe2+)

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3
Q

5b6. Hemoglobin-O2 Dissociation Curve

Arterial blood has a P(O2) of 100 mmHg. What is the level of oxygen saturation of hemoglobin at this point?

A

Hemoglobin is 98-100% saturated - Oxygen bound to all four heme groups on all hemoglobin molecules

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4
Q

5b6. Hemoglobin-O2 Dissociation Curve

Mixed venous blood has a P(O2) of 40 mmHg. What is the level of oxygen saturation of hemoglobin at this point?

A

Hemoglobin is 75% saturated - on average, 3 of the 4 heme groups on each hemoglobin have O2.

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5
Q

5b7. Hemoglobin-O2 Dissociation Curve

What is the level of oxygen saturation of hemoglobin at P(O2) of ~25 mmHg?

A

Hemoglobin is 50% saturated - on average, 2 of the 4 heme groups of each hemoglobin molecule have O2 bound

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6
Q

5b8. What is the shape of the hemoglobin-O2 dissociation curve? What do you call the relationship between PO2 and hemoglobin saturation? (what kind of cooperativity)?

A

Sigmoid shape

Positive cooperativity

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7
Q

5b10. What factors influence hemoglobin saturation at a given PO2?

A

P(CO2)
pH
Temperature
2,3-BPG Hemoglobin F

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8
Q

5b11. When will the hemoglobin-O2 dissociation curve shift to the right?

A

Increased P(CO2), decreased pH, increased temperature, or increased 2,3-BPG

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9
Q

5b11. When the hemoglobin-O2 dissociation graph shifts to the right, what does it mean for O2 unloading and for % saturation of hemoglobin?

A

O2 unloading from the arterial blood to tissues if facilitated

% saturation of hemoglobin is decreased

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10
Q

5b12. How does exercise affect the Hemoglobin-O2 dissociation curve?

A

Shifts to the right

  • More CO2 produced
  • Tissue pH decreased
  • Temperature increased
  • 2,3-DPG concentration incresaed
  • Stimulates O2 delivery to exercising muscles
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11
Q

5b14. What is an adaptation that the body makes in reaction to chronic hypoxemia (living at high altitude)?

A

Increased synthesis of 2,3-BPG, which binds to hemoglobin and facilitates unloading of O2 in the tissues

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12
Q

5b16. What changes can trigger a hemoglobin-O2 dissociation curve shift to the left?

A

Decreased P(CO2)
Increased pH
Decreased temperature
Decreased 2,3-BPG concentration

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13
Q

5b15. When the hemoglobin-O2 dissociation curve shifts to the left, is unloading O2 from arterial blood to the tissues more or less difficult?

A

More difficult

At any level of P02 - the % saturation of hemoglobin is increased

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14
Q

5b17. Which has a higher affinity for hemoglobin - CO or O2?

A

CO has a 200x affinity for hemoglobin than does O2

CO will occupy O2 binding sites on hemoglobin and decrease the O2 concentration of blood.

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15
Q

5b17. Will binding of CO shift the curve to the left or right?

A

CO will shift the curve to the left, increasing the affinity of the remaining site for O2.

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16
Q

5b18. What is hypoxemia?

A

Decrease in arterial P(O2)

17
Q

5b18. What is hypoxia?

A

Decreased O2 delivery to the tissues

18
Q

5b18. What are the factors that affect the levels of O2 content in the blood?

A

Hemoglobin concentration
O2 binding capacity of hemoglobin
% saturation of hemoglobin by O2 (which depends on P O2)

19
Q

5b18. What are three possible causes of hypoxia?

A
  1. Decreased cardiac output
  2. Decreased O2 - binding capacity of hemoglobin
  3. Decreased arterial P (O2)
20
Q

5b19. What is anemic hypoxia?

A

Anemic hypoxia reflects poor O2 delivery resulting from too few RBC or from RBC that contain abnormal or too little hemoglobin

21
Q

5b19. What causes ischemic (stagnant) hypoxia?

A

Impairment or blockage of blood circulation.

Congestive heart failure may cause body-wide ischemic hypoxia

22
Q

5b19. What regions of the body are affected by ischemic hypoxia via:
- Congestive heart failure
- Emboli/thrombi

A
  • Congestive heart failure may cause body-wide ischemic hypoxia
  • Embolic or thrombi block oxygen delivery only to tissues distal to the obstruction
23
Q

5b20. What is histotoxic hypoxia?

A

Occurs when body cells are unable to use O2 even though adequate amounts are delivered.

24
Q

5b20. What kind of hypoxia results from the use of metabolic poisons, like cyanide?

A

Histotoxic hypoxia

25
Q

5b20. What is hypoxemic hypoxia?

- Possible causes?

A

Reduced arterial P(O2).

  • Disordered/abnormal ventilation-perfusion coupling
  • Pulmonary diseases that impair ventilation
  • Breathing air containing scant amounts of O2
26
Q

5b21. What are the three forms that carbon dioxide is carried to the lungs?

A
  1. HCO3 (bicarbonate) - major form (70-90%) - from hydration of CO2 in RBC
  2. Dissolved CO2, free in solution (small amount)
  3. Carbaminohemoglobin - CO2 bound to hemoglobin (small amount)
27
Q

5b22. What is chloride shift in RBC in tissue?

A

HCO3 diffuses out of RBC in exchange for Cl- in order for the cell to maintain its osmotic equilibrium and prevent RBC shrinkage

28
Q

5b22. What is chloride shift in RBC at the lungs?

A

Cl leaves the RBC and HCO3 comes back in and is then converted into CO2 for exit out of the lungs

29
Q

5b23. What is V/Q ratio?

A

V/Q ratio - Ventilation-Perfusion ratio

The ratio of alveolar ventilation (V) to pulmonary blood flow (Q) Ventilation and perfusion matching is important to achieve ideal exchange of O2 and CO2.

30
Q

5b23. If frequency, tidal volume, and cardiac output are normal, what is the V/Q ratio?
- What is arterial P(O2)?
- What is arterial P(CO2)?

A

V/Q ratio - 0.8

Arterial P(O2) - 100 mm Hg
Arterial P(CO2) - 40 mm Hg
31
Q

5b24. What accounts for differences in V/Q ratio throughout the body?

A

Various parts of the lung have different V/Q ratio due to gravity.

Local changes in V/Q ratio are common in disease

32
Q

5b24. What happens if the V/Q ratio is too high?

A

Perfusion is reduced relative to ventilation

Alveolar p(O2) will rise because less O2 enters the blood

Alveolar p(CO2) will fall because less CO2 is delivered

33
Q

5b24. What happens if the V/Q ratio is too low?

A

Ventilation to an alveolus is reduced relative to its perfusion

Alveolar p(O2) falls because less O2 is delivered
Alveolar p(CO2) rises because less CO2 is expired
34
Q

5b25. What is V/Q ratio when airways are completely blocked?

A

Ventilation is zero, which means V/Q ratio is zero.

Called a shunt.

No gas exchange, but the P(O2) and P(CO2) of pulmonary capillary blood will approach its regular values in mixed venous blood.

35
Q

5b26. What is V/Q ratio when there is a pulmonary embolus (dead space)?

A

Perfusion is zero, which means V/Q ratio is infinite

No gas exchange in lung, but alveoli will approach their regular P(O2) and P(CO2).