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630: Medical Physiology > Respiratory Physiology (Part 3) > Flashcards

Respiratory Physiology (Part 3) Flashcards

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USMLE® Step 1 flashcards
1
Q

Describe the shape of the O2-hemoglobin dissociation curve

A

Percent saturation increases steeply as PO2 increases from zero to approximately 40 mmHg, and then it levels off between 50 mmHg and 100 mmHg

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2
Q

The shape of the steepest portion of the curve is the result of what?

A

a change in affinity of the heme groups for O2 as each successive O2 molecule binds, such that binding of the first molecule of O2 to a heme group increases the affinity for the second O2 moles, so on and so forth

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3
Q

When PO2 is 25 mmHg, percent saturation is __% and referred to as P(50)

A

50%

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4
Q

An increase in P50 reflects a(n) ____ in affinity and a decrease in P50 reflects a(n) ____ in affinity

A

decrease

increase

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5
Q

At the highest values of PO2 (in systemic arterial blood), the affinity of hemoglobin is ______.

A

highest

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6
Q

At lower values of PO2 (in mixed venous blood), the affinity of hemoglobin is ______.

A

lower

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7
Q

Alveolar air, pulmonary capillary blood, and systemic arterial blood all have a PO2 of ___ mmHg

A

100 mmHg

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8
Q

Mixed arterial blood has a PO2 of ___ mmHg

A

40 mmHg

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9
Q

A PO2 of 40 mmHg corresponds to approximately __% saturation and a ____ affinity of hemoglobin for O2. What is the significance of this?

A

75

lower

These changes n affinity facilitate loading of O2 in the lungs (where PO2 and affinity are highest) and unloading of O2 in the tissues (where PO2 and affinity are lower).

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10
Q

In the lungs, hemoglobin is __% saturated because affinity is _____.

A

100%

highest

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11
Q

In the tissues, hemoglobin is __% saturated because affinity is _____.

A

75%

decreased

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12
Q

Shifts of the O2-hemoglobin dissociation curve reflect what?

A

changes in the affinity of hemoglobin for O2

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13
Q

Shifts of the O2-hemoglobin dissociation curve produce changes in what?

A

P50

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14
Q

When does the O2-hemoglobin dissociation curve shift to the right?

A

When there is a decreased affinity of hemoglobin for O2

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15
Q

A decreased affinity of hemoglobin for O2 is reflected in a(n) ____ P50. What does this mean?

A

increase

This means that 50% saturation is achieved at higher-than-normal value of PO2

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16
Q

When the affinity decreases, unloading of O2 in the tissues is _______.

A

facilitated

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17
Q

What 4 things cause a decrease in affinity and a right shift in the O2-hemoglobin dissociation curve?

A
  • increases in PCO2
  • decreases in pH
  • increases in temperature
  • increases in 2,3-DPG concentration
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18
Q

The effect of PCO2 and pH on the 02-hemoglobin dissociation curve is called the ____ effect

A

Bohr

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19
Q

An increase in temperature shifts the curve to the right which does what?

A

provides more O2 to the tissue

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20
Q

Under what conditions does 2,3-DPG concentration increase?

A

under hypoxic conditions, such as living at high altitude

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21
Q

When does the O2-hemoglobin dissociation curve shift to the left?

A

When there is an increased affinity of hemoglobin for O2

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22
Q

An increased affinity of hemoglobin for O2 is reflected in a(n) ____ P50. What does this mean?

A

decrease

This means that 50% saturation occurs at a lower-than normal value of PO2

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23
Q

When the affinity increases, unloading of O2 in the tissues is _______. Why?

A

more difficult

binding is tighter

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24
Q

What 4 things cause an increase in affinity and a left shift in the O2-hemoglobin dissociation curve?

A
  • decreases in PCO2
  • increases in pH
  • decreases in temperature
  • decreases in 2,3-DPG concentration
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25
Q

Describe why the presence of hemoglobin F causes a shift to the left

A

The binding of 2,3-DPG does not bind as avidly to the gamma chains of the hemoglobin F as it does to the beta chains of hemoglobin A. This results in increased O2 affinity

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26
Q

Why is this increase in affinity beneficial to the fetus?

A

Their Pa(O2) levels are low (approximately 40 mmHg)

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27
Q

Carbon monoxide _______ the amount of O2 bound to hemoglobin

A

decreases

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28
Q

CO binds to hemoglobin with an affinity that is ___ times that of O2 to form what?

A

250

carboxyhemoglobin

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29
Q

What is the siginificance of CO having a much higher affinity to hemoglobin that O2?

A

The heme groups that are bound to CO decrease the number of O2-binding sites available on the hemoglobin. This means that the O2 content of blood and the delivery to tissues decreases dramatically

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30
Q

The effect of carbon monoxide causes a ____ shift of the O2-hemoglobin dissociation curve

A

left

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31
Q

The heme groups not bound to CO have an ______ affinity for O2. How does this affect P50 and what does it result in?

A

increased

P50 decreases, making it more difficult for O2 to be unloaded in the tissues

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32
Q

The overall effect of CO is that there is _____ O2-binding capacity of hemoglobin and the remaining heme sites bind O2 _____.

A

reduced

more tightly

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33
Q

What are the 3 forms CO2 is carried in the blood?

A
  • dissolved CO2
  • carbaminohemoblogin
  • bicarbonate (HCO3-)
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34
Q

Which form of CO2 in the blood is the most important quantitatively?

A

bicarbonate

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35
Q

What law gives the concentration of CO2 in solution?

A

Henry’s law

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36
Q

What does Henry’s law state?

A

The concentration of dissolved CO2 in blood is the partial pressure multiplied by the solubility of CO2

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37
Q

Dissolved CO2 accounts for _% of the total CO2 content of blood

A

5

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38
Q

When CO2 is bound to hemoglobin, what is it called?

A

carbaminohemoblogin

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39
Q

Carbaminohemoblogin accounts for _% of the total CO2 content of blood

A

3

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40
Q

O2 bound to hemoglobin changes its affinity for CO2, such that when less O2 is bound, the affinity of hemoglobin for CO2 ______. What is this effect called?

A

increases

Haldane effect

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41
Q

In the tissues, as CO2 is produced and binds to hemoglobin, hemoglobin’s affinity for O2 is ______, which causes what?

A

decreased, which results in the release of O2 to the tissues more readily

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42
Q

Release of O2 from hemoglobin ______ its affinity for the CO2 that is being produced in the tissues.

A

increases

43
Q

Bicarbonate accounts for __% of the total CO2 content of blood

A

90

44
Q

Describe the reactions that occur to produce bicarbonate from CO2

A

Co2 combines with H2O to form a weak acid H2CO3.
H2CO3 then dissociates into H+ and HCO3-.

*Both reactions are reversible

45
Q

What enzyme catalyzes the hydration of CO2 and the dehydration of H2CO3?

A

carbonic anhydrase, which is present in most cells

46
Q

Describe bicarbonate generation in the tissues.

A

CO2 is generated from aerobic metabolism and is added to system capillary blood where it is converted to HCO3- and transported to the lungs

47
Q

What happens to the H+ that is produced via the disassociation of H2CO3?

A

It is buffered as that the pH of the blood cells stays within physiological range

48
Q

The H+ is buffered in the red blood cells by what?

A

Deoxyhemoglobin

49
Q

What happens to the HCO3- that is produced via the disassociation of H2CO3?

A

It is exchanged for Cl- across the RBC membrane and then is carried to the lungs where it is reconverted to CO2 and expired

50
Q

What is pulmonary blood flow?

A

Cardiac output of the right heart, which is equal to the cardiac output of the left heart

51
Q

Pulmonary blood flow is _____ proportional to the pressure gradient between the pulmonary artery and the left atrium and is ______ proportional to the resistance of the pulmonary vasculature.

A

directly

inversely

52
Q

In comparison to systemic circulation, pulmonary circulation is characterized by _____ pressures and resistances

A

lower

53
Q

Pulmonary blood flow ____ systemic blood flow

A

equals

54
Q

Altering the resistance of the arterioles in the pulmonary circulation is mediated by what?

A

local vasoactive substances, especially O2

55
Q

What is by far the most major factor regulating pulmonary blood flow?

A

The partial pressure of O2 in alveolar gas (PAO2)

56
Q

Decreases in PAO2 produces pulmonary vaso______. What is this known as?

A

vasoconstriction

hypoxic vasoconstriction

57
Q

In the lungs, hypoxic vasoconstriction occurs as an adaptive mechanism, in which pulmonary blood flow _____ to poorly ventilated areas. Why?

A

decreases

Because blood flow to these areas would be “wasted”

58
Q

Hypoxic vasoconstriction is the mechanism by which pulmonary blood flow is directed ____ poorly ventilated regions of the lung and _____ well ventilated regions of the lung

A

away from

toward

59
Q

The mechanism of hypoxic vasoconstriction involves a direct action of what?

A

alveolar PO2 on the vascular smooth muscle of pulmonary arterioles

60
Q

What happens if PAO2 is reduced below 70 mmHg?

A

the vascular smooth muscle cells sense this hypoxia, vasoconstrict, and reduce pulmonary blood flow in that region

61
Q

Inhibition of nitric oxide synthase _____ hypoxic vasoconstriction

A

enhances

62
Q

Inhaled nitric oxide ____ hypoxic vasoconstriction

A

reduces

63
Q

Describe how hypoxic vasoconstriction functions to increase pulmonary vascular resistance at high altitude

A

PAO2 is reduced due to the low O2 mixture of the air. This produces global vasoconstriction of pulmonary arterioles and an increase in pulmonary vascular resistance.

64
Q

Other than high altitude, what is another example of global hypoxic vasoconstriction?

A

fetal circulation

65
Q

Because the fetus does not breathe, PAO2 is ____ in the fetus than in the mother, producing vaso_____ in the fetal lungs.

A

much lower

vasoconstriction

66
Q

Vasoconstriction of fetal lungs ______ pulmonary vascular resistance and ______ pulmonary blood flow

A

increases

decreases

67
Q

Describe what happens when a baby takes its firs breath

A

PAO2 increases to 100 mmHg, hypoxic vasoconstriction is reduced, and pulmonary blood flow increases

68
Q

What are 3 other substances that alter pulmonary vascular resistance?

A
  • Thromboxane A2
  • Prostacyclin
  • Leukotrienes
69
Q

How does Thromboxane A2 alter pulmonary vascular resistance?

A

It is a powerful local vasoconstrictor of both arterioles and veins

70
Q

How does Prostacyclin alter pulmonary vascular resistance?

A

It is a potent local vasodilator

71
Q

Leukotrienes causes constriction of what?

A

airway constriction

72
Q

What does the distribution of blood flow within the lung depend on?

A

gravity

73
Q

Describe the pattern of blood flow in a person who is standing

A

Zone 1: blood flow is the lowest
Zone 2: blood flow is medium
Zone 3: blood flow is highest

74
Q

The arterial pressure in zone one (apex) is _____ than alveolar pressure and _______ than venous pressure

A

lower

greater

75
Q

Describe what happens in zone one if arterial pressure is decreased (due to hemorrhage)

A

Alveolar pressure becomes greater than arterial pressure, which causes the blood vessels to compress and close. This results in zone 1 not being perfused and no gas exchange occurs

76
Q

The arterial pressure in zone 2 is _____ than alveolar pressure and _______ than venous pressure

A

greater

greater

77
Q

What drives blood flow in zone 2?

A

The difference between arterial and alveolar pressure

78
Q

The arterial pressure in zone 3 is _____ than alveolar pressure and _______ than venous pressure

A

greater

greater

79
Q

Zone 3 is the only zone in which alveolar pressure is _____ than both arterial venous pressures?

A

less

80
Q

What drives blood flow in zone 3?

A

The difference between arterial and venous pressure

81
Q

What are 3 types of pulmonary shunts?

A
  • Physiologic shunt
  • Right-to-left shunts
  • Left-to-right shunts
82
Q

What shunt type is the most common?

A

Left-to-right shunts

83
Q

Describe the 2 parts of the physiologic shunt

A
  • Part is the bronchial blood flow, which serves the metabolic functions of the bronchi
  • The other is the small amount of coronary blood flow that drains directly into the left ventricle through the thesbian veins and never perfuses the lungs
84
Q

When does shunting from the right heart to the left hear occur?

A

If there is a defect in the wall between the right and left ventricles

85
Q

What always occurs in a right-to-left shunt? Why?

A

Hypoxemia, because a significant fraction of the CO is not delivered to the lungs for oxygenation

86
Q

What is a defining characteristic of the hypoxemia caused by a right-to-left shunt?

A

It can NOT be corrected by having the person breathe a high O2 gas bevause the shunted blood never goes to the lungs to be oxygenated

87
Q

Left-to-right shunts are more ______.

A

common

88
Q

Do left-to-right shunts cause hypoxemia?

A

no

89
Q

What are 2 causes for a left-to-right shunt?

A
  • patent ductus arteriosus

- traumatic injury

90
Q

Pulmonary blood flow (right-heart CO) becomes _____ than system blood flow (left heart CO) in the presence of a left-to-right shunt

A

greater

91
Q

In the presence of a left-to-right shunt PO2 in the blood on the right side of the heart ____. Why?

A

increase, because oxygenated blood that has just returned from the lungs is added directly to the right heart without being delivered to the tissues

92
Q

The ventilation/perfusion ratio is a ratio between what 2 things?

A

alveolar ventilation to pulmonary blood flow

93
Q

Alveoli must be perfused in order for what to occur?

A

gas exchange

94
Q

What is the normal vatilation/perfusion (V/Q) ratio? What does this mean?

A

0.8

This means that alveolar ventilation is 80% of the value for pulmonary blood flow

95
Q

In what zone is the V/Q the highest? Lowest?

A

highest in zone 1

lowest in zone 3

96
Q

In zone 1 blood flow is _____, alveolar ventilation is _____, V/Q is _____, PAO2 is _____, and PACO2 is _____.

A 
Zone 1:
blood flow = lowest
alveolar ventilation = lower
V/Q = highest 
PAO2 = highest
PACO2 = lower
97
Q

In zone 3 blood flow is _____, alveolar ventilation is _____, V/Q is _____, PAO2 is _____, and PACO2 is _____.

A 
Zone 3:
blood flow = highest
alveolar ventilation = higher
V/Q = lowest
PAO2 = lowest
PACO2 = higher
98
Q

A mismatch of ventilation and perfusion is called what?

A

V/Q mismatch or V/Q defect

99
Q

What does V/Q mismatch result in?

A

abnormal gas exchange

100
Q

What may cause a V/Q defect?

A
  • ventilation of lung regions that are not perfused (dead space)
  • perfusion of lung regions that are not ventilated (shunt)
101
Q

Dead space is illustrated by what?

A

A pulmonary embolism, in which blood flow to a portion of the lung is occluded

102
Q

In regions of dead space, what does PAO2 and PACO2 equal?

A

PAO2 is 150 mmHg

PACO2 is 0 mmHg

103
Q

A shunt is illustrated by what?

A

Airway obstruction and right-to-left cardiac shunts

104
Q

In regions of a shunt, what does PAO2 and PACO2 equal?

A

PAO2 is 40 mmHg

PACO2 is 46 mmHg

630: Medical Physiology (24 decks)

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