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Physiology > Gas Exchange and Transport > Flashcards

Gas Exchange and Transport Flashcards

1
Q

Partial pressure

A

The pressure of each individual gas in a mixture of gases. It is used, rather than concentration, to define diffusion of gas because it allows comparisons of gas activities in both liquid and gaseous environments

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2
Q

Henry’s Law

A

C=aP
Expresses the relationship between partial pressure and the amount of gas in physical solution, Where C = concentration in mL gas/ml Liquid, a is solubility in mL gas/mL liquid/1 atm (760 mmHg), and P is partial pressure in mmHg

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3
Q

Dalton’s Law

A

Partial pressure = mole fraction of x * total pressure

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4
Q

Partial pressure of water

A

Evaporation of water causes gas to acquire water vapor. In lungs at 37 degrees celsius and 100% saturation, PH2O equals 47 mmHg
Proportionately lowers the partial pressure of the other gases
Temperature dependent

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5
Q

In dry air, the total pressure is

A

760 mmHg

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6
Q

In dry air, the patial pressure of oxygen is

A

159.4 mmHg

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7
Q

In dry air, the partial pressure of carbon dioxide is

A

3.04 mmHg

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8
Q

In dry air, the partial pressure of nitrogen is

A

593.3 mmHg

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9
Q

The partial pressure of gasses other than nitrogen, carbon dioxide, and oxygen is

A

4.26 mmHg

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10
Q

Composition of dry air

A

78.06% nitrogen, 20.98% oxygen, 0.4% carbon dioxide, and .56% other

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11
Q

In water saturated air, PH2O

A

47 mmHg

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12
Q

The remaining partial pressures in water saturated air

A 
760-47 - 713 mmHg.
PN2 = 556.6 mmHg
PO2 = 149.6 mmHg
PCO2 = 2.85 mmHg
Pother = 3.99 mmHg
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13
Q

Diffusion ratio for oxygen and carbon dioxide

A

Molecular weight:
.85 (Square root of molecular weight of oxygen over the molecular weight of carbon dioxide) (square root of 32/44)
Solubility in water:
Diffusion CO2/ Diffusion O2 = .85.567/.0244 = .8523 = ~20

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14
Q

Fick’s Law of Diffusion

A

V = (DA (P1-P2))/X
Where D = diffusion coefficient, A = surface area of membrane, P1-P2 = partial pressure on either side of the membrane, and X = membrane thickness (V = rate of diffusion(volume of gas moving per unit of time))

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15
Q

Membrane Resistance

A

= 1/Dm (Dm = membrane capacitance)
Resistance to diffusion of oxygen imposed by the alveolar-capillary interface (alveolar epithelium, alveolar basement membrane, interstitial space, capillary basement membrane, capillary epithelium), plasma and erythrocyte membrane

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16
Q

Chemical reaction resistance

A

1/ (theta*Vc) Where theta is volume of oxygen combining in one minute with hemoglobin in 1 mL of blood at partial pressure difference of 1 mmHg and Vc is pulmonary capillary blood volume
The resistance to diffusion of oxygen imposed by the chemical reaction of hemoglobin with oxygen

1/ the reaction rate of oxygen and hemoglobin for the entire lung

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17
Q

Diffusive resistance

A

1/ Dl

Sum of chemical reaction resistance and membrane resistance

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18
Q

Time for gas equilibrium to occur

A

250 miliseconds

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19
Q

Time required for RBC to transit the pulmonary capillary

A

750 miliseconds

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20
Q

Diffusion Capacity

A

= DA/X (Diffusion coefficient * surface area of the membrane/membrane thickness)
= Rate of diffusion(volume of gas moving per unit time)/ (alveolar pressure - capillary pressure)

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21
Q

Factors affecting diffusion capacity

A

DL increases with body surface area when comparing normal individuals of different sizes. DL increases with training due to recruitment of unused capillaries. DL increases with thickening of alveolar-capillary membrane as in pulmonary fibrosis, and interstitial edema (impaired heart function)
DL increases due to decrease in alveolar surface area as in COPD

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22
Q

Normal blood gas volumes

pH

A

7.35-7.45

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23
Q

Normal blood gas volumes

PaO2

A

80-100 mmHg

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24
Q 
Normal blood gas volumes
SA O2 (saturation)
A

95-100% (greater than 95%)

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25
Q

Normal blood gas volumes

PaCO2

A

35-45 mmHg

26
Q

Normal blood gas volumes

HCO3-

A

22-26 meq/liter

27
Q

Oxygen moves from ____.

A

Inspired air (to alveoli, to systemic arterial blood) to tissues

28
Q

Carbon dioxide moves from ____.

A

TIssues to (systemic venous blood, to alveoli, to) expired gas

29
Q

Why is inspired air different than alveolar air?

A

The partial pressure of water vapor is higher in the alveolar space. There are contributions to the gas composition from dead space (lack of complete exchange of alveolar air for fresh air), constant absorption of oxygen and secretion of carbon dioxide

30
Q

Anatomical shunting

A

2-3 percent of systemic arterial blood bypasses the pulmonary capillaries

31
Q

Thebesian circulation

A

coronary venous blood returning to the left atrium

32
Q

Ventilation Perfusion Ratio

A

Ratio of alveolar ventilation (liters/minute) to alveolar blood flow (Qa, Liters/minute)

33
Q

Average ventilation perfusion ratio

A

0.8 (4 L/min / 5 L/min)

34
Q

Why is there uneven ventilation in the lungs?

A

ventilation is greatest at the lung base and poorest at the apex due to a gradient of intrapleural pressure. The smaller alveoli at the base of the lung have a larger compliance (they are smaller before inspiration because gravity presses the column of lung tissue above it onto them and expand relatively more)

35
Q

Why is there uneven perfusion in the lungs?

A

Perfusion is greatest at the base of the lungs due to effects of gravity. Hydrostatic pressure is highest at the base of the lung and lowest above the heart.

36
Q

In a standing person, the base of the lung gets ____ ventilation but _____ blood.

A

twice as much,
ten times as much
(Lower V/Q ratio)

37
Q

When ventilation is much greater than perfusion

A

Physiological dead space can cause this

Bronchiolar constriction reduces ventilation and vascular dilation increases perfusion

38
Q

When ventilation is much less than perfusion

A

Caused by a physiologic shunt

Bronchiolar dilation increases ventilation and vascular constriction reduces perfusion

39
Q

Amount of oxygen dissolved in blood at 37 degrees celsius

A

0.29 mL/dL

40
Q

oxygen carrying capacity of blood

A

19.5 mL/dL

41
Q

What does F8 in hemoglobin do?

A

it binds Fe2+ (So that it doesn’t bind to O2 and become Fe3+)

42
Q

What does E7 in hemoglobin do?

A

It prevents apposition of a second heme group

43
Q

How much hemoglobin is in a deciliter of blood?

A

15 grams

44
Q

How much oxygen is in 100 mL of blood?

A

20.1 mL bound O2

45
Q

What is cooperativity?

A

The binding of one molecule of oxygen facilitates the the subsequent binding of other oxygen molecules

46
Q

Hill Plot

A 
Plotting log (theta/(1-theta)) vs Log PO2
Hill coefficient ~3
47
Q

What shifts the O2 disassociation curve to the right?

A

Increased concentrations of carbon dioxides or decreased pH (increase proton concentration)
(Decreased affinity of oxygen for hemoglobin. Means for a given PO2, less O2 is bound to hemoglobin)
Aka Bohr effect

48
Q

Haldane effect

A

High PO2 results in dissociation of protons and carbon dioxide from hemoglobin

49
Q

Increased temperature moves the dissociation curve to the ____.

A

right

50
Q

What is BPG?

A

2,3-bisphosphoglycerate is a highly anionic organic phosphate that is present in fetal erythrocytes (according to Rosen’s notes) The presence of BPG increases the oxygen affinity of fetal hemoglobin to a value greater than that of maternal hemoglobin.

However the notes were misleading. It actually right shifts the dissociation curve and leads to hemoglobin releasing more oxygen.
Fetal hemoglobin actually has a low affinity for BPG. So Rosen’s notes are wrong. Fetal hemoglobin does have a higher affinity for oxygen than maternal hemoglobin though.

51
Q

Molecular mechanisms underying hemoglobin oxygen binding

A

Subunit interactionns are essential. Unaffected by pH, BPG, PCO2. Hyperbolic curve.
Deoxygenated hemoglobin has 8 salt links formed by carboxy terminal amino acids of each chain and their side groups with groups on adjacent chains. The molecule is constrained by these links in what is called the Tense form. Initial oxygenation shifts alpha one and beta two subunits relative to one another breaking strong salt links for weaker ones. This allows greater molecular movement, with oxygenated hemoglobin being the relaxed form of the molecule
Movement of the porphyrin iron atom mediates oxygen cooperativity

52
Q

PO2 needed in cells to sustain life

A

30 mmHg

53
Q

Carbon dioxide transport

A

carbamino compounds - negligible
Dissolved carbon dioxide and bicarbonate ion (CO2 + H2O H2CO3- HCO3- + H+)
Transport as bicarbonate in erythrocytes

54
Q

Carbon dioxide transport in erythrocytes

A

92% of CO2 in RBC’s is as bicarbonate. Carbonic anhydrase converts CO2 and water to HCO3- in RBC’s. Anion exchanger transports HCO3- out by exchanging Cl-. Water moves into the RBC.
Carbonic anhydrase in endothelium of pulmonary capillaries, HCO3- converted to CO2 and expired.

55
Q

The binding position of oxygen can be occupied by ___.

A

H+ (oxygenation of hemoglobin frees the H+ to bind with HCO3-)

56
Q

The pulmonary circulatory system in contrast to the systemic circulation

A

low pressure, low resistance, high compliance
(Due to difference in thickness of right and left ventricles, little smooth muscle in pulmonary arterioles) (24/8 mmHg pulmonary blood pressure)

57
Q

The microcirculation is critical in determining ____.

A

Pulmonary pressure and flow

58
Q

Extra-alveolar vessels

A

Large extraparenchymal arteries and veins on lung surface which are directly exposed to subatmospheric intrathoracic pressure and smaller arteries and veins within the parenchyma which are tethered by connective tissue to alveoli and thus expand in response to alveolar inflation

59
Q

Alveolar vessels

A

less than 50 micrometers in diameter, decrease in diameter in response to alveolar inflation

60
Q

Approximately 70% of total compliance is accounted for by the _____. Increase in pulmonary artery pressure is associated with a decrease in ____ due to distension of these microvessels and recruitment of unperfused or poorly perfused capillaries.

A

small vessels

pulmonary vascular resistance

Physiology (11 decks)

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