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Physiology Pulmonary > Pulmonary: gas exchange and transport > Flashcards

Pulmonary: gas exchange and transport Flashcards

1
Q

diffusion of gases

A

governs the movement of gas between the liquid and gaseous environment-> the blood, interstitial fluid, respired air. Also responsible for movement of gas in the near zero velocity environment of alveolar sac. inversely proportional to molecular weight

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2
Q

Partial pressure

A

pressure of each individual gas in mixture of gases. Used to define diffusion of gas because it allows comparisons of gas activities in both liquid and gaseous environment

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3
Q

Henry’s law

A

expresses relationship between partial pressure and amount of gas in physical solution
C=(solubility)(pressure).
C-> concentration of ml gas/ml liquid
solubility-> in ml gas/ml liquid/1atm (760mmHG)
P= partial pressure in mmHg

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4
Q

Daltons law

A

molecules of gas exert pressure because they constantly move and collide wit the walls of their container. Sum effect of all these collisions is the total pressure of that gas. If gas is a mixture, total pressure is the sum of the pressures exerted b each of the gases.

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5
Q

Partial pressure good indicate of

A

relative activity of gas and is a good measure of tendency to diffuse. In a mixture, each gas behaves as if it occupies the entire volume and exerts pressure independently of the gases
P(x)-> Mole fraction of x times total pressure

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6
Q

P(H20)

A

evaporation of water causes gas to acquire water vapor. Amount of vapor that is acquired is determined by number of molecules leaving the liquid phase and this is temperature dependent. Must be accounted for as contributing to total gas pressure-> has effect of proportionately lowering the partial pressures of the gases

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7
Q

P(h20) of lungs

A

47 mmHg

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8
Q

diffusion and molecular weight and solubility

A

equilibrium of gases from area of high concentration to low concentration is achieved via diffusion.

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9
Q

diffusion and molecular weight

A

Diffusion is inversely proportional to the square root of M.W, light gases will achieve equilibrium faster. May be expressed mathematically, for Co2 and o2 (in notes)

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10
Q

diffusion and solubility

A

when gas contacts liquid, gas will diffuse through the liquid at a rate determined by the MW and solubility in the liquid.

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11
Q

CO2 versus O2

A

O2 has a smaller molecular weight than CO2, but CO2 diffuses 20 times faster in water due to its 23 times greater solubility in water.

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12
Q

Fick’s law of diffusion

A

rate of diffusion is expressed as volume of gas moving across membrane per unit time. (equation in notes)

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13
Q

capillary gas exchange of gases: relationship of erythrocyte transit to O2/CO2 transfer

A

transfer of O2 occurs in 2 phases, each with its unique resistance (diffusion is give as conductance, the inverse of which is resistance)

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14
Q

membrane resistance

A

resistance to diffusion of O2 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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15
Q

chemical resistance resistance

A

resistance to diffusion of O2 imposed by chemical reaction of O2 with hemoglobin. Equation in notes.

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16
Q

diffusive resistance

A

total diffusive resistance of lung is made up of two components: membrane resistance and chemical reaction resistance. two resistance are additive.

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17
Q

exchange for respiratory gases

A

is highly efficient owing to the time gas equilibrium to occur (250msec) versus time required for the RBC to transit the pulmonary capillary (750msec) (equation in notes)

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18
Q

exercise on breathing air

A

can shorten the RBC transit time by as much as two-thirds, but in normal person this still does not reduce final end capillary PO2 because of the large “safety factor” built into the transit time

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19
Q

exercise effect on end capillary pressure

A

if diffusion resistance is increased (due to an abnormal thickening of blood-gas barrier)-> end capillary P02 may not reach the alveolar PO2, which is accentuated by exercise.

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20
Q

lowered inspired/alveolar PO2

A

time for end-capillary PO2 to equilibrate with alveolar PO2 is prolonged. In a normal person at rest, end capillary PO2 will still reach alveolar PO2, but with exercise a diffusion limitation can be observed.

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21
Q

Diffusion capacity (DL)

A

volume of gas moving per unit of time given for difference in partial pressure of a gas. gives units of conductance that are the inverse of resistance (equation in notes).

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22
Q

DL increases with body surface area when

A

comparing normal individual of different sizes

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23
Q

DL increase with training due to

A

recruitment of unused capillaries

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24
Q

DL decreases with thickening of

A

alveolar capillary membrane as in pulmonary fibrosis and interstitial edema

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25
Q

DL decreases due to decreased

A

in alveolar surface area as in emphysema

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26
Q

normal pH

A

7.35-7.45

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27
Q

Pa (O2)

A

80-100mmHg

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28
Q

Sa (O2)

A

95-100%

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29
Q

Pa (Co2)

A

35-45mmHg

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30
Q

HCO3-

A

22-26 meq/liter

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31
Q

regional pressure gradients

A

exist to move O2

inspired air->alveoli->systemic arterial blood->tissues

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32
Q

regional pressure gradient for CO2

A

tissues->systemic venous blood->alveoli->expired gas

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33
Q

what ca cause differences in gas composition of inspired and alveolar air?

A

contribution of anatomic dead space-> lack of complete exchange of alveolar for fresh air), constant absorption of O2 and secretion of CO2 and humidification decreasing partial pressures of all gases

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34
Q

shunting of blood from pulmonary capillaries

A

2-3% of blood in systemic arteries is bypassed the pulmonary capillaries and does not contribute to gas exchange. bypass consist of blood passing through pulmonary circulation without going through gas exchanging areas in lungs

35
Q

Thebesian circulation

A

bypass consist of blood passing through pulmonary circulation without going through gas exchanging areas in lungs as well as coronary venous blood that drains directly to left ventricle.

36
Q

anatomic abnormalities can increase shunt

A

perfusion through areas of atelectasis

37
Q

ventilation to perfusion ratio

A

ratio of alveolar ventilation Va (liters/min) to alveolar blood flow Qa (liters/min) (Va/Qa)

38
Q

physiological shunt (counterpart to anatomic shunt)

A

Va/Qa=0, alveolus is unventilated, gas exchange is severely impaired

39
Q

physiological dead space

A

Va/Qa&raquo_space; 0, capillary is unperfused, gas exchange is severely impaired

40
Q

Uneven ventilation, Va

A

factor for ventilation-perfusion mismatch. Ventilation is greatest at lung base, poorest at lung apex. due to gradient of intrapleural pressure from apex to base of lungs

41
Q

gradient of intrapleural pressure

A

prior to inhalation, alveoli in base of lungs are less expanded due to gravitational force from column of lung tissue above, and alveoli at apex are more expanded. Smaller alveoli at base have a higher compliance due to surfactant effects, and lower potential energy due to relaxed elastic elements-> for a given pressure the smaller the alveoli at base will expand more than those at apex

42
Q

uneven perfusion Qa

A

greatest at base of lung due to also the gravitational effects. Hydrostatic pressure decreases above the heart and increases below the so blood at base of lung receives maximal hydrostatic pressure while blood at top receives less.-> blood flow at base is greatest.

43
Q

uneven perfusion on pulmonary vessels

A

effect of distending the very flexible pulmonary vessels decreasing their resistance and further increasing flow.

44
Q

in a standing person…

A

base of lung gets twice as much ventilation but ten times more blood->potential for a lower ventilation-perfusion ratio

45
Q

compensation for Va/Qa mistmatch

A

occurs in response to gas tension in alveoli.

46
Q

Va/Qa&raquo_space; 0

A

physiological dead space, bronchiolar constriction reduces Va and vascular dilation increases Qa.

47
Q

Va/Qa=0

A

physiological shunt, bronchiolar dilation increases Va and vascular constriction decreases Qa.

48
Q

oxygen transport in physical solution

A

amount of gas dissolved in solution and its rate of diffusion are both determined by gas partial pressure. Partial pressure in air, lungs, blood and tissues favor movement of O2 from air to tissue and converse for CO2.

49
Q

O2 in blood

A

amount of O2 dissolved in arterial blood at 37 degrees C is .29ml/dl-> amount insufficient to support metabolism and represents only 1.5% of total O2 carrying capacity of blood (19.5ml/dl). Remainder carried by Hb.

50
Q

CO2 versus O2 in blood

A

despite nearly equivalent partial pressure, CO2 dissolves in venous blood is about 25 times that of O2 due to higher solubility in water

51
Q

Hemoglobin

A

64.5k MW globular protein that makes up 90% of total cytoplasmic protein in erythrocyte. 4 subunits (2 alpha, 2 beta), heme moiety

52
Q

Heme group

A

porphyrin ring with 1 ferrous iron atom. binds O2 in an oxygenation reaction rather than an oxidation reaction.

53
Q

Fe3+ form heme

A

can’t bind O2.

54
Q

Protein function of heme group

A

prevent the heme sandwich condition. Histidine (F8) binds Fe2+ and histidine F7 prevents apposition of second heme group (no sandwich)

55
Q

free heme

A

can bind O2 briefly that does allow oxidation of iron (2+->3+) (forms heme sandwich )

56
Q

cooperativity

A

binding of one molecule of O2 facilitates the subsequent binding of other O2 molecules.

57
Q

slope of the Hill plot

A

slope indicates the independent binding of a single O2 molecule as for Mb. Hemoglobin the value of slope varies with O2 while for Mb it is constant

58
Q

What shifts dissociation curve of Hb-O2 (bohr effect)

A

increased CO2 or H+ shifts O2 dissociation curve to the right by decreasing the affinity for O2 to Hb.

59
Q

Haldane effect

A

high PO2 (pulmonary capillaries) results in dissociation of H+ and CO2 from Hb. depends on amount of oxygenation.

60
Q

What increases oxygen affinity for fetal Hb

A

BPG (2,3-biphosphoglycerate)

61
Q

subunit of interaction between O2 and Mb

A

hyperbolic O2-dissociation curve is not affected by pH, CO2 or BPG

62
Q

T (tense) form

A

Deoxy Hb has 8 salt links, constrains molecule in tense state.

63
Q

Relaxed state

A

initial oxygenation shifts alpha 1 and alpha 2 subunits, breaking strong salt link-> allows greater movement with oxyHb, now in R form

64
Q

what allows greater flexibility of the other subunits?

A

first O2 moves the Fe2+ into a planar position in porphyrin ring, this movement of Fe transmitted to proximal histidine (F8) shifting its subunit, breaking salk link

65
Q

what does the flattened relationship of O2 curve say?

A

at high PO2, complete saturation of Hb despite a wide variation of PO2.Large changes in PO2 only cause a small change in saturation.

66
Q

Amount of O2 delivered to tissues is unaffected by what?

A

moderate drop in alveolar PO2

67
Q

What do patients with anemia experience?

A

although the amount of O2 delivered to tissue may be adequate at high PO2 it falls dramatically as O2 saturation drops

68
Q

What direction does CO2 shift O2-dissociation curve?

A

to the right.

69
Q

what does CO2 cause?

A

since active tissues produce CO2 a a by product of glycogen metabolism, CO2 enhances O2 delivery (decrease Hb O2 affinity).

70
Q

what else shifts O2-dissociation curve to the right?

A

increased temperature, acidity

71
Q

what effect is important in high altitudes or some forms of lungs disease?

A

DPG (BPG) production increases in poorly oxygenated erythrocytes causes a right shift and greater O2 delivery

72
Q

what provides negligible CO2 transport

A

carbamino compounds

73
Q

CO2 and HCO3-

A

CO2 combined with water give H+ and HCO3-

74
Q

what is the equilibrium of CO2 and H2CO3?

A

CO2 is 1000 times greater than H2CO3.

75
Q

what is the difference between CO2 transport in RBC and plasma?

A

in RBC, CO2 is made into bicarbonate from CO2 and water, reaction is catalyzed by carbonic anhydrase.

76
Q

why is the Cl- shift in RBC important?

A

RBC has an anion exchanger for HCO3-, maintains electroneutrality, each HCO3- is exchanged for Cl-. each CO2 adds an HCO3- or Cl- to the cell, so there is a net movement of water into the cell-> hematocrit of venous blood is 3% greater than that of arterial blood

77
Q

what is the fate of bicarbonate?

A

in the pulmonary capillaries, carbonic anhydrase is in endothelium and converts bicarbonate to CO2 and diffuses from plasma to alveoli

78
Q

what helps facilitate the conversion of bicarbonate to CO2 in RBC in lungs?

A

binding position of O2 is occupied by H+, so oxygenation of Hb liberates H+-> this helps facilitate conversion of HCO3- to CO2

79
Q

How does CO2 bind Hb?

A

as a carbamino compound, relationship described as CO2-dissociation curve

80
Q

What does absence of haldane effect mean?

A

effects tissue PCO2 would have to increase to 51mmHg to produce similar amounts of venous CO2 return. Oxygenation also off-loads H+ causing production of CO2 at pulmonary capillaries

81
Q

pulmonary circulation characteristics?

A

low pressure, low resistance, and high compliance system.

82
Q

why is the pulmonary circulation so much different than the systemic?

A

difference in wall thickness between right and left ventricles, right is about 1/3 that of left, arterioles of pulmonary circulation have very little smooth muscle

83
Q

why is the microcirculation critical in determining pulmonary pressure and flow?

A

approximately 70% of total compliance is accounted for by small vessels: extra-alveolar and alveolar vessels, small arteries

84
Q

what can cause an decrease in pulmonary artery pressure?

A

exercise, associated with a decrease in pulmonary vascular resistance due to distension of micro-vessels and recruitment of un-perfused or poorly perfused capillaries

Physiology Pulmonary (4 decks)

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