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respiratory system year 1 > pulmonary blood flow, gas exchange and transport > Flashcards

pulmonary blood flow, gas exchange and transport Flashcards

1
Q

describe the blood supply to the lungs

A

pulmonary artery

pulmonary vein

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2
Q

what is the role of the pulmonary artery

A 
travels away from the heart
carries blood to the lungs
L and R arise from R ventricle 
carries entire cardiac output from RV 
supplies the dense capillary network surrounding the alveoli
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3
Q

pulmonary vein

A

travels into the heart

returns oxy blood to the LA

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4
Q

how is pulmonary circulation different to systemic circulation

A

opposite in function - delivers carbon dioxide to the lungs and picks up oxygen
high flow, low pressure system (systolic ~25mmHg)

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5
Q

bronchial circulation

A

supplied by the bronchial arteries arising from the systemic circulation
supply oxygenated blood to the airway smooth muscle, nerves and lung tissue (lung parenchyma)
remove waste
comes from the L side of the heart

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6
Q

describe the factors that influence diffusion of gases across the alveoli

A

obey the rules for siple diffusion
rate of diffusion across the membrane is:
directly proportional to pp grad
directly proportional to gas solubility
directly proportional to available SA
inversely proportional to thickness of the membrane
most rapid over short distances

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7
Q

pressure gradients for oxygen and carbon dioxide between alveoli and pulmonary arterial blood

A

OXYGEN: 100mmHg in alveoli –> 40mmHg in arterial blood

CARBON DIOXIDE: 46mmHg in arterial blood –> 40mmHg in alveoli

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8
Q

what is arterial blood pp equivalent to

A

alveoli

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9
Q

what is venous blood pp equivalent to

A

tissue

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10
Q

partial pressure of oxygen and carbon dioxide in tissues

A

oxygen: <40

carbon dioxide: >46

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11
Q

what is rate affected by

A

solubility of the molecule

oxygen isn’t very soluble in water but carbon dioxide is

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12
Q

how are the alveoli adapted for efficient diffusion

A

large SA
short diffusion distance
membranes are thin
elastic fibres and type II cells never sit between the capillary and the type I cell

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13
Q

impact of emphysema on gas exchange in the lung

A

destruction of the alveoli
reduced SA for gas exchange
low pO2 in the blood
normal alveolar PO2

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14
Q

impact of fibrosis on gas exchange

A

thickened alveolar membrane slows gas exchange
loss of lung compliance may decrease alveolar ventilation
normal or low alveolar PO2
low blood PO2

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15
Q

impact of pulmonary oedema on gas exchange

A

fluid in the interstitial space increases diffusion distance
arterial PCO2 may be normal due to higher solubility of CO2 in water
normal alveolar PO2
low PO2 in blood

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16
Q

impact of asthma on gas exchange

A

constricted bronchioles
increased airway resistance
decreased airway ventilation
low alveolar and blood PO2

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17
Q

explain the relationship between ventilation and perfusion and its significance in health

A

ventilation and perfusion ideally compliment each other
optimally, ventilation = blood flow
both blood flow and ventilation decrease with height across the lung

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18
Q

describe the V/Q relationship at the base of the lungs

A

V

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19
Q

describe the V/Q relationship at the apex of the lungs

A

low blood flow
arterial pressure < alveolar pressure
arteries are compressed

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20
Q

what % of the height of the healthy lung performs well in matching blood and air

A

75
the majority of the mismatch occurs in the apex
this is then auto-regulated to keep the ratio close to 1

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21
Q

what happens when ventilation decresaes in a group of alveoli

A

PCO2 increases
PO2 decreases
blood flowing past these alveoli isnt oxygenated
dilution of blood from better ventilated areas

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22
Q

describe the local control mechanisms that keep ventilation and perfusion matched

A

decreased PO2 around under ventilated alveoli constricts their arterioles, diverting blood to better ventilated alveoli
increased PCO2 causes mild bronchodilation
constriction in response to hypoxia is particular to pulmonary vessels

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23
Q

what occurs when ventilation > blood flow

A

alveolar dead space

air in the alveoli isn’t participating in gas exchange due to insufficient blood flow

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24
Q

what occurs with alveolar dead space

A

opposite to shunt
increased alveolar PO2 - pulmonary vasodilation
decreased alveolar PCO2 - mild bronchial constriction

this increases perfusion and decreases ventilation, bringing the ratio back towards 1

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25
Q

define shunt

A

the passage of blood through areas of the lung that are poorly ventilated
opposite of alveolar dead space

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26
Q

define anatomical dead space

A

air in the conducting zone of the resp tract unable to participate in gas exchange as walls of airway in this region are too thick

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27
Q

physiologic dead space

A

alveolar DS + anatomical dead space

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28
Q

dalton’s law

A

total pressure of a gas mixture is the sum of the pressures of the individual gases

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29
Q

henry’s law

A

amount of gas dissolved in a liquid is determined by the pressure of the gas and its solubility in the liquid

30
Q

define partial pressure

A

the pressure of a gas in a mixture of gases is equivalent to the % of that particular gas in the entire mixture multiplied by the pressure of the whole gaseous mixture

31
Q

how many ml of oxygen dissolve per L of plasma

A

3ml

32
Q

how does Hb in RBC influence the carrying capacity

A

increases it to 200ml/L
>98% bound to Hb, the rest is in the plasma
Hb is required to meet the oxygen demand of resting tissues

33
Q

what is the difference between arterial partial pressure of oxygen and arterial oxygen content

A

arterial pp of oxygen is not the same as arterial oxygen concentration/content
PaO2 refers to oxygen in solution in the plasma and is determined by oxygen solubility and pp of O2 in the gas phase

34
Q

what are the value assigned to pp of a gas in solution equal to

A

the pp of the gaseous phase that is driving that gas into solution
REMEMBER THAT GASES DONT TRAVEL IN THE GASEOUS PHASE IN THE PLASMA

35
Q

what is PaO2

A

100mmHg
same as in alveoli
aka oxygen tension

36
Q

how much of arterial oxygen is extracted by the peripheral tissues at rest

A

25%

37
Q

how does Hb bind to oxygen

A

cooperatively binds 4 molecules of O2

1.34ml O2 to 1g Hb

38
Q

HbA

A

92% of the Hb in RBC is HbA, the remaining 8% is HbA2 (delta chains replace beta), HbF (gamma replace beta) and glycosylated Hb (HbA1A, HbA1B, HbA1C)

39
Q

how is glycosylated Hb related to diabetes

A

if BG levels increase, glycosylation of Hb increases
indicative of diabetes management over time
glycosylation is permanent for the lifetime of that RBC

40
Q

what is the major determinant to the degree of % O2 saturation

A

PaO2

41
Q

Hb and oxygen transport

A

Hb sequesters O2 from the plasma

pp gradient is maintained until the Hb is saturated w/ O2

42
Q

How long does saturation of Hb w/ O2 take

A

complete after 0.25s contact w/ the alveoli

total contact time ~0.75s

43
Q

O2 Hb dissociation curve

A 
shows PO2 (mmHg) against Hb % saturation O2
sigmoidal shaped
max saturation = 98%
44
Q

when is Hb most saturated

A

at normal systemic PaO2
100mmHg

even at 60mmHg, Hb is still 90% saturated

at normal venous PO2 there is still 75% reserve capacity

45
Q

what happens to saturation below 40mmHg

A

small changes in PO2 create much larger changes in % saturation

46
Q

factors affecting the O2 - Hb dissociation curve

A

ph
PCO2
temp
2,3-DPG

47
Q

Effect of Ph on the O2 - Hb dissociation curve

A 
reduced pH (acidosis) - curve shifts right 
increased pH (alkalosis) - curve shifts left
48
Q

effect of PCO2 on the O2 - Hb dissociation curve

A

increased pp shifts the curve right

49
Q

effect of temp on the O2 - Hb dissociation curve

A

increase temp shifts the curve right - lower affinity for oxygen at higher temps, oxygen given off more readily to the peripheral tissues, low % bound to Hb

hypothermia - curve shifts L, Hb doesn’t release oxygen to peripheral tissues, high affinity

50
Q

effect of 2,3 DPG on the O2 - Hb dissociation curve

A

synthesised by RBC
increases in situations associated w/ inadequate oxygen supply and helps maintain oxygen release in the tissues
affinity of Hb for O2 is reduced by the binding of 2,3 - DPG

51
Q

foetal Hb and myoglobin compared to normal adult Hb

A

both have a higher affinity for oxygen than HbA - this is necessary for extracting oxygen from maternal/arterial blood (muscle requirers high amounts of oxygen delivery)

at any pp they have a higher % sat than HbA

52
Q

what is anaemia

A

any condition where the oxygen carrying capacity of the blood is compromised

NO CHANGE IN PaO2 (only RBC are affected)
total blood content is reduced as most O2 is associated w/ RBC
Hb present is still fully saturated as PaO2 is normal

53
Q

what are 3 causes of anaemia

A

iron deficiency
vit B12 deficiency
haemorrhage

54
Q

what does carbon monoxide bind to in the blood

A

Hb forming carboxyhaemoglobin
250x greater affinity than O2
only a small PCO is needed for progressive carboxyHb formation

55
Q

symptoms of CO poisoning

A 
hypoxia and aneamia
nausea and headaches
cherry red skin and mucous membranes
normal resp rate (normal PaO2)
potential brain damage and death
56
Q

define hypoxia

A

inadequate oxygen supply to tissues, various causes

57
Q

5 causes of hypoxia

A 
hypoxaemic
anaemic
stagnant
histotoxic
metabolic
58
Q

hypoxaemic hypoxia

A

most common
reduced oxygen diffusion at the lungs
either due to reduced PO2 in the atmosphere OR tissue pathology

59
Q

anaemic hypoxia

A

reduced oxygen carrying capacity of blood due to anaemia

60
Q

stagnant hypoxia

A

heart disease

insufficient pumping ability of blood to lungs/around the body

61
Q

histotoxic hypoxia

A

poisoning prevents cells using the oxygen delivered to them

e.g. CO, CN-

62
Q

metabolic hypoxia

A

oxygen delivery to tissues doesnt meet increased oxygen demand by cells

63
Q

carbon dioxide transport in the blood

A

7% dissolved in plasma and RBC
23% combined in RBC w/ deoxy Hb–> carbaminocompunds
70% combines in RBC w/ water (carbonic anhydrase) –> carbonic acid (dissociates into H+ and HCO3-)
most HCO3- moves out into plasma in exchange for Cl- (chloride shift)
XS H+ binds to Hb

64
Q

CO2 movement in pulmonary capillaries

A

the reverse occurs in pulmonary capillaries and CO2 moves down its conc grad from blood to alveoli

65
Q

acid-base balance

A

CO2 is capable of changing ECF pH

increased CO2 = reduced pH (increased H+)

66
Q

How does CO2 change ECF pH

A

CO2 + H2O H2CO3 HCO3- + H+

67
Q

why is pH normally stable

A

all the CO2 produced is eliminated in expired air

68
Q

what alters plasma PCO2

A

hypo/hyperventilation

plasma [H+] will vary accordingly

69
Q

hypoventilation and pH

A

CO2 retention
increased [H+]
respiratory acidosis

70
Q

hyperventilation and pH

A

more CO2 blown off
reduced [H+]
respiratory alkalosis

respiratory system year 1 (25 decks)

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