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Physiology 2 Flashcards

1
Q

What are the 2 main circulations that supply blood to the lungs?

A

bronchial and pulmonary circulation
Bronchial- bronchial arteries supply the airway smooth muscle, nerves and lung tissue
Pulmonary- the left and right pulmonary arteries each supply one lung and surround the alveoli with blood vessels; thus allowing transport of deoxygenated blood to the lungs and oxygenated away from lungs

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2
Q

what kind of system is the pulmonary system?

A

low pressure, high flow system

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3
Q

What is the CO of the RV and how does this flow rate compare to that of the rest of the body?

A

5L/min, which is the same as the left side of the heart

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4
Q

What is a difference between the pulmonary and systemic circulation?

A
  • pulmonary circulation is much lower pressure than systemic (approx 25mmHg in pulmonary & 120mmHg in systemic)
  • much lower difference in pressure between arterial and venous sides in pulmonary circulation than systemic
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5
Q

what is the difference between pulmonary artery and pulmonary vein and why is this significant?

A

only about 10mmHg, significant because since this is such a small pressure difference, it doesn’t take very much pathology to disrupt it, lose gradient and impede blood flow through lungs

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6
Q

what causes oxygen to go form inside alveoli to pulmonary vein and co2 to go from inside pulmonary artery to alveoli?

A

partial pressure gradient (high to low)

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7
Q

what is PA02?

A

alveolar partial pressure of o2 (100mmHg)

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8
Q

What is PACO2?

A

alveolar partial pressure of co2 (40mmHg)

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9
Q

Pa02?

A

arterial partial pressure of 02 (100mmHg)

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10
Q

PaCO2?

A

arterial partial pressure of co2 (40mmHg)

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11
Q

Pv02?

A

venous partial pressure of 02 (40mmHg)

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12
Q

PvCO2?

A

venous partial pressure of CO2 (46mmHg)

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13
Q

what do you do to calculate kPA from mmHg?

A

multiply by 0.133

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14
Q

what factors affect the rate of diffusion across a membrane? (5)

A
  • directly proportional to partial pressure gradient
  • directly proportional to gas solubility
  • inversely proportional to membrane thickness
  • directly proportional to available surface area
  • fastest over short distances
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15
Q

what is a way in which the lungs are set up to allow maximal diffusion?

A

nothing in between type 1 alveolar cells and blood vessels (aka elastic fibres etc)

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16
Q

what are characteristics of emphysema?

A

reduction in lung elasticity, degradation of alveolar wall, reduced surface area for gas exchange, decreased Pa02

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17
Q

what are characteristics of fibrotic lung disease and how it affects gas exchange?

A

fibrous tissues sit in between type 1 alveolar cells & capillaries and inhibit diffusion, and also reduce lung expansion- reduced PA02

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18
Q

what are the characteristics of pulmonary oedema and how it affects gas exchange?

A

fluid building up between alveolus and capillary - increases diffusion distance and therefore impedes movement of oxygen

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19
Q

what are the characteristics of asthma and how it affects gas exchange?

A

increased resistance to air flow, reduced ventilation, reduced PA02

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20
Q

what is ventilation and how is it measured?

A

air flow to alveoli, measured in L/min

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21
Q

what is perfusion and how is it measured?

A

local blood flow, L/min

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22
Q

why are ventilation and perfusion not ideally matched?

A

because of gravity

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23
Q

where is perfusion greatest?

A

at base of lung

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24
Q

where is ventilation greatest?

A

at base of lung

25
Q

what pressure is greatest at the base of the lung?

A

perfusion- more blood at base of lung (gravity), arterial pressure exceeds alveolar pressure & compresses alveoli, vascular resistance is low

26
Q

what pressure is greatest at the apex of the lung?

A

ventilation- alveolar pressure greater than BP, blood vessels get compressed, vascular resistance increased

27
Q

where is the middle point in the lungs where ventilation= perfusion?

A

rib 3

28
Q

where is ventilation/perfusion ratio > 1?

A

the apex

29
Q

where is ventilation / perfusion ratio <1?

A

base of the lung

30
Q

what happens when ventilation < perfusion ?

A

buildup of co2 in alveoli, so increase in PAco2 and decrease of Pa02 in capillaries. Increase in PAc02 will result in a loss in the partial pressure gradient between pulmonary artery and alveoli - this means blood going back to the heart is still almost completely deoxygenated; effectively being ‘shunted’ from right side to left side of heart

31
Q

what auto regulation mechanisms can happen to try keep ventilation and perfusion balanced in ventilation < perfusion scenario?

A
  • vasoconstriction as a result of hypoxia - divert blood to better ventilated regions
  • co2 increase causes mild bronchodilation
32
Q

what are the effects of auto regulation in a situation of ventilation < blood flow?

A

decreased perfusion

increased ventilation

33
Q

what happens when ventilation > perfusion?

A

alveolar dead space

  • increase in Pa02
  • reduced PAC02
34
Q

what are the effects of auto regulation in a situation of ventilation > perfusion?

A
  • increase in Pa02 –> pulmonary vasodilation

- reduced PAC02–> bronchial constriction

35
Q

what is alveolar dead space ?

A

alveoli that are ventilated but not perfused

36
Q

what is anatomical dead space ?

A

air that cannot take part in gas exchange because the walls of the conducting airways are too thick

37
Q

what is physiological dead space?

A

alveolar + anatomical

38
Q

how much oxygen dissolves per litre of plasma?

A

3ml/L

39
Q

what does arterial partial pressure of oxygen refer to?

A

the amount of oxygen dissolved in plasma

40
Q

why do gases not travel in gaseous phase in plasma?

A

this would result in bubbles of air in blood which would result in a fatal air embolism

41
Q

how much oxygen does Hb carry and how saturated is it?

A

carries 197ml/L, roughly 97-98% saturated because some Hb molecules only bind 3 molecules of oxygen

42
Q

how does haemoglobin work?

A

it has a very high affinity for oxygen and pulls oxygen out of plasma. Until it is fully saturated it will therefore continue to draw oxygen out of alveoli

43
Q

what is haemoglobin made up of?

A
  • 2 alpha and 2 beta chains
  • one molecule can bind 4 molecules of oxygen. When one molecule binds this increases the affinity of haemoglobin to oxygen and therefore more binds
  • when oxygen leaves, the binding sites shut down and reduces affinity (co-operative binding)
44
Q

What is the majority form of Hb in RBCs?

A

around 92% is in the form HbA

45
Q

Why is glycosylated haemoglobin important clinically?

A

gives indication of exposure to glucose

46
Q

what is the major determinant of the degree to which haemoglobin is saturated with oxygen?

A

partial pressure of oxygen in arterial blood (how much oxygen has dissolved in plasma)

47
Q

what 2 other types of haemoglobin are there and compare their affinities compared to normal adult haemoglobin

A

Myoglobin and Fetal Haemoglobin - much higher affinity to 02 than normal adult haemoglobin

48
Q

what is anaemia?

A

where the oxygen carrying capacity of the blood is compromised, mostly due to reduction of number of RBCs (iron deficiency, lack of vitamin B12)

49
Q

what remains normal in anaemia?

A

the partial pressure of oxygen in arterial blood

50
Q

what alters in anaemia (to do with no of RBCs)

A

reduced number of RBCs so total oxygen content falls, however % saturation remains the same

51
Q

affinity of Hb for oxygen remains high until the p02 falls below ..?

A

60mmHg

52
Q

what 4 factors affect the affinity of haemoglobin for oxygen by decreasing the affinity?

A
  • decrease pH
  • binding 2,3-DPG
  • increase in temperature
  • increase in pCO2
53
Q

how does CO lead to pathology?

A

CO binds to Haemoglobin to form CARBOXYHAEMOGLOBIN, and has a much higher affinity for Hb than oxygen does. It becomes very stable once it is bound to it and therefore does not easily dissociate from it which is problematic

54
Q

does CO affect respiratory rate?

A

no, because the PaCO2 is unaffected

55
Q

what are symptoms of CO poisoning?

A
  • anaemia
  • hypoxia
  • cherry red skin
  • mucous membranes
  • nausea and headaches
56
Q

what are the 5 types of hypoxia and describe them (mnemonic)

A

(HIHAM)
Hypoxic - reduction in diffusion a lungs due to decrease in Patm02 / pathology
Ischaemic- the heart does not receive enough oxygen and therefore cannot pump enough to lungs/around body
Histotoxic- poisoning prevents cells utilising oxygen e.g. CO
Anaemic - reduction in oxygen carrying capacity of blood due to anaemia
Metabolic- when blood pumped to a tissue is not enough to meet the increased energy demand by cells

57
Q

how is Co2 transported in the blood? (3 ways)

A
  • 7% dissolves in plasma & RBCs
  • 23% binds to deoxyhaemoglobin to form carbamino compounds in RBCs
  • 70% binds to water to from CARBONIC ACID which then dissociates to form bicarbonate ions and hydrogen
58
Q

how is co2 capable of changing blood pH?

A

CO2 + H20 H2CO3 HCO3 + H+
Normally pH stable because all CO2 produced is able to be expired through expiration however;
in hyperventilation, more co2 blown off than is being produced, decreased H+, respiratory alkalosis
in hypoventilation, co2 retention, H+ increases, respiratory acidosis

Resp. (9 decks)

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