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Case 5 > The Science of Gas Exchange and the Control of Breathing > Flashcards

The Science of Gas Exchange and the Control of Breathing Flashcards

1
Q

What is local matching of ventilation and perfusion important for

A

To optimise gas exchange in the lungs

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2
Q

Where is there better blood flow when upright and healthy

A

At the base of the lungs

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3
Q

What is each alveolus surrounded by

A

A dense capilliary network

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4
Q

What are the values of PO2 and PCO2 in normal lungs

A 
PO2= 100 mmHg/ 1.3. kPa
PCO2= 40 mmHg/ 5.3 kPa
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5
Q

What is the most efficient V:Q ratio

A

1

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6
Q

What does not participate in gas exchange

A

The anatomical dead space

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7
Q

What does the fact that Va:Q= infinity mean

A

The alveoli are ventilated but not perfused meaning there is an increase in physiological dead so no blood flow therefore gas in the lungs remains the same as atmospheric air

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8
Q

What does a clot in a capillary result in

A

An increase in physiological dead space so alveoli are ventilated but not perfusedso no blood flow and gas in the lungs remains the same as atmospheric air

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9
Q

What does poor perfusion in one lung result in

A

Overcompensation of perfusion in the other lung therefore little gas exchange in the lung with poor perfusion even though it is ventilated

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10
Q

Why are the lungs susceptible to emboli

A

When a blood clot in the leg breaks away it passes through widening vessels until it reaches the right atrium and then enters the pulmonary circulatory system. The pulmonary circulatory system has narrower vessels meaning that clots become trapped (therefore pulmonary circulatory system is most susceptible to emboli)

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11
Q

How is the pulmonary circulatory system arranged

A

It runs in series

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12
Q

How is the systemic circulatory system arranged

A

It runs in parallel

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13
Q

What does Va:Q=0 mean

A

There is a right-to-left shunting of blood so blood passes through the lung without coming into contact with air. There is perfusion but no ventilation. There is no airflow if the airways are completely blocked

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14
Q

Describe a physiological shunt that occurs in health

A

Bronchial blood supply (bronchial blood supply is a very minor portion of cardiac output, less than 2%)

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15
Q

Describe pathophysiological shunt

A

Due to fluid filled alveoli. Alveoli can be fileld with fluid due to infection, inflamamtion, pulmonary hypertension or trauma to the lungs. Fluid in the alveoli impairs gas exchange as the volume of alveoli is decreased and so diffusion is reduced.

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16
Q

What are mechanisms to defend Va:Q matching

A

Principally achieved by modulation of blood flow rather than ventilation. Vasoconstriction but low PO2 results in blood being directed away from poorly ventilated areas, the response is very non-linear

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17
Q

What is global hypoxia due to

A

Issues such as altitude and results in global vasoconstriction

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18
Q

What happens at low alveolar PO2

A

There is a significant drop in the amount of blood in a blood vessel due to localised hypoxia which causes vasoconstriction. There is higher blood in the lungs without an embolism

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19
Q

What happens in high alveolar PO2

A

Little effect on dilation

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20
Q

What happens in the systemic system in low PO2

A

There is an increase in blood supply (in pulmonary circulation a decrease in PO2 results in a decrease in blood flow)

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21
Q

What controls the rhythm and pattern of breathing

A

The medulla (brainstem)

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22
Q

What are the respiratory muscles

A

Diaphragm and intercostals

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23
Q

What do changes in the effectors do

A

Wither stimulate sensors or remove the stimulus

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24
Q

What plays a role in the fine tuning of breathing

A

The pons

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25
Q

What does the contraction of the diaphragm depend on

A

Neural input from the spinal cord to the respiratory muscles (C3, C4, C5 keeps the phrenic diaphragm alive)

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26
Q

What does the fact that the medulla is the respiratory centre mean

A

It is the rhythm and pattern generator

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27
Q

What does the medulla generate

A

Discrete bursting patterns resulting in a cycle of inflation and deflation

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28
Q

What is breathing modified by

A

The pons and other sensors

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29
Q

What is inspiration controlled by

A

The Pre-Botzinger complex which fires before inspiration

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30
Q

What is pre-inspiration/ expiration controlled by

A

The reterotrapezoid nucleus/ parafacial respiratory group which fires at the end of inspiration

31
Q

What does the Pre-Botzinger complex consist of

A

Specialised nerve endings located in the ventrolateral surface of the medulla which fire spontaneously resulting in a burst pattern causing contraction of the diaphragm

32
Q

What does the spontaneous pacemaker control

A

The diaphragm

33
Q

What does the pons consist of

A

The pneumotaxic centre and apneustic centre which is responsible for fine tuning of breathing

34
Q

What feed into the pons

A

Higher regions of the brain

35
Q

What does voluntary control mean

A

You are able to override your medulla and therefore can hold your breath, however you can’t hold your breath indefinitely

36
Q

Where are lung receptors

A

In the respiratory system itself and the peripheral receptors are in the body and the CNS

37
Q

What is the role of stretch receptors

A

Stimulate lung inflation, terminate inflation

38
Q

What is the role of juxta-pulmonary “J” receptors

A

Changes in pulmonary circulation halt inflation in the lungs

39
Q

What is the role of irritant receptors

A

Prevent damage to the lungs when you inhale an irritant resulting in a large expulsion of air, therefore these receptors provide a protective function

40
Q

What is the role of proprioceptors (position/ length sensors)

A

Sensitive to changes in stretch, they are golgi tendon organs in the ribcage which respond to changes in load. These receptors are also found in limbs

41
Q

Describe chemoreceptors

A

They also modify breathing and are the most important and major class of receptors

42
Q

What is the importance of the fact that ventilation must me matched to metabolism

A

The respiratory system should not be the limiting factor as there is lots of reserve in health

43
Q

What is CO2 production estimated from

A

PCO2

44
Q

What is O2 production estimated from

A

PO2

45
Q

What is H+ production estimated from

A

pH

46
Q

What are the 3 indices of metabolism in the body

A

CO2, O2 and H+

47
Q

What are changes in blood chemistry detected vy

A

Chemoreceptors which detect changes in indices

48
Q

What are the two types of chemoreceptors

A

Central and peripheral

49
Q

Where are central chemoreceptors located

A

In the brainstem near the ventrolateral surface of the medulla

50
Q

What do central chemoreceptors consist of

A

Chemosensitive neurones which detect changes in the cerebrospinal fluid

51
Q

What are central chemoreceptors sensitive to

A

pH of CSF (index of PCO2)

52
Q

Why does the pH in the capillary blood stay relatively constant

A

Due to protein buffers

53
Q

What moves freely across the blood brain barrier

A

Carbon dioxide

54
Q

What does an increase in carbon dioxide in the capillaries result in

A

An increase in carbon dioxide in the CSF

55
Q

What does an increase in CO2 in the CSF cause

A

There are no protein buffers in the CSF therefore pH changes regarding an increase in the concentration of H+ stimulate chemoreceptors

56
Q

What does acidification of the CSF result in

A

An increase in firing and then an increase in minute ventilation

57
Q

Describe central chemoreceptors

A

located near the ventrolateral surface of the medulla; sensitive to pH of CSF (index of PCO2); relatively slow response time, relatively insensitive to changes in PO2. Central chemoreceptors are not stimulated by hypoxia, therefore carbon dioxide is more important

58
Q

Where are peripheral chemoreceptors located

A

Neat the carotid and aortic arteries

59
Q

Why are the peripheral chemoreceptors located in the aortic and carotid arteries

A

They are areas of high blood flow, nerve endings project directly into the blood

60
Q

Why peripheral chemoreceptors are more significant in adults

A

Carotid bodies

61
Q

What do peripheral chemoreceptors respond to

A

Hypoxia, hypercapnia and acidification very rapidly resulting in an increase in firing and an increase in ventilation

62
Q

What is the peripheral chemoreceptor firing pattern due to

A

Rapid on and off responses from the carotid sinus nerve

63
Q

What stimulates peripheral chemoreceptors

A

Hypoxia and acidification of the blood

64
Q

Describe peripheral chemoreceptors

A

Located in carotid and aortic bodies (high blood flow); decrease in PO2 (hypoxia) resulting in an increase in firing; increase in the concentration of H+ or PCO2 results in an increase in firing; respond rapidly (detect oscillations between each breath)

65
Q

How is blood chemistry constrained to a very small range in health

A

Peripheral and central chemoreceptors act together to rapidly modify respiration

66
Q

What is normal arterial PCO2

A

5.3 kPa

67
Q

What is normal ventilation

A

6-7L/min

68
Q

What does the fact that there is a flat line between 4-5 arterial PCO2 show

A

Breathing doesn’t cease altogether so it is not completely dependent on chemoreceptors

69
Q

What controls basal tone

A

Chemoreceptors

70
Q

What is the ventilatory response to an increase in PCO2 (hypercapnia)

A

The ventilatory responds to increased CO2: breath air results in an increase in PCO2 resulting in an increase in tidal volume. 5 minutes later tidal volume is 1.5L (starts at 0.5L), there is also an increase in breathing frequency.

71
Q

What does hypoxia result in

A

(Decreased oxygen in inspired air) causes only a small increase in tidal volume, therefore our bodies are not very sensitive to hypoxia

72
Q

How do hypoxia and hypercapnia work together

A

There is a synergistic effect resulting in a more rapid increase in tidal volume (means that they both happen and the response is greater than the sum of both individually)

73
Q

Are you more sensitive to hypoxia or hypercapnia

A

Hypercapnia

74
Q

What is the main drive to breathe

A

A rise in PCO2

Case 5 (8 decks)

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