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respiratory lectures > regulation of the airways > Flashcards

regulation of the airways Flashcards

1
Q

what is airway resistance

A

the degree of resistance to air flow through the respiratory tract during inspiration and expiration

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2
Q

what does the degree of resistance to air flow depend on

A
  • airway diameter
  • whether flow is laminar or turbulent
  • surfactant
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3
Q

how is airway diameter regulated

A

by the regulation of airway smooth muscle which is done through contraction and relaxation

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4
Q

what is ohm’s law equation

A

Flow = Pressure gradient / Resistance

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5
Q

what does ohm’s law demonstrate

A

as resistance increases

the pressure gradient must also increase

to maintain the same rate of flow into the alveoli

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6
Q

what does Poiseuille’s Law represent

A

the relationship between airway resistance and the diameter of the airway

it shows that the airway resistance is inversely proportional to the radius, to the power of 4.

so a small change in diameter has a huge effect on the resistance of an airway

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7
Q

what is the Poiseuille’s Law equation

A

resistance = 8 x substance viscosity x length of tube / π radius4

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8
Q

when is poiseuille’s law only applied

A

when there is laminar flow

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9
Q

difference in airway resistance between smaller and larger airways

A

smaller airways = higher resistance

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10
Q

impact of downstream branching of airways on resistance

A
  • means that there are many smaller airways in parallel
  • this reduces total resistance to air flow
  • so because there are lots of bronchioles within the lungs running in parallel
  • the highest total resistance is actually in the trachea and larger bronchi
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11
Q

which nervous system usually determines airway diameter

A

autonomic nervous system

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12
Q

impact of sympathetic innervation on airway

A
  • causes relaxation of bronchial smooth muscle via beta-2 receptors
  • causes an increase in airway diameter to allow more airflow
  • useful during exercise - when sympathetic stimulation triggers airway muscle relaxation to allow more air into the lungs
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13
Q

impact of parasympathetic innervation on airway

A
  • works on muscarinic (M3) receptors
  • to increase smooth muscle contraction and reduce diameter
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14
Q

what does boyles law state

A

that the pressure of a gas is inversely proportional to its volume

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15
Q

what is laminar flow

A
  • the state of flow in which air moves through a tube in parallel layers
  • no disruption between the layers

-the central layers are flowing with the greatest velocity

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16
Q

what is turbulent flow

A
  • when air is not flowing in parallel layers
  • direction, velocity and pressure within the flow of air become chaotic
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17
Q

describe pressure differences in laminar and turbulent flow

A
  • turbulent requires a larger pressure difference to maintain flow through the airways.
  • increases turbulence
  • increases resistance.
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18
Q

how is a greater difference in pressure created in the lungs

A
  • ntercostal muscles and diaphragm would need to work harder to expand and contract the lungs
  • so there is an increase in the pressure difference between the outside air and the air within the lungs
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19
Q

define lung/pulmonary compliance

A

a measure of the lung’s ability to stretch and expand

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20
Q

describe lung compliance when theres no water

A
  • very compliant (stretchy)
  • because of large amounts of elastic tissue
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21
Q

describe lung compliance in humid airway s

A
  • alveoli are lined by fluid
  • results in surface tension limiting the compliance of lung tissue
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22
Q

define surface tension

A

the tendency of fluid to shrink to the smallest possible volume.

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23
Q

what generates surface tension in water

A

the pull of hydrogen bonds between molecules

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24
Q

impact of surface tension on lung compliance

A

the higher the surface tension, the harder it is for the lungs to stretch

overcome by respiratory surfactant

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25
Q

which cells secrete surfactant

A

type II alveolar cells

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26
Q

structure of surfactant

A

hydrophilic component - lies in the alveolar fluid

hydrophobic component - associates with the alveolar gas

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27
Q

what do surfactant molecules do

A

causes surfactant molecules to rise to the surface of the fluid (the gas/fluid interface)

they disrupt the H bonds between water molecules on the surface.

this helps to overcome surface tension and allows the alveoli to expand.

28
Q

when is surfactant most effective

A

at low alveolar volumes when the surfactant molecules are closest together

29
Q

what happens to surfactant at high alveolar volumes

A
  • surfactant molecules are further apart
  • they are less effective at reducing surface tension
  • there is resistance to further alveolar expansion
  • this is why once the lungs are mostly filled, further lung expansion is difficult.
30
Q

2 functions of surfactant

A
  • helps with lung expansion
  • stops the alveoli from collapsing into each other
31
Q

what is Laplace’s law

A

“The pressure within a cylinder or sphere is proportional to the surface tension divided by the radius”

32
Q

why is pressure lower in larger bubbles compared to smaller ones

A

due to the larger radius

  • as gas moves from areas of high pressure (small alveoli) to low pressure (large alveoli)
  • it would be possible for large alveoli to consume small alveoli
33
Q

how does surfactant stop alveoli from collapsing into each other

A
  • surfactant less effective at larger diameters
  • so surface tension remains proportional to the radius of the alveolus as size increases
  • ensures pressures are relatively similar between adjacent alveoli of different sizes
  • prevents them from collapsing into each other
34
Q

what happens to airways in an asthma attack

A

the already narrowed airways - due to mucosal inflammation and smooth muscle hypertrophy

are further constricted due to increased smooth muscle tone

35
Q

describe airway resistance during an asthma attack

A
  • very high
  • due to decreased diameter
  • so patient must work harder to overcome the increased resistance
  • lead to turbulent flow
  • causing the characteristic wheeze of an asthma attack.
36
Q

how to reverse airway constriction in asthma attack

A

Beta-receptor agonists eg salbutamol

37
Q

how do beta-receptor agonists work

A
  • acts on beta-2 receptors in the airway, acting on Gs G-proteins to open potassium channels.
  • allowing potassium channels to open hyperpolarises the cell, making contraction of the smooth muscle less likely
  • causing bronchodilation
38
Q

what happens in emphysema

A
  • destruction of elastin fibres within alveoli
  • less elastic recoil holding open the smaller airways
  • reduced radial traction
  • so during expiration, when the intrathoracic pressure is greater, the smaller airways collapse very easily
  • trapping an increased volume of air
39
Q

what happens in Chronic Obstructive Pulmonary Disease (COPD

A

the airway obstruction is compounded by chronic bronchitis

causes additional narrowing of airway lumens

40
Q

how do people with COPD exhale

A

through pursed lips in an effort to maintain a high intrapulmonary pressure and prevent premature collapse of the small airways.

41
Q

what does the peripheral autonomic nervous system divide into

A

sympathetic and paraysmpathetic

  • usually have opposing effects
42
Q

what are the 2 nerves involved in autonomic control

A

pre and post ganglionic fibres

43
Q

where does the autonomic nervous system convey outputs to

A

conveys all outputs from the CNS to the body, except for skeletal muscle control

44
Q

describe the ganglion in the sympathetic system

A

within a chain adjacent to the spinal cord

45
Q

describe the ganglion in the parasympathetic system

A

within or very close to the effector organ

46
Q

what are cholinergic receptors

A

related to the neurotransmitter acetylcholine

2 forms: differentiated by their activation with muscarine and nicotine

47
Q

what are the 2 forms of cholinergic receptors

A
  1. Muscarinic receptors
  2. Nicotinic receptor
48
Q

what do M3 muscarinic receptors do

A

post ganglionic receptors that induce airway smooth muscle contraction

49
Q

what activates nicotinic receptors

A

nicotine

50
Q

what do nicotinic receptors do

A

mediate effects of nicotine on breathing

51
Q

what activates M3 muscarinic receptors

A

acetylcholine released from the parasympathetic fibers

52
Q

where are M3 muscarinic receptors

A

on airway smooth muscle

53
Q

what causes parasympathetic bronchoconstriction

A
  1. parasympathetic nerves release acetylcholine onto muscarinic receptors
  2. stimulates airway smooth muscle construction (bronchoconstriction)
54
Q

what are anti-muscarinics

A

drugs that inhibit the parasympathetic nervous system

these block the M3 receptor

this is beneficial in diseases that narrow the airway eg asthma and COPD

55
Q

example of antimuscarinics

A
  • ipratropium bromide (atrovent)

it is short acting (sSAMA)
so less widely used
still used in high dose in nebulisers in acute management of severe asthma and COPD

56
Q

difference between SAMA and LAMA

A

short acting muscarinic
vs long acting muscarinic

57
Q

dosage of LAMAs

A

long duration of action
often given once daily

58
Q

what do LAMAs do

A

increase bronchodilation and relieve breathlessness in asthma and COPD
reduce acute attacks as well

59
Q

what does sympathetic nervous system regulate

A

the fight or flight response

60
Q

what do sympathetic nerve fibres release

A

noradrenaline

61
Q

what does noradrenaline activate

A

adrenergic receptors

62
Q

2 types of adrenergic receptors

A

alpha
beta

63
Q

what does activation of beta 2 receptors on airway smooth muscle do

A

causes muscle relaxation
by activating adenylate cyclase
raising cyclic AMP
causes bronchodilation

64
Q

what is Bronchomotor tone

A

controls the ease with which air is conducted through airways

65
Q

what do bronchodilators do

A

drugs that relax and open the airways
make breathing easier
used for asthma and COPD`

66
Q

where are Beta-2 adrenoceptors found

A

found throughout the lungs with a particularly high density in the bronchial smooth muscle

respiratory lectures (15 decks)

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