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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
which cells secrete surfactant
type II alveolar cells
26
structure of surfactant
hydrophilic component - lies in the alveolar fluid hydrophobic component - associates with the alveolar gas
27
what do surfactant molecules do
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
when is surfactant most effective
at low alveolar volumes when the surfactant molecules are closest together
29
what happens to surfactant at high alveolar volumes
- 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
2 functions of surfactant
- helps with lung expansion - stops the alveoli from collapsing into each other
31
what is Laplace's law
“The pressure within a cylinder or sphere is proportional to the surface tension divided by the radius”
32
why is pressure lower in larger bubbles compared to smaller ones
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
how does surfactant stop alveoli from collapsing into each other
- 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
what happens to airways in an asthma attack
the already narrowed airways - due to mucosal inflammation and smooth muscle hypertrophy are further constricted due to increased smooth muscle tone
35
describe airway resistance during an asthma attack
- 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
how to reverse airway constriction in asthma attack
Beta-receptor agonists eg salbutamol
37
how do beta-receptor agonists work
- 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
what happens in emphysema
- 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
what happens in Chronic Obstructive Pulmonary Disease (COPD
the airway obstruction is compounded by chronic bronchitis causes additional narrowing of airway lumens
40
how do people with COPD exhale
through pursed lips in an effort to maintain a high intrapulmonary pressure and prevent premature collapse of the small airways.
41
what does the peripheral autonomic nervous system divide into
sympathetic and paraysmpathetic - usually have opposing effects
42
what are the 2 nerves involved in autonomic control
pre and post ganglionic fibres
43
where does the autonomic nervous system convey outputs to
conveys all outputs from the CNS to the body, except for skeletal muscle control
44
describe the ganglion in the sympathetic system
within a chain adjacent to the spinal cord
45
describe the ganglion in the parasympathetic system
within or very close to the effector organ
46
what are cholinergic receptors
related to the neurotransmitter acetylcholine 2 forms: differentiated by their activation with muscarine and nicotine
47
what are the 2 forms of cholinergic receptors
1. Muscarinic receptors 2. Nicotinic receptor
48
what do M3 muscarinic receptors do
post ganglionic receptors that induce airway smooth muscle contraction
49
what activates nicotinic receptors
nicotine
50
what do nicotinic receptors do
mediate effects of nicotine on breathing
51
what activates M3 muscarinic receptors
acetylcholine released from the parasympathetic fibers
52
where are M3 muscarinic receptors
on airway smooth muscle
53
what causes parasympathetic bronchoconstriction
1. parasympathetic nerves release acetylcholine onto muscarinic receptors 2. stimulates airway smooth muscle construction (bronchoconstriction)
54
what are anti-muscarinics
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
example of antimuscarinics
- 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
difference between SAMA and LAMA
short acting muscarinic vs long acting muscarinic
57
dosage of LAMAs
long duration of action often given once daily
58
what do LAMAs do
increase bronchodilation and relieve breathlessness in asthma and COPD reduce acute attacks as well
59
what does sympathetic nervous system regulate
the fight or flight response
60
what do sympathetic nerve fibres release
noradrenaline
61
what does noradrenaline activate
adrenergic receptors
62
2 types of adrenergic receptors
alpha beta
63
what does activation of beta 2 receptors on airway smooth muscle do
causes muscle relaxation by activating adenylate cyclase raising cyclic AMP causes bronchodilation
64
what is Bronchomotor tone
controls the ease with which air is conducted through airways
65
what do bronchodilators do
drugs that relax and open the airways make breathing easier used for asthma and COPD`
66
where are Beta-2 adrenoceptors found
found throughout the lungs with a particularly high density in the bronchial smooth muscle

respiratory lectures (15 decks)

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