airways function

Question 1

C-shape

Answer 1

allows oesophagus to run down back of trachea; slightly off-set to confer greater tensile strength

Question 2

functions of conduit airways

Answer 2

conduct O2 to alveoli, conduct CO2 out of lung (gas exchange)

Question 3

how is it facilitated

Answer 3

mechanical stability (cartilage), control of calibre (smooth muscle), protection and ‘cleansing’

Question 4

organisation of airway structures

Answer 4

outside cartilage - smooth muscle - submucosal gland with tip in smooth muscle - systemic circulation - airway epithelium (ciliated (bend left and right) and goblet cells - mucociliary transport) - mucus in airway lumen

Question 5

human airway epithelium (EM)

Answer 5

mucin granules in goblet cells contain mucin in highly condensed form, ciliated cell have high mt to ensure beating; as soon as mucin secreted it takes on water and expands massively

Question 6

acini

Answer 6

functional mucus secreting units into collecting duct - wafted onto lumen surface by cilia

Question 7

mucous and serous acini

Answer 7

serous acini on outside secrete antibacterials (e.g. lysozyme - more water based); wash mucus into collecting duct

Question 8

ciliary structure

Answer 8

apical hooks, rods slide over each other to allow movement; 9+2 arrangement

Question 9

metachronal rhythm

Answer 9

layer of mucus; leading edge; field of cilia will move leading edge a little way along; cilia then move back and waft again after other cilia have moved

Question 10

mucus flakes

Answer 10

so much mucus can’t see cilia

Question 11

airway epithelium functions

Answer 11

Secretion of mucins, water and electrolytes (components of ‘mucus’ + plasma, mediators etc), movement of mucus by cilia – mucociliary clearance, physical barrier, production of regulatory and inflammatory mediators

Question 12

regulatory and inflammatory mediators

Answer 12

NO (by nitric oxide synthase, NOS), CO (by hemeoxygenase, HO), arachidonic acid metabolites (e.g. prostaglandins - COX), chemokines (e.g. interleukin - (IL)-8), cytokines (e.g. GM-CSF), proteases

Question 13

airway smooth muscle functions

Answer 13

structure, tone (airway calibre - contraction and relaxation), secretion (mediators, cytokines, chemokines)

Question 14

under chronic airway inflammation

Answer 14

structure - hypertrophy due to proliferation, massive increase in secretion to engage in inflammatory response and inflammatory cell recruitment

Question 15

tracheo-bronchial circulation

Answer 15

systemic; perfusion through airway mucosa is highest in body; massive input and output

Question 16

tracheo-bronchial circulation

Answer 16

slide 22

Question 17

subepithelial microvascular network

Answer 17

below epithelium is plexus of capillaries, veins and arteries - massive bloodflow for good gas exchange

Question 18

tracheo-bronchial circulation functions

Answer 18

good gas exchange (airway tissues and blood), contributes to warming of inspired air, contributes to humidification of inspired air, clears inflammatory mediators, clears inhaled drugs (good/bad, depending on drug), supplies airway tissue and lumen with inflammatory cells, supplies airway tissue and lumen with proteinaceous plasma

Question 19

mechanism of plasma exudation in airways

Answer 19

endothelial cell gaps leak plasma out to bathe tissue; C-fibre nerve, inflammatory mediators make it more leaky; Evans blue dye shows experimentally as binds to albumin (platelet activating factor - inflammatory mediator)

Question 20

control of airway function

Answer 20

nerves (parasympathetic (cholinergic) and sympathetic – adrenergic, sensory), regulatory and inflammatory mediators (histamine, arachidonic acid metabolites (e.g. prostaglandins, leukotrienes), cytokines, chemokines
Proteinases (e.g. neutrophil elastase)
Reactive gas species (e.g. O2-, NO)

Question 21

innervation of airways

Answer 21

if obstruction in airway, contrict airway by parasympathetic motor pathway, no sympathetic nerves to relax airway so NO relaxation - speeds up cilia and is vasorelaxant (same as blood vessels); adrenaline also induces relaxation

Question 22

cholinergic mechanisms in airways

Answer 22

sensory nerves - CNS - parasymp. - parasymp. ganglion - ACh - mucus to allow open more easily, vasodilation

Question 23

regulatory-inflammatory cells in airways: cells

Answer 23

eosinophil, neutrophil, macrophage, mast cell, T lymphocyte, structural cells (smooth muscle)

Question 24

regulatory-inflammatory cells in airways: mediators

Answer 24

complexity: cells produce more than one mediator and these do more than one thing

Question 25

regulatory-inflammatory cells in airways: effect of mediators

Answer 25

smooth muscle (airway, vascular: contraction, relaxation), secretion (mucins, water, etc), plasma exudation, neural modulation, chemotaxis, remodelling

Question 26

loss of airway control

Answer 26

asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF) - characterised by airway inflammation leading to obstruction due to airway remodelling

Question 27

asthma

Answer 27

clinical syndrome - increased airway responsiveness to variety of stimuli causing airway obstruction; varies over short periods of times and is reversible; symptoms are dyspnoea, wheezing and cough; lumen filled with mucus plug; more goblet cells; fragile epithelium; thickening of basement membrane; hypertrophy of smooth muscle and submucosal glands; vasodilation; massive cellular infiltrate (mainly eosinophils); airway wall thrown into folds - bronchoconstriction

Question 28

asthma theory

Answer 28

epithelial fragility - exposes sensory nerves - stimulated - set up cholinergic reflex - bronchoconstriction and mucus secretion - excessive mucus in airway lumen; influx of inflammatory cells - mediators released - remodelling so submucosal glands and smooth muscle undergo hypertophy, vasodilation, bronchoconstriction