5. Airways Function

Question 1

What is the main function of the conduction airways

Answer 1

• Conduct O2 to the alveoli and conduct CO2 out of the lung
• Facilitated by
- mechanical stability (cartilage)
- control of calibre (smooth muscle)
- protection and cleansing

Question 2

Describe the human airway epithelium

Answer 2

• Ciliated epithelial cells
• Goblet cells protruding through the layer into the lumen
- contain mucin granules
- expands using ATP absorbing water and swelling
• Mitochondria for cilia

Question 3

Describe the submucosal glands

Answer 3

• Acinus - sac-like cavity surrounded by secretory cells
• Smooth muscle contracts - secretion of mucus
• Serous cells - secrete antibacterials e.g. lysozyme
• Glands - secrete water and salts

Question 4

Describe the ciliary structure

Answer 4

• Apical hooks at end of cilia engage with mucus
• 9+2 microtubule arrangement
• Different fields of cilia are linked
• Metachronal rhythm - sequential wave
- one field catches the edge of mucus and moves
- recovers as the next field catches the mucou

Question 5

What is the function of the airway epithelia?

Answer 5

• Secretion of mucins (glycoproteins), water and electrolyte components (forming mucus)
• Movement of mucus 
• Physical barrier to foreign substances
• Production of regulatory and inflammatory mediators
- NO - controls ciliary beat
- CO [heme-oxygenase]
- Arachidonic acid metabolites 
- chemokines
- cytokines
- proteases

Question 6

What is the function of the airway smooth muscle?

Answer 6

• Structural effects - hypertrophy
• Airway calibre (tone) - contractile and relaxation effects
• Secretion - mediators, cytokines, chemokines
(• Bacterial products stimulate the following enzymes:
- NOS => NO release
- COX => prostaglandin release)

(all affected by inflammation)

Question 7

What is the function of the airway vasculature (trachea-bronchial circulation)?

Answer 7

• Good gas exchange between tissues and blood
• Warming of inspired air
• Humidification of inspired air
• Clears inflammatory mediators
• Clears inhaled drugs
• Supplies inflammatory cells
• Supplies proteinaceous plasma (exudation)
• Bronchial arteries arise from many sites e.g. aorta
• Blood returns from bronchial circulation via bronchial and pulmonary veins (both sides of the heart)
• Blood returns from tracheal circulation via systemic veins

Question 8

Describe the neuronal control of the function of the airway cells

Answer 8

• Parasympathetic (cholinergic) => constriction via vagus nerve
- sensory innervation to brainstem via nodose ganglion
- sensory innervation to spinal cord via dorsal root
• No sympathetic pathway
• Nitric oxide containing nerves (also contain NOS)
- NO causes relaxation
• Adrenaline from adrenal glands => relaxation

Question 9

Describe the cholinergic mechanisms

Answer 9

• Parasympathetic innervation of submucosal glands, smooth muscle cells and blood vessels
• Muscarinic receptors involving acetylcholine
• Activation:
- mucus secretion
- airway smooth muscle contraction
- vasodilation

Question 10

What is asthma (cause, mechanisms, symptoms)?

Answer 10

• Clinical syndrome
• Increased airways responsiveness to a variety of stimuli
• Obstruction varies over short periods of time
• Dyspnoea, wheezing and cough
• Airway inflammation => remodelling*
• Bronchoconstricton => airway wall folds*

*mucus plug on lumen => BM thickens => more fragile epithelial cells