Lung Structure and Airway Diseases

Question 1

describe the main structures in the respiratory tract

Answer 1

1. conducting airways
   - trachea: incomplete cartilage ring lined with smooth muscle and epithelium
   - primary bronchus
   - secondary bronchus
2. resistance airways
   - bronchiole: airway with any cartilage
   - terminal bronchiole
3. respiratory airways
   - respiratory bronchiole
   - alveolar duct
   - alveolar sac

Question 2

describe the structure of pulmonary blood vessels

Question 3

describe the function of pulmonary blood vessels

Answer 3

Pulmonary arteries and veins
– carry blood to (arteries) and from (veins) the lungs
– pulmonary veins carry O2
– pulmonary arteries carry CO2

Bronchial arteries and veins
– supply blood to and drain from the airways
– bronchial arteries carry O2
– bronchial veins carry CO2

Question 4

describe the structure of airway epithelium

Answer 4

• Lines the entire respiratory tract
• pseudostratified columnar structure

Question 5

describe the function of airway epithelium

Answer 5

1. Physical barrier
   – prevents access to submucosa
   * nerves, vascular tissue, airway
   smooth muscle
   - inhibits penetration of inhaled noxious substances
2. Housekeeping role
   – cilia beat synchronously, propel mucus towards throat
   – mucus and particulate matter continually cleared
3. Catabolic metabolism
   – via cytochrome P450 system
   – peptide degradation via neutral endopeptidase
   – protects sensitive targets - nerves, muscle, glands
4. Anabolic metabolism
   – synthesis of inhibitory mediators – PGE2 (prostoglandin E2)
   – rich source of peptides – endothelin (growth factor)
   – produces pro-inflammatory cytokines

Question 6

describe the structure of nerves

Question 7

describe the function of nerves

Answer 7

• Cholinergic (excitatory)
  – dominant neural pathway
  – major role in regulating airway smooth muscle tone
  and mucus production
• Noradrenergic (inhibitory)
  – noradrenaline decrease smooth muscle tone
  – no major role below main bronchi
• Inhibitory nonadrenergic noncholinergic (iNANC)
  – release nitric oxide (NO)
  – innervates smooth muscle directly
  – relaxation
• Excitatory nonadrenergic noncholinergic (eNANC)
  – release neuropeptides e.g., substance P, neurokinin A – increase airway tone, secretion of mucus and microvascular
  leakage

Question 8

describe the features of asthma

Answer 8

Chronic inflammatory disease of the airways characterised by bronchial obstruction and airflow limitation

• Characteristics
  – shortness of breath, wheeze, tight chest, cough
  – allergic, occupational, exercise-induced, aspirin
  – mild, moderate, severe

Question 9

Describe the asthma allergic response

Answer 9

– early phase response
* decrease in FEV1, peak at 30-40 min, resolves in 2-3 hrs
* mast cell-derived histamine and leukotrienes

– late phase response
* release of inflammatory mediators cause submucosal oedema, airway wall swelling, secretion of mucus
* epithelium remodelling, airway muscle hypertrophy/hyperplasia, subepithelial fibrosis

Question 10

Describe Reversible bronchial obstruction

Answer 10

Caused by a range of endogenous mediators

– increasing airway smooth muscle tone
– increasing secretion of mucus
– shedding of the epithelium and accumulation of debris in airway lumen
– oedema and swelling of the submucosa
– airway smooth muscle hypertrophy (increase cell size) and hyperplasia (increase cell number)
– sub-epithelial fibrosis makes the airway thicker

Question 11

Describe Airway hyperresponsiveness

Answer 11

Asthmatics are hyperresponsive to a range of unrelated stimuli
because:
* Airway narrowing
–increase airway smooth muscle force and/or mass
– microvascular leakage from post-capillary venules and resultant oedema

Airway narrowing causes changes to airway resistance

Question 12

Describe Airway wall remodelling

Answer 12

1. diluted blood vessels and leaking fluid are retained in the airway wall (oedema)
2. an influx of inflammatory cells in airway e.g. eosinophil, mononuclear cells
3. damaged epithelium can block the airway
4. fibrin is laid down under epithelium making it thicker and stiffer
5. Increase mucus blocks airway
6. thicker cell size and more cells

Question 14

describe the characteristic features of chronic obstructive pulmonary disease

Answer 14

• COPD = chronic bronchitis + emphysema
• Progressive degenerative disease causes death
  – primary causes – tobacco smoking and air pollution
• most important therapy is smoking cessation
• indoor air pollution – heating + cooking
• outdoor air pollution
• occupational dusts, chemicals, vapours, irritants, fumes

Question 15

Chronic Bronchitis Features

Answer 15

• Inflammatory disease with irreversible airflow limitation
• Hypersecretion of bronchial mucus
  – hypertrophy & hyperplasia of bronchial mucus-secreting cells
  – chronic cough, excessive sputum
• Secondary respiratory infections
  – excessive mucus production

Question 16

describe the mechanisms of action and therapeutic effects
of drugs used to treat chronic bronchitis

Answer 16

• Drugs provide symptom relief
  – b2-adrenoceptor agonists -> relax smooth muscle
  – muscarinic antagonists -> prevent bronchoconstriction
  – glucocorticoids -> reduce inflam
  – mucokine -> easier to cough up
  – antibiotics (secondary infections)
• Selective phosphodiesterase IV inhibitor (roflumilast)
• increases the break down of CAMP increasing the relaxation of airway smooth muscle

Question 17

Emphysema

Answer 17

• Degenerative, peripheral lung disease
• Involves destruction of alveolar membranes
  – causes severe impairment of
  
  • oxygen delivery
  • carbon dioxide clearance
• Often associated with smoking and
  chronic bronchitis