Histopathology of lung disease

• What type of epithelium is in the upper respiratory tract?

  Pseudostratified ciliated columnar
• Epithelium in trachea and bronchi


  Pseudostratified ciliated columnar epithelium
• Epithelium in bronchioles

  simple cuboidal
• Epithelium in alveoli

  Simple squamous
• What is the role of type 1 alveolar cells?

  gas exchange
• What are the features of type I alveolar cells?

  Thin and flattened
• What is the role of type II alveolar cells?

  Surfactant production
• Alveolar cells are also called pneumocytes
• Where are club cells located?

  Bronchioles
• What is the function of club cells?

  Secretory cells that protect bronchioles
• What are dust cells?

  Alveolar macrophages
• What role does the surfactant in the alveoli perform?

  Changes the surface tension in the alveoli preventing collapse
• What histological features keep the airway open in normal respiration?

  Cartilage and surfactant
• Histological changes in lung of smoker

  • increased number of dust cells - with uptake of carbon particles
  • decrease in cilia on cells in the upper respiratory tract
  • increase in mucus producing cells
  • low levels of metaplasia of the squamous epithelium cells in the lower respiratory tract
• Hypertrophy = increase in cell size
• Hyperplasia = increase in cell number
• Which inflammatory cells are characteristic of asthma?

  Eosinophils
• What are goblet cells?

  non-ciliated cells that secrete mucus
• Centriacinar emphysema - destruction/distension of respiratory bronchioles, usually in upper lobe
• Panacinar emphysema - destruction/distension from respiratory bronchioles to alveoli, usually in lower lobes
• What is the most common type of emphysema?

  Centriacinar
• What is the cause of centriacinar emphysema?

  Smoking
• What is the cause of panacinar emphysema?

  a1 antitrypsin deficiency
• Basal cells - attached to the basal lamina but do not extend to the lumen
• Lamina propria contains elastic fibres and smooth muscle
• Bronchioles - The height of the epithelial cells decreases. These are near a simple cuboidal epithelium (slightly columnar in shape).

  There is no cartilage or submucosal glands. Smooth muscle provides the structural support.
• Respiratory bronchioles - Epithelia reduces in height very dramatically to a simple squamous epithelium

  May contain alveoli (in contrast to terminal bronchioles).
• Chronic asthma changes observed:

  • thickening of bronchial walls
  • mucus lining bronchial lumen is thicker and contains immune cells - characteristic is eosinophils
  • immune infiltration especially eosinophils 
  • hyperplasia and hypertrophy of mucinous glands
  • hypertrophy and hyperplasia of smooth muscle layer
  • accumulation of mucus in the bronchial lumen
• Causes of bronchiectasis

  • persistent bacterial infection of the bronchi
  • blockage of the bronchi e.g. by foreign bodies or tumours
• Bronchiectasis changes observed:

  • irreversible airway dilation
  • thickening of the walls
  • chronic infection of walls
  • destruction of normal elastic fibres and muscle in the bronchus wall
  • tissue is replaced by fibrous tissue
  • results in weaker wall structure
  • mucus secretions are not moved as efficiently
  • increase in bacterial infections - chronic infection
• Chronic bronchitis - persistent cough for three consecutive months for at least two consecutive years
• Causes of chronic bronchitis

  • smoking or pollution irritating the bronchial mucosa
  • chronic infection e.g. acute bronchitis
• Chronic bronchitis changes observed:

  • changes are variable
  • hyperplastic changes result in a thicker bronchial wall
  • chronic inflammatory cells in the submucosa - macrophages, neutrophils and lymphocytes
  • hypertrophy of mucosal smooth muscle
  • hyperplasia of mucinous glands in trachea and bronchi results in more mucus production
  • hyperplasia of epithelial cells and loss of cilia
  • increase in number of goblet cells in epithelium of lower bronchi and bronchioles
• Changes observed in emphysema

  • permanent enlargement of airspaces distal to terminal bronchioles
  • destruction of alveoli walls
  • no fibrosis
  • may lead to pneumothorax
• Types of pneumonia

  • community acquired bacterial
  • community acquired viral
  • nosocomical
  • aspiration
  • chronic
  • necrotising
  • immunocompromised host
• Bronchopneumonia

  • infection around specific areas of lung rather than whole lobes
  • large areas appear normal but other areas infiltrated with inflammatory cells
• pneumonia resolves upon antibiotic treatment if the alveolar structure is maintained.
• Common fungal lung infections are candida albicans which is found in the normal flora of the oral, GI tract and vagina. Candidiasis can occur in immunocompromised individuals.

  Immunocompromised patients can also have infections from other yeast e.g. aspergillus.

  Infection may progress to necrotising pneumonia

  Asthmatic patients may develop a hypersensitivity reaction to the fungus - allergic bronchopulmonary aspergillosis