Respiratory System Diseases Overview

Respiratory System Diseases

• Developmental Anomalies:

  • Include lung agenesis/hypoplasia (complete/partial absence or underdevelopment of lungs, lobes), tracheal/bronchial anomalies (blockages, openings between trachea and esophagus), vascular abnormalities, congenital lobar overinflation (excess air in a lung lobe), foregut cysts, congenital pulmonary airway malformations, and pulmonary sequestrations.

• Atelectasis:

  • Lung tissue collapse resulting in an airless area.
  • Can be inherited or acquired.
  • Acquired Atelectasis:
    • Resorption (obstructive): Airway blockage leads to oxygen absorption, without affecting blood flow.
    • Compression: Fluid (pleural effusion), tumors, blood (hemothorax), or air (pneumothorax) in the pleural cavity compresses the lung.
    • Contraction: Fibrosis (scarring) of the lung or pleura prevents full lung expansion.
  • Significant atelectasis reduces oxygen and increases infection risk. It is usually reversible (except contraction).

• Pulmonary Edema:

  • Causes:
    • Hemodynamic: Increased pulmonary venous pressure (e.g., heart failure, volume overload, pulmonary vein obstruction) or decreased oncotic pressure (e.g., low protein levels, liver/kidney/intestinal diseases).
    • Microvascular injury: Infections (pneumonia, sepsis), inhaled substances (oxygen, smoke, gastric contents), drugs/chemicals (bleomycin, amphotericin B, heroin), shock, trauma, radiation, transfusion reactions.
    • Unknown etiology: High altitude, neurogenic causes.

• Acute Respiratory Distress Syndrome (ARDS) & Diffuse Alveolar Damage (DAD):

  • A severe respiratory insufficiency caused by diffuse alveolar damage.
  • Marked by rapid onset, life-threatening respiratory problems, cyanosis, severe arterial oxygen deficiency unresponsive to treatment, and potential for other organ damage.
  • Causes:
    • Infections: Sepsis, pneumonia (viral, mycoplasma, pneumocystis, miliary tuberculosis), gastric aspiration.
    • Physical/Injury: Trauma, near-drowning, pulmonary contusions, fat emboli, burns, radiation.
    • Inhaled Irritants: Oxygen toxicity, smoke, gases/chemicals.
    • Chemical Injury: Heroin/methadone overdose, aspirin, barbiturates, paraquat.
    • Hematologic Conditions: Multiple transfusions, disseminated intravascular coagulation.
    • Other: Pancreatitis, uremia, cardiopulmonary bypass.
    • Hypersensitivity Reactions: Organic solvents, drugs.

Obstructive Pulmonary Diseases

• Emphysema, Chronic Bronchitis, Asthma, Bronchiectasis:

  • Often grouped as COPD.

• Chronic Bronchitis: Persistent cough with sputum production for at least 3 months in 2 consecutive years (without other causes).

  • Common in smokers and polluted areas.
  • Pathology: Mucus hypersecretion due to submucous gland and goblet cell hyperplasia.
  • Potential consequences: COPD, cor pulmonale (heart failure), atypical respiratory epithelium changes (precancerous).
  • Histology: Goblet cell metaplasia (abnormal cell growth), mucus plugs, alveolar macrophage clustering, inflammation, bronchiolar wall fibrosis.

• Asthma: Chronic airway inflammation causing recurrent wheezing, breathlessness, chest tightness, and cough (especially at night).

  • Characterized by reversible bronchoconstriction and airflow limitation.
  • Causes: Immune reactions (atopic asthma), non-immune causes (viral infections).
  • Types: Atopic (allergy-related), non-atopic (non-allergic), drug-induced (e.g., aspirin), occupational.

• Bronchiectasis: Permanent dilation of bronchi/bronchioles due to muscle and elastic tissue destruction, commonly associated with chronic infections.

  • Causes: Congenital or hereditary (e.g., cystic fibrosis, immotile cilia syndrome), post-infectious complications (tuberculosis, aspergillosis), bronchial obstruction (tumor, foreign bodies), autoimmune diseases.

Pulmonary Infections

• Upper Respiratory Tract Infections: Common (pharyngitis, common cold).
• Lower Respiratory Tract Infections (Pneumonias): Compromised by:
  • Suppressed cough reflex.
  • Damaged mucociliary apparatus.
  • Impaired alveolar macrophage function.
  • Pulmonary congestion/edema.
  • Secretion accumulation.
• Bacterial Pneumonia:
  • Types: Bronchopneumonia (lobular), lobar pneumonia (congestion, red hepatization, grey hepatization, resolution).
  • Complications: Pleuritis, abscesses, infection spread, bacteremia.

Respiratory System Tumors

• Lung Cancer: Most frequent cancer worldwide and leading cause of cancer death.
• Risk Factors: Smoking (significantly increases risk via dose, inhalation, and duration), industrial hazards (ionizing radiation, asbestos), atmospheric pollutants.
• Types: Squamous cell carcinoma, adenocarcinoma, small cell carcinoma, large cell carcinoma.