Chapter 22 & 23

Introduction

  • Respiratory System Overview
    • Covers chapters 22 and 23.
    • Basic anatomy, physiology, and diagnostics discussed first before specific diseases.

Anatomy of the Respiratory System

  • Three Main Functions:

    1. Oxygen Exchange: Enriching blood with oxygen by inhalation and exchange in alveoli.
    2. Carbon Dioxide Removal: Exhaling carbon dioxide that is a byproduct of metabolism and can disturb acid-base balance.
    3. Acid-Base Homeostasis: Lungs (and kidneys) help maintain acid-base balance in the body.

  • Anatomical Components:

    • Upper Airways:
    • Nasal cavity, pharynx, larynx, trachea, bronchi.
    • Lower Airways:
    • Terminal bronchioles, respiratory bronchioles, alveoli (sacs per alveolus).

  • Differentiation:

    • Terminal bronchioles do not end in alveoli; respiratory bronchioles do.

Functions of Upper Airways

  • Nasal Cavity:
    • Contains cilia and mucous membranes for immunity and humidifying/warming incoming air.
  • Pharynx and Larynx: Path for air; vocal cords located in the larynx.
  • Trachea: Contains cartilages (maintains lumen structure against collapse) from trachea down to terminal bronchioles, which lack cartilage.

Lung Anatomy

  • Lobes:
    • Right lung: three lobes (superior, middle, inferior).
    • Left lung: two lobes (superior, inferior).

Respiratory Volumes and Capacities

  • Tidal Volume (TV): Volume of air inhaled/exhaled at rest (~500 ml).

  • Inspiratory Reserve Volume (IRV): Volume that can be inhaled after a normal inhalation (~3 L).

  • Expiratory Reserve Volume (ERV): Volume that can be exhaled after a normal exhalation (~1,200 ml).

  • Residual Volume (RV): Volume of air remaining in lungs after maximal exhalation (cannot be exhaled).

  • Vital Capacity (VC): Sum of TV + IRV + ERV.

  • Total Lung Capacity (TLC): Sum of VC and RV.

  • Functional Residual Capacity (FRC): Sum of RV and ERV.

Diagnostic Tests

  • Pulmonary Function Tests (PFTs):

    • FVC (Forced Vital Capacity): Volume exhaled forcefully after deep inhalation.
    • FEV1 (Forced Expiratory Volume in 1 second): Amount exhaled in the first second of FVC test.
    • Normal FEV1/FVC ratio ~80% (or 75%). Used to diagnose obstructive/restrictive lung diseases.

  • Arterial Blood Gas (ABG):

    • Key normal values:
    • Oxygen Pressure: 80-100 mmHg (average ~90).
    • Carbon Dioxide Pressure: 35-45 mmHg (average ~40).
    • Bicarbonate: 22-26 (average ~24).
    • Oxygen saturation: 96-100%.

Acid-Base Balance

  • Normal pH of blood: 7.35-7.45 (average ~7.4).
    • Below 7.35: Acidosis; Above 7.45: Alkalosis.
    • Critical levels:
Types of Acidosis/Alkalosis
  • Respiratory Conditions:
    • Respiratory Acidosis: Retention of CO2 leading to increased acidity.
    • Respiratory Alkalosis: Low CO2 due to hyperventilation.
  • Metabolic Disorders:
    • Imbalance due to kidney function affecting acid/base levels.

Types of Respiratory Diseases

  • Obstructive:
    • Obstruction of airflow (e.g., asthma, chronic bronchitis).
    • Typical FEV1/FVC ratio <80%.
  • Restrictive:
    • Reduced lung volumes/capacities, but FEV1/FVC ratio may remain normal or >80%.

Obstructive Lung Disease

Asthma
  • Definition: Chronic inflammatory disease of the airways.
  • Types:
    • Extrinsic: Allergic response, often in childhood.
    • Intrinsic: Non-allergic reactions, often in adulthood.
Chronic Bronchitis
  • Definition: Chronic coughing producing sputum lasting 3 months for 2 years.
  • Pathogenesis:
    • Hyperplasia of mucus glands & chronic inflammation due to irritants (e.g., smoking).
    • Excess mucus leads to airway obstruction.
Emphysema
  • Definition: Destruction of alveoli leading to enlarged air spaces.
  • Effects:
    • Reduced elastic recoil and surface area for gas exchange.
    • Typical sign: barrel chest appearance.

Diagnosis and Management

  • Key diagnostic tools include:
    • Spirometry: Measures FEV1 and FVC.
    • Chest X-ray: Detects lung hyperinflation in emphysema.
    • ABG: Detects carbon dioxide retention in chronic bronchitis.
Treatment Options
  • Asthma:
    • Bronchodilators, corticosteroids, avoidance of triggers.
  • Chronic Bronchitis/Emphysema:
    • Smoking cessation, bronchodilators, corticosteroids, pulmonary rehabilitation.

Conclusion

  • Understanding the anatomy and processes of the respiratory system is crucial for identifying and treating various lung diseases effectively.