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Lung Structure and Function Overview

Primary Bronchioles and Lung Anatomy

  • The trachea splits into the primary bronchi, with a left and right
  • Bronchi function: conducting airways, not yet the respiratory zone
  • Respiratory bronchioles lead to alveolar ducts and finally to alveoli
  • Definition: Alveoli are where gas exchange occurs, making them part of the respiratory zone

Lung Structure

  • Right lung: Contains three lobes
  • Types of fissures: One oblique fissure and one horizontal fissure

Monitoring Lung Function

  • Objective: Measure how well lungs function and gas exchange
  • Key metrics: Lung volumes and capacities
    • Tidal Volume (TV): The amount of air inhaled or exhaled at rest, approx. 500 mL per breath
    • % of air used for gas exchange: About 70% of tidal volume participates in gas exchange
    • Approximately 30% of lung air is within conducting airways, not involved in gas exchange

Lung Volumes

  • Inspiratory Reserve Volume (IRV): Additional air that can be inhaled after a tidal volume
  • Expiratory Reserve Volume (ERV): Additional air that can be exhaled after a tidal volume
  • Residual Volume (RV): Air remaining in lungs after maximum expiration; cannot be controlled
    • Necessary to prevent lung collapse

Lung Capacities

  • Inspiratory Capacity (IC): TV + IRV
  • Functional Residual Capacity (FRC): ERV + RV
  • Vital Capacity (VC): TV + IRV + ERV
  • Total Lung Capacity (TLC): Total of all lung volumes

Importance of Lung Measurements

  • Useful for diagnosing and understanding conditions such as COPD (Chronic Obstructive Pulmonary Disease)
    • Example of a condition where both inspiratory and expiratory functions may be limited depending on the cause (e.g., burns or obstruction)

Obstructive vs Restrictive Disorders

  • Obstructive Disorders: Difficulty in exhaling air (e.g., asthma, COPD)
    • Results in Limited Expiratory Reserve Volume (ERV)
  • Restrictive Disorders: Difficulty inhaling air (e.g., fibrosis)
    • Results in limited Inspiratory Reserve Volume (IRV)

Gas Exchange and Partial Pressures

  • Gas exchange principle: Oxygen moves into blood; carbon dioxide moves out of blood
  • External Respiration: Gas exchange at alveoli and blood
  • Internal Respiration: Gas exchange between blood and cells
  • Partial pressure: The pressure exerted by an individual gas in a mixture of gases
  • Atmospheric pressure example: Total pressure is 760 mmHg (Standard atmosphere)
  • Oxygen: ~20.9% => approx. 159 mmHg in ambient air
  • Nitrogen constitutes around 78.6% of air

Blood Gases Transported

  • Respiration involves three key processes:
    1. Ventilation: Movement of air in and out of lungs
    2. Gas Exchange: Between alveoli and blood (external), and moisture moving across skin or other surfaces.
    3. Transport: Systemic circulation carries blood gases to tissues

Factors Affecting Gas Exchange

  • Surface Area: Importance of having large areas for gas diffusion
  • Distance: Thin alveolar walls allow easier gas movement
  • Ventilation-Perfusion Coupling: Mismatch of air flow and blood flow in lungs
    • At rest, ventilation is highest at apex of the lungs, while blood flow is highest at the base

Oxygen Transport

  • Majority (98.5%) of oxygen is transported by hemoglobin; a small fraction is dissolved in plasma
  • Each hemoglobin can bind four oxygen molecules, forming oxyhemoglobin (Hb-O2)

Oxygen-Hemoglobin Dissociation Curve

  • Demonstrates the relationship between pO2 and hemoglobin saturation
  • Higher pO2 leads to increased saturation of hemoglobin with oxygen
  • Impacted by pH, carbon dioxide concentration, and temperature
    • Bohr Effect: Hemoglobin releases more oxygen in acidic or high CO2 environments

Summary of Critical Concepts

  • Tidal Volume, Inspiratory Reserve Volume, Expiratory Reserve Volume, Residual Volume defined
  • Differentiation between obstructive and restrictive pulmonary conditions
  • The necessity of gas exchange for metabolism as a physiological process
  • Understanding the hemoglobin function and the factors enhancing oxygen release in tissues under stress, like exercise.