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.