Ch23A_respiration

Chapter Overview

• Overview of the Respiratory System

  • Healthy lung vs. smoker’s lung

  • Key processes in gas exchange:

    • Physical principles

    • External respiration

    • Internal respiration

Functions of the Respiratory System

• Primary Functions:

  • Gas exchange

  • Regulation of blood pH

  • Voice production

  • Olfaction (sense of smell)

  • Innate immunity

Distinct Processes of Respiration

• Four Distinct Processes:

  1. Pulmonary Ventilation (Breathing)

     • Movement of air in and out of lungs

     • Exchange between environment and lungs

  2. Alveolar Gas Exchange (External Respiration)

     • Exchange of gases between air in alveoli and blood in lungs

  3. Gas Transport

     • Transport from lungs to tissues via the cardiovascular system and blood

  4. Systemic Gas Exchange (Internal Respiration)

     • Exchange of gases between blood and tissues (covered in lab)

Principles of Gas Exchange

• Diffusion:

  • The process of exchanging respiratory gases relies entirely on diffusion

    • Dispersion of atoms, molecules, or ions due to random thermal motion

    • No energy required

  • Factors Affecting Diffusion Rate:

    • Surface area

    • Concentration gradient

    • Gas pressure

Gas Pressure and Partial Pressure

• Gas Pressure:

  • Caused by moving molecules impacting a surface

  • Partial Pressure:

    • Pressure exerted by each gas in a mixture

    • Proportional to the concentration of that gas in the mixture

    • Example: PO2 (partial pressure of oxygen), PCO2 (partial pressure of carbon dioxide)

  • Diffusion Rate:

    • Proportional to the partial pressure of that specific gas, not the total gas pressure

Atmospheric Gas Composition

• Partial Pressures at Sea Level:

  • Atmospheric pressure at sea level = 760 mm Hg

  • Calculation of partial pressures:

    • N2: 78.6% -> 597 mm Hg

    • O2: 20.9% -> 159 mm Hg

    • CO2: 0.04% -> 0.3 mm Hg

    • H2O: 0.46% -> 3.7 mm Hg

Effect of Altitude on Gas Pressure

• Altitude Influence:

  • Gas composition remains the same with lower atmospheric pressure

  • Example: At 6000 ft, atmospheric pressure = 609 mm Hg, thus PO2 = 127 mm Hg

  • Lower partial pressures influence gas dissolution in bodily fluids

Gas Exchange Dynamics

• Gas Movement:

  • Gas moves between phases: air to liquid (water)

    • Initial conditions affected by capillary and alveolar interaction

• Gas Solubility and Partial Pressures:

  • The amount of gas dissolving in liquids depends on:

    • Partial pressure

    • Solubility of gases

      • CO2 > O2 > N2 based on solubility

    • Temperature effects: Increased temperature decreases gas solubility

Gas Diffusion Rates

• Highest Diffusion Rate:

  • Oxygen diffuses from alveoli into blood at the highest rate due to high partial pressure and better solubility compared to nitrogen

  • Carbon dioxide has low partial pressure but is highly soluble

External Respiration (Alveolar Gas Exchange)

• Key Factors:

  • Exchange of O2 and CO2 influenced by:

    • Structure of respiratory membrane

    • Partial pressure gradients

    • Gas solubility

    • Ventilation-perfusion coupling

Structure of the Respiratory Membrane

• Characteristics:

  • Incredibly thin (approx. 0.5 mm) with a large surface area

  • Facilitates efficient gas exchange

Ventilation-Perfusion Coupling

• Definitions:

  • Ventilation: The amount of gas reaching the alveoli

    • Bronchiole response to PCO2 affecting diameter

  • Perfusion: Blood flow through pulmonary capillaries

    • Arteriole response to PO2 & PCO2 affecting diameter

• Efficiency:

  • Requires close matching of ventilation and perfusion for optimal gas exchange

Internal Respiration (Systemic Gas Exchange)

• Process of Gas Exchange:

  • Gases diffuse down partial pressure gradients

    • O2 from blood to tissues

    • CO2 from tissues to blood

Review Questions

1. Air moves into the lungs during inspiration due to the force of __________. (c) Atmospheric pressure

2. Infant respiratory distress syndrome occurs due to lack of __________, which __________. (c) Surfactant; lowers surface tension

3. Two gases contributing to 99% of atmospheric pressure are __________. (b) N2 and O2

4. Rate of CO2 exchange is equal to that of O2 due to __________. (c) CO2 is more soluble in water than O2

5. Rate of oxygen diffusion across the respiratory membrane is influenced by all except __________. (partial pressure of carbon dioxide in the blood)

6. Low PO2 and high PCO2 cause __________. (a) Constriction of pulmonary capillaries and bronchioles.