Lecture Notes on Gas Exchange and Respiration

Overview

• Gas exchange involves the movement of gases like oxygen and carbon dioxide between blood, lungs, and tissues.
• Uses diffusion (no energy required).

Types of Respiration

External Respiration

• Definition: Exchange of gases between blood and lungs.
• Process:
  • Oxygen moves from lungs into blood.
  • Carbon dioxide moves from blood into the lungs.

Internal Respiration

• Definition: Exchange of gases between blood and body tissues.
• Process:
  • Oxygen moves from blood to tissues.
  • Carbon dioxide moves from tissues into blood.

Key Gases

• Oxygen (O2): Moves from high to low concentration.
• Carbon Dioxide (CO2): Moves from high to low concentration.

Gas Laws

Dalton's Law of Partial Pressures

• Total pressure of a gas mixture = sum of partial pressures of each gas.
• Each gas in a mixture exerts a pressure proportional to its percentage in the mixture.

Henry's Law

• The amount of gas that dissolves in a liquid is proportional to its partial pressure.
• Solubility and temperature affect gas solubility.
  • Higher solubility and lower temperature increase gas dissolution.
  • Example: Carbon dioxide more soluble than oxygen.

Atmospheric Air Composition

• Nitrogen (N2): ~78.6%
• Oxygen (O2): ~20.9%
• Carbon Dioxide (CO2): Very small percentage.

Factors Influencing Gas Exchange

Partial Pressure Gradients

• Main driving force for diffusion.
• Steep gradient for O2 from alveoli to blood.
• Smaller gradient for CO2 but compensated by higher solubility.

Thickness & Surface Area of Respiratory Membrane

• Thin membranes = efficient gas exchange.
• Large surface area of alveoli for more exchange.

Ventilation-Perfusion Coupling

• Goal: Match ventilation (airflow) to perfusion (blood flow).
• Autoregulatory mechanisms control levels:
  • Oxygen controls perfusion: Changes arteriole diameter.
  • Carbon dioxide controls ventilation: Changes bronchiole diameter.

Internal Respiration Details

• Capillaries and tissues exchange gases.
• Opposite gradient directions from external respiration.
• Metabolic activities in tissues use O2, producing CO2 as waste.
• Equilibrium is maintained through continuous exchange.

Summary

• Understanding gas laws and factors influencing gas exchange is crucial for understanding respiratory processes.
• Always consider the partial pressures and solubility of gases in different respiration phases.