Overview
This lecture explains the basic mechanics of gas exchange in the lungs and muscles, focusing on diffusion, concentration gradients, and their changes during exercise.
Structure and Function of the Alveolus
- The alveolus is a tiny air sac in the lungs where gas exchange occurs.
- Inhaled air enters the alveolus with a high concentration of oxygen (O₂) and low concentration of carbon dioxide (CO₂).
- A capillary runs alongside the alveolus containing red blood cells with many hemoglobin proteins.
Gas Concentrations and Diffusion
- Inside the alveolus: high O₂, low CO₂.
- In the capillary (before gas exchange): low O₂, high CO₂.
- Both alveolar and capillary walls are partially permeable membranes, allowing gases to move.
- Diffusion occurs from areas of high concentration to low concentration (down the concentration gradient).
- O₂ moves from alveolus into blood; CO₂ moves from blood into the alveolus.
Diffusion Gradients and Exercise
- A greater concentration gradient increases the rate of diffusion.
- During exercise, muscles use more O₂ and produce more CO₂, increasing diffusion gradients.
- More O₂ moves into muscles, and more CO₂ moves out, allowing for increased aerobic respiration.
Gas Exchange at the Muscle
- Capillaries deliver high O₂, low CO₂ blood to muscles.
- Exercising muscles have low O₂, high CO₂.
- O₂ diffuses into muscle; CO₂ diffuses out (some attaches to hemoglobin, some dissolves in plasma).
Kinetic Theory and Net Diffusion
- Gas molecules move randomly; kinetic theory explains diffusion.
- Net movement is from high to low concentration, though some movement occurs in both directions.
Key Terms & Definitions
- Alveolus — Tiny air sac in the lung where gas exchange occurs.
- Capillary — Smallest blood vessel where substances are exchanged with tissues.
- Diffusion — Movement of molecules from high to low concentration.
- Concentration Gradient — Difference in concentration between two areas.
- Partially Permeable Membrane — Allows some molecules to pass through.
- Kinetic Theory — The idea that particles move randomly, leading to diffusion.
Action Items / Next Steps
- Review kinetic theory from physics (Year 9/10) to better understand diffusion.
- Prepare for further lessons on oxygen dissociation and advanced gas exchange topics.