3.2.2 Dissecting the Gas Exchange System

Safety and Ethical Considerations:

1. Ethical Sourcing:

• Ensure the lungs and associated tissues used for dissection are ethically sourced (commonly from butchers or abattoirs).

2. Safety Precautions:

• Wear lab coats, gloves, and goggles to prevent contamination.
• Use clean and sharp dissection tools to ensure precision.
• Disinfect all surfaces and tools after the dissection.

3. Care During Handling:

• Handle the lungs and other tissues gently to avoid damage or accidental exposure to pathogens.

Equipment Needed:

• Fresh lungs (e.g., from sheep or pigs).
• Dissection tools:
  • Scissors.
  • Scalpel.
  • Tweezers.
• Gloves, goggles, and lab coat.
• Tray for dissection.

Procedure:

1. Observing the External Structure:

• Identify the trachea, bronchi, and lungs.
• Feel the trachea rings of cartilage, which keep the airways open.

2. Cutting into the Trachea:

• Using scissors, cut down the length of the trachea to observe the cartilage rings and the smooth muscle.

3. Exploring the Bronchi and Bronchioles:

• Trace the bronchi as they branch from the trachea into the lungs.
• Follow the bronchi as they split into narrower bronchioles.

4. Examining the Lungs:

• Gently inflate the lungs by blowing air through the trachea using a hand pump or your mouth (ensure a safety barrier is used).
• Observe how the lungs expand and the elastic properties of lung tissue.

5. Cutting into Lung Tissue:

• Cut a small section of the lung to observe its spongy texture, which provides the large surface area required for gas exchange.
• Identify the alveoli, which are too small to see individually but contribute to the lung's structure.

6. Optional Demonstrations:

• Use coloured liquids to trace the airflow pathways or mimic blood flow through capillaries.

Key Observations:

1. Trachea:

• Incomplete C-shaped cartilage rings prevent collapse during inhalation.
• Lined with ciliated epithelium and goblet cells to trap and move debris.

2. Bronchi and Bronchioles:

• Branching structures that become narrower as they divide.
• Contain smooth muscle to control airflow and some elastic fibres for flexibility.

3. Lung Tissue:

• Spongy and elastic, allowing expansion and recoil during breathing.
• Contains alveoli for efficient gas exchange.

Questions to Consider:

1. How do the cartilage rings in the trachea support its function?
2. Why is the lung tissue spongy?
3. What role does smooth muscle play in the bronchioles?
4. Why are alveoli not visible to the naked eye?