3.5.10 Required Practical: Dissecting Mass Transport Systems

Aims of the Practical:

1. Examine the external and internal structures of mass transport systems (e.g., the heart or blood vessels).
2. Understand how the structure relates to the function in the circulatory system.
3. Develop skills in scientific dissection and biological drawing.

Equipment Needed:

• Freshly obtained animal heart (e.g., sheep or pig).
• Dissecting board.
• Scissors, scalpel, and forceps.
• Gloves and lab coat for hygiene and safety.
• Ruler for measuring structures.
• Disinfectant and cleaning materials.

Procedure for Dissecting a Heart:

1. External Examination:

• Identify the left and right sides of the heart by locating the thicker muscular wall on the left (to pump blood to the body).
• Locate major blood vessels:
• Aorta: Exits the left ventricle.
• Pulmonary artery: Exits the right ventricle.
• Pulmonary veins: Enter the left atrium.
• Vena cava: Enters the right atrium.

2. Internal Examination:

• Make an incision down one side of the heart to expose the chambers.
• Observe the structure of the:
• Atria (smaller, thin-walled chambers).
• Ventricles (larger, thicker-walled chambers, particularly the left ventricle).
• Identify and examine the valves:
• Atrioventricular valves (bicuspid and tricuspid) between the atria and ventricles.
• Semilunar valves at the exits of the aorta and pulmonary artery.
• Note the tendons (chordae tendineae) attached to the valves and papillary muscles.

3. Compare Blood Vessel Structures:

• Use a scalpel to open blood vessels.
• Compare the thickness of the walls in arteries (thicker with elastic tissue) and veins (thinner with valves).

Key Observations:

• The left ventricle wall is significantly thicker than the right, reflecting its role in pumping blood to the entire body.
• Valves ensure one-way flow of blood and prevent backflow.
• Arteries have thick walls to withstand high pressure, while veins have valves to prevent backflow under low pressure.

Drawing and Labelling:

• Make clear biological drawings of the heart and blood vessels.
• Use ruled lines for labels and avoid shading.
• Label key features, including chambers, valves, and blood vessels.

Safety Considerations:

1. Wear gloves and a lab coat to avoid direct contact with animal tissues.
2. Use sharp instruments (scalpels and scissors) carefully to prevent injury.
3. Dispose of animal tissue and materials according to school/college guidelines.

Key Terms:

• Atrium: Thin-walled chamber of the heart receiving blood.
• Ventricle: Thick-walled chamber of the heart pumping blood out.
• Valves: Structures preventing backflow of blood.
• Chordae Tendineae: Tendons anchoring valves to papillary muscles.
• Semilunar Valves: Found at the exits of the heart (aorta and pulmonary artery).