9 – To Investigate the Structures of the Heart (LC 2027) (Leaving Cert Biology): Revision Notes

9 – To Investigate the Structures of the Heart

Heart dissection is a fundamental practical investigation in biology that allows you to explore the amazing structures of the mammalian circulatory system. This investigation helps you understand how the heart's anatomy relates to its function as the body's central pump.

Preparation and materials

Before beginning the investigation, you'll need a sheep's or pig's heart, which is smaller than a human heart but has essentially the same structure. The heart should be fresh and properly preserved. You'll also need basic dissection equipment including a scalpel, scissors, dissection board, and pins for labelling.

External examination of the heart

Start by examining the outside of the heart to identify key surface features and blood vessels.

Identifying the surfaces

The heart has two main surfaces that you need to distinguish:

• Ventral surface (front): This surface is more rounded and faces forwards in the living animal
• Dorsal surface (back): This surface is flatter and faces towards the spine

Feeling the heart chambers

Place your hand on different parts of the heart and notice the texture differences:

• The lower left side feels much firmer and more muscular than the lower right side
• This difference occurs because the left ventricle has much thicker walls than the right ventricle
• The upper chambers (atria) feel quite soft and look like small 'ears' on the outside of the heart

Locating coronary blood vessels

Examine the surface of the heart to find the coronary arteries and veins. These vital blood vessels supply the heart muscle itself with oxygen and nutrients. You should notice:

• Coronary arteries: Look for a major coronary artery that runs diagonally from the top right to the bottom left of the heart
• Coronary veins: These run alongside the arteries but have thinner walls
• These vessels appear as raised lines or tubes on the heart's surface

Internal examination procedures

Now you'll make careful cuts to examine the heart's internal structures. Follow these steps systematically to observe all four chambers and their associated valves.

Examining the left ventricle

Make cuts 1 and 2 to open the left ventricle:

• Wall thickness: Observe the very thick, muscular wall of the left ventricle
• Tendons: Look for white, string-like structures called tendons (or chordae tendineae) that hold the valve flaps in place
• Bicuspid valve: Find the valve between the left atrium and left ventricle, which has two flaps

Examining the right ventricle

Make cuts 3 and 4 to open the right ventricle:

• Wall thickness: Notice that the wall is much thinner than the left ventricle
• Tendons: Observe similar white string structures
• Tricuspid valve: Locate the valve between the right atrium and right ventricle, which has three flaps positioned between the atrium and ventricle

Examining the atria

Make cuts 5 and 6 to open both atria:

• Wall thickness: Notice the very thin walls of both atria
• Valve structures: Observe the bicuspid and tricuspid valves from above

Examining major blood vessels

Make additional cuts to examine the large blood vessels:

Cut 7 - Pulmonary artery:

• Locate the semilunar valve at the base of the pulmonary artery
• This valve has three flaps that prevent blood flowing back into the right ventricle

Cut 8 - Aorta:

• Find the second semilunar valve at the base of the aorta
• Look for the beginning of the coronary artery just above this valve
• If you squirt water into the coronary artery, you can see it flow down to supply the heart muscle

Finding the septum

The septum is the muscular wall that separates the left and right sides of the heart. This structure prevents oxygenated and deoxygenated blood from mixing.

Recording your observations

Create a detailed diagram of your dissected heart, similar to the one shown in your textbook. Use small pins and paper labels to identify all the structures you've found. This helps you remember the locations and relationships between different parts.

Make sure to label:

• All four chambers (left and right atria, left and right ventricles)
• Both types of valves (bicuspid, tricuspid, and semilunar valves)
• Major blood vessels (aorta, pulmonary artery)
• The septum
• Coronary blood vessels

Hygiene and safety

After completing the investigation:

• Wash your hands thoroughly and sterilise all equipment
• Dispose of biological material appropriately according to your school's guidelines
• Clean the dissection board with disinfectant