A sheep heart dissection offers a direct, tangible way to understand the complex anatomy of the mammalian heart. Due to its remarkable structural similarities to the human heart, the sheep heart serves as an excellent model for educational purposes. Dissection provides insights into the organization of cardiac chambers, valves, and major blood vessels, which can be challenging to grasp from two-dimensional diagrams alone. This guide details the steps for dissecting a sheep heart.
Preparing for Dissection
Gather all necessary materials before beginning the dissection. You will need a preserved sheep heart specimen, a dissection tray, a scalpel, dissection scissors, forceps, and a probe. For safety, wear disposable latex or nitrile gloves and safety goggles.
Set up your workspace in a clean, well-lit area, ideally away from food preparation areas. Place the dissection tray on a stable surface to contain any fluids or tissues. Rinse the preserved sheep heart specimen to remove excess preservative.
Ensure the specimen is fully thawed if it was frozen, and pat it dry to improve grip and reduce mess. Proper handling of the specimen before and during dissection helps maintain its integrity and allows for clearer identification of structures. Dispose of any packaging materials appropriately before starting.
External Examination and Initial Incisions
Begin by observing the external features of the sheep heart. Identify the broader, flat superior end as the base and the pointed, narrow inferior end as the apex. The apex is typically formed by the left ventricle. Orient the heart to identify its anterior (ventral) and posterior (dorsal) surfaces; the anterior surface often appears more rounded, and the pulmonary artery is generally positioned more anteriorly than the aorta.
Locate the major blood vessels emerging from the base of the heart. The pulmonary artery, which carries deoxygenated blood to the lungs, exits the top-front of the heart. Just behind the pulmonary artery, find the aorta, which distributes oxygenated blood to the rest of the body. On the posterior side, locate the superior and inferior vena cava, which bring deoxygenated blood into the right atrium, and the pulmonary veins, which return oxygenated blood to the left atrium.
Identify the coronary arteries and veins, visible as a diagonal line of vessels running across the surface, especially within the interventricular sulcus (the groove separating the ventricles). These vessels supply blood to the heart muscle. Make an initial incision into one of the auricles (ear-like flaps on the atria) to gain access to a chamber.
Exploring Internal Structures
To explore the internal anatomy, begin by inserting a probe or scissors into the superior vena cava and making an incision downwards through the wall of the right atrium and into the right ventricle, extending towards the apex. This exposes the right atrium, which receives deoxygenated blood from the body, and the right ventricle, which pumps blood to the lungs. Inside the right ventricle, observe the tricuspid valve, with three flaps, between the right atrium and ventricle. These flaps are tethered by thin, white fibrous cords called chordae tendineae, often referred to as “heartstrings,” which connect to papillary muscles on the ventricular wall.
Next, locate the pulmonary artery and carefully insert a probe. Make an incision along the length of this vessel and continue into the right ventricle. This will reveal the pulmonary semilunar valve, composed of three cusps, positioned at the base of the pulmonary artery, preventing backflow into the right ventricle. To examine the left side, insert a probe into one of the pulmonary veins leading into the left atrium. Extend an incision from the pulmonary vein through the wall of the left atrium and down into the left ventricle, moving towards the apex.
The left atrium receives oxygenated blood from the lungs, and the left ventricle pumps this blood to the entire body. Notice the left ventricle’s wall is considerably thicker and more muscular than the right, reflecting its role in generating higher systemic pressure. Between the left atrium and left ventricle, identify the bicuspid (mitral) valve, with two flaps, also connected by chordae tendineae to papillary muscles. Finally, locate the aorta, and make an incision along it from its origin in the left ventricle. Inside the aorta, the aortic semilunar valve, similar to the pulmonary valve with three cusps, will be visible, preventing backflow into the left ventricle.
Post-Dissection and Understanding
After completing the dissection and identifying all relevant structures, dispose of the specimen and clean tools and the workspace. Dispose of the preserved sheep heart specimen according to local biological waste guidelines, often in a designated biohazard bag. Clean all dissection tools with soap and water, then dry them completely to prevent rust and maintain their condition for future use.
Clean and sanitize the dissection tray and work surface to remove any biological residue. This practical experience provides a deeper understanding of the heart’s anatomy, moving beyond textbook diagrams to a tactile and visual appreciation of its complexity. Observing the chambers, valves, and major vessels firsthand helps solidify the concept of blood flow pathways through the heart and the circulatory system. Structural differences, like varying ventricular wall thickness, illustrate the functional demands on different heart parts, connecting form to physiological function.