Sheep Heart Dissection
In this investigation, the external and internal heart structure valves of a sheep’s heart organ were examined and identified by dissection. The heart is a muscular organ that pumps oxygenated blood and nutrients throughout the body. A sheep’s heart has four chambers like most mammals including humans. Two of those chambers are receiving chambers called the right and left atrium. The other two chambers are pumping chambers called the right and left ventricle. A sheep heart dissection can help to identify each of these different areas of the heart.
The efficiency in the cycle of blood depends on the sequential contraction of the atriums and ventricles. Whenever the atriums contract this is called the systolic phase and whenever the ventricles contract this is called the diastolic phase. These contractions ensure the regular flow of blood through the heart. The contractions occur one after another to make a heartbeat. The many heart valves such as the tricuspid and mitral heart valves control the flow of blood from each chamber.
Blood flow through the heart starts when the right atrium takes the blood that flows in through the superior or inferior vena cava. The right atrium then fills with blood and pressure causes the tricuspid valve to open. The blood then goes into the right ventricle where it contracts the blood into the pulmonary arteries. These arteries lead to the lungs where blood is then oxygenated. The oxygenated blood then flows from the lungs to the left atrium through the pulmonary veins. Due to pressure the mitral valve, which leads to the left ventricle, opens up and pushes the blood into the left ventricle. The left ventricle then contracts and forces the blood through the aorta, which provides the rest of the body with blood.
Objectives of a sheep heart dissection in a lab:
- Describe the appearance of the external and internal structures of the animal’s heart organ
- Name the structure and function of the animal’s heart organ
- Understand the anatomy and physiology of a sheep’s heart
What is a Sheep Heart Dissection?
A sheep heart dissection involves cutting into particular areas of a sheep’s heart so that we can see each of the different sections and learn more about what each part of a heart looks and feels like. A sheep’s heart and sheep internal anatomy are very similar to a human, so it gives us an opportunity to learn more about what a human heart might look like on the inside.
By dissecting into a heart, we can see each different section in detail and can learn how each section helps in pumping blood around the body. Following is a full explanation and sheep heart dissection guide so that you can easily and safely complete a sheep heart dissection yourself in a lab setting.
How to do a Heart Dissection
The materials needed in this dissection include sheep’s heart, a dissecting tray, a blunt metal probe, a pair of scissors, a scalpel, and a pair of tweezers. The safety equipment needed for this dissection is safety goggles, lab aprons, and gloves. The procedure must be completed according to the safety elements of the lab manual.
Sheep Heart Dissection Guide
Most diagrams of a heart show the left atrium and ventricle on the right-hand side of the picture. This is to show the heart in a way as if it is facing you. If a human was facing you, then the left-hand side of their heart would be on your right, and this is how diagrams usually portray a heart.
Observing the External Anatomy and Areas of the Heart
- Start by identifying the left and right sides of the heart. If you look closely, you will see a diagonal line of blood vessels on one side which divide the heart. The half of the heart that includes all of the apex is the left side. This can be confirmed by gently squeezing each side of the heart. The left side of the heart will feel much firmer than the right. This is due to all of the muscles that are required to pump blood to the entire body. The right side of the heart is less firm and weaker as this side only pumps blood to the lungs.
- Place the heart down so that the right side is on your right. Take a moment to examine the darker flaps that are located at the top of the heart. These flaps are named auricles. There should be a large opening at the top of the heart right next to the auricles. This is the opening to the superior vena cava – the area which brings blood from the top half of the body to the right atrium. If you stick a probe into this opening, you should feel it go right through into the right atrium. Slightly down and to the left of the superior vena cava lies another opening. Inserting a probe into this opening will also lead to the inside of the right atrium. This other opening is the inferior vena cava, which brings blood up to the heart from the lower tissues. Another blood vessel will be visible next to the left auricle. This is the pulmonary vein, which brings blood up from the lungs and into the left atrium.
- Right in the center of the heart, you will see the largest blood vessel. This is the aorta, which is responsible for taking oxygenated blood from the left ventricle to the rest of the body. The aorta branches out when it leaves the heart into more than one artery so it may have more than one opening on the heart that you are examining. If you look closely at the openings, you will see that they are connected to each other.
- To the left side of the back of the aorta, you will find another large vessel. This vessel is the pulmonary artery which is responsible for taking blood from the right ventricle to the lungs.
The Dissecting Process and Observing the Internal Anatomy and Areas of the Heart
- Insert your scalpal into superior vena cava and make an incision through the wall of the right-hand side atrium and ventricle. The area that we cut is called the pericardium. This is the sac that surrounds the internal areas of the heart. Pull the two sides apart and you should notice three flaps of membrane. These form the tricuspid valve between the right-hand atrium and ventricle. These are connected to flaps of muscle which are named the papillary muscles. They are connected via tendons called chordae tendinae, and these tendons are what are known as the “heartstrings”. This valve allows blood flow from the atrium into the ventricle and prevents blood from backflowing in the opposite direction.
- If you insert your probe into the pulmonary artery, you will see it appear in the right ventricle. Make an incision into this artery and look on the inside of it and you should see three small membrane pockets. These pockets form the pulmonary semilunar valve, which is responsible for preventing blood from flowing back into the right ventricle.
- Insert you scalpal into the base of the left auricle of the aorta and continue the incision down the left ventricular wall. Between the left atrium and ventricle, you will find the mitral valve. This will have two flaps of membrane connect via tendons to the papillary muscles.
- Insert your probe into the aorta and see where it emerges in the left ventricle. Proceed to make an incision in the aorta and observe the inside for three small membrane pockets. These are the aortic semilunar valve and are responsible for preventing blood from flowing backwards into the left ventricle.
Internal Anatomy and Physiology of the Heart & Blood Flow
1) Trace the path of blood from the right atrium to the aorta. The path of blood starts from the superior or inferior vena cava to the right atrium. Then it goes from there to the right ventricle to the pulmonary arteries. The blood flows to the lungs and comes back to the heart through pulmonary veins to the left atrium. The blood then flows down to the left ventricle. The blood then travels from there to the aorta and leaves the body.
2) Pulmonary circulation carries blood between the heart and the lungs. Systemic circulation carries blood to the rest of the body. In what chambers of the heart does pulmonary circulation begin and end? In what chambers does systemic circulation begin and end? Pulmonary circulation begins in the right ventricle and ends in the left atrium. Systemic circulation begins in the left ventricle and ends in the right atrium.
3) What is the function of the septum separating the left and right ventricles? The septum is sort of like a barrier between the two chambers.
4) What is the function of the mitral and tricuspid valves? These valves control the flow of blood into and out of each chamber in the heart. They also prevent blood from flowing backwards.
5) Why are the walls of the left ventricle thicker than the walls of the right ventricle? The left ventricle has thicker walls because it uses this extra muscle to propel blood to and through the aorta to the rest of the body.
Following the steps in the sheep heart dissection guide will give you the tools and knowledge to write a complete essay on the internal and external anatomy of a sheep’s heart.