Sheep’s Heart Dissection
Introduction
In this investigation, the external and internal structures of a sheep’s heart was
examined and identified by dissection. The heart is a muscle that pumps
oxygenated blood and nutrients throughout the body. A sheep’s heart has four
chambers like most mammals. 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.
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 valves such as the tricuspid
and mitral 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 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


Describe the appearance of the external and internal structures of a sheep’s
heart
Name the structure and function of a sheep’s heart
Materials
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.
Methods
The first step to this procedure is to put on the safety goggles, gloves, and the lab
apron. Next, place the sheep’s heart in the dissecting tray and turn the heart so that
the ventral surface is facing you. Locate the left and right atriums, the left and right
ventricles, the aorta, the pulmonary arteries, and the superior and inferior vena
cava. Turn the heart over to locate the pulmonary veins. Next, Use a blunt metal
probe to explore the blood vessels that lead into and out of the chambers in the
heart. Then, Locate a diagonal deposit of fat along the lower two-thirds of the
heart. Use this fatty deposit to help you guide your incision into the heart.
Following the cutting diagram below study the anatomy of the right side of the
heart. With the heart on the ventral side facing you and the apex pointing
downwards, cut along line 1. Cut just deep enough to go through the atria wall and
continue the cut into the right ventricle. With a probe, push open the heart at the
cut and examine the internal structure. Cut along line 2 and extend the cut upward
toward the pulmonary artery. Cut just deep enough to go through the ventricle
wall. Complete the cut on line 3. Cut downward along the pulmonary artery around
the wall of the right atrium and upward along the right of the superior vena cava.
With tweezers, carefully lift the resulting flap to expose the structures underneath.
Follow the cutting diagram below very carefully to study the anatomy of the left
side of the heart. Start to cut on line 4 at the top of the left atrium and continue into
the left ventricle. Cut just deep enough to go through the ventricle wall. Cut on line
5 across the middle of the left ventricle into the aorta. Leave a small margin
between this cut and the cut previously made for line 2. Begin to cut on line 6 on
the left atrium where cut 4 began. Extend this cut around and through the
pulmonary artery upward on the aorta to the right of cut 5. With tweezers, carefully
lift up the resulting flap to expose the structure underneath. Observe the thick
septum dividing the left and right ventricles. Also note the thickness of the walls of
the left ventricle. Locate the tricuspid valve between the right atrium and ventricle.
Locate the mitral valve between the left atrium and ventricles. Observe that the
valves are connected by fibers to the inner surface of the ventricle. Use a probe to
explore the openings in the valves. With a scalpel, cut across a section of the aorta
and a section of the vena cava. Compare the thickness of their walls. Dispose of
your materials according to the directions from your teacher. Finally, clean up your
work area and wash your hands before leaving the lab.
Results
Internal Anatomy of the Heart & Blood Flow
Error Analysis
The only error that was probably made during this dissection was that we didn’t
cut according to the diagram very good.
Conclusion
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.