Download Heart Dissection Lab

Anatomy of a Mammalian Heart
Background
This lab activity is designed to help you understanding the anatomy of the mammalian
heart. It is important to remember that we are only dissecting these hearts for an
educational purpose- to learn about and understand heart structure. The heart that
you will dissect was obtained from a calf that was slaughtered for food. The living
animal in which this heart came from was not sacrificed for this laboratory. You are
going to be dissecting a heart that would have been discarded or used for some other
purpose.
Procedure- External Anatomy of the Heart
Position the heart on in your dissection pan such that the pointed end is towards you
and the wide end is toward the top of the dissection pan. Use the model of the heart
and the accompanying diagrams to help with your identification
The pointed tip is called the apex and the top of the heart is called the base.
A. Orient the heart with the right and left auricles (small crinkled sac-like structures
above the atria) pointing upwards in the dissection pan. There will be cleft that runs
from the bottom right side of the heart to the upper left hand side of the heart, this
is called the anterior interventricular sulcus. “Anterior” means “front” and
“interventricular” means “between the ventricles”. This will help you remember what
this cleft is called. In the anterior interventricular groove you will see a large artery
which is a major branch of the coronary artery. This will be an important orientation
point as this divides the right and left hand sides of the heart.
B. Locate the positions of the right atrium, right ventricle, left atrium, and left
ventricle. There is a large artery that emerges from the left ventricle at the base
(top) of the heart as the heart is in the anterior position. This is called the aorta.
Notice that in the anterior position that there are blood vessels covering the exterior
of the heart. These are the vessels that nourish the heart muscle with blood such that
it can pump blood throughout the body. Locate some of these blood vessels. These
are called the coronary veins and coronary arteries.
C. Now turn the heart over to the posterior position. The right and left sides of the
heart are now reversed as they are normally viewed from the front of the body. You
will see a large number of vessels emerging from the base of the heart. Try to identify
the: 1.) aorta (it emerges from the left ventricle) 2.) the pulmonary artery (it
emerges from the right ventricle) 3.) the pulmonary veins (these enter the left
ventricle) 4.) the superior vena cava (this enters the right atrium) 5.) the inferior
vena cava (this enters the right atrium)
Procedure- Internal Anatomy of the Heart
1. Now turn the heart over to the anterior position but rotate it slightly clockwise
such that you are looking at the heart from the anterior position from the right hand
side. Locate the heart in the dissection pan such that the base is towards the top of
the pan and the apex is pointing towards you. Locate the interventricular sulcus
2. Begin the dissection by finding the superior vena cava and the inferior vena cava (if
present). Place your probe into the superior vena cava and feed it out through the
inferior vena cava.
Now carefully take your dissecting scissors and cut along the line of the probe thereby
opening up the vena cava. From the center of this initial incision, cut downward
through the right atrium across the right auricle.
3. Now observe the vena cava and the right atrium.
The superior vena cava returns deoxygenated blood from the head, neck and upper extremities. The
inferior vena cava returns deoxygenated blood from the lower body. The blood enters into the heart
into the right atrium.
Measure the thickness of the superior vena cava which is a vein that returns
deoxygenated blood to the heart. Now measure the thickness of the wall of the right
atrium. Record both measurements in centimeters to the nearest millimeter into a
data table. The walls of the vena cava as well as the right atrium are relatively thin
compared to the arteries which emerge from the heart and the ventricles of the heart
as the blood pressure in the vena cava and right atrium is rather low since blood is
returning to the heart in these areas.
4. Now you will examine the right ventricle. The next incisions will create a window
into the right ventricle. Make an incision parallel to the coronary groove and then
parallel to the interventricular sulcus. This will create a triangular “window” in which
you can view the right atrium. Once you have created this “window” observe the right
ventricle and measure the thickness of the wall of right ventricle in centimeters to
the nearest millimeter. Use your probe to find the AV valve from the prospective of
the right ventricle. Notice that it has three leaflets, or flaps and is therefore often
referred to as the tricuspid valve.
Deoxygenated blood flows into the right atrium and then moves into the right ventricle through the
AV valve. When the right ventricle contracts, the AV valve is closed such that blood can not backflow
into the atrium and the blood can only move forward through the pulmonary valve into the pulmonary
artery. As the right ventricle contracts, the right atrium fills with blood. Then as the right ventricle
relaxes, the right atrium pushes blood through the AV valve into the ventricle. Notice the chords of
tissue that are attached to the valve. These are called the chordae tendinae. When blood is pumped
from the right ventricle to the pulmonary artery out to the lungs, the AV valve closes as its leaflets
come together. A sound is created in this process- the “lub” of the “lub dub” sound of the heart.
Using your probe again, find the pulmonary artery (trunk) which leads out of the right
ventricle. Notice the pulmonary valve which separates the right ventricle from the
pulmonary artery.
When the right ventricle contracts, this valve is open. When the right ventricle relaxes and re-fills
with blood from the right atrium, the pulmonary valve closes, preventing blood from back flowing
from the pulmonary artery. The closing of the pulmonary valve causes a “dub” sound of the “lub
dub”. Note that all of the blood at this point in time is deoxygenated blood. Thus the “lub dub”
sounds of the heart as heard through the stethoscope are created by the AV valve and the pulmonary
valve as they prevent blood from back flowing in the heart and only moving forward- towards the
lungs.
6. Using your scalpel create a “window” on the left side of the heart. To do this, cut
parallel and up to the base of the heart just to the right of the interventricular
sulcus. Then turn your blade and cut across the left atrium. Using your probe, locate a
number of pulmonary veins and probe into them. Your probe should emerge in the left
atrium as you look through the “window” of muscle tissue. Measure the thickness of
the walls of the left atrium. Now find the mitral valve or bicuspid valve which
separates the left atrium and left ventricle. Also locate the chordae tendinae.
The Left Ventricle and Aorta
7. Now locate the left ventricle. Measure the thickness of the wall of the left
ventricle.
Blood enters the left side of the heart through the pulmonary veins from each of the lungs where it
has been oxygenated. As it fills the left atrium, the left ventricle contracts and pushes blood into the
aorta. When the left ventricle contracts, the mitral valve closes, thereby preventing blood from back
flowing into the left atrium. Once blood enters the atrium, the left ventricle relaxes, and the aortic
valve closes.
Find the aortic valve by locating the aorta and pushing your probe down through it
into the left ventricle. The valve you push the probe through is the aortic valve.
Once oxygenated blood enters the aorta it travels through many miles of arteries and capillaries until
it reaches the smallest capillaries where oxygen diffuses out of the red blood cells through the walls
of the capillaries into the surrounding cells where carbon dioxide is exchanged with it. Once the red
blood cells have obtained the carbon dioxide they begin their journey back to the heart via many
miles of veins. Eventually the blood reaches the superior or inferior vena cava and the journey begins
again!
8. To finish the dissection attempt a frontal cut that exposes the four chambers of the
heart
Draw a labeled diagram of your frontal section in the space below
1. Measure the thickness of the
right atria, left atria, right
ventricle, left ventricle, any blood
vessels entering the heart and any
blood vessels leaving the heart.
List your measurements in a chart
Account for any differences you
see in the measurements.
2. The body actually has two
circulatory systems, each powered
the heart. Describe each system
3. What is the function the thin
cords that you see in the
ventricles?
4. Research the physiological names
of the two AV and Semi lunar
valves