Download Dissection of the Sheep Heart

Dissection of the Sheep Heart
EFE Animal Science
EFE Veterinary Science
I <3 Heart Dissection!
Before beginning, assemble a dissection tray, scissors,
blunt probe, gloves for each person, and a couple of
paper towels.
You will be given a preserved sheep’s heart
It will likely be a bit deformed from vacuum packing.
Gently “smoosh” it into shape and squeeze out any
extra preservative fluid.
Next, remove excess fat from the outside surface
The fat is whitish, firm and is most easily removed
by picking at it with your fingers.
It is not necessary to remove all of the fat
So don’t get too obsessed over it!
You may wish to remove it by blunt dissection: slip the
closed scissors tip under the fat, then spread the blades.
Next, orient the heart.
The base is the broad part (top), and the apex is the
narrow (bottom) part. This is the ventral side (note
that you cannot see the auricles!)
Locate the auricles (earlike projections)
Orient the heart with the auricles downward on the
tray (ventral side up toward you).
You will begin your first cut in the vena cava
This is the large vessel that empties into the right
atrium and auricle. Probe with a finger to find it.
Cut from the vena cava toward the apex
Learn good habits: Surgical scissors are always
held by the thumb and 4th (ring) finger.
Spread the heart open and locate the following
structures (label with dissection pins):
Right auricle, right atrium, fossa ovalis (remnant of
the foramen ovale), interatrial septum,
Locate and label, continued:
Right ventricle, moderator bands, trabeculae carneae,
pulmonary artery, right atrioventricuar (AV) valve
Locate and label, continued
Right AV valve = tricuspid (in humans), chordae
tendonae, papillary muscles
Locate and Label
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right auricle
right atrium
fossa ovalis (remnant of the foramen ovale)
interatrial septum,
right ventricle
moderator bands
trabeculae carneae
pulmonary artery
right atrioventricuar (AV) valve = tricuspid (in humans)
chordae tendonae
papillary muscles
Now continue your cut around in a “U” shape
Picking up where you left off at the apex, and
continue up the base and up the coronary artery
Remove the flap; the right ventricle is now fully
open and structures are visible.
The probe is indicating the interventricular septum
Chordae tendinae of the right AV valve
Papillary muscle in the right ventricle
Fossa ovalis (remnant of the foramen ovale)
This is an oval depression on the interatrial septum.
Before birth, the foramen ovale allows blood to
bypass the lungs.
The fossa ovalis
Now locate the pulmonic (semilunar) valve
This prevents backflow of blood from the
pulmonary arteries. Note the lack of chordae
tendinae.
Next, turn your heart over.
The right side (where you have already cut) faces
downward toward your dissection tray.
Begin your cut at the left atrium
And continue as far as possible toward the apex of
the heart. What do you notice about the thickness of
the ventricular wall?
At the apex, turn and cut upward toward the
aorta at the heart base.
The aorta is the large, thick-walled vessel.
(Are you holding your scissors correctly?!)
Now, one last cut. Start where you began the last
cut, in the left atrium.
Continue around and through the pulmonary artery
and up the aorta. Lift the flap.
You have exposed the aortic semilunar valve.
This prevents backflow from the aorta and ensures
that blood moves forward throughout the body.
Moderator band in the left ventricle
This prevents the ventricle from over-distention.
These are more numerous and thicker than in the
right ventricle. Why?
Locate and Label
Pulmonary veins, left atrium, left auricle, interatrial
septum, aorta, aortic (semilunar) valve
Locate and label
Left atrioventricular (AV) valve = bicuspid valve in
humans
Locate and Label
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pulmonary veins
left atrium
left auricle
interatrial septum
aorta
aortic (semilunar) valve
left atrioventricular (AV) valve = bicuspid
valve in humans
Compare the size and wall thicknesses of the two
ventricles. Why is there a difference?
Be certain that, in addition to naming the structures,
you are able to trace the path of blood flow through
the heart.
Now, don’t you <3 the heart, too?!