Download To explore the structure of a heart that is similar in size and shape to

IB Bio 2 / Revised 2015-16
Sheep Heart Dissection
Objective: To explore the structure of a heart that is similar in size and shape to a human heart.
Materials (per pair):
 Preserved sheep heart, rinsed
 Dissecting tools (1 scissors, 2 probes, 2
forceps, 1 scalpel)
 2 goggles
 2 Apron or lab coats
 2 pairs of gloves
 Dissecting pan
Please note:
 “R” means right and “L” means left from the patient's (er… sheep's) perspective. Therefore the right side of
the heart corresponds with your left, and the left side with your right. .
 Please, be aware the hearts were once part of living vertebrate organisms, and the tissue should be respected.
There will be no mutilation of tissue. If any disrespectful behavior is observed, the student responsible will be
asked to leave the lab.
 If any student does not wish to participate in this lab for any reason, s/he can do an alternate activity.
Pre-lab (all students, even if opting out of the dissection)
Draw a full-page frontal section of a human heart for your portfolio, or you may use a B & W diagram.
Either way the picture should show all four chambers, all associated blood vessels, and all valves. Color
it in traditional red (for oxygenated blood) and blue (deoxygenated blood). Care should be taken to show
the relative wall thicknesses of the four chambers. Be sure to label all visible structures.
Procedure:
1. Obtain and put on goggles, gloves and lab aprons. You and your partner need one tray, a set of
tools, and one preserved sheep heart. Rinse the heart with tap water on the way back to your seat.
2. Before doing anything else, orient yourself so that you are looking at the heart's ventral surface.
When the heart is placed ventral side facing you, you are mostly looking at its ventricles. The
majority of its blood vessels open from the dorsal surface. But the butcher cuts the vessels close to
the heart, so they may not be easy to identify at this stage. Once you're inside the heart it is easier to
see where the vessels enter or leave the chambers.
3.
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Identify the following external features, checking them off as you and your teammate see them:
R and L atria
R and L ventricles
Interventricular sulcus (the groove between the ventricles; may be obscured by fat)
Coronary sulcus (the groove between the atria and the ventricles; may be obscured by fat)
Anterior (superior in humans) and posterior (inferior) vena cavae, maybe… will be thin-walled
Pulmonary trunk (splits into pulmonary arteries), maybe
Pulmonary veins, maybe
Aortic trunk (becomes the thick-walled aorta)
Coronary arteries (look within the coronary sulcus)
Hard yellow deposits of fat around the heart, insulating it and keeping it warm
NOW ask a lab teacher to make a frontal (coronal) section of the heart with a large knife. You may do
this yourself if you prefer!
4.
Identify the following internal features, checking them off as you and your teammate see them:
Let's move in the order that blood flows:
a) Inside the R atrium:
 Openings of the superior and inferior vena cavae
 Interarterial septum or wall (a hole called the foramen ovale used to be here; it closes at
birth)
b) Between the RA and the RV:
 Tricuspid valve, the atrioventricular (A/V) valve between RA and RV
c) Within the R ventricle
 Net-like, weird cardiac muscle called trabeculae carnae
 Chordae tendinae ("heart strings" attached to papillary muscles
 Interventricular septum
 Semilunar valve where the pulmonary trunk leaves the RV
Pretend here that the blood exits the heart, goes through the cap's of the lung
(any given RBC would go to either the right or left lung), and returns to the heart
d) Inside the L atrium
 Openings of the pulmonary veins (how many can you find?)
e) Between the LA and the LV:
 Bicuspid or mitral valve, the A/V valve between LA and LV
f) Within the L ventricle:
 Note again the papillary muscles and chordae tendinae
 See how much thicker the LV wall is, compared to the RV?
 Semilunar valve where the aortic trunk leaves the LV.
Clean-up
 Dispose of preserved tissue and used gloves in the labeled Tissue Waste Bucket.
 Rinse pan and dissecting tools with soap and water (CAREFUL rinsing off scalpel!!); set out on
towel to air dry so nothing rusts.
 Return other borrowed supplies, like the goggles and aprons, to their designated places.
Post Activity questions (for IB portfolio; please restate the questions in your answers).
1. Trace the path of a red blood cell (RBC) from the posterior vena cava to the aorta. List every
vessel, valve, and chamber of the heart it traverses.
2. You observed that the wall of the LV is much thicker than that of the RV; how is this
advantageous?
3. What is the function of the papillary muscles and the chordae tendinae?
4. What was the function of the foramen ovale in a fetus?
5. Come up with a metaphor for the four-chambered mammalian heart – but you can't use "pump."