NPHS / Anatomy

Dissection of the Sheep Heart

Objective: To study the structure of the heart in groups of 3.

Special Notes: (Will be reviewed in class)

• R= right and L= left (unless otherwise specified)

• The butcher will have trimmed most of the blood vessels away, so you may only find a hole where the blood vessel should be.

• It is instructive to pass a probe through a vessel or from one chamber of the heart to another.

Materials Needed:

 Sheep heart Dissecting tools (prove, forceps, scissors)

 Tray Gloves

I. Procedure – External Anatomy:

1) Gather your dissection equipment and a sheep heart.

2) Rinse the sheep heart thoroughly with cold water to remove excess preservatives and to flush out blood clots.

3) Examine the external surface of the heart. Notice the accumulation of adipose (fat) tissue. This adipose usually accumulates along the boundaries of the heart chambers and along the coronary arteries. Remove as much adipose as possible. Now you should be able to identify the apex (bottom left “point” of the heart) and the auricles (earlike flaps projecting from the atria).

4) See if you can find these External Features of the heart (suggestion: check them after every group member has seen them). Based on how the heart was cut, you may or may see them. At minimum, locate all “holes” indicating where vessels are so that you can determine which vessel the hole belonged to once you have opened up the heart.

R and L atria

R and L ventricles

Interventricular sulcus: the natural groove between the ventricles

Coronary sulcus: the natural groove between the atria and ventricles

Posterior VC: (thin walled); also known as superior vena cava (may be difficult to see)

Anterior VC: (thin walled); also known as the inferior vena cava (may be difficult to see)

Pulmonary trunk (splits into pulmonary arteries) (may be difficult to see)

Pulmonary veins (may be difficult to see)

Aortic trunk (becomes the thick walled aorta; you should see 3 smaller arteries openings coming from the aorta)

Coronary Arteries

The hard yellow deposits of fat around the organ

epicardium (thin, shiny, outer layer of tissue of the heart)

5) Observe the epicardium. Carefully remove part of this outer layer by pulling it up with the sharp probe.

6) Now you can observe the myocardium (muscular layer of the heart).

II. Procedure – Exploring Valve Action

*In this portion of the lab, you can imitate blood flow through the heart and observe valve action.

1) Locate the pulmonary trunk and the aorta on the superior aspect of the heart. Clear the adipose away from these arteries. The pulmonary trunk divides into the R and L pulmonary arteries (try to see if you can find them; look for small openings). The aorta will have a large branch coming from beneath the pulmonary trunk. This branch is the right brachiocephalic artery. The right brachiocephalic artery divides into the right subclavian and the right common carotid arteries (supply blood to the head and right arm). Notice the three distinct layers of all these arteries.

2) Locate the superior vena cava (SVC). Use your scissors to cut along the walls of the SVC in order to open up the right atrium. Do not cut through the entire atrial wall. Only cut enough so you can see the interior of the chamber.

3) Observe the right AV valve (the right AV valve has “three flaps” or is “tricuspid” in structure).

4) Slowly pour water into the right atrium and allow it to flow into the right ventricle.

5) Gently squeeze the right ventricle and watch the closing action of the right AV valve.

WARNING: Do not squeeze the ventricle too roughly or too quickly…if you do, be prepared to have water squirted on your face, in your mouth, nose, eyes, etc.

6) Drain the water from the heart.

III. Procedure – Internal Anatomy of the Heart

*As you follow this procedure, use the “checklist” of structures below and be sure to identify them as you work.

1) Starting at the apex and moving towards the base, make a coronal (frontal) cut through the heart. Stop cutting when your knife reaches the top portions of the atria (You are cutting to separate the font of the heart from the back of the heart).

2) Open the heart at the apex. Now you should be able to identify most of the heart’s anatomical structures.

3) Notice that the heart is made up of three layers: the epicardium (which is the same as the visceral pericardium), the myocardium (literally “heart muscle”), and the endocardium (“inside the heart”; it’s shiny). Locate the side with the thickest myocardial wall. This will orient you to the left side of the heart.

4) You should see that there are more spaces (or “chambers”) on the left and right sides of the lower heart. These are the L and R ventricles (“vent” referring to something coming out of the space, which is blood in this case).

5) You should also see a thick structure dividing the two ventricles, the bulk of which is comprised of cardiac muscle. This is the INTERVENTRICULAR SEPTUM.

6) The ventricles are divided from the chambers directly above them by atrioventricular (or “AV”) valves. These valves have flaps (or “cusps”) to which “heart strings” attach. The left AV valve has two cusps, so it can be referred to as a “bicuspid” valve. The R valve has three cusps, so it can be referred to as a “tricuspid” valve.

7) The strings that attach to the AV cusps are called CHORDAE TENDINEAE.

8) The chordae tendineae are anchored to the ventricular walls via PAPILLARY MUSCLES (papillary = “nipple like”).

9) You will need to cut through the rest of your heart in order to identify the remainder of its structures.

10) Note that you will need to remove the R ventricular wall and cut into the pulmonary trunk in order to view the pulmonary valve (or R semilunar valve).

11) Properly dispose of all organic materials and clean your dissecting tools and trays before leaving the lab.

CHECKLIST:

 R and L atria interatrial septum (wall) – where foramen ovale was!

 R and L ventricles tricuspid valve (between RA and RV)

 openings of the superior vena cava papillary muscles

 interventricular septum chordae tendineae (“heart strings”)

 pulmonary semilunar valve (leaving the RV) openings of the pulmonary veins

 bicuspid valve (between LA and LV) aortic semilunar valve (leaving the LV)

*NOTE the thicker wall of the LV muscle than that of the RV!

 Complete the post-lab questions and diagrams on the Lab Analysis Sheet. 

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LAB ANALYSIS SHEET: Sheep Heart Dissection

> Post-Lab Questions:

1) The heart is an organ of which body system?

2) What is the muscular layer of the heart called?

3) What is the name of the sac surrounding the heart?

4) What type of tissue comprises the bulk of the myocardium?

5) What bone protects the heart anteriorly?

6) The bulk of the heart rests on this side of the body.

7) Which chambers of the heart function to receive blood from the veins?

8) Which chambers of the heart function to pump blood out of the heart?

9) What is the scientific term for “heart strings” that attach to the AV cusps?

10) To which muscles do these “heart strings” attach?

11) What structure divides the R and L ventricles?

12) The superior vena cava attaches to this heart chamber.

13) What is the largest artery of the human body?

14) Why is the muscular wall of the LV thicker than that of the RV?

15) What is the function of the papillary muscles and chordae tendineae?

16) What is wrong with the statement: “Arteries always carry oxygen-rich blood and veins always carry oxygen-poor blood.”? Explain using specific examples.

17) Trace the path of a RBC as it travels from the superior vena cava to the aorta. List every vessel, valve, and part of the heart traveled through. (xxx  xxx  xxx  etc.) *At least 13 things!

19) Look at the heart diagram below. Write the letter of each structure next to the correct anatomical name.

aortic archleft ventriclepulmonary semilunar valve

aortic semilunar valvemyocardiumdescending aorta

bicuspid (mitral) valve(L A-V valve)epicardiuminterventricular septum

chordae tendineaeendocardiumright pulmonary artery

papillary musclesleft pulmonary veinleft atrium

inferior vena cavaright ventricleleft pulmonary artery

superior vena cavatricuspid valve(R A-V valve)right atrium

*Branches of the aortic arch:pulmonary trunkright pulmonary vein

-brachiocephalic artery

-left common carotid artery

-left subclavian artery