Physiology Lab: The Macroscopic and Microscopic View of ...



Physiology Lab Feb. 2014 Name: __________________ Class# _____

The Macroscopic and Microscopic View of the Heart

Introduction: Dissection of a pig heart is valuable because it is similar in size and structure to the human heart. Also, dissection allows you to view structures in a way not possible with models, diagrams and on-line activities. Cardiac muscle is found in only one place – the heart. Because the heart acts as a blood pump, propelling blood to all tissues of the body, cardiac muscle is very important to life. Cardiac muscle is involuntary, ensuring a constant blood supply. The cardiac cells are arranged in spiral or figure 8 shaped bundles. When the heart contracts, its internal chambers become smaller, forcing the blood upward into the large arteries leaving the heart.

Part I – The Pig Heart

NOTE – NO contacts allowed; before you begin you must 3 G!

Goggle, Gown and Gloves

1. Obtain a preserved pig heart, a dissecting tray and dissecting instruments.

2. Rinse off the excess preservative with tap water. Use the large double sink for this, not the ones at the ends of your lab table.

3. Observe the texture of the pericardium or pericardial sac that covers and surrounds the heart and anchors it. Note if there is any fat on the outside of the pericardium. Remember, these hearts come farms that raise pigs for the food industry. Also, find the sacs point of attachment to the heart. Where is it attached?

4. Cut open the pericardial sac and observe the epicardium. Using a sharp scalpel or pointy forceps, carefully pull a little of the epicardium away from the myocardium. How does its position and thickness to the heart differ from that of the parietal or fibrous pericardium?

5. Locate the tip or apex of the heart. Only the left ventricle extends all the way to the apex.

6. Examine the external surface of the heart. Notice the accumulation of adipose tissue, which in many cases marks the separation of the chambers and the location of the coronary arteries. Carefully scrape away some of the fat with a scalpel to expose the coronary blood vessels.

7. Identify the atria and ventricles from the outside of the heart. Make sure your heart is ventral side up and you will be able to locate the anterior coronary interventricular sulcus. This divides the heart into left and right sides.

8. The heart is now in the dissecting tray in the position it would be in a body as you facet the body. Locate the following chambers of the heart from this surface:

a. Left atria – upper chamber to your right- little cauliflower shaped flap

b. Left ventricle – lower muscular chamber to your right

c. Right atria – upper chamber to your left - little cauliflower shaped flap

d. Right ventricle – lower muscular chamber to your left

9. While the heart is still in the tray, locate the following blood vessels at the base of the heart (upper part where the blood vessels leave and enter):

a. Coronary arteries – you have done this in step 6 – review.

b. Pulmonary Artery – this blood vessel branches and carries blood to the lungs. It can be found curving out of the right ventricle.

c. Aorta – the largest blood vessel of the heart, near the right atria and just behind the pulmonary arteries. Locate the curved part of this vessel, known as either the aortic arch or the aortic trunk. Branching from this major vessel are 3 blood vessels that bring blood to the face, neck, head, shoulders and arms. Name these blood vessels and state each ones destination.

d. Pulmonary veins – these vessels return oxygenated blood from the right and left lungs to the left atrium.

e. Inferior and Superior Vena Cava – these two blood vessels are located on your left side of the heart and connect to the right atrium. Deoxygenated blood enters the body through these vessels into the right atrium. These veins do not use valves to control the blood flow into the heart.

Label this diagram and attach it to your lab report.

Labels:

1. ______________________ 6. __________________________

2. ______________________ 7. __________________________

3. ______________________ 8. __________________________

4. ______________________ 9. __________________________

5. ______________________ 10. __________________________

10. Clear away the fat between the pulmonary trunk and the aorta to expose the ligamentum arteriosum, a remnant of the ductus arteriosus.

11. Cut through the wall of the aorta until you see the aortic semilunar valve. Identify the two openings into the coronary arteries just above the valve. Insert a glass probe into one of these holes to see if you can follow the course of the coronary artery across the heart.

12. Turn the heart over it view its posterior surface. Identify the superior and inferior vena cavae entering the right atrium. Note the inferior vena cava comes from behind the right atrium. Compare the approximate diameter of the superior vena cava with that of the aorta. Which is larger, the aorta or the superior vena cava? Which has thicker walls? Why do you suppose these differences exist?

13. Insert a glass probe into the superior vena cava and use scissors to cut through its wall so that you can see the interior if the right atrium. DO NOT EXTEND YOUR CUT entirely through the right atrium or into the ventricle. Observe the right atrioventricular valve. What is the name of this valve? How many flaps does it have?

14. Note the chordae tendinae and papillary muscles that are attached to the av flaps on both sides of the heart. What is the function of the chordae tendinae and the papillary muscles?

15. Use your water bottles and squeeze a small amount of water into the right atrium and allow it to flow into the right ventricle. SLOWLY and GENTLY squeeze the right ventricle to watch the closing action of this valve. (If you squeeze TOO HARD, you will get a face full of water!) Drain the water from the heart before continuing.

16. Cut through the anterior wall of the pulmonary trunk until you see the pulmonary semilunar valve. Squeeze some water into the base of the pulmonary trunk to observe the closing action of this valve. How does its action differ from that of the atrioventricular valve?

17. Drain the heart again and return to the superior vena cava. Continue the cut made in its wall through the right atrium and right atrioventricular valve into the right ventricle.

18. Next, make a longitudinal cut through the aorta and continue it into the left ventricle. Again notice how much thicker the myocardium of the left ventricle is than that of the right ventricle. Compare the shape of the left ventricular cavity to the shape of the right ventricular cavity. Are there chordae tendinae in the right ventricular cavity as well? How does the number of cusps in the left av valve compare with the number of cusps seen in the right av valve? How do the pig valves compare with their human counterparts?

19. Continue your incision from the left ventricle superiorly into the left atrium. Locate the entry points of the pulmonary veins into the left atrium. Follow the pulmonary veins to the heart exterior with a probe.

20. Return all cut hearts to the bucket at the front of the classroom. Clean all utensils and properly dispose of all organic debris.

Part II – Cardiac Muscle

1. Using REAL ANATOMY on the computer. Go to the Histology section and look for a picture of cardiac muscle.

2. Draw a representative sample.

3. Identify the nucleus, striations and intercalated discs in your picture.

Assessment:

This will not be a typical lab report. So read carefully!!

On a separate sheet of paper,

• Have a cover page with your name, class, date and title of the lab.

• INCLUDE A CARTOON – I WILL BE ADDING THIS TO THE GRADE DENOMINATOR!!!

• Type your answers to all of the questions within the protocol of this lab.

• Label the heart diagrams on the last page of this lab protocol.

• Staple your answers, the labeled diagram and your drawing of the cardiac muscle cells together.

On the day of the heart practicum (after HSPA’s) you are to bring in this lab assignment for collection.

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