Info

Pulmonary arteries

Aorta

The heart has a left and a right side. It has two upper chambers, the left and right atria, and two lower chambers, the left and right ventricles. Why do multiple chambers result in a more efficient heart?

2. Blood enters the heart from the body through the superior or inferior vena cava. The blood then enters the right atrium and flows through valves into the right ventricle. Blood flows from the right ventricle through the pulmonary artery to the lungs. What process occurs in the lungs?

3. Oxygenated blood flows from the lungs through the pulmonary veins to the left atrium. Then, it flows through valves into the thick-walled left ventricle. Blood flows from the left ventricle through the large aorta to the rest of the body.

Procedure

1. In this lab, you will observe the external structure of a sheep's four-chambered heart and dissect the heart to study its internal structure.

2. ^^ Put on safety goggles, gloves, and a lab apron.

Left atrium

(a) DORSAL VIEW

Aorta

Left atrium

Pulmonary

Right ventricle

Left ventricle

Pulmonary

Left ventricle

Superior vena cava Inferior vena cava

Right atrium

Right ventricle

(b) VENTRAL VIEW

Aorta arteries

Superior vena cava

Right atrium

Right ventricle

(b) VENTRAL VIEW

Aorta

Superior vena cava

Right atrium

Right ventricle

arteries

Left

Left ventricle

Left

Left ventricle

6. Follow the cutting diagram below very carefully to study the anatomy of the right side of the heart.

7. Again, turn the heart with the ventral surface ^^ facing you and the apex pointing downward. Use scissors to cut along line 1. CAUTION Always cut in a direction away from your face and body. Cut just deep enough to go through the atrial wall. Continue the cut into the right ventricle. With a probe, push open the heart at the cut, and examine the internal structure.

(a) VENTRAL VIEW (b) VENTRAL VIEW

8. Cut along line 2, and extend the cut upward toward the pulmonary artery. Cut just deep enough to go through the ventricle wall. Complete the cut on line 3. Cut downward along the pulmonary artery, around through the wall of the right atrium, and upward along the right superior vena cava.

9. With tweezers, carefully lift the resulting flap to expose the structures underneath.

10. Follow the cutting diagram above very carefully to study the anatomy of the left side of the heart.

11. Start to cut on line 4 at the top of the left atrium, and continue into the left ventricle. Cut just deep enough to go through the ventricle wall.

12. Cut on line 5 across the middle of the left ventricle into the aorta. Leave a small margin between this cut and the cut previously made for line 2. Begin to cut on line 6 on the left atrium where cut 4 began. Extend this cut around and through the pulmonary artery upward on the aorta to the right of cut 5.

13. With tweezers, carefully lift up the resulting flap to expose the structure underneath.

14. Observe the thick septum dividing the left and right ventricles. Also, note the greater thickness of the walls of the left ventricle.

15. Locate the tricuspid valve between the right atrium and ventricle. Locate the mitral valve between the left atrium and ventricles. Observe that the valves are connected by fibers to the inner surface of the ventricle. Use a probe to explore the openings in the valves.

16. With a scalpel, cut across a section of the aorta ^^ and a section of the vena cava. Compare the thickness of their walls.

17. Jjt^ Dispose of your materials according to the ^^ directions from your teacher.

18. J^hb Clean up your work area, and wash your hands

▼ Defore leaving the lab.

Analysis and Conclusions

1. Trace the path of blood from the right atrium to the aorta.

2. Pulmonary circulation carries blood between the heart and the lungs. Systemic circulation carries blood to the rest of the body. In which chambers of the heart does pulmonary circulation begin and end? In which chambers does systemic circulation begin and end?

3. What is the function of the septum separating the left and right ventricles?

4. What is the function of the mitral and tricuspid valves?

5. Why are the walls of the left ventricle thicker than the walls of the right ventricle?

Further Inquiry

The heartbeat originates in a small bundle of tissue in the right atrium. This bundle is the sinoatrial, or S-A, node.

Read about the S-A node. What does it do? Why is the S-A

node known as the pacemaker?

(a) VENTRAL VIEW (b) VENTRAL VIEW

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