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The On The Dissection Board

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Materials:
- Scalpel
- Tweezers
- Blunt probe
- Disposable gloves
- Dissection board
- Sheep heart

Method:
1) Place the heart on the dissection board
2) Identify as many of the external features as you can: right and left atria, right and left ventricles, aorta, vena cava, pulmonary arteries and veins.
3) Use the blunt probe to investigate which chamber of the heart the blood vessels enter or leave. Use the scalpel to make cut as shown in Figure 1. Cut with the blade pointing upwards and away from you.
4) Observe the thickness of the wall of the right ventricle
5) Open out the right ventricle
6) Observe the tendon and the valves to which they are attached
7) Work out how the valves work to control the blood flow
8) Observe the flaps of
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The walls must be thick and elastic so as to absorb the sudden increase in pressure from the pulse of blood suddenly surging through the artery during ventricular systole (when the ventricles contract). As the blood passes through the dividing arteries and through the capillaries, the pressure from the pulse of blood is reduced to almost nothing. The blood flows evenly. With the reduced pressure, the walls of the veins do not need to have the thick layers. So, the vein walls are much thinner. Blood enters the heart slowly through the vena cava and is pumped out with tremendous force into the aortic artery. Since the pressure exerted on the blood vessels differs, they require different thicknesses to effectively cope with those pressures.
At the start of each heartbeat, blood returning from the body and the lungs fills the heart 's two upper chambers. The mitral and tricuspid valves are located at the bottom of these chambers. As the blood builds up in the upper chambers, these valves open to allow blood to flow into the lower chambers of your heart. After a brief delay, as the lower chambers begin to contract, the mitral and tricuspid valves shut tightly. This stops blood from flowing backward. As the lower chambers contract, they pump blood through the pulmonary and aortic valves. The pulmonary valve opens to allow blood to flow from the right lower chamber into the pulmonary artery. This
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