Elastic recoil in arteries and veins
The objectives of this activity are for you:
Wear eye protection.
Disinfect your work area thoroughly after the procedure.
Dispose of all animal material according to your teacher’s instructions.
Wash your hands thoroughly once your work area is clean.
Take a close look at the artery and vein material. Make notes on their appearance and how each feels to the touch.
Set up a box filled with crumpled paper beneath the apparatus to catch the masses if the tissues break.
Suspend a ring of blood vessel from a paperclip hook on a clamp stand. Attach a mass carrier to the bottom end of the ring. Use a ruler to record the length of the ring of blood vessel with the mass carrier attached. This is the ‘original length’ for the calculation below.
Attach a 10 g mass and record the new length of the blood vessel ring in a suitable table.
Remove the mass and record the length of the ring.
Repeat steps d and e using 20 g, 30 g, 40 g and 50 g masses.
Repeat steps c to f for the other kind of blood vessel.
Calculate percentage change in length as shown here.
% change in length = (new length – original length) x 100
Plot suitable graphs of percentage change in length against mass for each blood vessel as it was loaded, and as it was unloaded.
Use larger masses until the vessel does not return to its original length after loading.
What are the results for artery and vein in terms of a: percentage change in length on loading, and b: return to original length on unloading?
What does this tell you about the elasticity of arteries compared to veins?
Think about what you know about the heart cycle and the function of arteries and veins in the circulatory system. Use this knowledge to explain how a difference in elasticity suits the different functions of arteries and veins.
What observations have you made of the structure of the artery and vein?
Comment on safety precautions you have taken during this procedure.
Evaluate your graph and those of the rest of your class as a means of presenting your results. What features make the graphs easier to interpret?
a: Arteries will usually show a greater percentage increase in length than veins.
b: Arteries will also return closer to the original length than veins.
Arteries have greater elasticity than veins – they stretch more AND return to their original length more readily. Returning to the original length is the defining characteristic of elastic materials.
Arteries are stretched during systole. During diastole, the artery walls recoil, helping to smooth the flow of blood through the vessel. In the venous system, there is no pulse. In order for blood to return to the heart, it is important that veins do not distend when blood enters them.
Students should notice differences in the diameter of the artery and vein, and in the thickness of the wall, the texture and colour of the tissue.
Comments should include: hand washing after handling tissue, disinfection of equipment and bench, care with suspended masses.
Clear graphs will occupy most of the area of the paper, and use colour to distinguish artery from vein and loading from unloading.
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