Investigating the Stretch and Recoil of Arteries and Veins

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Investigating arteries and veins
1.Suspend a ring of artery from a hook on a clamp stand.
2.Use a metre rule to record the length of the ring once the mass carrier has been attached to the free end of the ring. 3. Attach a 10 g mass and record the length of the ring after the mass is added. 4. Remove the mass and record the length of the ring.

5. Repeat steps 2 and 3 using 20, 30, 40 and 50 g masses. Record the length with and without the masses each time.

When comparing the arteries and veins, the results show that the percentage change gradually increases as the amount of weights increases. The vein with mass started off with a small percentage increase of 4%, and then rose to 9%, which was maintained. The artery with mass varied from 10-29%. The artery walls contain collagen and elastic tissues which allow it to stretch and recoil, where as the veins do not have as much connective tissue containing collagen fibres. This is not a problem as the arteries, being closer to the heart, have to withstand a much higher pressure than the veins do. When returning to the original length, the vein without mass increased by 4% then ultimately grew to 9% and the artery without mass varied from 0-10% then back to 0% again. The artery went back to 0% at the end because of its ability to recoil to its original size. This proves that the arteries have more collagen in the muscle walls which allows them to stretch and recoil. The elastic fibres allow the arteries to dilate and constrict. The main properties of the artery are the connective tissue with collagen fibres which make up the outer coat, the smooth muscle and the elastic tissue. This elastic tissue gives the blood vessels their much needed flexibility. Furthermore the artery walls contain a fibre named collagen. Collagen works well with elastic fibres to provide the arteries with firmness and strength. It has a special network structure which gives the protein its unique characteristics. Collagen is a fibrous protein; it has several polypeptide chains which are cross-linked for additional strength. Hydroxyproline is a one of three components of collagen. Hydroxyproline and proline play key roles for collagen stability. They permit the sharp twisting of the collagen helix. The proline residue increases the stability of the collagen triple helix. The amino acid Glycine only accounts for 35% of the sequence. The large amount of smooth muscle in the artery provides it with more elastic tissue for recoiling. There has to be more elasticity in the artery for it to withstand the pressure from the heart. There is a big difference between the arteries with mass to recoil. i.e. 21cm stretched to 27cm, therefore increasing by 6 cm. The recoil is from 27cm to 21 cm, therefore there is 6cm of recoil. Whereas in the vein, the highest stretch was 23cm to 25cm, giving a stretch of 2 cm and its recoil was 0cm. If the vein was put under the same pressure as the artery, it would not be able to tolerate the amount of pressure because it cannot stretch then recoil. The small lumen in the artery means that there is a higher amount of pressure in the lumen compared to the vein. There is a smaller space for the blood to flow through, which increases the pressure. The veins are put under less pressure by the large lumen and the fact that they are situated quite far from the heart. They contain valves to prevent backflow and are surrounded by skeletal muscles to keep the blood moving in the same direction. Capillaries are only one epithelial cell thick. They are tubes of endothelium, freely permeable to small molecules and extremely good at diffusing molecules like oxygen e.g. in the lungs. The exchange of oxygen and carbon dioxide takes place through the thin capillary wall. Capillaries are also involved in releasing heat. For example, during exercise, the body’s temperature rises, the blood delivers the heat to the capillaries which then rapidly release it to the tissue....
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