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Definition
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Term
| Allows the walls to expand rather than burst under the high pressure. Also the recoil action, which follows drop in pressure, causes another surge of pressure that carries blood forward in series of pulses. |
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Definition
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Term
| Provides a tough outer layer that prevents the artery from bursting under the pressure of blood within |
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Definition
| Has no valves except where it leaves the heart because blood is under constant high pressure and so there is no risk of blood flowing backwards. |
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Term
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Definition
| The elastic wall is relatively thin because the low pressure of blood within the vessel will not allow the vessel to burst and the pressure is too low to create a recoil action |
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Term
| The muscular wall is relatively thin because this vessel carries blood away from the tissue and thefore their constriction and dilation cannot control the flow of blood to the tissue |
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Definition
| The collagen fibres provide a tough outer layer in order to prevent the vessels bursting- more from external pressures such as physical forces (they are nearer the skin surface) than from blood pressure within them. |
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Term
| Overall thickness of the wall is small because there is no need for a thick wall as the pressure whithin the vessel is too low to create any risk of bursting. It also allows them to become flattened easily to aid flow of blood. |
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Definition
| There are semi-lunar valves throughout to ensure that the blood does not flow backwards, which it might otherwise tend to do because the pressure is so low. |
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Term
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Definition
| Their walls consist only of enthothelium making them extremely thin. This allows for rapid diffusion of materials between the blood and the cells, due to the short distance over which diffusion take place. |
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Term
| They are numerous and highly branched thus providing a large surface area for diffusion. |
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Definition
| They have a narrow diameter and so permeate tissues, which means that no cell is far from this vessel. |
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Term
| Their lumen is so narrow- around 7um in diameter that red blood cells are squezed flat against the side of this vessel. |
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Definition
| There are spaces (fenestrations) between endothelial cells which allow white blood cells to scape in order to combat infections within tissues. |
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