- Every cell in the body needs oxygen in order to respire.
- Oxygenated blood is carried within the arteries this is generally the flow of blood going away from the heart, the exception being the Pulmonary Artery.
- When the blood leaves the heart it is under very high pressure and arteries need to be string enough to contain the high pressure blood.
- In order to do this the Arteries have thick muscular walls with elastic fibres to withstand the pressure which recalls as the heart beats.
- The Arteries have a small lumen compared to that of a vein, maintaining a high blood pressure.
- The walls surrounding the lumen are made up of layers of muscle and elastic fibre.
- The total diameter of the artery is large comapared to a vein.
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- Arterioles are able to control blood flow by restricting and opening the lumen.
- The muscle layer is thicker than in the Arteries:
- when the muscle contracts in the Arterioles, the lumen constricts and blood flow becomes restricted.
- The elastic layer is thinnner than in the Arteries:
- there is lower blood pressure in Arterioles so does not need to expand as much.
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- Veins carry deoxygenated blood, generally back towards the heart with exception to the pulmonary vein.
- Veins have thinner walls that are flexible and can expand holding large volumes of blood.
- The blood contained within the veins is at a much lower pressure than in the Arteries.
- Veins that run within or close to skeletal muscles have blood squezed as the muscles contract.
- Movement of the blood is assited by valves which prevent backflow of blood.
- Veins have a very large lumen and thin walls surrounding the lumen.
- there are valves within the veins preventing back flow.
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- Arteries and veins are linked by a series of capillaries.
- These are tiny blood vessels with walls one cell thick, to allow exchange of oxygen, carbon dioxide, nutrients and waste between the blood and tissue.
- The capillary walls have small pores in the wall through which tissue fluid and White blood cells can pass.
- Diffusion of lipid soluble subtances passes through the plasma membrane.
- Diffusion of lipid Insoluble substances passes though pores in capillary wall.
- Bulk flow of water with dissolved substances also passes though pores in capillary walls.
- Osmosis of water passes out of the capilary.
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