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• capillaries- these are involved in the exchanges of materials at the tissue
• veins- carry blood to the heart
• arteries carry blood under pressure so their walls are thick, strong and elastic. they contain thick layers of muscle and elastic fibres to allow them to stretch and spring back
• capillaries have thin walls, only one cell thick to allow them to easily diffuse substances. also they are really small
• capillaries join up to form veins
• veins have valves to help blood flow in the right direction
• lumen- holes in veins
• red blood ells carry oxygen
• red blood cells shape is a biconcave disc- this gives it a large surface area for absorbing oxygen
• red blood cells don't have a nucleolus so it has more room for transporting oxygen
• red blood cells contain a red pigment called haemoglobin. in the lungs, haemoglobin binds to oxygen to become oxyhaemoglobin. in body tissues the reverse happens, oxyhaemoglobin splits up into haemoglobin and oxygen to release oxygen