Capillary connection
Capillaries connect arteries and veins. The wall of each capillary is formed from an ultra-thin layer of flattened cells. This lets gases and nutrients pass easily through the wall. Some capillaries also have pores, called fenestrations, to make the exchange even quicker.
Vein valve
The long veins in the leg have valves to make sure that blood travels up towards the heart and doesn’t fall back down to the feet. When the muscles around the vein contract, they open the valve and push blood upwards. When the surrounding muscles relax, the valves close to stop the blood flowing back down.
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