Flashcards · Biology · The Circulatory System
Blood Vessels
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What is an artery?
A vessel that carries blood away from the heart.
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What is a vein?
A vessel that carries blood back to the heart.
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What is a capillary?
A tiny vessel with a wall one cell thick, where exchange happens.
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Why do arteries have thick walls?
The blood is at high pressure, so the walls must be strong and able to stretch and recoil.
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What are in an artery wall to help it stretch?
Muscle and elastic fibres.
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Why do veins have valves?
To stop the low-pressure blood flowing backwards.
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Why is a vein's lumen wide?
It gives less resistance to the flow of low-pressure blood.
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Why is a capillary wall only one cell thick?
It gives a short diffusion path for exchanging substances.
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Why do capillaries form huge networks?
They give a large surface area for exchange with the cells.
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Does an artery always carry oxygenated blood?
No. The pulmonary artery carries deoxygenated blood to the lungs.
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Does a vein always carry deoxygenated blood?
No. The pulmonary vein carries oxygenated blood from the lungs.
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What is the formula for rate of blood flow?
Rate = volume of blood ÷ time.
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600 cm³ of blood flows through a vessel in 2 minutes. What is the rate?
600 ÷ 2 = 300 cm³ per minute.
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Which vessel type can you feel a pulse in?
An artery.
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Why does blood move slowly through capillaries?
It gives more time for substances to diffuse.
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Name the vessel marked X and say how its structure suits its job. A valve in a vein. It closes to stop blood flowing backwards, because the blood is at low pressure.
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Label the three blood vessels and their features. 
Artery: thick muscular wall, elastic fibres, narrow lumen. Vein: thin wall, wide lumen, valve. Capillary: wall one cell thick.