Blood vessels
Introduced| English | Meaning |
|---|---|
| arteries/ˈɑːtəriz/ | Thick-walled vessels carrying blood away from the heart under high pressure. |
| veins/veɪnz/ | A blood vessel that carries blood towards the heart. |
| capillaries/ˈkæpɪləriz/ | The smallest blood vessels, whose thin walls permit exchange between blood and surrounding tissues. |
Three kinds of pipe
- Blood travels in vessels — but not all vessels are the same.
- Arteries 动脉, veins 静脉 and capillaries 毛细血管 each have a structure that fits their job.
Arteries carry blood:
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Arteries carry blood away from the heart.
The pulmonary artery carries deoxygenated blood, showing "artery = away from heart", not "artery = oxygen-rich".
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Arteries are defined by direction, not oxygen content.
Arteries
- Arteries carry blood away from the heart, usually at high pressure.
- They have thick, muscular, elastic walls to withstand and smooth the pressure.
Arteries, veins and capillaries are each built for their job
The three blood vessels
Compare an artery, a vein and a capillary — their walls and lumens suit the pressure and job of each.
Veins contain valves to:
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Valves keep low-pressure blood moving one way.
Veins
- Veins carry blood back to the heart, at low pressure.
- They have thinner walls and valves to stop blood flowing backwards.
A scanning electron micrograph of blood: biconcave red cells, two rounded white cells and small platelets
Capillary walls are one cell thick so that:
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Thin walls allow exchange of oxygen, glucose and waste.
The smallest blood vessels, where exchange happens, are the ______.
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Capillaries have walls one cell thick.
Capillaries
- Capillaries are tiny vessels with walls one cell thick.
- This lets substances (oxygen, glucose, waste) exchange between blood and cells.
Arteries carry blood away; veins carry it back — regardless of oxygen. The pulmonary artery carries deoxygenated blood (to the lungs), and the pulmonary vein carries oxygenated blood. "Artery = away" is the rule, not "artery = oxygen-rich".
You've got it
- arteries: away from heart, high pressure, thick muscular walls
- veins: back to heart, low pressure, thin walls + valves
- capillaries: one cell thick, for exchange of substances