The circulatory system
Introduced| English | Meaning |
|---|---|
| closed double circulation/kləʊzd ˈdʌbl ˌsɜːkjʊˈleɪʃn/ | Blood in vessels, through the heart twice. |
| pulmonary circulation/ˈpʌlmənəri ˌsɜːkjʊˈleɪʃn/ | The blood pathway from the right ventricle through the lungs and back to the left atrium. |
| systemic circulation/sɪˈstemɪk ˌsɜːkjʊˈleɪʃn/ | The blood pathway from the left ventricle through the body tissues and back to the right atrium. |
| vein/veɪn/ | A blood vessel that carries blood towards the heart. |
| artery/ˈɑːtəri/ | A thick-walled vessel carrying blood away from the heart under high pressure. |
| aorta/eɪˈɔːtə/ | The largest artery, carrying oxygenated blood from the left ventricle to the body. |
| lumen/ˈluːmen/ | The internal space of a tube, vessel or membrane-bound structure. |
| capillary/kəˈpɪləri/ | A very small blood vessel with thin walls that allow exchange between blood and tissues. |
The body's transport network
- Mammals have a closed double circulation 闭锁双循环.
- Closed: blood stays inside vessels the whole time.
- Double: blood passes through the heart twice per full trip.
A "closed double circulation" means that:
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Closed = blood always in vessels; double = it passes through the heart twice (pulmonary then systemic).
Two loops
- The pulmonary circulation 肺循环 carries blood from the heart to the lungs and back.
- The systemic circulation 体循环 carries blood from the heart to the rest of the body and back.
- Blood flows: arteries → arterioles → capillaries → venules → veins 静脉.
Closed double circulation through the heart, lungs and body
Double circulation
Follow one red blood cell around the loop. It passes through the heart twice each circuit — once to the lungs, once to the body.
The circulation that carries blood from the heart to the lungs and back is the ______ circulation.
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Pulmonary = to the lungs; systemic = to the rest of the body.
The main vessels
- pulmonary artery 动脉 — heart → lungs (low oxygen).
- pulmonary vein — lungs → heart (oxygen-rich).
- aorta 主动脉 — heart → body (oxygen-rich).
- vena cava — body → heart (oxygen-poor).
Vessels suited to their jobs
| Vessel | Structure | Function |
|---|---|---|
| artery | thick muscle + elastic wall, narrow lumen 管腔 | high-pressure flow away from heart; walls recoil to smooth flow |
| capillary 毛细血管 | wall just one cell thick | short distance for exchange with cells |
| vein | thin wall, wide lumen, valves | low-pressure return to heart; valves stop backflow |
Cross-sections of an artery (thick wall), vein (wide lumen, valves) and capillary (one cell thick)
Match each vessel to its feature.
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Arteries carry high-pressure blood away; veins return it (valves stop backflow); capillaries are where exchange happens.
Arteries have thick, elastic, muscular walls because they:
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High-pressure blood leaving the heart needs strong walls that stretch and recoil to smooth the flow.
Arteries contain valves because their blood is at low pressure.
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False. Veins carry blood at low pressure and contain valves to stop backflow. Arteries carry high-pressure blood and have no valves along their length.
A capillary wall is just one cell thick because this:
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A one-cell-thick wall means a short diffusion distance, so substances exchange quickly.
You've got it
- closed double circulation: blood in vessels, through the heart twice
- pulmonary loop = lungs; systemic loop = body
- artery: thick wall, high pressure, away from heart; vein: valves, low pressure, back to heart
- capillary: one cell thick → fast exchange
Write from arteries leaving the heart
- Blood leaves the heart under pressure.
- It later returns at lower pressure.
Which vessels carry blood away from the heart?
Artery means away from the heart in this course.
Which vessels leave the heart?
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Arteries carry blood away. Veins bring it back.