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.
Veins carry blood at low pressure, so they contain valves to stop it flowing backwards.
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Low-pressure blood could flow back, so valves keep it moving one way toward the heart.
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