📚 The Heart and Circulation | 心脏与血液循环
The human circulatory system is a closed network of blood vessels, a muscular pump and transport medium that ensures every cell receives oxygen and nutrients while removing waste products. In the Edexcel IGCSE Science specification, understanding the structure of the heart, the path of blood through the chambers, the roles of arteries, veins and capillaries, and how cardiac output responds to exercise forms the foundation for topics on health, disease and lifestyle choices.
人体循环系统是由血管、肌肉泵和运输介质组成的封闭网络，确保每个细胞获得氧气和营养，同时清除废物。在爱德思 IGCSE 科学大纲中，理解心脏结构、血液在心腔内的流动路径、动脉、静脉和毛细血管的作用，以及心输出量如何随运动而变化，是学习健康、疾病和生活方式选择等主题的基础。
1. The Heart as a Double Pump | 作为双重泵的心脏
The mammalian heart is a four-chambered organ that acts as two pumps working side by side. The right side pumps deoxygenated blood to the lungs through the pulmonary circulation, while the left side pumps oxygenated blood to the rest of the body through the systemic circulation. This separation prevents mixing of oxygen-rich and oxygen-poor blood, making oxygen delivery highly efficient – a feature essential for maintaining a high metabolic rate in warm-blooded organisms.
哺乳动物的心脏是一个四腔器官，相当于两个并排工作的泵。右侧将缺氧血泵入肺部，完成肺循环；左侧将富氧血泵至全身，完成体循环。这种分隔防止了富氧血与缺氧血的混合，使氧气输送变得高效，这是恒温动物维持高代谢率的关键特征。
2. Chambers and Valves | 心腔与瓣膜
The upper chambers, called atria (singular: atrium), receive blood returning to the heart. The right atrium collects deoxygenated blood from the body via the vena cava, while the left atrium receives oxygenated blood from the lungs through the pulmonary veins. Below them are the thick-walled ventricles, which contract to force blood out of the heart. The right ventricle pumps blood into the pulmonary artery, and the left ventricle, with the thickest muscular wall, pushes blood into the aorta and around the whole body.
上部腔室称为心房（单数：atrium），接收回心血液。右心房通过腔静脉收集来自全身的缺氧血，左心房通过肺静脉接收来自肺部的富氧血。下方是壁厚的心室，收缩时将血液泵出心脏。右心室将血液泵入肺动脉，左心室肌肉壁最厚，将血液推入主动脉并循环至全身。
Four valves keep blood flowing in one direction. The atrioventricular valves (tricuspid on the right, bicuspid or mitral on the left) prevent backflow from ventricles to atria during ventricular contraction. The semilunar valves (pulmonary and aortic) stop blood from flowing back into the ventricles when they relax. The ‘lub-dub’ heart sounds are produced when these valves snap shut.
四个瓣膜确保血液单向流动。房室瓣（右侧三尖瓣，左侧二尖瓣）在心室收缩时防止血液回流至心房。半月瓣（肺动脉瓣和主动脉瓣）在心室舒张时阻止血液倒流回心室。“咚哒”心音正是这些瓣膜关闭时发出的。
3. The Cardiac Cycle | 心动周期
The cardiac cycle consists of three main stages: atrial systole, ventricular systole and diastole. During diastole, both atria and ventricles relax, and blood flows passively into the atria and through the open atrioventricular valves into the ventricles. Atrial systole then contracts the atria, forcing any remaining blood into the ventricles. Ventricular systole follows; the ventricles contract, building pressure that slams the atrioventricular valves shut (‘lub’), opens the semilunar valves, and ejects blood into the arteries. As the ventricles relax, the semilunar valves snap shut (‘dub’) to prevent backflow.
心动周期包括三个主要阶段：心房收缩期、心室收缩期和舒张期。舒张期时，心房和心室均舒张，血液被动流入心房，并通过开启的房室瓣进入心室。随后心房收缩，将剩余血液挤入心室。接着是心室收缩，心室内压力升高，房室瓣猛然关闭（“咚”声），半月瓣打开，血液被射入动脉。当心室舒张时，半月瓣迅速关闭（“哒”声）以防止回流。
Cardiac output (cm³ min⁻¹) = heart rate (beats min⁻¹) × stroke volume (cm³ beat⁻¹)
心输出量（cm³ min⁻¹）= 心率（次 min⁻¹）× 每搏输出量（cm³ beat⁻¹）
4. Blood Vessels | 血管类型
Arteries carry blood away from the heart under high pressure, so their walls are thick, elastic and muscular. The largest artery, the aorta, can stretch and recoil to maintain pressure. Veins return blood to the heart at lower pressure; they have wider lumens and thinner walls, and many contain valves that prevent backflow. Capillaries are microscopic vessels only one cell thick, allowing efficient exchange of gases, nutrients and waste between blood and tissues by diffusion.
动脉将血液带离心脏，承受高压，因此管壁厚、富有弹性和肌肉。最大的动脉——主动脉可以扩张和回缩以维持血压。静脉将血液送回心脏，压力较低，管腔较宽，管壁较薄，许多静脉含有防止回流的瓣膜。毛细血管是直径仅有一层细胞厚的微小血管，通过扩散作用有效实现血液与组织之间的气体、营养物质和废物交换。
The table below summarises key structural and functional differences.
下表总结了关键的结构与功能差异。
| Feature | Artery | Vein | Capillary |
|---|---|---|---|
| Direction of blood flow | Away from heart | Towards heart | From arteries to veins |
| Pressure | High | Low | Decreasing |
| Wall thickness | Thick, muscular, elastic | Thin, less muscle | One cell thick |
| Valves | None (except semilunar) | Present | None |
| Lumen | Narrow | Wide | Very narrow, one red blood cell at a time |
The structural features of each vessel are directly related to its function. For example, the thick elastic wall of an artery withstands pressure pulses, while the thin wall of a capillary minimises the diffusion distance for efficient exchange.
每种血管的结构特征与其功能直接相关。例如，动脉厚实的弹性管壁可以承受压力搏动，而毛细血管极薄的壁则最大限度地缩短扩散距离，实现高效交换。
5. Composition of Blood | 血液的组成
Blood is a specialised connective tissue made up of plasma, red blood cells, white blood cells and platelets. Plasma is a straw-coloured liquid that transports dissolved nutrients such as glucose and amino acids, hormones, carbon dioxide, urea and heat. Red blood cells (erythrocytes) are biconcave discs that lack a nucleus, packed with the protein haemoglobin, which binds oxygen in the lungs and releases it in respiring tissues. White blood cells (leucocytes) are part of the immune system, defending the body against pathogens through phagocytosis and antibody production. Platelets are tiny cell fragments that initiate blood clotting at wound sites.
血液是一种特殊的结缔组织，由血浆、红细胞、白细胞和血小板组成。血浆是一种淡黄色液体，运输溶解的营养物质如葡萄糖和氨基酸、激素、二氧化碳、尿素和热量。红细胞（erythrocytes）呈双凹圆盘状，无细胞核，富含血红蛋白，后者在肺部结合氧气，并在呼吸组织处释放氧气。白细胞（leucocytes）属于免疫系统，通过吞噬作用和产生抗体来抵御病原体。血小板是微小的细胞碎片，能在伤口处启动血液凝固过程。
The equation for oxygen transport can be represented simply: haemoglobin + O₂ ⇌ oxyhaemoglobin. This reversible reaction allows loading in high oxygen partial pressures (lungs) and unloading where oxygen pressure is low (active muscles).
氧的运输过程可用简单方程式表示：血红蛋白 + O₂ ⇌ 氧合血红蛋白。这一可逆反应使得在氧分压高的地方（肺部）负载氧气，在氧分压低的地方（活跃肌肉）释放氧气。
6. Coronary Circulation | 冠状循环
The heart is a tirelessly working muscle, and it requires its own blood supply. The coronary arteries branch from the base of the aorta and deliver oxygenated blood directly to the heart muscle (myocardium). If these arteries become narrowed or blocked by fatty deposits (plaques), the cardiac muscle is starved of oxygen, leading to chest pain (angina) or a heart attack (myocardial infarction). The coronary veins drain deoxygenated blood into the right atrium.
心脏是一块不知疲倦的肌肉，需要自身的血液供应。冠状动脉从主动脉基部分出，将富氧血直接送往心肌（myocardium）。如果这些动脉因脂肪沉积（斑块）变得狭窄或堵塞，心肌会缺氧，导致胸痛（心绞痛）或心脏病发作（心肌梗死）。冠状静脉则将缺氧血导入右心房。
7. Heart Rate and Exercise | 心率与运动
During physical activity, muscles respire more rapidly, demanding extra oxygen and glucose while producing more carbon dioxide. The body responds by increasing heart rate and stroke volume, thereby raising cardiac output. Adrenaline, released from the adrenal glands, stimulates the sinoatrial node (the heart’s natural pacemaker) to increase the frequency of electrical impulses. The heart pumps faster and more forcefully, redirecting blood flow away from the digestive system to working muscles.
在体育运动时，肌肉呼吸作用加快，需要更多氧气和葡萄糖，同时产生更多二氧化碳。人体通过增加心率和每搏输出量来做出反应，从而提高心输出量。肾上腺释放的肾上腺素会刺激窦房结（心脏的天然起搏器）增加电脉冲频率。心脏跳动更快、更有力，将血液从消化系统重新分配至工作肌肉。
A fit individual typically has a lower resting heart rate and a larger stroke volume, meaning their heart works more efficiently. The recovery time – how quickly the heart rate returns to normal after exercise – is a useful indicator of cardiovascular fitness.
身体强健者通常静息心率较低，每搏输出量较大，这意味着他们的心脏工作效率更高。恢复时间——运动后心率恢复正常的快慢——是衡量心血管健康的有用指标。
8. Cardiovascular Disease | 心血管疾病
Coronary heart disease (CHD) is a major cause of death worldwide. It is often linked to lifestyle factors such as a diet high in saturated fat and cholesterol, smoking, lack of exercise and excessive alcohol consumption. Cholesterol carried by low-density lipoproteins (LDL) contributes to the formation of atheromas – fatty streaks in the artery wall. Over time, these can harden into plaques, narrowing the lumen and making the artery less elastic. If a plaque ruptures, a blood clot (thrombus) may form, completely blocking the artery and causing a heart attack.
冠心病（CHD）是全球主要的死亡原因之一，通常与生活习惯有关，如高饱和脂肪和高胆固醇饮食、吸烟、缺乏运动以及过量饮酒。低密度脂蛋白（LDL）运载的胆固醇会促进动脉壁中粥样斑块的形成。随着时间推移，这些斑块可能硬化，使管腔变窄，动脉弹性下降。如果斑块破裂，可能形成血栓（thrombus），完全堵塞动脉，导致心肌梗死。
Treatments include lifestyle changes, medication such as statins to lower cholesterol, and surgical interventions like angioplasty (inserting a stent) or coronary artery bypass grafting. The Edexcel IGCSE specification encourages students to evaluate the risks and benefits of such treatments.
治疗方法包括生活方式改变、药物（如他汀类药物降低胆固醇）以及手术干预，如血管成形术（植入支架）或冠状动脉搭桥术。爱德思 IGCSE 课程鼓励学生评估这些治疗的风险和益处。
9. Maintaining Heart Health | 维护心脏健康
Prevention is always better than cure. A balanced diet rich in fruits, vegetables, whole grains and unsaturated fats helps control body mass and blood cholesterol. Regular aerobic exercise strengthens the heart, lowers resting heart rate and improves circulation. Avoiding smoking reduces the concentration of carbon monoxide in the blood, which would otherwise combine permanently with haemoglobin, reducing oxygen-carrying capacity. Monitoring blood pressure, managing stress and moderating salt intake all contribute to a healthy cardiovascular system.
预防总是胜于治疗。富含水果、蔬菜、全谷物和不饱和脂肪的均衡饮食有助于控制体重和血胆固醇水平。定期进行有氧运动可以增强心脏功能，降低静息心率，并改善循环。远离吸烟能减少血液中的一氧化碳浓度，否则一氧化碳会与血红蛋白永久结合，降低携氧能力。监测血压、管理压力和适量摄取盐分都有助于维持心血管系统健康。
10. Key Connections and Exam Focus | 核心关联与考试重点
In the Edexcel IGCSE Double Science papers, heart and circulation questions often combine with topics like respiration, gas exchange, homeostasis and immunology. You may be asked to interpret data from an ECG trace or a graph showing heart rate changes during exercise. Be prepared to apply the cardiac output formula, explain valve action using pressure differences, and discuss the consequences of artery blockage. Linking the structure of red blood cells to their function – no nucleus, biconcave shape, full of haemoglobin – is a classic mark-earner.
在爱德思 IGCSE 双科学考试中，心脏和循环系统问题常与呼吸作用、气体交换、稳态和免疫学等主题结合起来考查。考生可能需要解读心电图迹线或运动期间心率变化图。要做好准备运用心输出量公式、运用压力差解释瓣膜作用、并讨论动脉堵塞的后果。将红细胞的结构（无核、双凹形、富含血红蛋白）与其功能联系起来是经典的得分要点。
Remember to use precise terminology: sinoatrial node, atrioventricular valves, pulmonary vein (note it carries oxygenated blood), pulmonary artery (carries deoxygenated blood), and so on. Drawing a simple flow diagram of the circulatory route is always helpful.
记住使用精确术语：窦房结、房室瓣、肺静脉（注意其运输的是富氧血）、肺动脉（运输缺氧血）等等。画一张简单的循环路径流程图总是有帮助的。
Published by TutorHao | IGCSE Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导