📚 Heart Structure and Function | 心脏的结构与功能
The heart is a vital muscular organ that acts as the body's central pump, driving blood through the circulatory system to deliver oxygen and nutrients while removing waste products. In IGCSE Biology, understanding its structure and how it functions is fundamental to grasping the whole topic of circulation. This article covers the essential knowledge required for the Edexcel specification, from the external appearance to the detailed internal chambers, valves, vessels, and the cardiac cycle, as well as how the heartbeat is controlled and responds to exercise.
心脏是关键的肌肉器官，作为身体的中心泵，推动血液在循环系统中流动，输送氧气和营养物质并带走代谢废物。在IGCSE生物学中，理解心脏的结构及其功能是掌握整个循环主题的基础。本文涵盖了Edexcel考纲要求的核心知识，从外观到内部腔室、瓣膜、血管、心动周期，以及心跳如何被调控和如何响应运动。
1. External Structure and Pericardium | 外部结构与心包
The heart is located in the thoracic cavity, between the lungs and slightly to the left of the midline. It is roughly the size of a clenched fist. Externally, the heart is surrounded by a double-layered membrane called the pericardium. The inner layer (visceral pericardium) adheres tightly to the heart muscle, while the outer layer (parietal pericardium) forms a tough protective sac. Between the two layers is a small amount of pericardial fluid, which acts as a lubricant, reducing friction as the heart beats.
心脏位于胸腔内，两肺之间，略偏向身体中线左侧，大约有握紧的拳头那么大。心脏外部被一层称为心包的双层膜包裹。内层（脏层心包）紧贴心肌肉，而外层（壁层心包）形成一个坚韧的保护囊。两层之间有少量心包液，起到润滑剂的作用，减少心脏跳动时的摩擦。
The main mass of the heart is composed of cardiac muscle, a specialised involuntary muscle tissue that can contract rhythmically without fatigue. The outer surface also shows grooves that mark the boundaries of internal chambers and contain the coronary blood vessels, which supply the heart muscle itself with oxygen and nutrients.
心脏的主体由心肌构成，这是一种特化的不随意肌组织，能够有节律地收缩而不易疲劳。外表面还可见到一些沟，标示着内部腔室的边界，并容纳冠状动脉血管，为心肌自身提供氧气和营养。
2. The Four Chambers | 四个腔室
The human heart has four chambers: two upper atria (singular: atrium) and two lower ventricles. The right atrium receives deoxygenated blood from the body through the superior and inferior vena cavae, while the left atrium receives oxygenated blood from the lungs via the pulmonary veins. The atria are thin-walled chambers because they only need to push blood down into the adjacent ventricles over a short distance.
人类心脏有四个腔室：两个上部的心房和两个下部的心室。右心房通过上腔静脉和下腔静脉接受来自全身的脱氧血，左心房通过肺静脉接受来自肺部的富氧血。心房壁较薄，因为它们只需将血液推送一小段距离进入下方的心室即可。
The ventricles are much thicker and more muscular. The right ventricle pumps deoxygenated blood to the lungs through the pulmonary artery, while the left ventricle pumps oxygenated blood to the rest of the body through the aorta. Because the left ventricle must generate enough pressure to overcome the higher resistance of the systemic circulation, its muscular wall is about three times thicker than that of the right ventricle.
心室壁更厚，肌肉更发达。右心室将脱氧血经肺动脉泵入肺部，而左心室将富氧血经主动脉泵往全身。由于左心室必须产生足够的压力来克服体循环较高的阻力，其肌肉壁大约是右心室的三倍厚。
3. Blood Vessels Connected to the Heart | 连接心脏的血管
Five major blood vessels are directly connected to the heart. The superior and inferior vena cavae bring deoxygenated blood from the upper and lower parts of the body into the right atrium. The pulmonary veins (typically four) carry oxygenated blood from the lungs into the left atrium. The pulmonary artery leaves the right ventricle to carry deoxygenated blood to the lungs – note that it is the only artery in the body that carries deoxygenated blood. The aorta, the largest artery, emerges from the left ventricle and distributes oxygenated blood to all body tissues.
五条主要血管直接与心脏相连。上腔静脉和下腔静脉将身体上部和下部的脱氧血带回右心房。肺静脉（通常有四条）将来自肺部的富氧血送入左心房。肺动脉从右心室发出，将脱氧血运往肺部——注意，这是人体内唯一输送脱氧血的动脉。主动脉是最大的动脉，从左心室发出，将富氧血分配至全身所有组织。
A simple table can help you remember the relationships:
一个简单的表格有助于记忆这些关系：
| Blood vessel 血管 | Connected chamber 连接腔室 | Blood type 血液类型 |
|---|---|---|
| Superior / Inferior vena cava 上/下腔静脉 | Right atrium 右心房 | Deoxygenated 脱氧血 |
| Pulmonary veins 肺静脉 | Left atrium 左心房 | Oxygenated 富氧血 |
| Pulmonary artery 肺动脉 | Right ventricle 右心室 | Deoxygenated 脱氧血 |
| Aorta 主动脉 | Left ventricle 左心室 | Oxygenated 富氧血 |
4. Valves of the Heart | 心脏瓣膜
The heart contains four valves that ensure unidirectional blood flow and prevent backflow. The two atrioventricular (AV) valves lie between the atria and ventricles. The right AV valve is called the tricuspid valve because it has three flaps, while the left AV valve is the bicuspid (or mitral) valve, having two flaps. These valves are anchored by chordae tendineae (tendinous cords) to papillary muscles in the ventricle walls, which prevent the valve flaps from inverting during ventricular contraction.
心脏内有四个瓣膜，保证血液单向流动并防止倒流。两个房室瓣位于心房和心室之间。右房室瓣称为三尖瓣，因为它有三个瓣叶；左房室瓣是二尖瓣，有两个瓣叶。这些瓣膜由腱索连接到心室壁上的乳头肌，从而防止心室收缩时瓣膜翻转。
The two semilunar valves are located at the exits of the ventricles. The pulmonary semilunar valve sits at the entrance of the pulmonary artery, and the aortic semilunar valve at the entrance of the aorta. Shaped like half-moons, these valves open when ventricular pressure exceeds arterial pressure and snap shut when the ventricles relax, preventing blood from flowing back into the heart.
两个半月瓣位于心室出口处。肺动脉半月瓣位于肺动脉入口，主动脉半月瓣位于主动脉入口。它们形如半月，当心室内压高于动脉压力时打开，心室舒张时迅速关闭，防止血液倒流回心脏。
5. The Cardiac Cycle – How the Heart Pumps | 心动周期——心脏如何泵血
The cardiac cycle refers to the sequence of events in one complete heartbeat. It consists of three stages: atrial systole, ventricular systole, and diastole. During atrial systole, the atria contract, pushing blood through the open AV valves into the relaxed ventricles. The semilunar valves remain closed at this stage.
心动周期指一次完整心跳中的事件序列，包括三个阶段：心房收缩期、心室收缩期和舒张期。心房收缩时，心房收缩，将血液通过打开的房室瓣推入舒张的心室，此时半月瓣保持关闭。
Ventricular systole follows, in which the ventricles contract strongly. The rising pressure inside the ventricles forces the AV valves to snap shut (producing the first heart sound, 'lub'), and shortly afterwards the semilunar valves open, ejecting blood into the pulmonary artery and aorta. Finally, during diastole, both atria and ventricles relax. The semilunar valves close to prevent backflow (producing the second heart sound, 'dub'), and the atria begin to fill with blood again. The pressure in the ventricles falls below that in the atria, causing the AV valves to reopen, and the cycle repeats.
随后是心室收缩期，心室强力收缩。心室内升高的压力迫使房室瓣猛然关闭（产生第一心音“lub”），片刻后半月瓣打开，将血液射入肺动脉和主动脉。最后，在舒张期，心房和心室均舒张。半月瓣关闭以防止倒流（产生第二心音“dub”），心房重新开始充满血液。心室内压降至低于心房内压，房室瓣重新打开，周而复始。
The whole cycle typically lasts about 0.8 seconds at a resting heart rate of 75 beats per minute, with diastole being the longest phase, allowing the coronary circulation to perfuse the heart muscle.
整个周期在静息心率75次/分时大约持续0.8秒，其中舒张期最长，有利于冠状动脉对心肌进行灌注。
6. The Pacemaker and Electrical Control | 起搏器与电控系统
The heart can beat independently of the nervous system because it contains its own intrinsic pacemaker – the sinoatrial node (SAN), located in the wall of the right atrium. The SAN initiates an electrical impulse that spreads across the atria, causing them to contract. The impulse then reaches the atrioventricular node (AVN) at the base of the right atrium, where it is delayed slightly to allow the ventricles to fill fully before they contract.
心脏可以不依赖于神经系统自主跳动，因为它有自己的内在起搏器——窦房结（SAN），位于右心房壁。窦房结发出电脉冲，向心房传播，导致心房收缩。脉冲随后传至位于右心房底部的房室结（AVN），在此稍有延迟，以确保心室在收缩前被完全充盈。
From the AVN, the impulse travels along the bundle of His and through Purkinje fibres within the interventricular septum and ventricle walls, triggering coordinated ventricular contraction from the apex upwards. This electrical conduction system ensures that the heart chambers contract in the correct sequence and with maximum efficiency.
由房室结开始，脉冲沿希氏束及浦肯野纤维传导，通过室间隔和心室壁，引发从心尖向上的协调性心室收缩。这种传导系统确保了心脏各腔室按正确顺序且高效地收缩。
7. Heart Rate and Its Regulation | 心率及其调节
Although the SAN sets the basic rhythm of the heart, the rate can be modified by the autonomic nervous system and hormones. The sympathetic nerve releases noradrenaline, which increases heart rate and the force of contraction, preparing the body for 'fight or flight'. The parasympathetic nerve (vagus nerve) releases acetylcholine, which slows the heart rate, promoting a 'rest and digest' state.
尽管窦房结构建了心脏的基础节律，但心率可被自主神经系统和激素调节。交感神经释放去甲肾上腺素，提高心率和收缩力，使身体进入“战斗或逃跑”状态。副交感神经（迷走神经）释放乙酰胆碱，减慢心率，促进“休息与消化”状态。
The hormone adrenaline, produced by the adrenal glands, also binds to receptors on the SAN and cardiac muscle cells, increasing heart rate and stroke volume. This explains why heart rate rises during excitement, stress, or in preparation for physical activity. The normal resting heart rate for an adult is 60–100 beats per minute, which can increase to well over 150 bpm during vigorous exercise.
肾上腺分泌的激素肾上腺素也可与窦房结和心肌细胞上的受体结合，提高心率和每搏输出量。这就解释了为什么在兴奋、紧张或准备运动时心率会加快。正常成人静息心率为60–100次/分，剧烈运动时可升至150次/分以上。
8. Coronary Blood Supply | 冠状动脉供血
The heart muscle, like any other tissue, needs its own blood supply. This is provided by the coronary arteries, which branch off from the base of the aorta just above the aortic semilunar valve. The left and right coronary arteries run over the surface of the heart, penetrating into the muscle to deliver oxygen and nutrients to the cardiac cells. Deoxygenated blood is collected by coronary veins and drains into the right atrium via the coronary sinus.
心肌与任何其他组织一样，需要自身的血液供应。这由冠状动脉提供，它们从主动脉瓣上方的主动脉基部发出。左、右冠状动脉沿心脏表面走行，分支穿入心肌，为心肌细胞输送氧气和养分。脱氧血由冠状静脉收集，经冠状窦汇入右心房。
Blockage of a coronary artery by a blood clot or fatty plaque can starve a region of heart muscle of oxygen, leading to a heart attack (myocardial infarction). This is why a healthy diet and regular exercise are essential to keep these vessels clear.
冠状动脉被血栓或脂质斑块阻塞可使部分心肌缺氧，引发心脏病发作（心肌梗死）。因此，健康饮食和规律运动对保持这些血管畅通至关重要。
9. Comparing Left and Right Sides of the Heart | 左右心对比
A common exam question asks students to compare the left and right sides of the heart. The key differences arise because the right side pumps blood only to the nearby lungs (pulmonary circulation), while the left side pumps blood to the entire body (systemic circulation). As a result, the left ventricle has a much thicker muscular wall, generating higher pressure. The left AV valve is bicuspid, while the right is tricuspid; both prevent backflow during ventricular systole.
常见的考题要求学生比较心脏的左右两侧。关键差异在于，右侧仅将血液泵往近处的肺部（肺循环），而左侧将血液泵往全身（体循环）。因此，左心室壁较厚，产生的压力较高。左房室瓣为二尖瓣，右为三尖瓣；两者都在心室收缩时防止血液倒流。
Furthermore, the blood carried by the pulmonary artery is deoxygenated, while the aorta carries oxygenated blood. Students often confuse this, but remembering that arteries carry blood away from the heart, and the pulmonary artery takes deoxygenated blood to the lungs, will clarify the concept.
此外，肺动脉输送的是脱氧血，而主动脉输送的是富氧血。学生经常混淆这一点，但记住动脉是把血液带离心脏的血管，而肺动脉是把脱氧血带到肺部，就能澄清概念。
10. Key Points Summary | 重点总结
Here is a recap of the most important points about heart structure and function for IGCSE Biology:
以下是IGCSE生物学中心脏结构与功能最重要的知识点回顾：
- Four chambers 四个腔室: Right atrium, right ventricle, left atrium, left ventricle. 右心房、右心室、左心房、左心室。
- Major vessels 主要血管: Vena cavae → right atrium; pulmonary veins → left atrium; pulmonary artery ← right ventricle; aorta ← left ventricle. 腔静脉→右心房；肺静脉→左心房；肺动脉←右心室；主动脉←左心室。
- Valves 瓣膜: Tricuspid (right AV), bicuspid/mitral (left AV), pulmonary and aortic semilunar valves. Prevent backflow. 三尖瓣（右房室瓣）、二尖瓣（左房室瓣）、肺动脉瓣和主动脉半月瓣。防止倒流。
- Cardiac cycle 心动周期: Atrial systole → ventricular systole → diastole. 'lub-dub' sounds caused by valve closures. 心房收缩→心室收缩→舒张期。心音“lub-dub”由瓣膜关闭产生。
- Pacemaker 起搏器: SAN in right atrium initiates heartbeat; AVN delays impulse; bundle of His and Purkinje fibres spread it. 窦房结位于右心房，发出心跳起始冲动；房室结延迟冲动；希氏束和浦肯野纤维传导。
- Control of heart rate 心率控制: Sympathetic nerve (noradrenaline) increases rate; parasympathetic (acetylcholine) decreases; hormone adrenaline boosts rate and force. 交感神经（去甲肾上腺素）升心率；副交感神经（乙酰胆碱）降心率；激素肾上腺素提高心率和收缩力。
- Coronary circulation 冠状循环: Coronary arteries supply O₂ to heart muscle; blockages can cause myocardial infarction. 冠状动脉为心肌供氧；阻塞可导致心肌梗死。
- Left vs right 左心对比右心: Left ventricle wall thicker, pumps blood further, generates higher pressure. 左心室壁更厚，泵血距离更远，产生压力更高。
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