📚 The Heart | 心脏
The mammalian heart is a muscular pump that drives blood around the double circulatory system. Understanding its structure, electrical activity and mechanical events is central to A-Level CIE Biology, and exam questions often ask you to link pressure changes to valve movements.
哺乳动物的心脏是一个肌肉泵，推动血液在双循环系统中流动。理解其结构、电活动和机械事件是 A-Level CIE 生物的核心，考题常要求学生将压力变化与瓣膜开闭联系起来。
1. Gross Structure of the Heart | 心脏的大体结构
The heart lies in the thoracic cavity, protected by the pericardium, a double-walled sac containing a small amount of fluid to reduce friction during beating.
心脏位于胸腔内，由心包保护；心包是双层囊，内含少量液体以减少跳动时的摩擦。
Internally, a muscular septum divides the heart into left and right sides. The atria are thin-walled receiving chambers, while the ventricles have much thicker muscular walls because they generate the pressure that pumps blood to the lungs or the whole body.
内部有肌性室间隔将心脏分为左、右两侧。心房是壁较薄的接受腔室，而心室肌壁厚得多，因为它们要产生将血液泵入肺或全身的压力。
The left ventricular wall is thicker than the right ventricular wall. This is because the left ventricle pumps blood through the systemic circulation at high pressure, whereas the right ventricle only pumps blood to the nearby lungs at lower pressure.
左心室壁比右心室壁更厚。因为左心室需在高压下将血液泵入体循环，而右心室仅以较低压力将血液泵入较近的肺循环。
2. Chambers and Associated Blood Vessels | 心腔与相连血管
The right atrium receives deoxygenated blood from the superior and inferior vena cavae and from the coronary sinus. The right ventricle then sends this blood to the lungs through the pulmonary artery.
右心房接受来自上腔静脉、下腔静脉和冠状窦的缺氧血。右心室随后将这部分血液经肺动脉送入肺。
The left atrium receives oxygenated blood from the four pulmonary veins. The left ventricle pumps this blood into the aorta, which distributes it to the systemic circulation.
左心房接受来自四条肺静脉的富氧血。左心室将这些血液泵入主动脉，再分配到体循环。
This double circulation separates oxygenated and deoxygenated blood, allowing the systemic circuit to be supplied at a higher pressure than the pulmonary circuit.
这种双循环将富氧血与缺氧血分开，使体循环能在高于肺循环的压力下获得血液供应。
3. Valves Prevent Backflow | 瓣膜防止血液倒流
The atrioventricular valves lie between the atria and ventricles. The tricuspid valve is on the right side and has three flaps; the bicuspid or mitral valve is on the left side and has two flaps.
房室瓣位于心房与心室之间。三尖瓣在右侧，有三个瓣叶；二尖瓣在左侧，有两个瓣叶。
The semilunar valves are located at the bases of the pulmonary artery and aorta. They open when ventricular pressure exceeds arterial pressure, and close when arterial pressure exceeds ventricular pressure, preventing backflow into the ventricles.
半月瓣位于肺动脉和主动脉根部。当心室压力高于动脉压力时打开；当动脉压力高于心室压力时关闭，防止血液倒流入心室。
The atrioventricular valve flaps are attached to papillary muscles by tendinous cords. These cords prevent the valves from turning inside out during ventricular systole.
房室瓣瓣叶通过腱索连接到乳头肌。腱索可防止心室收缩时瓣膜翻转。
4. Properties of Cardiac Muscle | 心肌的特性
Cardiac muscle is myogenic, meaning it can contract and relax without nervous stimulation. It is striated, branched, and contains intercalated discs that allow rapid spread of electrical impulses between cells.
心肌是肌源性的，即无需神经刺激即可收缩和舒张。心肌有横纹、呈分支状，并含闰盘，可使电冲动在细胞间快速传播。
Cardiac muscle cells contain many mitochondria and a good blood supply through the coronary arteries, supporting continuous aerobic respiration. Blockage of a coronary artery can deprive heart muscle of oxygen and cause a myocardial infarction.
心肌细胞含有大量线粒体，并通过冠状动脉获得良好的血液供应，以支持持续的有氧呼吸。冠状动脉阻塞会使心肌缺氧，可能导致心肌梗死。
5. The Cardiac Cycle: An Overview | 心动周期概述
The cardiac cycle is the sequence of events in one heartbeat, consisting of diastole and systole. During diastole the heart muscle relaxes and the chambers fill with blood; during systole the heart muscle contracts and pumps blood out.
心动周期是一次心跳中发生的一系列事件，包括舒张期和收缩期。舒张期心肌放松，心腔充盈血液；收缩期心肌收缩，将血液泵出。
A common exam description divides the cycle into atrial systole, ventricular systole and diastole. Atrial systole pushes the final volume of blood into the ventricles; ventricular systole then ejects blood into the arteries; diastole allows all chambers to relax and refill.
考试常将心动周期分为心房收缩期、心室收缩期和舒张期。心房收缩将最后一部分血液推入心室；随后心室收缩将血液射入动脉；舒张期所有心腔放松并重新充盈。
6. Pressure and Volume Changes in Detail | 压力与容积变化的详细过程
At the start of atrial systole, the atria contract, causing a small rise in atrial pressure and forcing blood through the open atrioventricular valves into the ventricles. Ventricular volume increases slightly.
心房收缩开始时，心房收缩使心房压力小幅上升，将血液经开放的房室瓣压入心室，心室容积略增。
During ventricular systole, the ventricles contract. Ventricular pressure rises rapidly; when it exceeds atrial pressure, the atrioventricular valves close. Pressure continues to rise until it exceeds the pressure in the aorta or pulmonary artery, opening the semilunar valves and ejecting blood.
心室收缩期，心室收缩使心室压力迅速升高；当超过心房压力时房室瓣关闭。压力继续升高，直到超过主动脉或肺动脉压力，半月瓣打开并射血。
During ventricular diastole, ventricular muscle relaxes, pressure falls below arterial pressure so the semilunar valves close. When ventricular pressure falls below atrial pressure, the atrioventricular valves open and the ventricles fill passively from the atria.
心室舒张期，心室肌松弛，压力下降至低于动脉压力，半月瓣关闭。当心室压力低于心房压力时，房室瓣打开，心室从心房被动充盈。
A typical left ventricular pressure is about 120 mmHg at peak systole and close to 0 mmHg during relaxation, while aortic pressure oscillates between about 80 mmHg diastolic and 120 mmHg systolic. The right ventricle generates much lower peak pressures, around 25 mmHg.
左心室收缩期峰值压力约120 mmHg，舒张期接近0 mmHg；主动脉压在80 mmHg舒张压与120 mmHg收缩压之间波动。右心室峰值压力低得多，约25 mmHg。
7. Initiation and Conduction of the Heartbeat | 心跳的启动与传导
The heartbeat is initiated by the sinoatrial node, a group of specialised cells in the wall of the right atrium. Because the SAN has the fastest intrinsic rate of depolarisation, it acts as the natural pacemaker.
心跳由窦房结启动，窦房结是右心房壁内的一组特化细胞。由于窦房结内在去极化速率最快，因此成为天然起搏器。
Excitation spreads across both atria, causing atrial systole. It then reaches the atrioventricular node, where conduction is delayed for about 0.1 seconds, allowing the ventricles to fill before they contract.
兴奋传遍两侧心房，引起心房收缩。随后到达房室结，在此传导延迟约0.1秒，使心室在收缩前有足够时间充盈。
From the AVN, the impulse travels down the Bundle of His and through the Purkinje fibres in the ventricular walls. This causes ventricular contraction from the apex upwards, pushing blood efficiently toward the arteries.
冲动从房室结沿希氏束下传，并经心室壁内的浦肯野纤维传导。这使心室从心尖向上收缩，有效地将血液推向动脉。
8. Nervous and Hormonal Control of Heart Rate | 心率的神经与激素调节
The medulla oblongata in the brain controls heart rate through the autonomic nervous system. The sympathetic nerve speeds up the heart by releasing noradrenaline at the SAN, while the parasympathetic vagus nerve slows it down by releasing acetylcholine.
延髓通过自主神经系统控制心率。交感神经在窦房结释放去甲肾上腺素使心跳加快，副交感迷走神经释放乙酰胆碱使心跳减慢。
The hormone adrenaline, released from the adrenal glands, also increases heart rate by acting on the SAN. This prepares the body for fight or flight during exercise or stress.
肾上腺释放的激素肾上腺素也作用于窦房结，使心率加快。这使身体在运动或应激时做好战斗或逃跑准备。
Baroreceptors in the aorta and carotid arteries detect changes in blood pressure; chemoreceptors detect changes in blood carbon dioxide and oxygen. These receptors send impulses to the medulla, which adjusts heart rate to maintain homeostasis.
主动脉和颈动脉中的压力感受器检测血压变化；化学感受器检测血液中二氧化碳和氧气的变化。这些感受器向延髓发送冲动，从而调节心率以维持稳态。
9. The Electrocardiogram (ECG) | 心电图
An ECG records the electrical activity of the heart using electrodes on the skin. The P wave represents atrial depolarisation, the QRS complex represents ventricular depolarisation, and the T wave represents ventricular repolarisation.
心电图通过皮肤电极记录心脏电活动。P波代表心房去极化，QRS波群代表心室去极化，T波代表心室复极化。
Doctors use ECGs to diagnose arrhythmias, myocardial infarction and other cardiac abnormalities. In an exam, you may need to recognise a missing P wave, an abnormal QRS complex, or an irregular trace.
医生用心电图诊断心律失常、心肌梗死和其他心脏异常。考试中可能需要识别P波缺失、QRS波群异常或节律不齐的图形。
10. Cardiac Output and Calculations | 心输出量及其计算
Cardiac output is the volume of blood pumped by one ventricle per minute. It is calculated as stroke volume multiplied by heart rate.
心输出量是每分钟一个心室泵出的血液量。它等于每搏输出量乘以心率。
Cardiac output = stroke volume × heart rate
If a person has a stroke volume of 70 cm³ and a heart rate of 75 beats per minute, then cardiac output = 70 × 75 = 5250 cm³ per minute, or about 5.25 dm³ per minute.
Published by TutorHao | A-Level Biology 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Cancel reply