📚 6B1 The Circulatory System: Illustrated Memory Guide | 6B1 循环系统图解记忆指南
The circulatory system is a fundamental topic in A-Level Biology, yet students often struggle to memorise its intricate structures and pathways. This guide offers visual memory techniques to help you grasp the heart’s anatomy, blood vessel types, double circulation, and the cardiac cycle with ease.
循环系统是 A-Level 生物的基础课题，但学生们常难以记住其复杂的结构和路径。本指南提供图解记忆方法，助你轻松掌握心脏解剖、血管类型、双循环及心动周期。
1. Introduction to the Circulatory System | 循环系统简介
The circulatory system transports nutrients, oxygen, hormones, and waste products throughout the body. It consists of the heart, blood vessels (arteries, veins, capillaries), and blood. In mammals, it is a closed, double circulatory system.
循环系统负责运输营养、氧气、激素及废物至全身。它由心脏、血管（动脉、静脉、毛细血管）和血液组成。哺乳动物拥有闭管式双循环系统。
There are two main circuits: the pulmonary circuit (heart → lungs → heart) and the systemic circuit (heart → body → heart). The right side of the heart handles deoxygenated blood for the pulmonary circuit; the left side pumps oxygenated blood to the entire body.
主要有两条回路：肺循环（心脏→肺→心脏）和体循环（心脏→身体→心脏）。右半心处理缺氧血输送至肺循环；左半心将富氧血泵至全身。
2. The Heart: Structure and Chambers | 心脏：结构与腔室
The heart has four chambers: right atrium, right ventricle, left atrium, and left ventricle. A useful visual memory is to imagine the heart as a house with two floors (atria upstairs, ventricles downstairs) and two wings (right and left).
心脏有四个腔室：右心房、右心室、左心房和左心室。一个形象的记忆是想象心脏为两层楼（心房在上层，心室在下层）和两翼（右侧与左侧）。
The atria are thin-walled reception chambers, while the ventricles are thick-walled pumping chambers. The left ventricle wall is the thickest because it must pump blood to the entire body against high resistance.
心房壁薄，为接收腔；心室壁厚，为泵送腔。左心室壁最厚，因为它需要克服高阻力将血液泵至全身。
| Feature | Right Ventricle | Left Ventricle |
|---|---|---|
| Wall thickness 壁厚 |
Thinner 较薄 |
Thickest 最厚 |
| Pressure generated 产生压力 |
Lower (pulmonary) 较低（肺循环） |
Higher (systemic) 较高（体循环） |
| Blood pumped to 泵入 |
Pulmonary artery 肺动脉 |
Aorta 主动脉 |
3. Visualising Blood Flow: Double Circulation | 图解血流：双循环
Right atrium receives deoxygenated blood from the body via the superior and inferior vena cavae, then passes it to the right ventricle which pumps it to the lungs through the pulmonary artery. In the lungs, CO₂ is exchanged for O₂.
右心房通过上、下腔静脉接收来自全身的缺氧血，然后输送到右心室，再由肺动脉泵入肺。肺部交换二氧化碳与氧气。
Oxygenated blood returns via four pulmonary veins to the left atrium, moves into the left ventricle, and is ejected through the aorta to the body. This double circulation ensures that oxygen-rich and oxygen-poor blood do not mix, and that blood pressure can be regulated separately for the lungs and body.
富氧血经四条肺静脉返回左心房，进入左心室，再通过主动脉输送到全身。这种双循环确保了富氧血与缺氧血不相混合，并且肺循环与体循环的血压可分别调节。
Memory trick: ‘Right is blue, pumps to the lung zoo; Left is red, pumps to the body’s bed.’ Draw a diagram with blue lines on the right side and red lines on the left side to reinforce the visual separation.
记忆妙法：‘右方蓝色，泵向肺部；左方红色，泵往全身。’ 在图上右侧用蓝线、左侧用红线，增强视觉分隔。
4. Blood Vessels: Arteries, Veins, Capillaries | 血管：动脉、静脉、毛细血管
Arteries carry blood away from the heart; they have thick muscular and elastic walls to withstand high pressure. Veins carry blood towards the heart; they have thinner walls and valves to prevent backflow. Capillaries are microscopic, one-cell-thick walls for efficient exchange of gases and nutrients.
动脉将血液带离心脏，管壁厚、富有肌肉和弹性纤维以承受高压。静脉将血液带回心脏，管壁较薄，并有瓣膜防止倒流。毛细血管壁极薄，仅一层细胞，便于气体和营养物的交换。
| Vessel type 血管类型 |
Wall structure 管壁结构 |
Function 功能 |
Unique features 特色 |
|---|---|---|---|
| Artery 动脉 |
Thick muscle + elastin 厚肌肉层和弹性蛋白 |
Carry high-pressure blood away 将高压血液带离心脏 |
No valves (except aorta/pulmonary) 无瓣膜（主动脉、肺动脉除外） |
| Vein 静脉 |
Thin muscle, wide lumen 薄肌层，管腔宽 |
Return low-pressure blood 低压血液回心 |
Valves present 有瓣膜 |
| Capillary 毛细血管 |
Single endothelial layer 单层内皮细胞 |
Exchange site 物质交换场所 |
Tiny diameter, no muscle 极细，无平滑肌 |
5. The Cardiac Cycle: Systole & Diastole | 心动周期：收缩与舒张
The cardiac cycle consists of three phases: atrial systole, ventricular systole, and diastole. During atrial systole, atria contract, forcing blood into ventricles. The atrioventricular (AV) valves are open, semilunar valves closed.
心动周期分三个阶段：心房收缩期、心室收缩期和舒张期。心房收缩时，心房收缩将血液压入心室。房室瓣开启，动脉瓣关闭。
During ventricular systole, ventricles contract; the AV valves close (‘lub’ sound), and semilunar valves open, ejecting blood into arteries. In diastole, the heart relaxes, semilunar valves close (‘dub’ sound), and ventricles fill passively from the atria. The whole cycle takes about 0.8 seconds at a resting heart rate of 75 bpm.
心室收缩时，心室收缩；房室瓣关闭（‘lub’音），动脉瓣开启，血液喷入动脉。舒张期心肌松弛，动脉瓣关闭（‘dub’音），心室从心房被动充盈。静息心率75次/分时，整个周期约0.8秒。
Cardiac output can be calculated using the formula:
CO = SV × HR
where CO = cardiac output (L/min), SV = stroke volume (mL/beat), HR = heart rate (beats/min).
心输出量计算公式：
CO = SV × HR
其中 CO = 心输出量（升/分）， SV = 每搏输出量（毫升/次）， HR = 心率（次/分）。
6. Heart Valves: One-Way Flow | 心脏瓣膜：单向流动
The tricuspid valve is located between right atrium and right ventricle; the bicuspid (mitral) valve between left atrium and left ventricle. The semilunar valves (aortic and pulmonary) are situated at the exits of the ventricles, preventing backflow into the heart from arteries.
三尖瓣位于右心房与右心室之间；二尖瓣（僧帽瓣）位于左心房与左心室之间。半月瓣（主动脉瓣和肺动脉瓣）位于心室出口，防止动脉血液倒流回心脏。
Helpful mnemonics: ‘LAB RAT’ – Left Atrium Bicuspid, Right Atrium Tricuspid. Another: ‘Try before you Buy’ – Tricuspid is on the Right, Bicuspid on the Left. Visualise the valves as doors that open only one way, ensuring unidirectional blood flow.
记忆口诀：‘LAB RAT’ ——左心房二尖瓣，右心房三尖瓣。或者 ‘买前先试’——三尖瓣在右，二尖瓣在左。将瓣膜想象为只能单向打开的门，确保血液单向流动。
7. Coronary Circulation: The Heart’s Own Supply | 冠脉循环：心脏自身的供血
The heart muscle requires its own blood supply via the coronary arteries, which branch off the aorta just beyond the aortic valve. These arteries deliver oxygenated blood to the myocardium. Blockage or narrowing of coronary arteries (e.g., by atherosclerosis) leads to angina or myocardial infarction (heart attack).
心肌自身需要血液供应，通过从主动脉瓣上方的主动脉分支——冠状动脉实现。这些动脉输送富氧血至心肌。冠状动脉堵塞或狭窄（如动脉粥样硬化）会导致心绞痛或心肌梗死（心脏病发作）。
The coronary veins collect deoxygenated blood and drain into the coronary sinus, which empties directly into the right atrium. Remember that the heart receives its own blood during diastole, when the myocardium relaxes and vessels are not compressed.
冠状静脉收集缺氧血，汇入冠状窦，直接注入右心房。记住，心脏在舒张期获得自身供血，此时心肌松弛，血管不受挤压。
8. Electrical Conduction: Pacemaker to Purkinje | 电传导：从起搏点到浦肯野纤维
The sinoatrial (SA) node, located in the right atrial wall, acts as the natural pacemaker. It generates electrical impulses that spread across the atria, causing atrial contraction. The signal then reaches the atrioventricular (AV) node at the junction of the atria and ventricles.
窦房结（SA 结）位于右心房壁，是天然起搏点。它产生的电信号传播至心房，引起心房收缩。信号随后到达房室交界处的房室结（AV结）。
The AV node briefly delays the impulse (about 0.1 s), allowing the ventricles to fill completely. The impulse then travels rapidly down the Bundle of His in the interventricular septum and through the Purkinje fibres, triggering ventricular contraction from the apex upwards. This coordinated sequence ensures efficient pumping.
房室结将冲动延迟约0.1秒，让心室充分充盈。然后冲动沿室间隔的希氏束快速下传，经浦肯野纤维从心尖向上引发心室收缩。这一协调序列确保了高效泵血。
Visual sequence: SA node → Atria contract → AV node delay → Bundle of His → Purkinje fibres → Ventricles contract. Think ‘Start Atrial, Pause, then Ventricular Go’.
视觉序列：窦房结→心房收缩→房室结延迟→希氏束→浦肯野纤维→心室收缩。记住‘启动心房、暂停、然后心室起步’。
9. Blood Composition: Plasma & Cells | 血液成分：血浆与血细胞
Blood is composed of plasma (~55%) and formed elements (red blood cells, white blood cells, platelets). Plasma is 90% water and contains dissolved proteins (albumin, globulins, fibrinogen), nutrients, hormones, ions, and waste products (urea, CO₂).
血液由血浆（约占55%）和有形成分（红细胞、白细胞、血小板）组成。血浆90%为水，含有溶解的蛋白质（白蛋白、球蛋白、纤维蛋白原）、营养物、激素、离子和废物（尿素、CO₂）。
Red blood cells (erythrocytes) are biconcave discs without a nucleus, packed with haemoglobin for oxygen transport. White blood cells (leukocytes) are part of the immune system and include phagocytes and lymphocytes. Platelets are cell fragments essential for blood clotting.
红细胞为双凹圆盘状，无核，含有大量血红蛋白以运输氧气。白细胞属于免疫系统，包括吞噬细胞和淋巴细胞。血小板是细胞碎片，对血液凝固至关重要。
10. Transport Functions: Oxygen & Nutrients | 运输功能：氧气与营养物质
Oxygen is carried mainly by binding to the haem group of haemoglobin in red blood cells, forming oxyhaemoglobin. Only about 1.5% of O₂ dissolves directly in plasma. Carbon dioxide is transported in three ways: dissolved in plasma (~7%), bound to haemoglobin as carbaminohaemoglobin (~23%), and as bicarbonate ions (HCO₃⁻) in plasma (~70%).
氧气主要与红细胞中血红蛋白的血红素基团结合，形成氧合血红蛋白。仅有约1.5%的氧气直接溶于血浆。二氧化碳以三种方式运输：溶于血浆（约7%）、与血红蛋白结合成氨基甲酰血红蛋白（约23%）、以碳酸氢根离子（HCO₃⁻）形式存在于血浆（约70%）。
Nutrients such as glucose, amino acids, fatty acids, and vitamins are dissolved in plasma and delivered to cells. Plasma proteins like albumin help maintain osmotic balance and transport hydrophobic molecules. The circulatory system also distributes heat and hormones throughout the body.
葡萄糖、氨基酸、脂肪酸和维生素等营养物质溶于血浆，输送至细胞。白蛋白等血浆蛋白质有助于维持渗透平衡并运输疏水分子。循环系统还在全身散布热量和激素。
11. Lymphatic System Connection | 淋巴系统关联
The lymphatic system is a network of vessels that collects excess tissue fluid (lymph) from interstitial spaces and returns it to the circulatory system via the subclavian veins. Lymph nodes along the vessels filter out pathogens and contain lymphocytes that mount immune responses.
淋巴系统是一套脉管网，收集组织间隙中多余的组织液（淋巴），并通过锁骨下静脉送回循环系统。沿淋巴管的淋巴结过滤病原体，并含有启动免疫应答的淋巴细胞。
This system is essential for maintaining fluid balance, defending against infection, and absorbing dietary lipids from the small intestine via lacteals. Although not part of the circulatory system per se, it works intimately with the cardiovascular system.
该系统对维持体液平衡、防御感染以及通过乳糜管从小肠吸收膳食脂质至关重要。尽管淋巴系统本身不属于循环系统，但它与心血管系统紧密协同。
12. Visual Memory Tips & Diagrams | 图解记忆技巧
Create a simplified heart diagram: draw a box divided into four quadrants. Label the upper chambers as atria, lower as ventricles. Use red colouring for the left side (oxygenated) and blue for the right side (deoxygenated). This instant colour code reinforces the double circulation concept.
绘制简化心脏图：画一个四等分的方框。上层标注心房，下层标注心室。左侧用红色（富氧），右侧用蓝色（缺氧）。这种即时颜色编码强化双循环概念。
For blood flow sequence through the heart, remember ‘Vena cava → Right Atrium → Right Ventricle → Pulmonary artery → Lungs → Pulmonary vein → Left Atrium → Left Ventricle → Aorta’. A memorable phrase: ‘Very Red Rabbits Play Loudly; Please Leave Aunty.’ Alternatively, draw arrows and label each chamber, then trace the path with your finger while reciting
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