📚 A-Level Science: Human Body Key Exam Points | A-Level 科学：人体考点精讲
Welcome to this comprehensive revision guide on the human body for A-Level Science. We cover the circulatory, respiratory, digestive, nervous, endocrine, excretory, immune, and musculoskeletal systems – all presented with exam-focused clarity. Each section pairs key concepts in English and Chinese to strengthen your understanding and recall.
欢迎来到 A-Level 科学人体考点精讲。本指南系统梳理循环、呼吸、消化、神经、内分泌、排泄、免疫和肌肉骨骼系统，紧扣考纲，以中英双语配对呈现核心考点，助你高效学习、轻松备考。
1. The Circulatory System | 循环系统
The circulatory system is a closed double loop consisting of the pulmonary circuit (heart to lungs) and systemic circuit (heart to body). It ensures oxygenated and deoxygenated blood never mix, maintaining high pressure for efficient delivery.
循环系统是一个闭合的双循环系统，由肺循环（心脏至肺）和体循环（心脏至全身）组成。这保证了氧合血与脱氧血不会混合，维持高压以实现高效输送。
Blood transports oxygen bound to haemoglobin, dissolved nutrients, hormones, metabolic wastes and heat. Red blood cells lack nuclei to maximise oxygen capacity.
血液运输与血红蛋白结合的氧、溶解的营养物、激素、代谢废物和热量。红细胞无细胞核，以最大化携氧能力。
The heart’s myogenic nature means it beats independently via the sinoatrial (SA) node, which sets the rhythm. The atrioventricular (AV) node delays impulses to allow complete ventricular filling.
心脏具有自搏性，由窦房结自主发放节律。房室结延迟传导，确保心室在收缩前充分充盈。
| Component | Function |
|---|---|
| Plasma | Carries cells, nutrients, hormones, carbon dioxide, urea |
| Red blood cells | Transport oxygen via haemoglobin |
| White blood cells | Defence – phagocytes and lymphocytes |
| Platelets | Blood clotting at injury sites |
表格：血液成分与功能。血浆运输细胞、养分、激素、二氧化碳和尿素；红细胞通过血红蛋白运氧；白细胞负责防御（吞噬细胞和淋巴细胞）；血小板在伤口处凝血。
2. Heart Structure and Cardiac Cycle | 心脏结构与心动周期
The heart has four chambers: right atrium and ventricle receive deoxygenated blood and pump it to the lungs; left atrium and ventricle receive oxygenated blood and pump it to the body. The left ventricular wall is much thicker to generate higher pressure.
心脏有四个腔室：右心房和右心室接受脱氧血并将其泵入肺部；左心房和左心室接受氧合血并将其泵入全身。左心室壁厚得多，以产生更大压力。
Atrioventricular valves (tricuspid on right, bicuspid on left) and semilunar valves prevent backflow. The ‘lub-dub’ heart sound arises from valve closure.
房室瓣（右侧三尖瓣、左侧二尖瓣）和半月瓣防止血液倒流。“咚哒”心音来自瓣膜关闭。
Cardiac cycle: atrial systole pushes blood into ventricles; ventricular systole forces blood out through arteries; diastole is relaxation and filling.
心动周期：心房收缩将血液推入心室；心室收缩将血液射入动脉；舒张期则心室舒张、重新充盈。
Cardiac output = stroke volume x heart rate
心输出量 = 每搏输出量 × 心率
3. Blood Vessels and Blood Pressure | 血管与血压
Arteries carry blood away from the heart under high pressure; they have thick, elastic muscular walls. Arterioles control blood flow via vasoconstriction and vasodilation.
动脉将血液从心脏导出，承受高压，管壁厚且有弹性肌肉层。微动脉通过收缩和舒张调节血流量。
Veins return blood to the heart at low pressure; they contain valves to prevent backflow and rely on skeletal muscle contractions to assist return.
静脉在低压下将血液引回心脏，内含瓣膜防止倒流，并依赖骨骼肌收缩辅助回流。
Capillaries are one-cell-thick to allow rapid diffusion of gases, nutrients and wastes between blood and tissues. Their narrow lumen brings red blood cells into close contact with the wall.
毛细血管仅由单层细胞构成，利于气体、营养物和废物在血液与组织间快速扩散。其狭窄管腔使红细胞贴近管壁。
4. The Respiratory System | 呼吸系统
Ventilation is driven by the diaphragm and intercostal muscles. During inhalation, the diaphragm contracts and flattens, the external intercostals raise the rib cage, increasing thoracic volume and lowering pressure, drawing air in.
通气由膈肌和肋间肌驱动。吸气时膈肌收缩变平，外肋间肌提升肋骨，胸腔容积扩大、压力降低，空气被吸入。
Gas exchange occurs in the alveoli: oxygen diffuses into blood down a concentration gradient, carbon dioxide diffuses out. Alveoli are adapted with thin walls, large surface area and moist lining.
气体交换在肺泡发生：氧顺浓度梯度扩散入血液，二氧化碳扩散排出。肺泡具有薄壁、巨大表面积和湿润内衬以利于交换。
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP)
葡萄糖 + 氧 → 二氧化碳 + 水 + 能量（ATP）
Haemoglobin binds oxygen in the lungs (forming oxyhaemoglobin) and releases it in respiring tissues where oxygen concentration is low. Carbon dioxide is transported mainly as hydrogencarbonate ions in plasma.
血红蛋白在肺中结合氧（形成氧合血红蛋白），在氧浓度低的组织处释放氧。二氧化碳主要以碳酸氢根离子形式在血浆中运输。
5. The Digestive System and Enzymes | 消化系统与酶
Digestion breaks down large insoluble molecules into soluble, absorbable units. Mechanical digestion (chewing, stomach churning) increases surface area for enzyme action.
消化将大分子不溶性物质分解为可溶、可吸收的小单位。机械消化（咀嚼、胃的搅拌）增大酶作用的表面积。
Amylase (mouth and pancreas) breaks starch into maltose. Proteases (stomach pepsin, pancreatic trypsin) break proteins into amino acids. Lipase (pancreas) digests fats into fatty acids and glycerol; bile emulsifies fats to aid this.
淀粉酶（口腔和胰腺）将淀粉分解为麦芽糖。蛋白酶（胃蛋白酶、胰蛋白酶）将蛋白质分解为氨基酸。脂肪酶（胰腺）将脂肪分解为脂肪酸和甘油；胆汁乳化脂肪以辅助分解。
Absorption takes place chiefly in the small intestine. Villi and microvilli provide an enormous surface area; products enter blood capillaries (sugars, amino acids) or lacteals (fatty acids and glycerol recombined into chylomicrons).
吸收主要在小肠进行。绒毛和微绒毛提供了极大的表面积；消化产物进入毛细血管（糖类、氨基酸）或乳糜管（脂肪酸和甘油重新合成乳糜微粒）。
- Enzymes are biological catalysts, specific to substrates, and lower activation energy.
- 酶是生物催化剂，具底物专一性，能降低活化能。
- They are affected by temperature and pH; extremes cause denaturation.
- 酶受温度和 pH 影响；极端条件会导致变性。
6. The Nervous System and Reflexes | 神经系统与反射
The nervous system coordinates rapid responses to stimuli. It consists of the central nervous system (brain and spinal cord) and peripheral nerves (sensory and motor).
神经系统协调对刺激的快速反应。它由中枢神经系统（脑和脊髓）和周围神经（感觉与运动神经）组成。
A reflex arc is a rapid, involuntary response that bypasses the brain. The pathway: receptor -> sensory neurone -> relay neurone (in spinal cord) -> motor neurone -> effector (muscle or gland).
反射弧是一种快速、不自主的反应，无需大脑参与。通路为：感受器 → 感觉神经元 → 中间神经元（位于脊髓）→ 运动神经元 → 效应器（肌肉或腺体）。
At a synapse, the arrival of an impulse triggers vesicles to release neurotransmitter into the cleft. This binds to receptors on the postsynaptic membrane, initiating a new impulse. Synapses ensure one-way transmission.
在突触处，冲动到达促使突触小泡释放神经递质到间隙。递质与突触后膜受体结合，引发新冲动。突触确保了单向传递。
7. Hormonal Control and Homeostasis | 激素调控与稳态
Homeostasis is the maintenance of a constant internal environment. Negative feedback loops detect changes from a set point and initiate corrective responses.
稳态是维持内部环境稳定的机制。负反馈回路检测相对于设定值的变化并启动纠正反应。
Blood glucose regulation: when glucose rises (after eating), the pancreas releases insulin, which stimulates liver and muscle cells to convert glucose to glycogen. When glucose falls, glucagon promotes glycogen breakdown into glucose.
血糖调节：血糖升高（进食后），胰腺释放胰岛素，促进肝和肌细胞将葡萄糖转化为糖原。血糖降低时，胰高血糖素促进糖原分解为葡萄糖。
Insulin lowers blood glucose; glucagon raises it.
胰岛素降低血糖；胰高血糖素升高血糖。
Thermoregulation: the hypothalamus monitors core temperature. Cooling causes vasoconstriction, shivering and hair erection; warming causes vasodilation and sweating.
体温调节：下丘脑监测核心体温。寒冷导致血管收缩、颤抖和毛发竖立；温热导致血管舒张和出汗。
Adrenaline is released in ‘fight or flight’ situations, increasing heart rate, dilating airways and raising blood glucose for quick energy.
肾上腺素在“战斗或逃跑”时释放，使心率加快、气道扩张、血糖升高，为快速供能做好准备。
8. Excretion and Kidney Function | 排泄与肾功能
Excretion removes metabolic wastes, mainly urea, from the body. The kidney contains millions of nephrons, each filtering blood and producing urine.
排泄将代谢废物（主要是尿素）排出体外。肾脏含有数百万肾单位，每个都能滤过血液并生成尿液。
Filtration occurs in the glomerulus under high pressure, forcing water, ions, glucose and urea into Bowman’s capsule. Large proteins and blood cells remain in the blood.
滤过在肾小球高压下进行，将水、离子、葡萄糖和尿素压入鲍曼氏囊。大分子蛋白质和血细胞留在血液中。
Selective reabsorption happens in the proximal convoluted tubule, where all glucose, most ions and much water are reabsorbed into capillaries. Loop of Henle creates a concentration gradient to concentrate urine.
选择性重吸收发生在近曲小管，所有葡萄糖、大部分离子和大量水被重吸收回毛细血管。髓袢建立浓度梯度以浓缩尿液。
Antidiuretic hormone (ADH) controls water reabsorption in the collecting duct. When water level is low, more ADH is secreted, making the ducts more permeable, so more water is reabsorbed.
抗利尿激素（ADH）控制集合管对水的重吸收。缺水时 ADH 分泌增多，管壁通透性加大，更多的水被重吸收。
9. The Immune System and Vaccination | 免疫系统与疫苗接种
Non-specific defences include skin, mucus, stomach acid and phagocytosis. Phagocytes engulf pathogens and digest them with enzymes.
非特异性防御包括皮肤、黏液、胃酸和吞噬作用。吞噬细胞吞噬病原体并用酶将其消化。
Specific immune response involves lymphocytes. B cells produce antibodies that bind to specific antigens, neutralising pathogens or marking them for destruction. T helper cells activate B cells and cytotoxic T cells.
特异性免疫反应涉及淋巴细胞。B 细胞产生抗体与特定抗原结合，中和病原体或将其标记以供消灭。辅助 T 细胞激活 B 细胞和细胞毒性 T 细胞。
Memory cells remain after infection, providing long-term immunity. Vaccination introduces a harmless form of the antigen, triggering memory cell production without causing illness.
记忆细胞在感染后存留，提供长期免疫。疫苗接种引入无害的抗原形式，引发记忆细胞产生，而不会致病。
Herd immunity occurs when a high proportion of a population is immune, reducing the spread of the disease and protecting vulnerable individuals.
当人群中很大比例具有免疫力时，形成群体免疫，可降低疾病传播并保护易感个体。
10. Musculoskeletal System and Movement | 肌肉骨骼系统与运动
The human skeleton provides support, protection and a framework for movement. Joints are where bones meet; synovial joints (e.g. knee) allow free movement. Cartilage reduces friction and ligaments connect bone to bone.
人体骨骼提供支撑、保护和运动框架。关节是骨与骨相接处；滑膜关节（如膝关节）允许大幅度活动。软骨减少摩擦，韧带将骨与骨连接。
Antagonistic muscle pairs: for example, the biceps and triceps at the elbow. When the biceps contracts, the triceps relaxes to flex the arm; opposite for extension.
拮抗肌对：例如肘部的肱二头肌和肱三头肌。二头肌收缩、三头肌舒张时屈臂；伸臂时则相反。
Muscle fibres contain myofibrils with repeating sarcomeres. According to the sliding filament theory, myosin heads pull actin filaments towards the centre, shortening the sarcomere, using ATP for energy.
肌纤维内含肌原纤维，上有重复的肌节。根据肌丝滑动学说，肌球蛋白头将肌动蛋白丝向中心拉动，缩短肌节，此过程消耗 ATP。
Tendons attach muscle to bone, transmitting force. Regular exercise increases muscle strength and bone density through adaptation.
肌腱将肌肉附着于骨，传递力量。规律运动通过适应性变化增强肌肉力量和骨密度。
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