📚 IGCSE WJEC Science: Human Body Key Points | IGCSE WJEC 科学：人体 考点精讲
Master the human body section for IGCSE WJEC Science with this focused revision guide. We will cover the essential organ systems, their structures, functions, and how they work together to maintain homeostasis. Each topic is broken down into clear key points to help you excel in your exams.
通过这份重点复习指南，掌握 IGCSE WJEC 科学中的人体部分。我们将涵盖主要的器官系统、它们的结构和功能，以及它们如何协同工作以维持体内平衡。每个主题都分解为清晰的关键点，帮助你取得优异成绩。
1. Organisation of the Human Body | 人体的结构层次
The human body is organised into cells, tissues, organs, and organ systems. Cells are the basic functional units; similar cells group to form tissues (e.g. muscle tissue). Different tissues work together to form an organ (e.g. the stomach), and organs are organised into systems that perform a major function (e.g. the digestive system).
人体由细胞、组织、器官和器官系统构成。细胞是基本功能单位；相似的细胞聚集形成组织（例如肌肉组织）。不同的组织共同工作形成器官（例如胃），而器官则组织成执行主要功能的系统（例如消化系统）。
- Cell – smallest unit of life, e.g. red blood cell, neurone. / 细胞 – 生命的最小单位，例如红细胞、神经元。
- Tissue – group of similar cells working together, e.g. epithelial tissue lining the gut. / 组织 – 一组相似的细胞协同工作，例如肠道内壁的上皮组织。
- Organ – structure made of different tissues, e.g. the heart, lung. / 器官 – 由不同组织构成的结构，例如心脏、肺。
- Organ system – group of organs with a shared function, e.g. circulatory system. / 器官系统 – 具有共同功能的一组器官，例如循环系统。
In the exam, you may be asked to explain how structure relates to function at each level, for instance, the folding of the small intestine increases surface area for absorption.
在考试中，你可能会被要求解释每个结构层次如何与功能相关，例如，小肠的褶皱增加了吸收表面积。
2. Digestive System and Enzymes | 消化系统与酶
The digestive system breaks down large insoluble food molecules into small soluble molecules that can be absorbed into the blood. Mechanical digestion (chewing, churning) increases surface area, while chemical digestion uses enzymes.
消化系统将大的不溶性食物分子分解成可被血液吸收的小分子可溶物质。物理消化（咀嚼、搅拌）增加表面积，而化学消化则利用酶。
Key organs and their functions: mouth (chewing, salivary amylase breaks down starch into maltose), oesophagus (peristalsis), stomach (protease pepsin breaks proteins into peptides, hydrochloric acid kills bacteria and provides optimum pH for pepsin), small intestine (enzymes from pancreas and intestinal wall complete digestion; absorption of nutrients via villi), large intestine (absorbs water, forms faeces).
关键器官及其功能：口腔（咀嚼，唾液淀粉酶将淀粉分解为麦芽糖）、食道（蠕动）、胃（蛋白酶胃蛋白酶将蛋白质分解为多肽，盐酸杀菌并为胃蛋白酶提供最适pH）、小肠（来自胰腺和肠壁的酶完成消化；通过绒毛吸收营养）、大肠（吸收水分，形成粪便）。
| Enzyme / 酶 | Substrate / 底物 | Product / 产物 | Production site / 产生部位 |
|---|---|---|---|
| Amylase / 淀粉酶 | Starch / 淀粉 | Maltose / 麦芽糖 | Salivary glands, pancreas / 唾液腺、胰腺 |
| Protease / 蛋白酶 | Protein / 蛋白质 | Amino acids / 氨基酸 | Stomach, pancreas / 胃、胰腺 |
| Lipase / 脂肪酶 | Lipids (fats) / 脂类（脂肪） | Fatty acids + glycerol / 脂肪酸 + 甘油 | Pancreas / 胰腺 |
Bile, produced by the liver and stored in the gall bladder, emulsifies fats (breaks large droplets into smaller ones) to increase the surface area for lipase action. Bile also neutralises stomach acid, providing an alkaline pH for enzymes in the small intestine.
胆汁由肝脏产生并储存在胆囊中，它乳化脂肪（将大的脂肪滴分解成小的）以增加脂肪酶作用的表面积。胆汁还中和胃酸，为小肠中的酶提供碱性pH。
Remember the lock-and-key model: each enzyme has an active site that is complementary to its specific substrate. Denaturation (by high temperature or extreme pH) changes the shape of the active site permanently, preventing the substrate from binding.
记住锁钥模型：每种酶都有一个与其特定底物互补的活性位点。变性（由于高温或极端pH）会永久改变活性位点的形状，阻止底物结合。
3. Respiratory System and Gas Exchange | 呼吸系统与气体交换
The respiratory system supplies oxygen to the blood and removes carbon dioxide. Air enters through the nose/mouth, passes the trachea, bronchi, bronchioles, and finally reaches the alveoli – tiny air sacs where gas exchange occurs.
呼吸系统为血液提供氧气并清除二氧化碳。空气通过鼻/口进入，经过气管、支气管、细支气管，最终到达肺泡——发生气体交换的微小气囊。
Adaptations of alveoli for efficient gas exchange: large surface area (many alveoli), thin walls (one cell thick), moist lining (helps gases dissolve), rich capillary network (maintains concentration gradient). The gases move by diffusion: oxygen from high concentration in alveoli to low in blood; carbon dioxide from high in blood to low in alveoli.
肺泡高效气体交换的适应性：大的表面积（许多肺泡）、薄壁（单细胞厚度）、湿润的内衬（帮助气体溶解）、丰富的毛细血管网（维持浓度梯度）。气体通过扩散移动：氧气从肺泡中高浓度扩散到血液中低浓度；二氧化碳从血液中高浓度扩散到肺泡中低浓度。
Breathing (ventilation) involves the diaphragm and intercostal muscles. During inhalation: diaphragm contracts and flattens, external intercostal muscles contract, lifting the ribcage up and out; chest volume increases, pressure decreases, air rushes in. Exhalation is largely passive: diaphragm and intercostals relax, volume decreases, pressure increases, air is pushed out.
呼吸（通气）涉及膈肌和肋间肌。吸气时：膈肌收缩并变平，外肋间肌收缩，提升肋骨笼向上向外；胸腔容积增大，压力降低，空气涌入。呼气主要是被动的：膈肌和肋间肌放松，容积减小，压力升高，空气被排出。
You should be able to interpret a spirometer trace showing tidal volume, vital capacity, and breathing rate. Also understand the difference between aerobic respiration and anaerobic respiration in humans.
你应该能够解读肺活量计图，显示潮气量、肺活量和呼吸频率。还要理解人体有氧呼吸与无氧呼吸的区别。
4. Circulatory System | 循环系统
The circulatory system consists of the heart, blood, and blood vessels. It transports oxygen, nutrients, hormones, and waste products around the body. Humans have a double circulatory system: pulmonary circulation (heart to lungs and back) and systemic circulation (heart to body and back).
循环系统由心脏、血液和血管组成。它将氧气、营养物质、激素和废物运送到全身。人类具有双循环系统：肺循环（心脏到肺再回来）和体循环（心脏到全身再回来）。
Structure of the heart: four chambers – right atrium, right ventricle, left atrium, left ventricle. The right side pumps deoxygenated blood to the lungs; the left side pumps oxygenated blood to the body. Valves prevent backflow: atrioventricular valves (tricuspid, bicuspid) and semilunar valves. The cardiac muscle in the left ventricle is thicker because it needs to pump blood at high pressure to the whole body.
心脏的结构：四个腔室——右心房、右心室、左心房、左心室。右侧将脱氧血泵送至肺部；左侧将含氧血泵送至全身。瓣膜防止回流：房室瓣（三尖瓣、二尖瓣）和半月瓣。左心室的心肌更厚，因为它需要以高压将血液泵送到全身。
| Blood vessel / 血管 | Structure / 结构 | Function / 功能 |
|---|---|---|
| Artery / 动脉 | Thick, muscular, elastic walls; narrow lumen | Carry blood away from heart at high pressure |
| Vein / 静脉 | Thin walls, wide lumen, valves present | Carry blood back to heart at low pressure |
| Capillary / 毛细血管 | One-cell-thick wall, very narrow | Site of exchange of substances between blood and tissues |
Blood components: red blood cells (no nucleus, contain haemoglobin to bind oxygen), white blood cells (defence against pathogens), platelets (clotting), and plasma (liquid carrying dissolved substances like glucose, carbon dioxide, urea).
血液成分：红细胞（无细胞核，含血红蛋白来结合氧气）、白细胞（防御病原体）、血小板（凝血）和血浆（携带溶解物质的液体，如葡萄糖、二氧化碳、尿素）。
5. Excretory System – The Kidneys | 排泄系统——肾脏
The kidneys filter the blood, removing urea (produced in the liver from excess amino acids), excess water, and salts to form urine. They also regulate the water balance of the body (osmoregulation).
肾脏过滤血液，清除尿素（肝脏从过量氨基酸中产生）、多余的水和盐，形成尿液。它们还调节体内的水分平衡（渗透调节）。
Each kidney contains about a million nephrons. In a nephron, ultrafiltration occurs in the glomerulus: high pressure forces water, urea, ions, and glucose through the capillary wall into the Bowman’s capsule. Large molecules (proteins, blood cells) stay in the blood. The filtrate then passes through the tubule where selective reabsorption takes place: all glucose, some water, and some ions are reabsorbed back into the blood. The remaining fluid, now urine, flows to the collecting duct and then to the ureter, bladder, and urethra.
每个肾脏包含大约一百万个肾单位。在肾单位中，超滤作用发生在肾小球：高压迫使水、尿素、离子和葡萄糖通过毛细血管壁进入鲍曼囊。大分子（蛋白质、血细胞）留在血液中。滤液随后经过肾小管，在那里发生选择性重吸收：所有葡萄糖、部分水和部分离子被重吸收回血液。剩余的液体，即尿液，流向集合管，然后到输尿管、膀胱和尿道。
The amount of water reabsorbed is controlled by anti-diuretic hormone (ADH). When the blood water content is low, the pituitary gland releases more ADH, making the collecting ducts more permeable to water so more water is reabsorbed, producing concentrated urine. When water intake is high, ADH release is reduced, so less water is reabsorbed and dilute urine is produced. This is a negative feedback mechanism.
重吸收的水量由抗利尿激素（ADH）控制。当血液含水量低时，垂体释放更多的ADH，使集合管对水的通透性增加，从而更多的水被重吸收，产生浓缩尿液。当水摄入量高时，ADH释放减少，因此重吸收的水减少，产生稀释尿液。这是一个负反馈机制。
6. Nervous System and Reflex Arc | 神经系统与反射弧
The nervous system uses electrical impulses to coordinate rapid responses. It consists of the central nervous system (CNS: brain and spinal cord) and peripheral nerves. Neurones are specialised cells that transmit impulses: sensory neurone (from receptor to CNS), relay neurone (within CNS), and motor neurone (from CNS to effector).
神经系统利用电冲动来协调快速反应。它由中枢神经系统（CNS：脑和脊髓）和周围神经组成。神经元是传递冲动的特化细胞：感觉神经元（从感受器到CNS）、联络神经元（CNS内）和运动神经元（从CNS到效应器）。
A reflex action is an automatic, rapid response to a stimulus that does not involve conscious thought, and it often protects the body from harm. The pathway of a reflex arc: stimulus → receptor → sensory neurone → relay neurone in spinal cord → motor neurone → effector (muscle or gland) → response. The synapse is a gap between neurones where a chemical neurotransmitter diffuses across to continue the impulse.
反射动作是对刺激的自动、快速反应，不涉及意识思维，通常保护身体免受伤害。反射弧的路径：刺激 → 感受器 → 感觉神经元 → 脊髓中的联络神经元 → 运动神经元 → 效应器（肌肉或腺体） → 反应。突触是神经元之间的间隙，化学神经递质扩散穿过以继续传递冲动。
A simple example: touching a hot object triggers heat receptors in the skin, impulses travel to the spinal cord, and a response is sent back to contract the biceps muscle, pulling the hand away. This happens before the brain is aware of the pain.
一个简单的例子：触摸热物体会触发皮肤中的热感受器，冲动传到脊髓，然后发出反应，收缩肱二头肌，将手拉回。这发生在大脑意识到疼痛之前。
7. Endocrine System and Blood Glucose Regulation | 内分泌系统与血糖调节
The endocrine system uses hormones – chemical messengers secreted by glands into the bloodstream. They travel to specific target organs and produce a slower but longer-lasting effect compared to the nervous system. Key glands include the pituitary (master gland), thyroid, pancreas, adrenals, ovaries, and testes.
内分泌系统使用激素——由腺体分泌到血液中的化学信使。它们到达特定的靶器官，产生比神经系统更慢但更持久的效果。关键腺体包括垂体（主腺体）、甲状腺、胰腺、肾上腺、卵巢和睾丸。
The pancreas plays a crucial role in regulating blood glucose concentration. When blood glucose rises (e.g. after a meal), the pancreas releases insulin. Insulin stimulates the liver and muscle cells to take up glucose and convert it into glycogen for storage, lowering blood glucose. When blood glucose falls, the pancreas secretes glucagon, which stimulates the liver to break down glycogen into glucose and release it into the blood. This negative feedback keeps blood glucose within a narrow range.
胰腺在调节血糖浓度中起关键作用。当血糖升高时（例如餐后），胰腺释放胰岛素。胰岛素刺激肝脏和肌肉细胞摄取葡萄糖，并将其转化为糖原储存，降低血糖。当血糖下降时，胰腺分泌胰高血糖素，刺激肝脏将糖原分解为葡萄糖并释放到血液中。这种负反馈将血糖维持在一个狭窄的范围内。
Diabetes mellitus type 1 is a condition where the pancreas fails to produce enough insulin, resulting in high blood glucose levels. It is managed by insulin injections and careful diet. Type 2 diabetes develops when body cells become resistant to insulin; it is often linked to obesity and can be controlled by diet, exercise, and sometimes medication.
1型糖尿病是一种胰腺不能产生足够胰岛素的疾病，导致高血糖水平。通过注射胰岛素和谨慎饮食来控制。2型糖尿病是当身体细胞对胰岛素产生抵抗时发生的；通常与肥胖有关，可以通过饮食、运动和有时药物治疗来控制。
Adrenaline is another important hormone – released by the adrenal glands in response to stress or danger (‘fight or flight’). It increases heart rate, breathing rate, and blood flow to muscles, and causes the liver to release glucose for energy.
肾上腺素是另一种重要的激素——在压力或危险时由肾上腺释放（“战斗或逃跑”反应）。它增加心率、呼吸频率和肌肉血流量，并促使肝脏释放葡萄糖以提供能量。
8. Homeostasis – Temperature Control | 体内平衡——体温控制
Homeostasis is the maintenance of a stable internal environment. Body temperature must be kept around 37 °C for optimal enzyme activity. The thermoregulatory centre in the hypothalamus of the brain monitors blood temperature and coordinates responses.
体内平衡是维持稳定的内部环境。体温必须维持在约37°C以保证最佳的酶活性。大脑下丘脑中的体温调节中枢监测血液温度并协调反应。
When body temperature rises (e.g. during exercise), mechanisms to cool down include: vasodilation (arterioles near the skin surface widen, increasing blood flow to skin, so more heat is lost by radiation), sweating (sweat glands secrete sweat, which evaporates, removing heat energy), and hair muscles relax (hairs lie flat, reducing insulating air layer).
当体温升高时（例如运动时），降温机制包括：血管舒张（皮肤表面的小动脉扩张，增加皮肤血流量，从而通过辐射散失更多热量），出汗（汗腺分泌汗液，蒸发带走热量），以及毛发肌肉放松（毛发平躺，减少绝缘空气层）。
When body temperature falls, heat conservation mechanisms are activated: vasoconstriction (arterioles constrict, reducing blood flow to skin, conserving heat), shivering (muscles contract involuntarily, generating heat from respiration), sweating decreases, and hair muscles contract (hairs stand on end, trapping an insulating layer of air – though less effective in humans).
当体温下降时，启动保温机制：血管收缩（小动脉收缩，减少皮肤血流量，保存热量），颤抖（肌肉不自主收缩，通过呼吸产生热量），出汗减少，毛发肌肉收缩（毛发竖起，捕获绝缘空气层——尽管在人类中效果较差）。
9. Reproductive System | 生殖系统
The human reproductive system is adapted for the production of gametes (sperm and egg), fertilisation, and the development of the foetus. Key structures of the male reproductive system: testes (produce sperm and testosterone), sperm ducts, prostate gland (adds fluid to semen), urethra, penis.
人类生殖系统适应于配子（精子和卵子）的产生、受精和胎儿的发育。男性生殖系统的关键结构：睾丸（产生精子和睾酮）、输精管、前列腺（为精液添加液体）、尿道、阴茎。
Female reproductive system: ovaries (produce eggs and oestrogen/progesterone), oviducts/fallopian tubes (site of fertilisation), uterus (womb where the foetus develops), cervix, vagina. The menstrual cycle lasts about 28 days and involves the maturation and release of an egg (ovulation around day 14) and preparation of the uterus lining. If fertilisation does not occur, the lining is shed during menstruation.
女性生殖系统：卵巢（产生卵子和雌激素/孕激素）、输卵管（受精部位）、子宫（胎儿发育的场所）、宫颈、阴道。月经周期约28天，包括卵子的成熟和释放（排卵约在第14天）以及子宫内膜的准备。如果没有受精，内膜在月经期间脱落。
Hormonal control: FSH (follicle-stimulating hormone) stimulates follicle development and oestrogen production. Oestrogen causes the uterus lining to thicken and triggers a surge in LH (luteinising hormone). LH stimulates ovulation. After ovulation, the empty follicle becomes a corpus luteum, secreting progesterone, which maintains the thick lining and inhibits FSH and LH (negative feedback). If pregnancy occurs, the placenta secretes hCG to maintain the corpus luteum.
激素控制：FSH（促卵泡激素）刺激卵泡发育和雌激素产生。雌激素使子宫内膜增厚，并引发LH（黄体生成素）激增。LH刺激排卵。排卵后，空卵泡变成黄体，分泌孕激素，维持厚内膜并抑制FSH和LH（负反馈）。如果怀孕，胎盘分泌hCG以维持黄体。
10. Musculoskeletal System | 肌肉骨骼系统
The skeleton provides support, protection for vital organs, and enables movement together with muscles. Bones are connected at joints by ligaments. Synovial joints (e.g. knee, elbow) are freely movable and contain synovial fluid to reduce friction, and cartilage to cushion bone ends.
骨骼提供支撑、保护重要器官，并与肌肉一起实现运动。骨骼在关节处由韧带连接。滑液关节（例如膝盖、肘部）可自由活动，包含滑液以减少摩擦，并有软骨缓冲骨端。
Muscles work in antagonistic pairs because they can only contract, not push. For example, at the elbow joint: the biceps (flexor) contracts and triceps (extensor) relaxes to bend the arm; to straighten, the triceps contracts and biceps relaxes. This coordinated action is controlled by the nervous system.
肌肉以拮抗对的形式工作，因为它们只能收缩，不能推开。例如，在肘关节处：肱二头肌（屈肌）收缩，肱三头肌（伸肌）放松，以弯曲手臂；要伸直，肱三头肌收缩，肱二头肌放松。这种协调动作由神经系统控制。
When a muscle contracts, it pulls on a tendon, which is attached to a bone, causing movement at the joint. The origin is where the tendon attaches to the stationary bone, and the insertion is where it attaches to the moving bone.
当肌肉收缩时，它拉动肌腱，肌腱附着在骨骼上，导致关节运动。起点是肌腱附着在静止骨骼上的位置，止点是附着在移动骨骼上的位置。
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