📚 IGCSE CIE Science: Human Body Key Points Revision | IGCSE CIE 科学：人体考点精讲
The human body is a complex, integrated system in which each organ and tissue contributes to maintaining life. For IGCSE CIE Science, understanding the structure and function of major body systems is crucial. This revision guide summarises the key points you need to know about digestion, circulation, respiration, nerves, hormones, excretion, movement, immunity, and homeostasis. Each section pairs exam-ready facts with clear explanations, helping you master the ‘Human Body’ topic efficiently.
人体是一个复杂的综合系统，每个器官和组织都对维持生命起着重要作用。对于 IGCSE CIE 科学考试，掌握主要身体系统的结构和功能至关重要。这篇复习指南概括了消化、循环、呼吸、神经、激素、排泄、运动、免疫和稳态等关键考点，以清晰易懂的方式梳理核心知识点，帮助你高效掌握“人体”这一主题。
1. Organisation of the Human Body | 人体的组织层次
Living organisms are built from cells, which group together to form tissues. A tissue is a collection of similar cells that work together to perform a specific function. Several tissues combine to make an organ, and organs work together in organ systems. In the human body, cells such as muscle cells contract, while red blood cells transport oxygen; tissues such as epithelial tissue line surfaces; organs such as the stomach churn and digest food; and systems such as the digestive system process and absorb nutrients.
生物体由细胞构成，细胞聚集形成组织。组织是一群相似细胞的集合，它们共同执行特定功能。多个组织结合形成器官，器官协同工作构成器官系统。在人体中，肌细胞会收缩，红细胞运输氧气；上皮组织覆盖体表或管腔；胃这样的器官研磨和消化食物；消化系统这样的器官系统则负责加工和吸收营养物质。
Within cells, the nucleus controls activities by regulating gene expression, mitochondria carry out aerobic respiration to release energy, and ribosomes synthesise proteins. Specialised cells, such as ciliated epithelial cells in the airways, have adaptations that allow them to perform their roles efficiently. Understanding this hierarchy – cells → tissues → organs → systems – helps make sense of how the body functions as a whole.
细胞内部，细胞核通过调控基因表达来控制活动，线粒体进行有氧呼吸释放能量，核糖体合成蛋白质。特化细胞，例如呼吸道中的纤毛上皮细胞，具有与其功能相适应的结构。理解细胞→组织→器官→系统这一等级结构，有助于从整体上把握人体的运作方式。
2. Digestive System | 消化系统
The digestive system breaks down large, insoluble food molecules into small, soluble ones that can be absorbed into the blood. Mechanical digestion includes chewing in the mouth and churning in the stomach, while chemical digestion relies on enzymes. The alimentary canal consists of the mouth, oesophagus, stomach, small intestine, large intestine, rectum, and anus; associated organs include the salivary glands, pancreas, liver, and gall bladder.
消化系统将大而不可溶的食物分子分解为小而可溶的小分子，以便吸收进入血液。物理性消化包括口腔咀嚼和胃的搅拌，化学性消化则依赖酶。消化道由口腔、食道、胃、小肠、大肠、直肠和肛门组成；附属器官包括唾液腺、胰腺、肝脏和胆囊。
Amylase, produced by salivary glands and the pancreas, breaks down starch into maltose. Proteases (such as pepsin in the stomach and trypsin from the pancreas) digest proteins into amino acids. Lipase, secreted by the pancreas, hydrolyses fats into fatty acids and glycerol, aided by bile from the liver which emulsifies fats, increasing surface area for enzyme action. The stomach also produces hydrochloric acid, which kills bacteria and provides an acidic optimum pH for pepsin.
淀粉酶由唾液腺和胰腺分泌，将淀粉分解为麦芽糖。蛋白酶（如胃中的胃蛋白酶和胰腺分泌的胰蛋白酶）将蛋白质消化成氨基酸。脂肪酶由胰腺分泌，在肝脏分泌的胆汁帮助下将脂肪水解为脂肪酸和甘油；胆汁能乳化脂肪，增大酶作用的表面积。胃还分泌盐酸，既能杀灭细菌，也为胃蛋白酶提供酸性最适pH。
Absorption mainly takes place in the small intestine, whose inner wall is lined with villi and microvilli. These finger-like projections provide a huge surface area, a thin epithelium (one cell thick), and a dense network of blood capillaries for efficient uptake of digested food. Glucose and amino acids pass into the blood, while fatty acids and glycerol enter the lacteals of the lymphatic system.
吸收主要发生在小肠，小肠内壁遍布绒毛和微绒毛。这些指状突起提供了巨大的表面积，只有一层细胞的上皮很薄，还有密集的毛细血管网，使消化产物的吸收非常高效。葡萄糖和氨基酸进入血液，脂肪酸和甘油则进入淋巴系统的乳糜管。
3. Circulatory System | 循环系统
The human circulatory system is a double circulation: blood is pumped from the heart to the lungs (pulmonary circulation) and then back to the heart before being pumped to the rest of the body (systemic circulation). This keeps oxygenated and deoxygenated blood separate and delivers oxygen under high pressure to body tissues. The heart consists of four chambers – right atrium, right ventricle, left atrium, left ventricle – separated by valves that prevent backflow.
人体的循环系统是双循环：血液从心脏泵到肺部（肺循环）再返回心脏，然后泵送到全身（体循环）。这使得含氧血和缺氧血分开，并以较高压力向身体组织输送氧气。心脏有四个腔室——右心房、右心室、左心房、左心室——由防止回流的瓣膜分隔。
Blood enters the right atrium from the vena cava, passes through the tricuspid valve into the right ventricle, and is pumped via the pulmonary artery to the lungs. Oxygenated blood returns through the pulmonary veins to the left atrium, goes through the bicuspid (mitral) valve into the left ventricle, and is ejected through the aorta to the body. The wall of the left ventricle is thicker because it must generate higher pressure for systemic circulation.
血液从上腔静脉进入右心房，经三尖瓣流入右心室，再经肺动脉泵入肺部。氧合血通过肺静脉回到左心房，经二尖瓣进入左心室，然后通过主动脉泵向全身。左心室壁更厚，因为它需要产生更高的压力以驱动体循环。
Blood is composed of plasma, red blood cells, white blood cells, and platelets. Red blood cells contain haemoglobin which binds oxygen in the lungs and releases it in tissues; they are biconcave discs with no nucleus, maximising space for haemoglobin. White blood cells defend against pathogens, and platelets are involved in blood clotting. Arteries have thick, elastic walls to withstand high pressure; veins have thinner walls and valves to prevent backflow; capillaries are tiny, one-cell-thick vessels where exchange of materials occurs.
血液由血浆、红细胞、白细胞和血小板组成。红细胞含有血红蛋白，在肺部结合氧气并在组织中释放；它们是双凹圆盘状无核细胞，最大限度地容纳血红蛋白。白细胞抵御病原体，血小板参与凝血。动脉壁厚且有弹性，能承受高压；静脉壁较薄，有瓣膜防止回流；毛细血管是仅一层细胞厚的微小血管，是物质交换的场所。
4. Respiratory System | 呼吸系统
The respiratory system supplies oxygen for aerobic respiration and removes carbon dioxide, a waste product. Air enters through the nose or mouth, passes the pharynx and larynx, travels down the trachea, bronchi, and bronchioles, finally reaching the alveoli – tiny air sacs in the lungs. The trachea and bronchi are supported by C-shaped cartilage rings that keep the airways open. Ciliated epithelial cells lining the airways move mucus upward, trapping dust and pathogens.
呼吸系统为有氧呼吸提供氧气，并排出代谢废物二氧化碳。空气从鼻或口进入，经过咽和喉，沿气管、支气管和细支气管下行，最终到达肺泡——肺内的微小气囊。气管和支气管有C形软骨环支撑，以保持气道通畅。气道上皮的纤毛细胞向上摆动，将粘液连同灰尘和病原体一同移出。
Ventilation (breathing) is achieved by changing the volume of the thoracic cavity. During inhalation, the diaphragm contracts and flattens, and the external intercostal muscles contract, pulling the ribcage up and out. This increases chest volume, lowers pressure inside the lungs, and air flows in. During exhalation, the diaphragm relaxes, the intercostal muscles relax, and the ribcage moves down and in, decreasing volume and pushing air out.
肺通气通过改变胸腔容积来实现。吸气时，膈肌收缩变得扁平，外肋间肌收缩，提拉肋骨向上向外移动，胸腔容积增大，肺内压降低，空气流入。呼气时，膈肌舒张，肋间肌放松，肋骨向下向内移动，胸腔容积减小，排出空气。
Gas exchange occurs in the alveoli. Alveoli have several adaptations: an enormous surface area, a very thin wall (one cell thick), a moist surface, and a dense network of blood capillaries. Oxygen diffuses from the alveolar air into the blood, while carbon dioxide diffuses in the opposite direction. The equation for aerobic respiration summarises the overall process:
气体交换在肺泡进行。肺泡有多项适应特征：巨大的表面积、极薄的壁（仅一层细胞）、湿润的表面和致密的毛细血管网。氧气从肺泡内空气扩散进入血液，二氧化碳则反向扩散。有氧呼吸的方程式总结了这一过程：
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy)
5. Nervous System | 神经系统
The nervous system enables rapid communication between the body and the environment. It consists of the central nervous system (brain and spinal cord) and the peripheral nervous system (nerves). Neurones are the functional units, consisting of a cell body, dendrites, and a long axon. Sensory neurones carry impulses from receptors (such as those in skin or eyes) to the CNS; motor neurones carry impulses from the CNS to effectors (muscles or glands). Relay neurones are found within the CNS and connect sensory to motor neurones.
神经系统使身体能与环境进行快速通信。它由中枢神经系统（脑和脊髓）以及周围神经系统（神经）组成。神经元是功能单位，由细胞体、树突和长轴突构成。感觉神经元将神经冲动从感受器（如皮肤或眼中的感受器）传至中枢神经系统；运动神经元将冲动从中枢神经传至效应器（肌肉或腺体）。中间神经元存在于中枢神经系统内，连接感觉和运动神经元。
A reflex action is a rapid, automatic response to a stimulus that does not involve conscious thought. The pathway is called a reflex arc. For example, touching a hot object triggers a receptor in the skin; the sensory neurone sends an impulse to the spinal cord, where it passes to a relay neurone and then directly to a motor neurone; the motor neurone stimulates a muscle to contract, pulling the hand away. This bypasses the brain, making responses faster and protecting the body from harm.
反射动作是对刺激的一种迅速、自动的反应，无需意识参与。其神经通路称为反射弧。例如，碰到烫的物体时，皮肤的痛觉感受器产生冲动，感觉神经元将冲动传入脊髓，再通过中间神经元直接传递给运动神经元；运动神经元刺激肌肉收缩，使手迅速收回。这一过程不经过大脑，反应更快，有助于保护身体免受伤害。
At the synapse, the junction between two neurones, the electrical impulse triggers the release of a neurotransmitter (chemical messenger). The transmitter diffuses across the gap and binds to receptors on the next neurone, initiating a new impulse. This ensures impulses travel in one direction only.
在神经元之间的突触处，电信号触发神经递质（化学信使）的释放。递质扩散过间隙，与下一个神经元上的受体结合，引发新的神经冲动。这保证了冲动只能单向传递。
6. Endocrine System | 内分泌系统
Hormones are chemical messengers produced by endocrine glands, transported in the blood, and act on specific target organs. Compared with nervous impulses, hormonal effects are slower but longer-lasting. The pancreas secretes insulin and glucagon to regulate blood glucose concentration. After a meal, when blood glucose rises, insulin is released; it stimulates the liver and muscles to convert glucose into glycogen for storage, lowering blood glucose. When blood glucose is too low, glucagon promotes the breakdown of glycogen back into glucose.
激素是由内分泌腺分泌的化学信使，通过血液运输，作用于特定的靶器官。与神经冲动相比，激素的作用较慢但更持久。胰腺分泌胰岛素和胰高血糖素来调节血糖浓度。进餐后血糖升高，胰岛素释放，刺激肝脏和肌肉将葡萄糖转化为糖原储存，使血糖降低。当血糖过低时，胰高血糖素促进糖原分解为葡萄糖。
Adrenaline is the ‘fight or flight’ hormone released by the adrenal glands in times of stress or excitement. It increases heart rate and breathing rate, diverts blood to muscles, and stimulates the liver to convert glycogen to glucose, providing extra energy for muscular activity. The response is rapid and prepares the body for action.
肾上腺素是肾上腺在应激或兴奋时释放的“战斗或逃跑”激素。它使心率和呼吸频率加快，将血液导向肌肉，并刺激肝脏将糖原转化为葡萄糖，为肌肉活动提供额外能量。这种反应迅速，使身体做好应对准备。
Thyroxine from the thyroid gland controls metabolic rate, and its levels are regulated by negative feedback involving the pituitary gland. Negative feedback ensures that any deviation from the normal set point triggers a response that counteracts the change, restoring balance. For example, a rise in thyroxine inhibits further release from the pituitary.
甲状腺分泌的甲状腺素控制代谢速率，其水平通过垂体的负反馈机制调节。负反馈确保任何偏离正常设定点的变化都会引发与之对抗的反应，以恢复平衡。例如，甲状腺素水平升高会抑制垂体的进一步释放。
7. Excretory System | 排泄系统
Excretion is the removal of metabolic waste products from the body. The kidneys are the main excretory organs, filtering blood to remove urea, excess water, and salts, forming urine. The urinary system includes the kidneys, ureters, bladder, and urethra. The functional unit of the kidney is the nephron, a tiny tubule where filtration and reabsorption take place.
排泄是指将新陈代谢产生的废物排出体外。肾脏是主要的排泄器官，通过过滤血液清除尿素、多余的水分和盐，形成尿液。泌尿系统包括肾脏、输尿管、膀胱和尿道。肾脏的功能单位是肾单位，即一个微小的管状结构，在这里进行滤过和重吸收。
Blood enters the nephron through the afferent arteriole and reaches the glomerulus, a knot of capillaries. High pressure forces water, glucose, salts, and urea out of the blood into the Bowman’s capsule – this is ultrafiltration. The filtrate then passes along the nephron. Useful substances such as all glucose, some water, and some salts are reabsorbed back into the blood capillaries surrounding the tubule. Urea is retained and eventually removed in urine. The hormone ADH (antidiuretic hormone) controls water reabsorption by making the collecting duct more permeable to water, helping regulate the body’s water content.
血液经入球小动脉进入肾单位，到达肾小球——一团毛细血管。高压迫使水、葡萄糖、盐和尿素从血液滤出进入肾小囊，这一过程称为超滤。滤液随后流经肾小管，所有葡萄糖、部分水和部分盐等有用物质被重吸收回管周的毛细血管中。尿素则留在管液中，最终随尿排出。激素ADH（抗利尿激素）通过增加集合管对水的通透性来控制水分的重吸收，调节体内含水量。
8. Musculoskeletal System | 骨骼肌肉系统
The skeleton provides support, protection, and movement, while muscles generate force by contracting. Bones are hard and rigid due to calcium compounds, but also contain protein fibres for a degree of flexibility. The skeleton protects delicate organs: the skull protects the brain, the ribcage shields the heart and lungs, and the vertebrae surround the spinal cord.
骨骼提供支持、保护和运动功能，而肌肉则通过收缩产生力量。骨骼因含有钙化合物而坚硬，但也含有蛋白质纤维，具有一定弹性。骨骼保护柔弱的器官：颅骨保护大脑，胸廓保护心脏和肺，脊椎包围脊髓。
Movement occurs at joints, where two or more bones meet. A synovial joint, such as the elbow or knee, allows free movement. The ends of bones are covered with smooth cartilage to reduce friction, and the joint cavity contains synovial fluid as a lubricant. Ligaments connect bone to bone, while tendons attach muscle to bone. Muscles work in antagonistic pairs because they can only contract, not push. For example, to bend the arm, the biceps contracts while the triceps relaxes; to straighten the arm, the triceps contracts and the biceps relaxes.
运动发生在两块或多块骨骼连接的关节处。滑膜关节（如肘关节或膝关节）允许自由活动。骨端覆盖光滑的软骨以减少摩擦，关节腔内有滑液作为润滑剂。韧带连接骨与骨，肌腱附着肌肉与骨。肌肉成对拮抗工作，因为它们只能收缩而不能推。例如，弯曲手臂时，肱二头肌收缩，肱三头肌舒张；伸直手臂时，肱三头肌收缩，肱二头肌舒张。
When a muscle contracts, myosin filaments slide over actin filaments, shortening the sarcomere. This is the sliding filament theory. Energy for contraction comes from ATP produced by respiration. Regular exercise strengthens muscles and increases bone density, but excessive strain can cause fractures or dislocations.
肌肉收缩时，肌球蛋白丝在肌动蛋白丝上滑动，使肌小节缩短。这就是肌丝滑动学说。收缩所需的能量来自呼吸作用产生的ATP。经常锻炼能增强肌肉、增加骨密度，但过度负荷可能导致骨折或脱臼。
9. Immune System | 免疫系统
The immune system defends the body against pathogens, including bacteria, viruses, fungi, and protists. The first line of defence consists of physical and chemical barriers: skin, mucus, stomach acid, and tears containing lysozyme. If pathogens enter the body, white blood cells provide a second line of defence through phagocytosis and antibody production.
免疫系统保护身体免受病原体侵袭，病原体包括细菌、病毒、真菌和原生生物。第一道防线是物理和化学屏障：皮肤、粘液、胃酸以及含有溶菌酶的泪水。若病原体侵入体内，白细胞则通过吞噬作用和产生抗体提供第二道防线。
Phagocytes, such as neutrophils and macrophages, engulf and digest pathogens in a process called phagocytosis. They recognise foreign cells, surround them, and break them down using enzymes. Lymphocytes produce specific antibodies that bind to antigens on the surface of a pathogen, marking it for destruction. Each antibody is specific to one antigen due to its complementary shape. Memory lymphocytes remain after an infection, providing long-term immunity; if the same pathogen invades again, the response is faster and stronger.
吞噬细胞（如中性粒细胞和巨噬细胞）通过吞噬作用吞入并消化病原体。它们识别异己细胞，将其包围并用酶分解。淋巴细胞产生特异性的抗体，抗体与病原体表面的抗原结合，标记其以供摧毁。每种抗体由于形状互补而与特定的抗原结合。感染后记忆淋巴细胞留在体内，提供长期免疫；若同一种病原体再次入侵，应答会更快更强。
Vaccination exploits this memory. A vaccine contains weakened or dead pathogens, or their antigens, which stimulate the immune system to produce memory cells without causing disease. This prepares the body to respond rapidly upon actual infection. Herd immunity occurs when a large proportion of a population is vaccinated, reducing the spread of the disease.
疫苗接种正是利用了这种记忆效应。疫苗含有减弱或灭活的病原体或其抗原，能刺激免疫系统产生记忆细胞而不会引发疾病。这使身体在面对真实感染时能迅速反应。当人群中大部分接种疫苗后，疾病传播减少，形成群体免疫。
10. Homeostasis and Body Temperature | 稳态与体温调节
Homeostasis is the maintenance of a constant internal environment, vital for enzyme activity and cell function. Key factors regulated include body temperature, blood glucose, water balance, and pH. Negative feedback mechanisms automatically detect any change and trigger a corrective response to return the condition to the set point.
稳态是指保持稳定的内环境，这对酶活性和细胞功能至关重要。受调控的关键因素包括体温、血糖、水分平衡和pH。负反馈机制能自动检测任何变化并触发修正反应，使状态回到设定点。
Body temperature in humans is kept around 37 °C, the optimum for enzymes. The thermoregulatory centre in the hypothalamus of the brain monitors blood temperature and receives signals from skin receptors. When the body is too hot, blood vessels in the skin dilate (vasodilation) to increase heat loss by radiation, sweating occurs and uses heat to evaporate, cooling the skin. When too cold, vasoconstriction reduces blood flow to the skin, conserving heat; shivering generates heat through muscle contractions; and hairs on the skin stand up to trap an insulating layer of air (though this is less effective in humans). Behavioural changes, such as putting on a coat or moving into shade, also help regulate temperature.
人体温度维持在约37°C，这是酶的最适温度。大脑下丘脑的体温调节中枢监测血液温度，并接收皮肤感受器的信号。当身体过热时，皮肤血管扩张（血管舒张），通过辐射散失更多热量；出汗并利用体热蒸发，从而冷却皮肤。过冷时，血管收缩减少皮肤血流量以保存热量；颤抖通过肌肉收缩产生热量；体毛竖立（鸡皮疙瘩）以留住一层隔热空气，尽管在人类收效甚微。行为改变，如穿上外套或移到阴凉处，也有助于调节体温。
Water balance is controlled by ADH (described in Section 7). Blood glucose regulation by insulin and glucagon is another classic example of homeostasis, covered in Section 6. Understanding how these systems interact ensures you see the body not as isolated parts, but as an integrated whole.
水分平衡由ADH调控（见第7节）。胰岛素和胰高血糖素对血糖的调节是另一个稳态的经典例子（见第6节）。理解这些系统如何相互作用，有助于你把身体看作一个统一的整体，而非彼此孤立的部件。
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