📚 IGCSE Science: Human Body Key Concepts | IGCSE 科学：人体考点精讲
This revision guide covers all essential human body topics tested in IGCSE Science, from digestion and circulation to reproduction and hormonal coordination. Each section is carefully designed to help you understand key structures, processes, and how systems work together to maintain life.
本篇考点精讲涵盖 IGCSE 科学中人体部分的全部核心内容，从消化、循环到生殖和激素协调。每个小节都旨在帮你理清关键结构、生理过程以及各大系统如何协同工作以维持生命。
1. Digestive System and Enzymes | 消化系统与酶
The digestive system breaks down large, insoluble food molecules into small, soluble ones that can be absorbed into the blood. Mechanical digestion occurs in the mouth and stomach; chemical digestion relies on enzymes produced by glands.
消化系统将大分子不溶性食物分解为可吸收进入血液的小分子可溶物质。物理消化发生在口腔和胃；化学消化依赖于各种腺体分泌的酶。
Amylase is produced in the salivary glands and pancreas. It digests starch into maltose and works best at a neutral to slightly alkaline pH (around pH 7).
淀粉酶由唾液腺和胰腺产生，将淀粉分解为麦芽糖，其最适 pH 为中性偏碱（约 pH 7）。
Proteases are produced in the stomach (pepsin), pancreas (trypsin) and small intestine. They break proteins into amino acids. Pepsin works in the highly acidic stomach (pH 2), while trypsin works in the alkaline small intestine.
蛋白酶在胃（胃蛋白酶）、胰腺（胰蛋白酶）和小肠中产生，将蛋白质分解为氨基酸。胃蛋白酶在胃的强酸环境（pH 2）中工作，胰蛋白酶则在碱性小肠中起作用。
Lipase is produced by the pancreas and digests lipids (fats and oils) into fatty acids and glycerol. Bile, made in the liver and stored in the gall bladder, emulsifies fats into smaller droplets and neutralises stomach acid, creating alkaline conditions for lipase to function at its optimum pH around 8.
脂肪酶由胰腺产生，将脂类分解为脂肪酸和甘油。肝脏分泌并储存在胆囊中的胆汁能将脂肪乳化成微小的脂肪微滴，并中和胃酸，为脂肪酶营造 pH 8 左右的碱性最适环境。
Absorption mainly occurs in the small intestine. Its wall is folded into villi with a single layer of epithelial cells and a dense capillary network, providing a large surface area and short diffusion distance. Glucose and amino acids are absorbed into the blood capillaries; fatty acids and glycerol enter the lacteals.
吸收主要在小肠进行。小肠壁折叠成绒毛，表面为单层上皮细胞，内部有丰富的毛细血管网，提供了巨大的表面积和极短的扩散距离。葡萄糖和氨基酸被吸收入毛细血管，脂肪酸和甘油进入乳糜管。
| Enzyme (酶) | Substrate (底物) | Product(s) (产物) | Optimum pH (最适 pH) |
|---|---|---|---|
| Amylase | Starch | Maltose | ~7 |
| Protease (pepsin) | Proteins | Amino acids | 2 (stomach) |
| Protease (trypsin) | Proteins | Amino acids | ~8 |
| Lipase | Lipids | Fatty acids + glycerol | ~8 |
2. Circulatory System and Blood | 循环系统与血液
Humans have a double circulatory system. The right side of the heart pumps deoxygenated blood to the lungs (pulmonary circulation), while the left side pumps oxygenated blood to the rest of the body (systemic circulation).
人类拥有双循环系统。心脏右侧将缺氧血泵入肺部（肺循环），左侧将富氧血泵送至全身各处（体循环）。
Blood is composed of plasma, red blood cells, white blood cells and platelets. Plasma transports dissolved nutrients, hormones, carbon dioxide and urea. Red blood cells contain haemoglobin, which binds oxygen to form oxyhaemoglobin. They are biconcave discs without a nucleus, maximising space for haemoglobin.
血液由血浆、红细胞、白细胞和血小板组成。血浆运输溶解的营养物质、激素、二氧化碳和尿素。红细胞含血红蛋白，能与氧气结合形成氧合血红蛋白。红细胞呈双凹圆盘状，无细胞核，为血红蛋白提供最大空间。
White blood cells defend the body against pathogens. Lymphocytes produce antibodies, while phagocytes engulf and digest microbes by phagocytosis. Platelets are cell fragments that help blood clot at wounds.
白细胞保护机体抵御病原体。淋巴细胞产生抗体，吞噬细胞通过吞噬作用摄取和消化微生物。血小板是细胞碎片，能在伤口处帮助血液凝固。
Arteries carry blood away from the heart. They have thick muscular and elastic walls to withstand high pressure. Veins carry blood back to the heart and contain valves to prevent backflow. Capillaries are one-cell thick to allow fast diffusion of gases, nutrients and waste.
动脉将血液从心脏运走，管壁肌层厚、弹性强以承受高压。静脉将血液送回心脏，内含瓣膜防止倒流。毛细血管只有一层细胞厚，可进行快速的气体和物质交换。
3. The Heart and Blood Vessels | 心脏与血管
The heart has four chambers: right atrium, right ventricle, left atrium and left ventricle. The ventricles have thicker muscular walls than the atria because they pump blood out of the heart. The left ventricular wall is the thickest as it must pump blood around the entire body.
心脏有四个腔室：右心房、右心室、左心房和左心室。心室壁比心房厚，因为要将血液泵出心脏。左心室壁最厚，因为它需要将血液泵送至全身。
Valves between atria and ventricles (tricuspid on the right, bicuspid on the left) prevent backflow of blood. Semilunar valves at the exits of the pulmonary artery and aorta also prevent backflow into the ventricles.
房室瓣（右侧为三尖瓣，左侧为二尖瓣）防止血液回流。肺动脉和主动脉出口处的半月瓣同样防止血液倒流回心室。
The heartbeat is controlled by a natural pacemaker located in the right atrium, which initiates electrical impulses. Exercise increases heart rate to deliver more oxygen and glucose to muscles and to remove carbon dioxide faster.
心跳由位于右心房的天然起搏器控制，它能发出电脉冲信号。运动会使心率加快，从而向肌肉输送更多氧气和葡萄糖，并更快地清除二氧化碳。
Coronary arteries supply the heart muscle itself with oxygenated blood. A blockage can lead to coronary heart disease. A balanced diet, regular exercise and not smoking reduce the risk.
冠状动脉为心肌自身供应富氧血。血管阻塞可导致冠心病。均衡饮食、定期锻炼和不吸烟能降低风险。
4. Respiratory System and Gas Exchange | 呼吸系统与气体交换
Air enters through the nose or mouth, passes the pharynx, larynx, trachea, bronchi, bronchioles and finally reaches the alveoli – tiny air sacs where gas exchange occurs. The ribs, intercostal muscles and diaphragm work together to ventilate the lungs.
空气经鼻或口进入，通过咽、喉、气管、支气管、细支气管，最终抵达肺泡——进行气体交换的微小气囊。肋骨、肋间肌和膈肌协同完成肺的通气。
During inhalation, the diaphragm contracts and flattens, the external intercostal muscles contract, lifting the rib cage upwards and outwards. This increases the volume of the thorax and lowers the pressure, drawing air into the lungs. Exhalation is largely passive at rest.
吸气时，膈肌收缩变平，外肋间肌收缩使胸廓向上向外抬起。胸腔容积增大，压力降低，空气被吸入肺部。静息时呼气主要为被动过程。
Gas exchange at the alveoli relies on diffusion. Alveolar walls are one cell thick, surrounded by a dense capillary network. Oxygen diffuses from alveolar air into the blood, binding to haemoglobin; carbon dioxide diffuses from the blood into the alveoli to be exhaled.
肺泡处的气体交换依赖于扩散。肺泡壁仅一层细胞厚，周围密布毛细血管网。氧气从肺泡空气扩散入血，与血红蛋白结合；二氧化碳由血液扩散入肺泡被呼出。
Inhaled air contains about 21% oxygen and 0.04% carbon dioxide. Exhaled air contains about 16% oxygen and 4% carbon dioxide, and is saturated with water vapour. Test exhaled air with limewater: it turns milky due to CO₂.
吸入空气约含 21% 氧气和 0.04% 二氧化碳。呼出气体约含 16% 氧气和 4% 二氧化碳，且水蒸气饱和。用石灰水检测呼出气体，会因 CO₂ 存在而变浑浊。
5. Excretory System and Kidney Function | 排泄系统与肾脏功能
Excretion is the removal of metabolic waste, mainly urea, excess water and salts. The kidneys filter blood and produce urine. Each kidney contains around one million nephrons – the functional filtration units.
排泄是指排除代谢废物，主要为尿素、多余的水和盐。肾脏过滤血液并形成尿液。每个肾脏约有 100 万个功能性的滤过单位——肾单位。
A nephron consists of Bowman’s capsule, glomerulus, proximal convoluted tubule, loop of Henlé, distal convoluted tubule and collecting duct. Ultrafiltration occurs in the Bowman’s capsule under high pressure: small molecules like water, glucose, salts and urea are forced out of the glomerular blood into the capsule, while blood cells and large proteins remain.
肾单位由鲍曼氏囊、肾小球、近曲小管、亨利氏袢、远曲小管和集合管组成。在鲍曼氏囊内，高压实现超滤：水、葡萄糖、盐和尿素等小分子从肾小球血液中被压入囊内，而血细胞和大分子蛋白质停留在血液中。
Selective reabsorption then takes place mainly in the proximal convoluted tubule. All glucose, most water and many useful salts are actively transported back into the blood capillaries. The remaining filtrate becomes urine, which is transported to the bladder.
随后，选择性重吸收主要在近曲小管进行。所有葡萄糖、大部分水和许多有用盐类被主动转运回血液。剩下的滤液成为尿液，输送到膀胱。
The hormone ADH (antidiuretic hormone) controls water reabsorption in the collecting duct. When the blood is too concentrated, more ADH is released, making the collecting duct walls more permeable to water, so more water is reabsorbed and urine volume decreases.
抗利尿激素 ADH 控制着集合管对水的重吸收。当血液过浓时，ADH 释放增多，使集合管壁对水的通透性增强，更多的水被重吸收，尿量减少。
6. Nervous System and Reflexes | 神经系统与反射
The human nervous system consists of the central nervous system (CNS) – brain and spinal cord – and the peripheral nervous system. It coordinates responses to stimuli via electrical impulses transmitted along neurones.
人体神经系统由中枢神经系统（脑和脊髓）与周围神经系统组成。它通过神经细胞传递的电脉冲来协调对刺激的反应。
A neurone has a cell body, dendrites, an axon and axon terminals. Sensory neurones carry impulses from receptors to the CNS, relay neurones connect neurones within the CNS, and motor neurones carry impulses from the CNS to effectors (muscles or glands).
神经元包含细胞体、树突、轴突和轴突终末。感觉神经元将冲动从感受器传向中枢神经系统，中间神经元在中枢神经系统内连接各神经元，运动神经元将冲动从中枢神经系统传至效应器（肌肉或腺体）。
Synapses are tiny gaps between neurones where neurotransmitters diffuse across, allowing impulses to pass from one neurone to the next. Many drugs affect transmission across synapses.
突触是神经元之间的微小间隙，神经递质在此扩散，使冲动得以从一个神经元传至下一个。许多药物会影响突触间的传递。
A reflex action is a rapid, automatic response to a stimulus that minimises harm. The pathway is called a reflex arc: stimulus → receptor → sensory neurone → relay neurone (in spinal cord) → motor neurone → effector → response. Because the impulse bypasses conscious brain areas, reflexes are extremely fast.
反射是对刺激作出的迅速、自动的反应，能最大限度地减少伤害。其通路称为反射弧：刺激 → 感受器 → 感觉神经元 → 中间神经元（在脊髓） → 运动神经元 → 效应器 → 反应。由于冲动不经大脑意识区域，反射非常快。
7. The Eye as a Sense Organ | 眼睛作为感觉器官
The eye contains light-sensitive receptor cells in the retina. Light passes through the cornea, pupil and lens before being focused onto the fovea. The cornea does most of the refraction; the lens fine-tunes the focus.
眼睛的视网膜上含有光敏感的感受器细胞。光线依次经过角膜、瞳孔和晶状体，最终聚焦在黄斑中央凹上。角膜完成大部分折射，晶状体进行精细调焦。
The iris controls the size of the pupil and thus the amount of light entering the eye. In bright light, circular muscles contract and radial muscles relax, making the pupil smaller. In dim light, radial muscles contract and circular muscles relax, dilating the pupil.
虹膜控制瞳孔的大小，从而调节进入眼内的光线量。在强光下，环行肌收缩，放射肌舒张，瞳孔缩小；在弱光下，放射肌收缩，环行肌舒张，瞳孔扩大。
Accommodation is the adjustment of the lens shape to focus on near or distant objects. For near objects, the ciliary muscles contract, relaxing the suspensory ligaments, so the lens becomes more rounded and light is bent more strongly. For distant objects, the opposite happens and the lens flattens.
调节就是指晶状体改变形状以聚焦近处或远处的物体。看近物时，睫状肌收缩，悬韧带松弛，晶状体变得更凸，光线折射增强。看远物时相反，晶状体变平。
Common defects include short-sightedness (myopia) where the eyeball is too long or the lens too powerful, causing distant images to focus in front of the retina. It is corrected with a concave diverging lens.
常见视力缺陷包括近视，即眼球过长或晶状体折射过强，使远处物体的像落在视网膜之前，可用凹透镜（发散透镜）矫正。
8. Endocrine System and Hormones | 内分泌系统与激素
The endocrine system uses chemical messengers called hormones, which are secreted by glands and travel in the blood to target organs. Responses are slower but longer-lasting than nervous responses.
内分泌系统使用被称为激素的化学信使，它们由腺体分泌，经血液运送到靶器官。其反应比神经系统慢，但持续时间更长。
Insulin is released by the pancreas when blood glucose is high (e.g. after a meal). It stimulates the liver and muscle cells to convert excess glucose into glycogen for storage, lowering blood glucose back to normal. Glucagon has the opposite effect when blood glucose falls.
当血糖水平升高时（如饭后），胰腺释放胰岛素。胰岛素刺激肝脏和肌肉细胞将多余的葡萄糖转化为糖原储存，使血糖恢复正常。血糖降低时，胰高血糖素起相反作用。
Adrenaline is produced by the adrenal glands in times of fear or stress. It increases heart rate, dilates pupils, increases blood flow to muscles and boosts the conversion of glycogen to glucose – preparing the body for ‘fight or flight’.
肾上腺素在恐惧或应激时由肾上腺分泌。它使心率加快、瞳孔放大、肌血流量增加、促进糖原转化为葡萄糖——让身体做好“战斗或逃跑”的准备。
Thyroxine from the thyroid gland controls metabolic rate. Its release is regulated by TSH (thyroid-stimulating hormone) from the pituitary gland, forming a classic negative feedback loop.
甲状腺分泌的甲状腺素控制代谢率。其释放受垂体分泌的促甲状腺激素（TSH）调控，形成一个典型的负反馈环路。
9. Human Reproduction | 人体生殖
The male reproductive system includes testes (produce sperm and testosterone), sperm ducts, seminal vesicles and prostate gland. The female system includes ovaries (produce eggs, oestrogen and progesterone), oviducts, uterus and vagina.
男性生殖系统包括睾丸（产生精子和睾酮）、输精管、精囊和前列腺。女性系统包括卵巢（产生卵子、雌激素和孕酮）、输卵管、子宫和阴道。
Fertilisation occurs when the nucleus of a sperm fuses with the nucleus of an egg in the oviduct, forming a zygote. The zygote implants into the lining of the uterus (endometrium) and develops into an embryo.
受精发生在输卵管内，精子核与卵子核融合形成合子。合子植入子宫内膜，并发育成胚胎。
The placenta acts as the interface between mother and baby, allowing the exchange of nutrients, oxygen, antibodies and wastes without the two bloodstreams mixing. The amniotic fluid protects the fetus from mechanical shocks.
胎盘是母儿之间的交换界面，允许营养、氧气、抗体和废物的交换，而双方血液并不混合。羊水保护胎儿免受机械冲击。
The menstrual cycle is controlled by hormones. FSH (follicle-stimulating hormone) causes an egg to mature; oestrogen rebuilds the uterine lining and triggers a surge of LH (luteinising hormone), which causes ovulation. After ovulation, progesterone maintains the uterine lining. If fertilisation does not occur, oestrogen and progesterone levels drop, leading to menstruation.
月经周期由激素调控。FSH（卵泡刺激素）使卵子成熟；雌激素修复子宫内膜，并引发 LH（黄体生成素）激增，导致排卵。排卵后，孕酮维持子宫内膜。若未受精，雌激素和孕酮水平下降，引发月经。
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