📚 Human Body: Key Exam Points for IB & CIE Science | 人体：IB与CIE科学考试重点精讲
The human body is a complex system that integrates multiple physiological processes. For IB and CIE science exams, understanding how organ systems work together is essential. This revision guide covers key exam points in human biology, from digestion and circulation to immunity and reproduction, presented in a bilingual format to strengthen your learning.
人体是一个复杂的系统，整合了多种生理过程。对于IB和CIE科学考试，理解各个器官系统如何协同工作至关重要。本复习指南以双语形式涵盖了从消化和循环到免疫与生殖的人体生物学关键考点，帮助巩固你的学习。
1. Digestive System and Nutrient Absorption | 消化系统与营养吸收
The digestive system breaks down large insoluble food molecules into small soluble ones that can be absorbed into the blood. Digestion involves both physical breakdown (chewing, churning) and chemical breakdown by enzymes.
消化系统将大分子不溶性食物分解为可溶的小分子以便被血液吸收。消化涉及物理性分解（咀嚼、搅动）和酶促化学性分解。
Key digestive enzymes include amylase (starch → maltose), protease (proteins → amino acids), and lipase (lipids → fatty acids + glycerol). Bile from the liver emulsifies fats, increasing surface area for lipase action.
主要的消化酶包括淀粉酶（淀粉 → 麦芽糖）、蛋白酶（蛋白质 → 氨基酸）和脂肪酶（脂质 → 脂肪酸 + 甘油）。来自肝脏的胆汁乳化脂肪，增大脂肪酶作用的表面积。
| Enzyme | Substrate | Product | Optimum pH |
|---|---|---|---|
| Salivary amylase | Starch | Maltose | ~7 |
| Pepsin (stomach) | Proteins | Polypeptides | ~1.5 |
| Pancreatic lipase | Lipids | Fatty acids + glycerol | ~8 |
消化酶汇总：唾液淀粉酶分解淀粉，胃蛋白酶分解蛋白质，胰脂肪酶分解脂肪。它们的最适pH各不相同，以适应消化道不同区域环境。
Absorption occurs mainly in the small intestine. Villi and microvilli increase surface area; each villus contains a network of capillaries for sugars and amino acids, and a lacteal for fatty acids and glycerol.
吸收主要发生在小肠。绒毛和微绒毛增大了表面积；每条绒毛内含有毛细血管网吸收葡萄糖和氨基酸，以及乳糜管吸收脂肪酸和甘油。
2. Circulatory System: Heart, Blood Vessels, and Blood | 循环系统：心脏、血管与血液
The circulatory system transports nutrients, gases, hormones, and waste products. In mammals, it is a double circulatory system: pulmonary circulation to the lungs and systemic circulation to the rest of the body.
循环系统运输营养物质、气体、激素和废物。哺乳动物具有双循环系统：肺循环通往肺部，体循环通往全身其他部分。
The heart has four chambers: right atrium, right ventricle, left atrium, left ventricle. Valves prevent backflow of blood. The cardiac cycle is controlled by the sinoatrial node (pacemaker). Cardiac output = heart rate × stroke volume.
心脏有四个腔室：右心房、右心室、左心房、左心室。瓣膜防止血液倒流。心动周期由窦房结（起搏点）控制。心输出量 = 心率 × 每搏输出量。
Cardiac output (CO) = Heart rate (HR) × Stroke volume (SV)
心输出量 (CO) = 心率 (HR) × 每搏输出量 (SV)
Blood consists of plasma, red blood cells (erythrocytes, carry oxygen via haemoglobin), white blood cells (leukocytes, immune defence), and platelets (thrombocytes, blood clotting).
血液由血浆、红细胞（携带血红蛋白运输氧气）、白细胞（免疫防御）和血小板（参与凝血）组成。
Arteries carry blood away from the heart under high pressure, with thick muscular walls. Veins return blood to the heart at low pressure and contain valves. Capillaries are one-cell thick to allow exchange of substances.
动脉将血液从心脏运出，壁厚且富有弹性，可承受高压；静脉将血液送回心脏，血压低且有瓣膜；毛细血管仅由一层细胞构成，便于物质交换。
3. Respiration and Gas Exchange | 呼吸与气体交换
Gas exchange occurs in the alveoli of the lungs. Oxygen diffuses from the alveolar air into the blood, while carbon dioxide diffuses in the opposite direction. Alveoli are adapted with a large surface area, thin walls, and a rich capillary network.
气体交换在肺的肺泡中进行。氧气从肺泡空气扩散入血，而二氧化碳反向扩散。肺泡具有巨大表面积、薄壁和丰富毛细血管网等适应性特征。
Breathing involves the diaphragm and intercostal muscles. During inhalation, the diaphragm contracts and flattens, the ribcage moves up and out, increasing thoracic volume and drawing air in. Exhalation is largely passive at rest.
呼吸运动涉及膈肌和肋间肌。吸气时膈肌收缩变平，肋骨上提外展，胸腔容积增大，空气被吸入。安静时的呼气主要是被动过程。
Aerobic respiration releases energy using oxygen. The overall equation for glucose breakdown is:
有氧呼吸利用氧气释放能量。葡萄糖分解的总方程式为：
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP)
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 能量 (ATP)
Oxygen is transported in the blood mainly bound to haemoglobin in red blood cells, forming oxyhaemoglobin. Carbon dioxide is carried as bicarbonate ions, dissolved CO₂, and bound to haemoglobin.
氧气主要在红细胞中与血红蛋白结合形成氧合血红蛋白运输。二氧化碳以碳酸氢根离子、溶解的CO₂和与血红蛋白结合的形式运输。
4. Nervous System: Neurones, Synapses, and Reflexes | 神经系统：神经元、突触与反射
The nervous system coordinates rapid responses to stimuli. Neurones are specialised cells that transmit electrical impulses. A typical motor neurone has a cell body, dendrites, and a long axon covered by a myelin sheath for insulation and faster conduction.
神经系统协调对刺激的快速反应。神经元是特化的传导电冲动的细胞。一个典型的运动神经元具有胞体、树突和由髓鞘包绕的轴突，髓鞘起绝缘作用并加快传导速度。
At a synapse, the impulse triggers release of neurotransmitter (e.g. acetylcholine) from vesicles into the synaptic cleft. The neurotransmitter diffuses across and binds to receptors on the next neurone, generating a new impulse.
在突触处，冲动触发囊泡释放神经递质（如乙酰胆碱）到突触间隙。神经递质扩散并与其后神经元上的受体结合，产生新的冲动。
A reflex arc provides a rapid, automatic protective response. A simple reflex (e.g. withdrawing from a hot object) follows the pathway: receptor → sensory neurone → relay neurone in CNS → motor neurone → effector (muscle).
反射弧提供快速、自动的保护性反应。一个简单的反射（如缩手反射）遵循通路：感受器 → 感觉神经元 → 中枢神经系统中的中间神经元 → 运动神经元 → 效应器（肌肉）。
5. Homeostasis and Thermoregulation | 稳态与体温调节
Homeostasis is the maintenance of a stable internal environment, including temperature, blood pH, and water balance. Negative feedback mechanisms detect deviations from a set point and trigger corrective responses.
稳态是指维持稳定的内环境，包括温度、血液pH值和水盐平衡。负反馈机制检测偏离调定点的变化并触发纠正性反应。
Body temperature is regulated by the hypothalamus. When the body is too warm, skin blood vessels dilate (vasodilation) and sweating increases to promote heat loss. When cold, vasoconstriction reduces skin blood flow, and shivering generates heat.
体温由下丘脑调节。体热过多时，皮肤血管扩张（舒血管作用）并增加出汗以促进散热。寒冷时，血管收缩减少皮肤血流，肌肉颤抖产热。
The skin plays a key role: hairs stand up (piloerection) to trap insulating air in many mammals, though the effect is minor in humans. Insulating fat layers also help conserve heat.
皮肤起关键作用：许多哺乳动物竖毛肌收缩使毛发直立以滞留保温空气，在人类此效应微小。皮下脂肪层也有助于保温。
6. The Endocrine System and Hormonal Control | 内分泌系统与激素调控
Hormones are chemical messengers produced by endocrine glands and transported in the blood to target organs. They bring about slower, longer-lasting changes compared to nerve impulses.
激素是由内分泌腺产生并通过血液运输到靶器官的化学信使。与神经冲动相比，它们引起较慢但更持久的变化。
Blood glucose regulation is a classic example of negative feedback. After a meal, the pancreas releases insulin, which stimulates cells to uptake glucose and the liver to store glycogen. When blood glucose falls, the pancreas secretes glucagon, promoting glycogen breakdown.
血糖调节是负反馈的经典例子。餐后胰腺释放胰岛素，刺激细胞摄取葡萄糖，肝脏储存糖原。血糖下降时胰腺分泌胰高血糖素，促进糖原分解。
Adrenaline, released from the adrenal glands during stress, prepares the body for ‘fight or flight’: increasing heart rate, dilating airway passages, and directing blood to muscles. Thyroxine from the thyroid gland controls metabolic rate and is regulated by TSH from the pituitary.
肾上腺素在应激时由肾上腺释放，使机体做好“战斗或逃跑”准备：提高心率，扩张气道，将血液导向肌肉。甲状腺分泌的甲状腺素控制代谢率，受垂体TSH调控。
7. The Excretory System and Kidney Function | 排泄系统与肾功能
The kidneys filter blood and produce urine, removing urea and excess water, salts, and toxins. Each kidney contains about a million nephrons, the functional units of filtration and selective reabsorption.
肾脏过滤血液并产生尿液，清除尿素、多余水分、盐分和毒素。每个肾脏含约一百万个肾单位，这是过滤和选择性重吸收的功能单位。
In the glomerulus, high pressure forces small molecules (water, glucose, urea, ions) out of the blood into Bowman’s capsule, forming filtrate. Large proteins and blood cells remain in the blood. This process is called ultrafiltration.
在肾小球中，高压迫使小分子（水、葡萄糖、尿素、离子）滤出血液进入肾小囊，形成原尿。大分子蛋白质和血细胞留在血液中。这一过程称为超滤。
As the filtrate travels through the proximal convoluted tubule, useful substances like glucose and some ions are actively reabsorbed back into the blood. Water is reabsorbed by osmosis in the collecting duct, regulated by ADH (antidiuretic hormone). Urea remains and forms urine.
当原尿流经近曲小管时，葡萄糖和某些离子等有用物质被主动重吸收回血液。在集合管中，水在抗利尿激素（ADH）调控下通过渗透作用重吸收。尿素存留并形成终尿。
8. Immune System and Defense Mechanisms | 免疫系统与防御
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