IB AQA Science: Human Body Key Points | IB AQA 科学：人体考点精讲

📚 IB AQA Science: Human Body Key Points | IB AQA 科学：人体考点精讲

This revision guide consolidates the most essential topics on the human body required for IB and AQA science courses. From digestion and circulation to neural control and homeostasis, every section pairs core concepts with clear explanations to support your exam preparation.

本文精讲 IB 与 AQA 科学课程中人体部分的核心考点，涵盖消化、循环、神经调控与内稳态等关键系统，每个要点均配中英双语解析，助你高效备考。

1. Digestive System and Enzymes | 消化系统与酶

The human digestive system breaks down large, insoluble food molecules into small, soluble ones that can be absorbed into the blood. Mechanical digestion begins in the mouth with chewing, while chemical digestion relies on specific enzymes.

人体消化系统将大分子不溶性食物分解为可溶于水的小分子，以便吸收进入血液。口腔的咀嚼启动物理消化，化学消化则由专一酶负责。

Amylase, produced in the salivary glands and pancreas, catalyses the hydrolysis of starch into maltose. It works best at a slightly alkaline pH (around 7-8) and requires chloride ions as a cofactor.

唾液腺和胰腺分泌的淀粉酶催化淀粉水解为麦芽糖，其最适 pH 约 7-8，需氯离子作为辅助因子。

Proteases (pepsin in the stomach, trypsin in the small intestine) hydrolyse proteins into peptides and amino acids. Pepsin requires the highly acidic environment of the stomach (pH 1.5-2), while trypsin functions in the alkaline small intestine (pH 8).

蛋白酶（胃蛋白酶、胰蛋白酶）将蛋白质水解为肽和氨基酸。胃蛋白酶需强酸环境（pH 1.5-2），胰蛋白酶则在小肠碱性条件（pH 8）下工作。

Lipase, aided by bile salts that emulsify fats, breaks down lipids into fatty acids and glycerol. Bile is produced in the liver and stored in the gallbladder.

脂肪酶在胆汁盐乳化作用下将脂肪分解为脂肪酸和甘油。胆汁由肝脏分泌，储存在胆囊。

2. Circulatory System: Heart and Blood Vessels | 循环系统：心脏与血管

The human circulatory system is a closed, double-loop system. The heart has four chambers: two atria receive blood, and two ventricles pump blood out. The right side handles deoxygenated blood to the lungs; the left side pumps oxygenated blood to the body.

人体循环系统为闭管式双循环。心脏有四个腔：心房接收血液，心室泵出血液。右心将缺氧血送往肺部，左心将富氧血泵至全身。

Arteries carry blood away from the heart under high pressure; they have thick, elastic walls. Veins return blood at lower pressure, possessing valves to prevent backflow. Capillaries are one-cell-thick vessels that allow exchange of materials with tissues.

动脉在高压下将血液输离心脏，管壁厚而富有弹性。静脉于低压下回送血液，具有防止倒流的瓣膜。毛细血管壁仅一层细胞，利于物质交换。

The cardiac cycle is myogenic, initiated by the sinoatrial (SA) node. The sequence of atrial systole, ventricular systole, and diastole ensures efficient pumping. A typical resting heart rate is 60-80 beats per minute.

心动周期是肌源性的，由窦房结触发。心房收缩、心室收缩和舒张依次进行，保证高效泵血。静息心率通常为 60-80 次/分。

3. Respiratory System and Gas Exchange | 呼吸系统与气体交换

Air enters through the nasal passages, passes the pharynx, larynx, trachea, bronchi, and bronchioles, finally reaching the alveoli. The alveoli provide a vast surface area (~70 m²) for gas exchange.

空气经鼻腔、咽、喉、气管、支气管和细支气管，最终到达肺泡。肺泡提供约 70 m² 的巨大表面积用于气体交换。

Oxygen diffuses from alveolar air into the blood down a concentration gradient, while carbon dioxide diffuses in the opposite direction. This process is driven by differences in partial pressure.

氧气沿浓度梯度由肺泡气扩散入血，二氧化碳反向扩散，由分压差驱动。

Ventilation involves the diaphragm and intercostal muscles. During inhalation, the diaphragm contracts and flattens, external intercostals lift the rib cage, reducing thoracic pressure and drawing air in. Exhalation is largely passive at rest.

通气依靠膈肌和肋间肌。吸气时膈肌收缩变平，外肋间肌上提胸廓，胸内压降低，气体进入；安静呼气主要靠被动回弹。

4. Excretory System and Kidney Function | 排泄系统与肾脏功能

The kidneys filter blood, removing urea, excess water, and ions to form urine. The functional unit is the nephron, which consists of Bowman’s capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct.

肾脏滤过血液，清除尿素、多余水分和离子以形成尿液。功能单位肾单位包括肾小囊、近曲小管、髓袢、远曲小管和集合管。

Ultrafiltration occurs in the glomerulus, where high blood pressure forces water, urea, glucose, and ions out of the capillary into Bowman’s capsule, retaining proteins and cells.

超滤在肾小球发生：高血压迫使水、尿素、葡萄糖和离子滤入肾小囊，蛋白质和血细胞被截留。

Selective reabsorption reclaims useful substances. In the proximal tubule, all glucose and most salts are reabsorbed by active transport; water follows by osmosis. The loop of Henle establishes a concentration gradient for water recovery.

选择性重吸收回收有用物质。近曲小管通过主动转运重吸收全部葡萄糖和大部分盐类；水经渗透跟随。髓袢形成浓度梯度以促进水的重吸收。

5. Nervous System and Reflex Arc | 神经系统与反射弧

The nervous system uses electrical impulses to enable rapid communication. A reflex arc is the simplest nerve pathway, bypassing the brain for quicker responses, e.g., withdrawal from a hot object.

神经系统依靠电冲动快速通信。反射弧是最简单的神经通路，绕开大脑以实现快速响应，例如手遇热回缩。

A reflex arc follows: receptor → sensory neuron → relay neuron (in spinal cord) → motor neuron → effector (muscle or gland). Synapses between neurons use neurotransmitters such as acetylcholine.

反射弧路径：感受器→感觉神经元→中间神经元（脊髓）→运动神经元→效应器（肌肉或腺体）。神经元之间的突触利用乙酰胆碱等神经递质传递信号。

The pupil reflex and knee-jerk reflex are common examples. Reflexes are innate and involuntary, helping to protect the body from harm.

瞳孔对光反射和膝跳反射是常见实例。反射是先天、不随意的，有助于保护机体免受伤害。

6. Endocrine System and Hormonal Control | 内分泌系统与激素调控

Hormones are chemical messengers secreted by glands, travelling through the bloodstream to target organs. Compared to nerve impulses, hormonal responses are slower but longer-lasting.

激素是腺体分泌的化学信使，经血液运送至靶器官。与神经冲动相比，激素反应较慢但持续时间更长。

Insulin lowers blood glucose by promoting cellular uptake and conversion to glycogen. Glucagon raises blood glucose by stimulating glycogen breakdown. These two pancreatic hormones maintain glucose homeostasis via negative feedback.

胰岛素通过促进细胞摄取和糖原合成降低血糖；胰高血糖素通过刺激糖原分解升高血糖。这两种胰腺激素经负反馈维持血糖稳态。

Adrenaline, released in stress, increases heart rate and blood flow to muscles, preparing for “fight or flight”. Thyroxine regulates metabolic rate, and its production is controlled by TSH from the pituitary.

应激时释放的肾上腺素提高心率与肌肉血流，启动“战斗或逃跑”反应。甲状腺素调节代谢率，其分泌受垂体 TSH 调控。

7. Immune System and Defence Mechanisms | 免疫系统与防御机制

The body’s first line of defence includes physical barriers like skin and mucous membranes. If pathogens enter, the innate immune response engages phagocytes that engulf microbes non-specifically.

人体第一道防线为皮肤、黏膜等物理屏障。病原体入侵后，先天免疫启动，吞噬细胞非特异地吞食微生物。

Lymphocytes provide specific immunity. B cells produce antibodies that bind to antigens, neutralising pathogens or marking them for destruction. T cells destroy infected cells and assist B cells.

淋巴细胞赋予特异性免疫。B 细胞产生抗体，结合抗原以中和病原体或标记其供摧毁。T 细胞破坏受感染细胞并辅助 B 细胞。

Vaccination introduces a harmless form of antigen, stimulating memory cell production. Upon re-exposure, the secondary response is faster and stronger, preventing illness.

疫苗接种引入无毒抗原，刺激记忆细胞生成。再次接触时，二次应答更快、更强，从而预防疾病。

8. Homeostasis and Feedback Mechanisms | 内稳态与反馈机制

Homeostasis is the maintenance of a stable internal environment. Core regulated variables include temperature, blood glucose, water balance, and pH. Most regulation operates through negative feedback loops.

内稳态指维持内部环境稳定，核心调控变量包括体温、血糖、水平衡和 pH。多数调控通过负反馈回路实现。

In thermoregulation, thermoreceptors in the skin and hypothalamus detect changes. Cooling responses include vasodilation and sweating; warming responses involve vasoconstriction, shivering, and hair erection.

体温调节中，皮肤和下丘脑的温度感受器感知变化。散热反应包括血管舒张和出汗；产热保守反应包括血管收缩、颤抖和竖毛。

Osmoregulation is managed by ADH. When blood water potential is low, the pituitary releases ADH, making collecting ducts more permeable to water, producing concentrated urine.

渗透调节由抗利尿激素 (ADH) 掌管。血液水势低时，垂体释放 ADH，提高集合管对水的通透性，形成浓缩尿。

9. Musculoskeletal System and Movement | 骨骼肌肉系统与运动

Muscles work in antagonistic pairs, e.g., biceps and triceps in the upper arm. When one muscle contracts, the other relaxes, allowing controlled movement across a joint.

骨骼肌成对抗配对工作，如上臂的肱二头肌和肱三头肌。一肌收缩时另一肌舒张，使关节产生受控运动。

A synovial joint, such as the knee or elbow, features cartilage to reduce friction, synovial fluid for lubrication, and ligaments to connect bones. Tendons attach muscle to bone.

滑膜关节（如膝、肘）含有减少摩擦的软骨、润滑用的滑液，以及连接骨头的韧带。肌腱将肌肉附着于骨。

Aerobic respiration in muscles provides energy for contraction; during strenuous exercise, anaerobic respiration leads to lactic acid build-up, causing fatigue and oxygen debt.

肌肉有氧呼吸提供收缩能量；剧烈运动中无氧呼吸导致乳酸堆积，引起疲劳和氧债。

10. Reproductive System and Development | 生殖系统与发育

The male reproductive system produces sperm in the testes, with the hormone testosterone governing sperm production and secondary sexual characteristics. The female system releases eggs from the ovaries; oestrogen and progesterone regulate the menstrual cycle.

男性生殖系统由睾丸产生精子，睾酮调控精子发生和第二性征。女性系统由卵巢排卵，雌激素和孕酮控制月经周期。

Fertilisation occurs in the oviduct when a sperm fuses with an egg, forming a diploid zygote. The zygote undergoes mitosis as it travels to the uterus for implantation.

受精在输卵管发生，精卵融合形成二倍体合子。合子一边进行有丝分裂一边移行至子宫着床。

The placenta allows exchange of oxygen, nutrients, and waste without mixing maternal and foetal blood. Hormonal changes during pregnancy maintain the uterine lining and prepare for birth.

胎盘实现氧、营养与废物的交换，同时避免母儿血液混合。妊娠期激素变化维持子宫内膜并为分娩做准备。

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IB AQA Science: Human Body Key Points | IB AQA 科学：人体 考点精讲