Human Respiratory System: Breathing and Gas Exchange | 人体呼吸系统：呼吸与气体交换

📚 Human Respiratory System: Breathing and Gas Exchange | 人体呼吸系统：呼吸与气体交换

The human respiratory system is essential for life. It supplies oxygen to the blood and removes carbon dioxide from the body. Strong knowledge of this system is a core requirement for IGCSE Biology.

人体呼吸系统是生命所必需的。它为血液提供氧气，并清除体内的二氧化碳。掌握该系统是IGCSE生物学的核心要求。

1. Overview of the Respiratory System | 呼吸系统概述

The respiratory system consists of the airways, the lungs, and the muscles that drive breathing, mainly the diaphragm and intercostal muscles.

呼吸系统由气道、肺以及驱动呼吸的肌肉组成，主要是横膈膜和肋间肌。

Its main functions are ventilation and gas exchange. Ventilation moves air in and out of the lungs, while gas exchange occurs at the alveoli where oxygen and carbon dioxide are exchanged between air and blood.

其主要功能是通气和气体交换。通气使空气进出肺部，而气体交换发生在肺泡处，氧气和二氧化碳在空气与血液之间交换。

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2. The Passage of Air | 空气的通道

Air enters through the nostrils or mouth and passes through the nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles and finally reaches the alveoli.

空气通过鼻孔或口腔进入，流经鼻腔、咽、喉、气管、支气管、细支气管，最终到达肺泡。

The nasal cavity contains vibrissae and mucus that filter, warm and moisten the air. The trachea is supported by C-shaped cartilage rings to prevent collapse.

鼻腔内有鼻毛和黏液，能够过滤、温暖和湿润空气。气管由C形软骨环支撑，以防止塌陷。

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3. The Lungs and Alveoli | 肺与肺泡

The lungs are a pair of spongy organs located in the thoracic cavity. Each lung contains millions of tiny air sacs called alveoli.

肺是一对位于胸腔内的海绵状器官。每个肺包含数百万个称为肺泡的微小气囊。

Alveoli are highly adapted for gas exchange. They provide a large surface area, have very thin walls (one cell thick), are kept moist, and are surrounded by dense networks of capillaries.

肺泡高度适应气体交换。它们提供了巨大的表面积，壁极薄（仅一个细胞厚），保持湿润，并且被丰富的毛细血管网包围。

Feature | 特征	How It Aids Gas Exchange | 如何帮助气体交换
Large number | 数量众多	Increases surface area for diffusion | 增大扩散表面积
Thin walls | 壁薄	Shortens diffusion distance | 缩短扩散距离
Moist surface | 表面湿润	Helps dissolve gases | 有助于气体溶解
Rich capillary network | 丰富的毛细血管网	Maintains concentration gradients | 维持浓度梯度

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4. Mechanism of Ventilation | 通气机制（呼吸运动）

Breathing involves two phases: inspiration (inhalation) and expiration (exhalation).

呼吸涉及两个阶段：吸气（吸入）和呼气（呼出）。

During inspiration, the external intercostal muscles contract and the ribcage moves up and out. The diaphragm contracts and flattens. This increases the volume of the thorax, reducing the pressure inside the lungs, so air rushes in.

吸气时，肋间外肌收缩，胸腔上移并向外扩展。横膈膜收缩并变平。这使胸腔容积增大，肺内压力降低，因此空气涌入。

During expiration, these muscles relax, the diaphragm becomes dome-shaped, the thorax volume decreases and air is pushed out.

呼气时，这些肌肉放松，横膈膜恢复穹顶状，胸腔容积减小，空气被挤出。

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5. Gaseous Exchange in the Alveoli | 肺泡内的气体交换

Gas exchange occurs by simple diffusion at the thin respiratory membrane. Oxygen diffuses from the air in the alveoli into the blood capillaries, while carbon dioxide diffuses in the opposite direction.

气体交换依靠呼吸膜上的简单扩散进行。氧气从肺泡内的空气扩散进入毛细血管，而二氧化碳向相反方向扩散。

The blood arriving in the alveolar capillaries is deoxygenated and has a high concentration of carbon dioxide. After exchange, it becomes oxygenated blood and returns to the heart.

到达肺泡毛细血管的血液是脱氧的，且二氧化碳浓度高。交换后，它变成含氧血并返回心脏。

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6. Transport of Oxygen and Carbon Dioxide | 氧气和二氧化碳的运输

Oxygen is transported mainly by haemoglobin in red blood cells, forming oxyhaemoglobin. About 97% of oxygen is carried this way.

氧气主要通过红细胞中的血红蛋白运输，形成氧合血红蛋白。大约97%的氧气以此方式携带。

Carbon dioxide is transported in three ways: dissolved in plasma (~5%), bound to haemoglobin (~10%), and mostly as hydrogencarbonate ions in plasma (~85%).

二氧化碳以三种方式运输：溶解在血浆中（约5%），与血红蛋白结合（约10%），以及主要以血浆中的碳酸氢根离子运输（约85%）。

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7. Cellular Respiration | 细胞呼吸

Cellular respiration is the process by which cells release energy from glucose. Aerobic respiration requires oxygen.

细胞呼吸是细胞从葡萄糖中释放能量的过程。有氧呼吸需要氧气。

The balanced equation for aerobic respiration is:

有氧呼吸的平衡方程式为：

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy

In this reaction, glucose is oxidised, releasing energy that is used to synthesise ATP. Water and carbon dioxide are waste products.

在此反应中，葡萄糖被氧化，释放出用于合成ATP的能量。水和二氧化碳是废物。

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8. Exercise and Breathing Rate | 运动与呼吸频率

During exercise, muscles respire faster. The breathing rate and depth increase to supply more oxygen and remove more carbon dioxide.

运动期间，肌肉呼吸加快。呼吸频率和深度增加，以提供更多氧气并清除更多二氧化碳。

Heart rate also increases to deliver oxygen faster. These changes are controlled by the medulla oblongata and induced by the rising carbon dioxide concentration.

心率也增加以更快地输送氧气。这些变化由延髓控制，由二氧化碳浓度升高引起。

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9. Effects of Smoking | 吸烟的影响

Cigarette smoke contains many harmful substances, including tar, carbon monoxide and nicotine.

香烟烟雾含有许多有害物质，包括焦油、一氧化碳和尼古丁。

Tar damages the cilia in airways, causing a buildup of mucus and chronic bronchitis. It also increases the risk of lung cancer. Carbon monoxide binds permanently to haemoglobin, reducing oxygen transport.

焦油损害气道纤毛，导致黏液堆积和慢性支气管炎，同时增加肺癌风险。一氧化碳永久结合血红蛋白，减少氧气运输。

Long-term smoking can cause emphysema, where alveolar walls break down, reducing the surface area for gas exchange.

长期吸烟可导致肺气肿，肺泡壁破裂，减少气体交换表面积。

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10. Respiration vs Breathing | 呼吸作用与呼吸（通气）的区别

Breathing is the physical movement of air in and out of the lungs. Respiration is a chemical reaction that releases energy in cells.

呼吸（通气）是空气进出肺的物理运动。呼吸作用是在细胞中释放能量的化学反应。

Respiration can be aerobic or anaerobic, while breathing only has two phases, inspiration and expiration.

呼吸作用可分为有氧呼吸和无氧呼吸，而呼吸（通气）只有吸气和呼气两个阶段。

Breathing 呼吸（通气）	Respiration 呼吸作用
Physical process 物理过程	Chemical reaction 化学反应
Occurs in the lungs 发生于肺部	Occurs in cells 发生于细胞
Moves air 使空气流动	Releases energy 释放能量

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