📚 Gas Exchange and Smoking | 气体交换与吸烟
Gas exchange is the process by which oxygen is taken up from the environment and carbon dioxide is removed from the body. In humans, this occurs in the lungs across the alveolar surface. Smoking damages the gas exchange system at every level, from the airways to the alveoli, and is a major cause of chronic obstructive pulmonary disease and lung cancer.
气体交换是从环境中摄取氧气并从体内排出二氧化碳的过程。在人体中，这一过程发生在肺部的肺泡表面。吸烟会对气体交换系统的各个层面造成损害，从气道到肺泡，并且是慢性阻塞性肺病和肺癌的主要原因。
1. The Human Gas Exchange System | 人体气体交换系统
In humans, gas exchange occurs in the lungs. Air enters through the nasal cavity or mouth, passes down the trachea, and then divides into two bronchi, one for each lung. The bronchi branch repeatedly into smaller bronchioles, which end in clusters of alveoli. This branching structure provides a very large surface area for diffusion.
在人体中，气体交换发生在肺部。空气通过鼻腔或口腔进入，沿气管向下，然后分为两根支气管，每根通向一侧肺。支气管反复分支为更细的细支气管，最终末端为成簇的肺泡。这种分支结构为扩散提供了非常大的表面积。
The trachea and bronchi are supported by C-shaped rings of cartilage, which prevent collapse during breathing. Smooth muscle in the bronchioles can contract or relax to control airflow.
气管和支气管由 C 形软骨环支撑，防止呼吸时塌陷。细支气管中的平滑肌可以收缩或舒张，以控制气流。
2. Ventilation Mechanics | 通气机制
Inspiration is an active process. The external intercostal muscles contract and the diaphragm flattens, increasing the volume of the thorax. This decreases the pressure inside the lungs below atmospheric pressure, so air moves in.
吸气是一个主动过程。外肋间肌收缩，膈肌变平，使胸腔容积增大。这使肺内压力降至大气压以下，因此空气进入肺部。
Expiration at rest is mainly passive. The intercostal muscles and diaphragm relax, the rib cage moves down and inward, and elastic recoil of the lungs forces air out.
平静呼气主要是被动过程。肋间肌和膈肌放松，胸廓向下向内移动，肺的弹性回缩将空气排出。
During exercise, expiration becomes active, with contraction of internal intercostal muscles and abdominal muscles.
运动时，呼气变为主动过程，内肋间肌和腹肌收缩。
Pulmonary ventilation = tidal volume × breathing rate
This equation shows that the volume of air moved into the lungs per minute depends on how much air is taken in per breath and how many breaths occur per minute.
该方程表明，每分钟进入肺部的空气量取决于每次呼吸吸入的空气量以及每分钟的呼吸次数。
3. Alveolar Structure and Function | 肺泡结构与功能
Alveoli are tiny air sacs surrounded by a dense network of pulmonary capillaries. Their walls consist of a single layer of squamous epithelial cells, which minimises the diffusion distance between air and blood.
肺泡是微小气囊，周围有密集的肺毛细血管网。其壁由单层扁平上皮细胞构成，最大限度地缩短了空气与血液之间的扩散距离。
The inner surface of each alveolus is coated with a thin film of water containing pulmonary surfactant. Surfactant reduces surface tension, preventing alveolar collapse during expiration.
每个肺泡内表面覆盖一层含有肺表面活性物质的薄水膜。表面活性物质可降低表面张力，防止呼气时肺泡塌陷。
4. Fick’s Law Applied to Gas Exchange | 菲克定律在气体交换中的应用
Rate of diffusion = (surface area × concentration gradient) ÷ diffusion distance
Fick’s law states that the rate of diffusion is directly proportional to surface area and concentration gradient, and inversely proportional to diffusion distance.
菲克定律指出，扩散速率与表面积和浓度梯度成正比，与扩散距离成反比。
The alveoli provide a surface area of about 70 m² in an adult, a steep concentration gradient maintained by ventilation and blood flow, and an extremely thin diffusion barrier of roughly 0.5 μm.
成年人肺泡提供约 70 m² 的表面积，通气和血流维持陡峭的浓度梯度，扩散屏障极薄，约为 0.5 μm。
5. Oxygen and Carbon Dioxide Transport | 氧气与二氧化碳的运输
Hb + 4O₂ ⇌ Hb(O₂)₄
Oxygen is transported mainly by binding reversibly to haemoglobin in red blood cells to form oxyhaemoglobin. A small percentage dissolves in plasma.
氧气主要通过与红细胞中的血红蛋白可逆结合形成氧合血红蛋白进行运输。少量氧气溶解在血浆中。
Carbon dioxide is carried in the blood in three forms: dissolved in plasma, as carbaminohaemoglobin, and mostly as hydrogen carbonate ions (HCO₃⁻) formed in red blood cells.
二氧化碳在血液中以三种形式运输：溶解在血浆中、以氨基甲酰血红蛋白形式存在，以及大部分在红细胞内形成碳酸氢根离子（HCO₃⁻）运输。
6. Components of Tobacco Smoke | 烟草烟雾的成分
Tobacco smoke contains more than 7,000 chemicals, including tar, nicotine, carbon monoxide, and many carcinogens such as benzo[a]pyrene and nitrosamines.
烟草烟雾含有超过 7000 种化学物质，包括焦油、尼古丁、一氧化碳以及苯并[a]芘和亚硝胺等多种致癌物。
Tar is a sticky mixture that deposits in the airways and alveoli. Nicotine is highly addictive and stimulates the nervous system. Carbon monoxide binds strongly to haemoglobin.
焦油是一种黏性混合物，沉积在气道和肺泡中。尼古丁具有高度成瘾性并刺激神经系统。一氧化碳与血红蛋白强烈结合。
7. Chronic Obstructive Pulmonary Disease (COPD) | 慢性阻塞性肺病
COPD is a group of lung diseases that includes chronic bronchitis and emphysema. It is characterised by progressive airflow limitation that is not fully reversible.
慢性阻塞性肺病是一组包括慢性支气管炎和肺气肿的肺部疾病，其特征是进行性气流受限且不完全可逆。
The main cause of COPD is long-term exposure to tobacco smoke, although air pollution and occupational dusts can also contribute.
慢性阻塞性肺病的主要病因是长期接触烟草烟雾，但空气污染和职业粉尘也可促进发病。
| Feature | Chronic bronchitis | Emphysema |
|---|---|---|
| Main site | Bronchi and bronchioles | Alveoli |
| Key changes | Excess mucus, damaged cilia | Alveolar wall breakdown, loss of elasticity |
This table compares the main features of chronic bronchitis and emphysema, the two major forms of COPD.
该表比较了慢性支气管炎和肺气肿这两种主要慢阻肺类型的主要特征。
8. Chronic Bronchitis | 慢性支气管炎
Chronic bronchitis is inflammation of the lining of the airways. Tar and irritants stimulate goblet cells to produce excess mucus and damage cilia.
慢性支气管炎是气道内壁的炎症。焦油和刺激物刺激杯状细胞产生过多黏液，并损伤纤毛。
Damaged cilia cannot remove mucus effectively, so mucus accumulates. This narrows the airways and provides a site for bacterial growth, leading to persistent cough and infections.
受损的纤毛无法有效清除黏液，因此黏液积聚。这使气道变窄，并为细菌生长提供场所，导致持续咳嗽和感染。
9. Emphysema | 肺气肿
Emphysema is caused by the breakdown of alveolar walls. Enzymes such as elastase are released by inflammatory cells and digest elastin in the alveolar walls, reducing elasticity and surface area.
肺气肿由肺泡壁破裂引起。炎症细胞释放弹性蛋白酶等酶，消化肺泡壁中的弹性蛋白，降低弹性和表面积。
The destruction of alveoli creates large, irregular air spaces and causes air trapping. Patients experience severe breathlessness because gas exchange is much less efficient.
肺泡破坏形成大而不规则的空气腔并导致气体滞留。患者出现严重呼吸困难，因为气体交换效率大大降低。
10. Carbon Monoxide and Nicotine | 一氧化碳与尼古丁
Hb + CO ⇌ HbCO
Carbon monoxide combines with haemoglobin about 250 times more readily than oxygen, forming carboxyhaemoglobin. This reduces the oxygen-carrying capacity of the blood.
一氧化碳与血红蛋白的结合能力约为氧气的 250 倍，形成碳氧血红蛋白。这降低了血液的携氧能力。
Nicotine stimulates the sympathetic nervous system, causing increased heart rate and blood pressure. It also makes platelets stickier, raising the risk of blood clots and cardiovascular disease.
尼古丁刺激交感神经系统，导致心率和血压升高。它还使血小板更易黏附，增加血栓和心血管疾病的风险。
11. Lung Cancer and Carcinogenesis | 肺癌与致癌作用
Carcinogens in tobacco smoke, such as polycyclic aromatic hydrocarbons and nitrosamines, cause mutations in oncogenes and tumour suppressor genes.
烟草烟雾中的致癌物，如多环芳烃和亚硝胺，会引起癌基因和抑癌基因发生突变。
Mutations can lead to uncontrolled cell division and the formation of a tumour. Malignant lung tumours can invade surrounding tissues and metastasise to other organs.
突变可导致细胞分裂失控并形成肿瘤。恶性肺部肿瘤可侵犯周围组织并转移到其他器官。
12. Data Interpretation and Exam Skills | 数据分析与应试技巧
Exam questions often present data on smoking prevalence, lung function tests such as FEV₁, or graphs showing the incidence of COPD and lung cancer. You should describe trends, quote figures, and link changes to biological mechanisms.
考试题目常给出吸烟率、肺功能测试（如 FEV₁）或显示慢阻肺和肺癌发病率的数据或图表。你应描述趋势、引用数据，并将变化联系到生物学机制。
Remember that correlation does not prove causation, but epidemiological studies and experimental evidence together support a causal link between smoking and lung disease.
请记住，相关性不能证明因果关系，但流行病学研究和实验证据共同支持吸烟与肺部疾病之间存在因果联系。
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