📚 Tobacco Smoke: From Lung Damage to Chronic Disease | 烟草烟雾：从肺损伤到慢性疾病
Tobacco smoke is a major preventable cause of respiratory disease, cardiovascular disease and cancer. For Cambridge A-Level Biology, it provides an important example of how environmental chemicals can disrupt gas exchange, damage epithelial tissues and lead to chronic non-communicable diseases. Understanding the components of tobacco smoke and their biological effects is essential for explaining conditions such as chronic bronchitis, emphysema and lung cancer.
烟草烟雾是呼吸系统疾病、心血管疾病和癌症的主要可预防病因。在剑桥 A-Level 生物课程中，它是一个重要实例，用来说明环境化学物质如何破坏气体交换、损伤上皮组织并导致慢性非传染性疾病。理解烟草烟雾的成分及其生物学效应，对于解释慢性支气管炎、肺气肿和肺癌等疾病至关重要。
1. Composition of Tobacco Smoke | 烟草烟雾的组成
Cigarette smoke is a complex mixture of gases, volatile chemicals and solid particles. More than 7000 compounds have been identified, of which at least 70 are known carcinogens. The three components most commonly examined in A-Level Biology are tar, nicotine and carbon monoxide, but many other substances also contribute to tissue damage.
香烟烟雾是由气体、挥发性化学物质和固体颗粒组成的复杂混合物。已鉴定出 7000 多种化合物，其中至少 70 种是已知致癌物。A-Level 生物中最常考查的三种成分是焦油、尼古丁和一氧化碳，但许多其他物质也会造成组织损伤。
Tar is the sticky particulate material collected when cigarette smoke is cooled. It settles on the lining of the airways and alveoli and contains many carcinogens. Nicotine is an addictive alkaloid that acts on nicotinic acetylcholine receptors in the brain and autonomic nervous system. Carbon monoxide is a colourless, odourless gas produced by incomplete combustion; it competes with oxygen for binding sites on haemoglobin.
焦油是香烟烟雾冷却后收集到的黏性颗粒物质。它沉积在气道和肺泡内壁，并含有多种致癌物。尼古丁是一种致瘾生物碱，作用于大脑和自主神经系统中的烟碱型乙酰胆碱受体。一氧化碳是不完全燃烧产生的无色无味气体，它与氧气竞争血红蛋白上的结合位点。
| Component | Main biological effect |
|---|---|
| Tar | Paralyses cilia, irritates airways, contains carcinogens |
| Nicotine | Addiction, increased heart rate and blood pressure, vasoconstriction |
| Carbon monoxide | Binds to haemoglobin, reduces oxygen transport |
| Formaldehyde and benzene | Toxic and carcinogenic, irritate epithelial surfaces |
2. Damage to Ciliated Epithelium and Mucus Clearance | 纤毛上皮与黏液清除的损伤
In healthy airways, the trachea and bronchi are lined with ciliated epithelial cells and mucus-secreting goblet cells. Cilia beat in a coordinated upward wave, moving mucus along with trapped dust, bacteria and other particles toward the pharynx, where it is swallowed and destroyed by stomach acid. This mechanism is called the mucociliary escalator.
在健康的气道中，气管和支气管内壁覆盖着纤毛上皮细胞和分泌黏液的杯状细胞。纤毛以协调的向上波动方式摆动，将黏液以及截留的灰尘、细菌和其他颗粒推向咽部，随后被吞下并由胃酸破坏。这种机制称为黏液纤毛清除系统。
Tobacco smoke disrupts this defence system in two main ways. First, chemicals in the smoke paralyse cilia, slowing or stopping their beating. Second, irritants stimulate goblet cells and submucosal glands to secrete excess mucus. Because cilia are damaged, the extra mucus cannot be cleared efficiently, so it accumulates in the airways. This trapped mucus provides a warm, nutrient-rich environment for bacterial growth and causes the characteristic smoker’s cough.
烟草烟雾主要通过两种方式破坏这一防御系统。首先，烟雾中的化学物质使纤毛麻痹，减缓或停止其摆动。其次，刺激性物质刺激杯状细胞和黏膜下腺分泌过多黏液。由于纤毛受损，多余的黏液无法被有效清除，因此积聚在气道中。这些滞留的黏液为细菌生长提供了温暖且营养丰富的环境，并导致典型的吸烟者咳嗽。
After prolonged exposure, ciliated epithelial cells may die and be replaced by stratified squamous epithelium. This change is known as metaplasia. Although the new tissue is more resistant to irritation, it lacks cilia and mucus-clearing ability, further reducing respiratory defence.
长期暴露后，纤毛上皮细胞可能死亡并被复层鳞状上皮取代。这种变化称为化生。虽然新组织对刺激更具抵抗力，但它缺少纤毛和清除黏液的能力，进一步削弱了呼吸道防御功能。
3. Chronic Bronchitis | 慢性支气管炎
Chronic bronchitis is a long-term inflammatory condition of the bronchi. It is defined clinically as a productive cough that lasts for at least three months in each of two consecutive years. Together with emphysema, it forms part of chronic obstructive pulmonary disease, often abbreviated as COPD.
慢性支气管炎是一种支气管的长期炎症性疾病。临床定义是连续两年中每年至少持续三个月的咳痰咳嗽。它与肺气肿一起构成慢性阻塞性肺疾病，通常缩写为 COPD。
The pathogenesis of chronic bronchitis begins with irritation by tobacco smoke. This causes inflammation and swelling of the bronchial mucosa, goblet cell hyperplasia and mucus hypersecretion. The damaged cilia are unable to clear this mucus, leading to airway narrowing and obstruction. Over time, inflammatory cells release proteases and cytokines that contribute to tissue remodelling and further damage.
慢性支气管炎的发病机制始于烟草烟雾的刺激。这会引起支气管黏膜的炎症和肿胀、杯状细胞增生以及黏液分泌过多。受损的纤毛无法清除这些黏液，导致气道狭窄和阻塞。随着时间推移，炎症细胞释放蛋白酶和细胞因子，参与组织重塑并造成进一步损伤。
Reduced airflow causes breathlessness, wheezing and reduced gas exchange. Because oxygenation is impaired, patients may show cyanosis, a bluish discolouration of the lips and skin. Frequent bacterial infections are common because stagnant mucus provides a site for microbial colonisation.
气流减少会引起呼吸困难、喘息和气体交换减弱。由于氧合受损，患者可能出现发绀，即嘴唇和皮肤呈现蓝色。由于滞留的黏液为微生物定植提供了场所，因此频繁的细菌感染很常见。
4. Emphysema | 肺气肿
Emphysema is a disease in which the alveolar walls are progressively destroyed, producing abnormally large air spaces. The loss of alveolar partitions reduces the total surface area available for gas exchange. It also destroys elastic fibres in the lung, making the lungs less able to recoil during expiration.
肺气肿是一种肺泡壁逐渐被破坏、形成异常大气腔的疾病。肺泡间隔的丧失减少了可供气体交换的总表面积。它还会破坏肺中的弹性纤维，使肺在呼气时难以回缩。
Smoke triggers an inflammatory response in the alveoli. Macrophages and neutrophils are recruited to the lungs and release elastase, a protease that digests elastin. In healthy lungs, the enzyme alpha-1-antitrypsin inhibits elastase and protects alveolar walls. However, chemicals in tobacco smoke inactivate this inhibitor and increase protease release. The imbalance between proteases and antiproteases leads to destruction of elastin and alveolar walls.
烟雾引发肺泡内的炎症反应。巨噬细胞和中性粒细胞被招募到肺部，并释放弹性蛋白酶，这是一种消化弹性蛋白的蛋白酶。在健康肺中，α-1-抗胰蛋白酶抑制弹性蛋白酶并保护肺泡壁。然而，烟草烟雾中的化学物质会使这种抑制剂失活并增加蛋白酶的释放。蛋白酶与抗蛋白酶之间的失衡导致弹性蛋白和肺泡壁被破坏。
As alveolar walls break down, small alveoli merge into larger air sacs called bullae. These large spaces have a much smaller surface area for diffusion of oxygen and carbon dioxide. Patients become severely breathless even at rest. The loss of elastic recoil also traps air in the lungs, giving a barrel-shaped chest and prolonged expiration.
随着肺泡壁破裂，小肺泡合并成称为肺大疱的较大气腔。这些大气腔用于氧气和二氧化碳扩散的表面积大大减少。患者即使在休息时也会严重呼吸困难。弹性回缩力的丧失还使空气滞留在肺内，导致桶状胸和呼气延长。
5. Lung Cancer and Carcinogenesis | 肺癌与致癌过程
Tobacco smoke is the leading cause of lung cancer. Tar contains numerous carcinogens, including polycyclic aromatic hydrocarbons such as benzo[a]pyrene, N-nitrosamines, benzene and formaldehyde. These compounds can directly damage DNA or be converted into reactive intermediates that bind to DNA bases.
烟草烟雾是肺癌的首要病因。焦油含有多种致癌物，包括苯并[a]芘等多环芳烃、N-亚硝胺、苯和甲醛。这些化合物可直接损伤 DNA，或被转化为与 DNA 碱基结合的活性中间体。
Mutations in two main classes of genes drive cancer development. Proto-oncogenes normally promote cell division, but mutations can convert them into oncogenes that are constantly active. Tumour suppressor genes normally slow the cell cycle or trigger apoptosis, but loss-of-function mutations allow damaged cells to survive and multiply. For example, mutations in the TP53 tumour suppressor gene are found in many lung cancers.
两类主要基因的突变驱动癌症的发展。原癌基因通常促进细胞分裂，但突变可将其转变为持续活跃的癌基因。肿瘤抑制基因通常减缓细胞周期或触发细胞凋亡，但功能丧失突变使受损细胞得以存活并增殖。例如，在许多肺癌中发现 TP53 肿瘤抑制基因发生突变。
Most lung cancers arise from the epithelial lining of the bronchi. Common types include squamous cell carcinoma, small-cell lung carcinoma and adenocarcinoma. Cancer cells divide uncontrollably, forming a tumour that can block airways, invade surrounding tissues and spread to other organs through the blood or lymph in a process called metastasis. Chronic inflammation caused by smoking also promotes tumour growth by increasing DNA damage and stimulating cell division.
大多数肺癌起源于支气管的上皮衬里。常见类型包括鳞状细胞癌、小细胞肺癌和腺癌。癌细胞不受控制地分裂，形成可阻塞气道、侵入周围组织并通过血液或淋巴扩散到其他器官的肿瘤，这一过程称为转移。吸烟引起的慢性炎症还会增加 DNA 损伤并刺激细胞分裂，从而促进肿瘤生长。
6. Carbon Monoxide and Cardiovascular Effects | 一氧化碳与心血管效应
Carbon monoxide binds to the haem group of haemoglobin with an affinity approximately 250 times greater than oxygen. It forms carboxyhaemoglobin, which reduces the oxygen-carrying capacity of the blood. Even low concentrations of carbon monoxide therefore significantly reduce the amount of oxygen delivered to tissues.
一氧化碳与血红蛋白的血红素基团结合，其亲和力约为氧气的 250 倍。它形成碳氧血红蛋白，从而降低血液的携氧能力。因此，即使是低浓度的一氧化碳也会显著减少输送到组织的氧气量。
To compensate for chronic hypoxia, the body produces more red blood cells. This increases blood viscosity and raises blood pressure, forcing the heart to work harder. Nicotine also stimulates the sympathetic nervous system, causing vasoconstriction and an increase in heart rate. It promotes platelet aggregation, making blood clots more likely.
为了补偿慢性缺氧，身体会产生更多的红细胞。这会增加血液黏度并升高血压，迫使心脏更费力地工作。尼古丁还会刺激交感神经系统，引起血管收缩和心率加快。它促进血小板聚集，使血栓更易形成。
Together, these effects damage the endothelial lining of arteries and accelerate atherosclerosis. Atherosclerotic plaques can narrow coronary arteries, causing angina or myocardial infarction. They can also affect cerebral arteries, leading to stroke, or peripheral arteries, causing peripheral artery disease. This is why smoking is a major risk factor for cardiovascular disease as well as lung disease.
这些效应共同损伤动脉内皮并加速动脉粥样硬化。动脉粥样硬化斑块会使冠状动脉变窄，导致心绞痛或心肌梗死。它们还会影响脑动脉，导致中风，或影响外周动脉，引起外周动脉疾病。因此，吸烟不仅是肺部疾病的主要危险因素，也是心血管疾病的主要危险因素。
7. Effects on Pregnancy and Foetal Development | 对妊娠和胎儿发育的影响
Nicotine and carbon monoxide cross the placenta from the mother’s blood into the foetal circulation. Carbon monoxide binds to foetal haemoglobin, reducing oxygen supply to developing tissues. Nicotine constricts blood vessels in the uterus and placenta, further decreasing blood flow and nutrient delivery.
尼古丁和一氧化碳会从母体血液穿过胎盘进入胎儿循环。一氧化碳与胎儿血红蛋白结合，减少对发育中组织的氧气供应。尼古丁使子宫和胎盘中的血管收缩，进一步减少血流和营养物质输送。
Foetal hypoxia has serious consequences. Smoking during pregnancy increases the risk of miscarriage, premature birth and low birth weight. Low birth weight is associated with impaired lung and brain development in infancy and an increased risk of metabolic and cardiovascular disorders in later life. Maternal smoking also raises the risk of sudden infant death syndrome, often called SIDS.
胎儿缺氧会造成严重后果。孕期吸烟会增加流产、早产和低出生体重的风险。低出生体重与婴儿期肺部和大脑发育受损以及日后代谢和心血管疾病风险增加相关。母亲吸烟还会增加婴儿猝死综合征（通常称为 SIDS）的风险。
8. Epidemiological Evidence Linking Smoking to Disease | 将吸烟与疾病联系起来的流行病学证据
Epidemiological studies provide much of the evidence that smoking causes disease. In the 1950s, Richard Doll and Austin Bradford Hill carried out a long-term cohort study of British doctors. They found a strong positive correlation between cigarette smoking and death from lung cancer, with a clear dose-response relationship: heavier smokers had much higher mortality rates than light smokers or non-smokers.
流行病学研究提供了吸烟导致疾病的大部分证据。20 世纪 50 年代，Richard Doll 和 Austin Bradford Hill 对英国医生进行了一项长期队列研究。他们发现吸烟与肺癌死亡之间存在很强的正相关，并且具有明显的剂量-反应关系：重度吸烟者的死亡率远高于轻度吸烟者或不吸烟者。
Case-control studies have also shown that patients with lung cancer are significantly more likely to have a history of smoking than matched controls. Animal experiments support these findings: tar painted on the skin of mice induces tumours. However, epidemiological correlations alone do not prove causation, so scientists must consider confounding variables, reliability of self-reported smoking habits and the long latent period between exposure and disease.
病例对照研究也表明，肺癌患者有吸烟史的比例显著高于匹配的对照组。动物实验支持这些发现：将焦油涂在小鼠皮肤上可诱发肿瘤。然而，单凭流行病学相关性并不能证明因果关系，因此科学家必须考虑混杂变量、自我报告吸烟习惯的可靠性以及暴露与发病之间的长潜伏期。
9. Passive Smoking and Wider Health Effects | 被动吸烟与更广泛的健康影响
Passive smoking, also called second-hand smoke, is the inhalation of smoke from other people’s cigarettes. Non-smokers exposed to second-hand smoke inhale the same toxic and carcinogenic chemicals as active smokers, although usually at lower concentrations. There is strong evidence that passive smoking increases the risk of lung cancer and coronary heart disease in non-smokers.
被动吸烟，也称为二手烟，是指吸入他人香烟产生的烟雾。接触二手烟的非吸烟者会吸入与主动吸烟者相同的有毒和致癌化学物质，尽管浓度通常较低。有充分证据表明，被动吸烟会增加非吸烟者患肺癌和冠心病的风险。
Children are particularly vulnerable because their lungs are still developing. Second-hand smoke exposure in childhood increases the risk of lower respiratory infections, asthma, middle ear infections and sudden infant death syndrome. Smoking inside homes and cars therefore creates significant health risks for others, which is why many countries have introduced smoke-free public spaces.
儿童尤其容易受到影响，因为他们的肺部仍在发育。儿童期接触二手烟会增加下呼吸道感染、哮喘、中耳炎和婴儿猝死综合征的风险。因此，在家庭和汽车内吸烟会给他人带来显著健康风险，这也是许多国家推行无烟公共场所的原因。
10. Quitting, Reversibility and Public Health Measures | 戒烟、可逆性与公共卫生措施
Many of the harmful effects of smoking can be reduced by quitting. After a few weeks without smoking, cilia begin to regrow and mucus clearance improves. The decline in lung function slows, and the risk of cardiovascular disease drops substantially within one to two years. However, emphysema involves permanent destruction of alveolar walls, so lost alveolar surface area cannot be regenerated.
戒烟可以减轻吸烟的许多有害影响。戒烟数周后，纤毛开始再生，黏液清除功能改善。肺功能下降速度减慢，心血管疾病风险在一到两年内大幅降低。然而，肺气肿涉及肺泡壁的永久性破坏，因此丧失的肺泡表面积无法再生。
The risk of lung cancer falls after quitting but remains higher than that of a never-smoker for many years. This is because some mutations persist in long-lived epithelial stem cells. Nevertheless, stopping smoking at any age improves life expectancy and quality of life.
戒烟后肺癌风险会下降，但在许多年内仍高于从不吸烟者。这是因为一些突变在长寿的上皮干细胞中持续存在。尽管如此，任何年龄戒烟都能改善预期寿命和生活质量。
Public health strategies include taxation on tobacco products, bans on advertising, plain packaging with health warnings, smoke-free legislation and educational campaigns. Nicotine replacement therapy, varenicline and bupropion can help reduce withdrawal symptoms, while behavioural support increases the chance of successful quitting. Evaluating these measures requires understanding both biological addiction and social influences on smoking behaviour.
公共卫生策略包括对烟草制品征税、禁止广告、采用带有健康警示的平装包装、无烟立法以及教育宣传。尼古丁替代疗法、伐尼克兰和安非他酮有助于减轻戒断症状，而行为支持可提高成功戒烟的机会。评估这些措施既需要理解生物成瘾机制，也需要理解影响吸烟行为的社会因素。
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