Smoking and Respiratory Health
Smoke Irritants and the Respiratory Tract
Cigarette smoke contains over 4000 chemical compounds, many of which are toxic Irritants. The major classes of harmful components include tar, carbon monoxide, nicotine, and a range of carcinogenic compounds such as benzene and formaldehyde. When inhaled through the Nostril and Nasal Cavity, these chemicals travel along the entire Air Passageway before reaching the delicate Alveoli where gas exchange occurs. The mucous membrane lining the nasal cavity normally filters smaller foreign particles, but the volume and chemical complexity of cigarette smoke overwhelm these defences.
Tar: A dark, sticky mixture of hundreds of chemicals that coats the lining of the airways and alveoli, paralysing protective mechanisms and introducing carcinogens directly into respiratory tissue
Carbon Monoxide (CO): Binds to haemoglobin with roughly 240 times the affinity of oxygen, reducing the oxygen-carrying capacity of blood and forcing the heart to work harder to deliver adequate oxygen to tissues
Nicotine: Stimulates the nervous system, raises heart rate and blood pressure, and is the primary compound responsible for addiction to cigarette smoking
Carcinogens: Chemicals such as benzene, formaldehyde, and nitrosamines that directly damage DNA in respiratory epithelial cells, initiating mutations that can lead to cancer
Major Classes of Cigarette Smoke Components
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Tar — sticky particulate matter that coats airways
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Carbon Monoxide — gas that competes with oxygen for haemoglobin
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Nicotine — addictive alkaloid affecting cardiovascular and nervous systems
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Carcinogens (benzene, formaldehyde, nitrosamines) — DNA-damaging compounds
Once cigarette smoke passes through the Nasal Cavity, it travels through the Pharynx and Larynx before entering the Trachea. The Trachea is lined with ciliated epithelium and goblet cells that produce mucus, forming the Mucociliary Escalator. Smoke irritants destroy the coordination and function of this system, allowing toxic particles to penetrate deeper into the bronchial tree. From the trachea, smoke travels through the Bronchi and Bronchioles, irritating each level of the airway. The Bronchioles are particularly vulnerable because they lack cartilage and rely on thin, smooth-muscle walls that spasm in response to irritants, narrowing the airway lumen.
Mucous hypersecretion: Chronic smoke exposure stimulates goblet cells in the airway lining to produce excess mucus, thickening the mucus layer and overwhelming the ciliary clearing mechanism
Bronchial irritation: The linings of bronchi become inflamed and swollen, reducing the effective diameter of the airway and increasing resistance to airflow
Bronchiolar constriction: Irritant reflexes cause the circular smooth muscles of bronchioles to contract, further narrowing the already delicate passageways into the lungs
Cilia Damage and Loss of Respiratory Defences
The Mucociliary Escalator is the primary mechanical defence of the respiratory tract. Cilia are microscopic hair-like projections on the surface of the epithelial cells lining the Trachea and larger Bronchi. These cilia beat in a coordinated, upward wave that moves a thin film of mucus — along with trapped dust, microbes, and debris — toward the Pharynx, where it is swallowed or coughed out. This mechanism operates continuously and is essential for keeping the lower respiratory tract sterile and clear.
Ciliary beat frequency: Under normal conditions, cilia beat approximately 12–20 times per second, creating a steady upward current that clears mucus from the airways within minutes
Mucus layer: A thin, watery periciliary layer sits beneath the gel-like mucus layer, allowing cilia to beat freely while the mucus traps particles on its surface
Particle trapping: Dust particles, bacteria, and other foreign material become embedded in the sticky mucus and are transported upward before they can reach the delicate alveolar surfaces
Cigarette smoke directly damages Cilia in multiple ways. The toxic components of smoke — particularly tar and other chemical irritants — paralyse ciliary movement, alter ciliary structure, and ultimately destroy the ciliated epithelial cells themselves. Goblet cells respond by producing even more mucus, but without functional cilia the excess mucus accumulates in the airways instead of being cleared. This creates a persistent wet cough (smoker's cough) as the body attempts to expel mucus through forceful expiration rather than the normal ciliary mechanism.
Ciliary paralysis: Smoke toxins immediately slow and eventually stop ciliary beating, halting the upward transport of mucus within seconds of exposure
Epithelial metaplasia: Chronic exposure causes the ciliated columnar epithelium to be replaced by stratified squamous epithelium through a process called metaplasia — this new tissue lacks cilia entirely and cannot perform mucus clearance
Mucus accumulation: Without ciliary clearance, thick mucus plugs build up in the bronchi and bronchioles, becoming breeding grounds for bacteria and further obstructing airflow
Reduced Gas Exchange at the Alveolar Level
Normal Gas Exchange takes place across the walls of the Alveoli, which are microscopic, single-layered sacs with an extremely thin diffusion barrier. Each alveolus is surrounded by a dense network of blood capillaries. Oxygen diffuses from the alveolar air into the blood, while carbon dioxide diffuses from the blood into the alveolar air to be exhaled. The efficiency of this exchange depends on a large total surface area (approximately 70 m² in healthy adult lungs), a very thin diffusion distance (alveolar epithelium plus capillary endothelium), and a maintained concentration gradient between alveolar air and blood.
Diffusion barrier: Composed of alveolar epithelial cells, a shared basement membrane, and capillary endothelial cells — together only about 0.5 μm thick in healthy lungs
Surface area: Millions of alveoli provide an enormous combined surface area that ensures rapid and sufficient gas exchange even during vigorous activity
Concentration gradient: Maintained by continuous blood flow through pulmonary capillaries on one side and fresh air ventilation of alveoli on the other
Smoking compromises Gas Exchange through several simultaneous mechanisms. Carbon monoxide from smoke binds to haemoglobin, forming Carboxyhaemoglobin, which cannot carry oxygen. This directly reduces the amount of oxygen transported by each molecule of haemoglobin. Additionally, tar and other irritants damage alveolar walls, reducing the total surface area available for diffusion. Inflammation and mucus in the airways reduce ventilation to affected regions of the lung, lowering the concentration of fresh oxygen reaching those alveoli. The combined effect is significantly reduced oxygen delivery to body tissues.
$$\%\,COHb = \frac{\text{CO bound to Hb}}{\text{Total Hb capacity}} \times 100$$
Percentage of haemoglobin bound to carbon monoxide, representing the fraction of oxygen-carrying capacity that is lost
$\%\,COHb$=Carboxyhaemoglobin percentage(%)
$\text{CO bound to Hb}$=Amount of haemoglobin saturated with carbon monoxide(g/dL)
$\text{Total Hb capacity}$=Total oxygen-carrying capacity of haemoglobin(g/dL)
$\%\,COHb > 10\%$
→Noticeable reduction in exercise tolerance and shortness of breath on exertion
$\%\,COHb > 50\%$
→Severe tissue hypoxia, confusion, loss of consciousness, and potential death
Carboxyhaemoglobin formation: CO binds to haemoglobin with approximately 240 times the affinity of O₂, forming a stable complex that reduces the oxygen-carrying capacity of blood by the corresponding percentage
Alveolar wall destruction: Tar deposits and chronic inflammation break down the thin walls between adjacent alveoli, merging small sacs into fewer, larger ones and drastically reducing total surface area
Ventilation-perfusion mismatch: Mucus plugs and narrowed bronchioles prevent fresh air from reaching some alveoli while blood continues to flow past them, creating regions where gas exchange is essentially absent
Emphysema and Bronchitis — Major Smoking-Linked Diseases
Emphysema is a degenerative lung disease in which the walls between adjacent Alveoli are progressively destroyed, merging many small alveoli into fewer, larger air spaces. This destruction is primarily caused by enzymes called Elastase that break down the elastic fibres (elastin) in alveolar walls. Normally, these enzymes are kept in check by a protective protein called Alpha-1 Antitrypsin, but cigarette smoke both inactivates alpha-1 antitrypsin and stimulates inflammatory cells (macrophages and neutrophils) to release excess elastase. The loss of elastic tissue means that alveoli cannot recoil properly during exhalation, trapping stale air in the lungs and reducing the volume of fresh air that can enter with each breath.
Alveolar destruction: Elastase enzyme breaks down elastin fibres in alveolar septa, creating enlarged, irregular air spaces (bullae) that have very thin or absent walls
Loss of elastic recoil: Without intact elastin, the lungs cannot passively deflate during exhalation, forcing the person to use active muscular effort to breathe out and causing chronic air trapping
Reduced capillary surface: As alveolar walls are destroyed, the surrounding capillary networks are also lost, dramatically reducing the surface area available for Gas Exchange
Chronic Bronchitis is defined clinically as a productive cough lasting at least three months in each of two consecutive years. It results from chronic irritation of the Bronchi and larger Bronchioles by cigarette smoke. The persistent irritation causes the mucous membrane lining these airways to become inflamed, swollen, and hypersecretory — producing far more mucus than normal. Because Cilia are damaged or destroyed by smoke, this excess mucus cannot be cleared effectively. Thick mucus plugs obstruct the airways, and the chronic inflammation narrows the airway lumen through mucosal oedema and smooth muscle hypertrophy.
Mucus hypersecretion: Goblet cells and submucosal glands hypertrophy under chronic irritation, producing large volumes of thick, tenacious mucus that obstructs airflow
Airway obstruction: Inflammation causes swelling of the airway walls, while chronic irritation leads to thickening of the smooth muscle layer, both of which narrow the airway lumen
Recurrent infections: Stagnant mucus in the airways provides an ideal medium for bacterial growth, leading to frequent respiratory infections that further damage lung tissue
Emphysema vs. Chronic Bronchitis — Key Differences
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Primary site of damage — Emphysema: alveoli and alveolar walls; Chronic Bronchitis: bronchi and bronchioles
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Main structural change — Emphysema: loss of elastic tissue and alveolar septa; Chronic Bronchitis: mucus hypersecretion and airway wall thickening
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Dominant symptom — Emphysema: breathlessness on exertion (dyspnoea); Chronic Bronchitis: persistent productive cough
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Key mechanism — Emphysema: elastase/alpha-1 antitrypsin imbalance; Chronic Bronchitis: ciliary damage and chronic inflammation
Cigarette smoking is the single largest preventable cause of Lung Cancer. The carcinogens in tobacco smoke — particularly benzene, formaldehyde, nitrosamines, and polycyclic aromatic hydrocarbons — directly damage the DNA of epithelial cells lining the Bronchi and Bronchioles. Chronic exposure leads to accumulated mutations, first causing Metaplasia (replacement of ciliated columnar epithelium with stratified squamous epithelium), then Dysplasia (abnormal, pre-cancerous cell changes), and eventually malignant transformation into carcinoma. The risk of lung cancer is directly proportional to the number of cigarettes smoked per day and the total duration of smoking.
Progression of cellular changes: Normal ciliated epithelium → metaplasia (stratified squamous replacement) → dysplasia (abnormal cell growth) → carcinoma in situ → invasive lung cancer
Dose-response relationship: Risk increases with both the number of cigarettes per day and the number of years of smoking — a person smoking 20 cigarettes a day for 30 years has a dramatically higher risk than either parameter alone would suggest
Types associated with smoking: The most common smoking-related lung cancers are squamous cell carcinoma (arising from bronchial epithelium) and small cell carcinoma, both of which are strongly linked to tobacco exposure
Cumulative Impact on Respiratory Health
The effects of smoking on the respiratory system are not isolated to any single structure — they compound across every level from Nasal Cavity to Alveoli. Ciliary paralysis and metaplasia in the upper airways allow irritants to penetrate deeper. Bronchial inflammation and bronchiolar constriction increase airway resistance. Alveolar wall destruction and mucus plugging reduce the effective gas exchange surface. Carbon monoxide reduces the oxygen-carrying capacity of blood. Together, these changes produce a progressive decline in respiratory function that manifests as shortness of breath, reduced exercise tolerance, chronic cough, and increased susceptibility to respiratory infections. The damage accumulates over years and is partly irreversible even after cessation.
Progressive decline: Lung function measured by forced expiratory volume (FEV₁) declines faster in smokers than in non-smokers — roughly 25–30 mL per year in smokers versus 20–25 mL per year from normal ageing
Partial reversibility: Ciliary function and airway inflammation can improve significantly after quitting, but destroyed alveolar walls and metaplastic tissue changes are permanent
Systemic consequences: Chronic hypoxia from reduced gas exchange forces the cardiovascular system to compensate through increased heart rate, elevated blood pressure, and polycythaemia
Summary of Smoking Effects by Respiratory Structure
1
Nasal cavity — mucus membrane irritation, reduced filtration efficiency
2
Trachea — ciliary paralysis, mucus hypersecretion, epithelial metaplasia
3
Bronchi — chronic inflammation, airway narrowing, excess mucus production
4
Bronchioles — smooth muscle constriction, mucus plugging, reduced airflow
5
Alveoli — wall destruction (emphysema), reduced surface area, impaired gas exchange
6
Blood — carboxyhaemoglobin formation, reduced oxygen delivery to tissues
Application Strategy
Worked Examples
Problem Statement
A person's haemoglobin concentration is 15 g/dL and their carboxyhaemoglobin level is measured at 8%. How much haemoglobin is available for oxygen transport, and what percentage of the total oxygen-carrying capacity is lost?
Carboxyhaemoglobin
Strategic Toolkit
$$\text{Available Hb} = \text{Total Hb} \times \left(1 - \frac{\%\,COHb}{100}\right)$$
Step 1
Calculate haemoglobin occupied by carbon monoxide
Multiply the total haemoglobin concentration by the fraction bound to CO to find how much is unavailable for oxygen transport.
$$\text{CO-bound Hb} = 15 \times 0.08 = 1.2 \text{ g/dL}$$
Step 2
Calculate available haemoglobin for oxygen
Subtract the CO-bound fraction from total haemoglobin to find the usable oxygen-carrying capacity.
$$\text{Available Hb} = 15 - 1.2 = 13.8 \text{ g/dL}$$
Step 3
State the percentage lost
The carboxyhaemoglobin level directly equals the percentage of oxygen-carrying capacity that is lost.
$$\text{Capacity lost} = 8\%$$
Problem Statement
A smoker's lungs show an elastase concentration of 120 units/mL and an alpha-1 antitrypsin concentration of 80 units/mL. A healthy non-smoker would have an elastase level of 60 units/mL and an alpha-1 antitrypsin level of 120 units/mL. Compare the enzyme balance ratios and explain the clinical significance.
EmphysemaAlpha-1 AntitrypsinElastase
Strategic Toolkit
$$\text{Balance Ratio} = \frac{\text{Alpha-1 Antitrypsin}}{\text{Elastase}}$$
Step 1
Calculate the healthy balance ratio
In a healthy person, alpha-1 antitrypsin should exceed elastase, providing a protective ratio greater than 1.
$$\text{Healthy Ratio} = \frac{120}{60} = 2.0$$
Step 2
Calculate the smoker's balance ratio
In the smoker, both sides of the balance are disrupted — more elastase and less protective antitrypsin.
$$\text{Smoker Ratio} = \frac{80}{120} = 0.67$$
Step 3
Interpret the clinical significance
A ratio below 1 means elastase exceeds the protective capacity of alpha-1 antitrypsin, resulting in unchecked destruction of alveolar elastin and progressive emphysema. The smoker's ratio has dropped from 2.0 to 0.67, a three-fold worsening of the imbalance.
$$\text{Imbalance Factor} = \frac{2.0}{0.67} \approx 3.0$$
Problem Statement
A 40-year-old smoker with a 20 pack-year history has a measured FEV₁ of 2.8 L. The predicted normal FEV₁ for their age, sex, and height is 3.6 L. Calculate the FEV₁ percentage and assess the degree of functional impairment.
EmphysemaChronic Bronchitis
Strategic Toolkit
$$\text{FEV}_{1}\%\,\text{predicted} = \frac{\text{Measured FEV}_{1}}{\text{Predicted FEV}_{1}} \times 100$$
Step 1
Calculate FEV₁ as percentage of predicted
Divide the measured value by the predicted normal value and multiply by 100 to express it as a percentage of expected lung function.
$$\text{FEV}_{1}\% = \frac{2.8}{3.6} \times 100 = 77.8\%$$
Step 2
Classify the degree of impairment
FEV₁ values above 80% are considered normal, 50–79% indicate mild-to-moderate obstruction, and below 50% indicates severe obstruction.
$$77.8\% \rightarrow \text{Mild-to-moderate obstruction (COPD stage I–II)}$$
Step 3
Relate to smoking history
A 20 pack-year smoking history (1 pack per day for 20 years) is sufficient to cause measurable airway obstruction, reflecting combined effects of chronic bronchitis and early emphysema.
$$\text{Pack-years} = 1 \times 20 = 20$$
Problem Statement
If a gas mixture contains equal partial pressures of oxygen and carbon monoxide, and haemoglobin has available binding sites, what fraction of the sites will bind CO versus O₂, and what is the resulting carboxyhaemoglobin percentage?
Carboxyhaemoglobin
Strategic Toolkit
$$\frac{\text{CO-bound sites}}{\text{O}_2\text{-bound sites}} = \frac{P_{\text{CO}} \times 240}{P_{\text{O}_2} \times 1}$$
Step 1
Apply the relative binding affinity
With equal partial pressures, CO will bind 240 times more sites than O₂ due to its 240-fold greater affinity for haemoglobin.
$$\text{Ratio} = \frac{P_{\text{CO}} \times 240}{P_{\text{O}_2} \times 1} = \frac{1 \times 240}{1 \times 1} = 240$$
Step 2
Calculate the fraction of sites bound to CO
Out of every 241 binding events (240 for CO + 1 for O₂), 240 are occupied by CO.
$$\%\,\text{CO-bound} = \frac{240}{240 + 1} \times 100 \approx 99.6\%$$
Step 3
State the clinical significance
Even trace amounts of CO in inhaled air can produce dangerously high carboxyhaemoglobin levels because of this enormous affinity difference. This is why CO poisoning from cigarette smoke or environmental sources is so dangerous even at low concentrations.
$$\text{At } P_{\text{CO}} = P_{\text{O}_2}: \; \text{COHb} \approx 99.6\%$$
Memorize formulas
Carboxyhaemoglobin Formation
CO binds haemoglobin with 240× the affinity of O₂. A 10% COHb level means 10% of oxygen-carrying capacity is lost. Units: % of total Hb binding sites.
Formula
$$\text{Hb} + \text{CO} \rightarrow \text{COHb}$$
Elastase–Antitrypsin Balance
Emphysema results when elastase exceeds alpha-1 antitrypsin. Smoking increases elastase release and inactivates antitrypsin, tipping the balance. Ratio < 1 indicates alveolar destruction.
Formula
$$\text{Balance} = \frac{\text{Alpha-1 Antitrypsin}}{\text{Elastase}}$$
FEV₁ Percentage of Predicted
Forced Expiratory Volume in 1 second, expressed as percentage of predicted normal value. Above 80% = normal, 50–79% = mild-to-moderate COPD, below 50% = severe. Units: litres, expressed as %.
Formula
$$\text{FEV}_{1}\%\,\text{predicted} = \frac{\text{Measured FEV}_{1}}{\text{Predicted FEV}_{1}} \times 100$$
CO : O₂ Relative Affinity
Carbon monoxide binds haemoglobin 240 times more readily than oxygen at equal partial pressures. Even low CO concentrations produce high COHb levels.
Formula
$$\frac{\text{CO-bound}}{\text{O}_2\text{-bound}} = 240 \times \frac{P_{\text{CO}}}{P_{\text{O}_2}}$$
Review
1
Which part of the respiratory tract is first exposed to cigarette smoke irritants during inhalation?
Ans
Nasal cavity
Review
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Identify the air entry point
Air enters the respiratory system through the nostril into the nasal cavity, which filters, warms, and humidifies inhaled air. Smoke irritants contact this mucosal surface first.
Nasal cavity = first contact site
Trace the pathway beyond the nasal cavity
After the nasal cavity, smoke travels through progressively smaller passages: pharynx → larynx → trachea → bronchi → bronchioles → alveoli.
Nasal cavity → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli
2
Which sequence correctly represents the path of inhaled smoke from the nostril to the gas exchange surface?
Ans
Nostril → pharynx → larynx → trachea → bronchi → bronchioles → alveoli
Review
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Upper respiratory tract order
From the nostril, air passes through the nasal cavity into the pharynx (throat), then through the larynx (voice box) into the trachea (windpipe).
Nostril → Pharynx → Larynx → Trachea
Lower respiratory tract order
The trachea branches into bronchi, which further divide into smaller bronchioles, ending at the alveoli where gas exchange occurs.
Trachea → Bronchi → Bronchioles → Alveoli
3
Chronic exposure to cigarette smoke irritants causes the respiratory epithelium to undergo a reversible change in which one differentiated cell type is replaced by another. This process is called:
Ans
Metaplasia
Review
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Define the cellular change
Cigarette smoke causes chronic irritation, prompting the respiratory epithelium to transform from ciliated columnar to stratified squamous epithelium as an adaptive response.
One differentiated cell type replaced by another = metaplasia
Distinguish from similar terms
Hyperplasia = more cells; hypertrophy = larger cells; dysplasia = abnormal maturation (pre-cancerous); metaplasia = different cell type replacement.
Correct term is metaplasia
4
What is the primary role of cilia in the healthy respiratory tract?
Ans
Beating rhythmically to move mucus-trapped particles upward and out
Review
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Identify the ciliary function
Cilia line the air passageway from the trachea to the bronchioles. Their coordinated beating moves the mucus layer upward, carrying trapped particles and pathogens away from the lungs.
Cilia propel mucus upward = mucociliary escalator
Eliminate incorrect options
Mucus secretion is performed by goblet cells. Oxygen absorption occurs at the alveoli. Bronchiole constriction is controlled by smooth muscle fibres.
Only the mucociliary transport function is correct
5
Cigarette smoke paralyzes the cilia lining the air passageway. What is the most immediate consequence of this paralysis?
Ans
Accumulation of mucus and trapped particles in the lower respiratory tract
Review
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Mucociliary escalator mechanism
The mucociliary escalator depends on ciliary beating to continuously clear mucus. When cilia are paralyzed, clearance stops but mucus production continues.
Mucus accumulates in airways
Classify consequences by time frame
Immediate: mucus accumulation and cough. Long-term: emphysema, chronic bronchitis, metaplasia, lung cancer. CO binding occurs simultaneously with smoke inhalation but is unrelated to cilia.
Most immediate effect = mucus and debris accumulation
6
A smoker's persistent cough develops primarily because:
Ans
Mucus accumulates in the airways as the mucociliary escalator is impaired
Review
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Link ciliary paralysis to mucus buildup
Cilia paralysis eliminates the normal clearance mechanism. Mucus secretion by goblet cells continues, causing secretions to pool in the airways.
Impaired mucociliary escalator → mucus accumulation
Connect mucus buildup to cough reflex
Accumulated mucus irritates airway receptors, triggering the cough reflex as a compensatory attempt to clear the blockage.
Smoker's cough = compensatory response to ciliary failure
7
Carbon monoxide from cigarette smoke binds to haemoglobin forming carboxyhaemoglobin (COHb). Compared to oxygen, the affinity of CO for haemoglobin is approximately how many times greater?
Ans
240 times
Review
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Apply the CO : O₂ affinity formula
The formula is: $$\frac{\text{CO-bound}}{\text{O}_2\text{-bound}} = 240 \times \frac{P_{\text{CO}}}{P_{\text{O}_2}}$$. At equal partial pressures (P_CO = P_O₂), the ratio simplifies to 240.
CO affinity = 240 × O₂ affinity
Interpret the clinical significance
Because CO binds 240 times more strongly than O₂, even small concentrations of CO in smoke can occupy a large fraction of haemoglobin binding sites, severely reducing oxygen transport to tissues.
Even low P_CO produces significant COHb formation
8
If the partial pressure of CO in a heavy smoker's alveolar air is 0.2 mmHg and the partial pressure of O₂ is 80 mmHg, what is the approximate ratio of CO-bound to O₂-bound haemoglobin?
Ans
0.60
Review
Tap to reveal
Substitute into the affinity formula
$$\frac{\text{CO-bound}}{\text{O}_2\text{-bound}} = 240 \times \frac{P_{\text{CO}}}{P_{\text{O}_2}} = 240 \times \frac{0.2}{80}$$
$$= 240 \times 0.0025$$
Calculate the final ratio
$$240 \times 0.0025 = 0.60$$
$$\text{Ratio} = 0.60$$
Clinical interpretation
A ratio of 0.60 means CO occupies a substantial proportion of haemoglobin binding capacity, reducing oxygen transport by a corresponding fraction.
Significant gas exchange impairment
9
Carboxyhaemoglobin reduces the oxygen-carrying capacity of blood because:
Ans
CO occupies haemoglobin binding sites that would normally transport O₂
Review
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Write the COHb formation reaction
$$\text{Hb} + \text{CO} \rightarrow \text{COHb}$$
CO binds directly to haemoglobin
Explain the competitive binding
Since CO binds 240 times more strongly than O₂, it preferentially occupies haemoglobin's four binding sites, leaving fewer sites available for oxygen transport.
Oxygen-carrying capacity is directly reduced
10
In emphysema, alveolar walls are destroyed because smoking disrupts the balance between elastase and alpha-1 antitrypsin. Which statement correctly describes this imbalance?
Ans
Elastase activity increases while alpha-1 antitrypsin activity decreases
Review
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Identify the elastase–antitrypsin balance
Normally, alpha-1 antitrypsin inhibits elastase to protect alveolar elastic fibres: $$\text{Balance} = \frac{\text{Alpha-1 Antitrypsin}}{\text{Elastase}}$$
Balance must be maintained to protect alveolar walls
Explain smoking's dual effect
Smoking increases elastase release from inflammatory cells and simultaneously oxidizes alpha-1 antitrypsin, inactivating it. Both effects shift the balance toward unchecked elastase activity.
↑ Elastase + ↓ Alpha-1 antitrypsin → alveolar wall destruction
11
Which of the following is a characteristic feature of chronic bronchitis in smokers?
Ans
Chronic inflammation and excessive mucus production in the bronchial tree
Review
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Define chronic bronchitis
Chronic bronchitis is the long-term inflammation of the bronchi with excessive mucus production, caused by repeated exposure to irritants such as cigarette smoke.
Inflammation + hypersecretion of mucus
Distinguish from emphysema
Emphysema involves alveolar wall destruction and loss of elastic recoil. Chronic bronchitis involves airway inflammation and mucus obstruction. Both are components of COPD.
Chronic bronchitis ≠ emphysema; different mechanisms, same cause
12
A patient's measured FEV₁ is 1.8 L. The predicted FEV₁ for their age, sex, and height is 3.6 L. What is their FEV₁ as a percentage of predicted, and what level of airflow obstruction does this indicate?
Ans
50%, indicating moderate to severe obstruction
Review
Tap to reveal
Apply the FEV₁ formula
$$\text{FEV}_{1}\%\,\text{predicted} = \frac{\text{Measured FEV}_{1}}{\text{Predicted FEV}_{1}} \times 100 = \frac{1.8}{3.6} \times 100$$
$$= 0.5 \times 100 = 50\%$$
Interpret the result
FEV₁ below 80% predicted indicates obstructive lung disease. Values of 50–69% indicate moderate to severe obstruction, commonly seen in long-term smokers with COPD.
50% = moderate to severe airflow obstruction
13
Dysplasia in the respiratory epithelium refers to:
Ans
Abnormal maturation and disorganized arrangement of cells that may progress to cancer
Review
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Define dysplasia
Dysplasia involves abnormal cell maturation with variation in cell size, shape, and nuclear morphology. It represents a pre-neoplastic change in the respiratory epithelium.
Abnormal maturation + disorganized arrangement
Place dysplasia in the pathological sequence
Normal epithelium → metaplasia (reversible cell type change) → dysplasia (pre-cancerous abnormal maturation) → carcinoma (invasive cancer). Dysplasia is the critical warning sign before malignancy.
Dysplasia = precancerous stage between metaplasia and cancer
14
Which of the following is NOT a direct effect of cigarette smoke on the respiratory system?
Ans
Strengthening of elastic fibres in alveolar walls
Review
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Evaluate each option against known smoking effects
Cilia paralysis — confirmed direct effect of smoke toxins. Increased mucus — smoke irritates goblet cells causing hypersecretion. CO binding — CO in smoke binds Hb forming COHb. Elastic fibre strengthening — smoke destroys elastase inhibitors, causing elastic fibre degradation, not strengthening.
Elastic fibre strengthening is the false statement
Identify the actual effect on elastic fibres
Smoking disrupts the elastase–antitrypsin balance, leading to excess elastase activity that degrades elastic fibres in alveolar walls, causing emphysema.
Smoke weakens elastic fibres, it does not strengthen them
15
Lung cancer most commonly originates from bronchial epithelial cells that have undergone which sequential cellular changes due to smoking?
Ans
Normal epithelium → metaplasia → dysplasia → carcinoma
Review
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Identify the initiating change
Chronic smoke irritation first causes metaplasia — the reversible replacement of normal ciliated columnar epithelium by stratified squamous epithelium in the bronchi.
Normal → Metaplasia (first step)
Trace progression to malignancy
Continued exposure drives metaplastic cells into dysplasia (abnormal maturation, nuclear atypia), which can eventually transform into invasive carcinoma if the irritant exposure persists.
Metaplasia → Dysplasia → Carcinoma
Question 1 of 15
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1
Which part of the respiratory tract is first exposed to cigarette smoke irritants during inhalation?