Overview
The upper airway (nose, pharynx and larynx) warms, filters and humidifies air. The lower airway starts at the trachea, which divides at the carina into the right and left main bronchi. The airways keep branching into bronchioles and end in about 300 million alveoli, where gas exchange happens.
The right lung has three lobes and the left lung two, leaving room for the heart. Each lung is covered by pleura, a double membrane with a thin layer of fluid that lets the lungs glide during breathing and keeps them expanded against the chest wall.
Main functions
- Gas exchange: oxygen into the blood, carbon dioxide out
- Acid–base balance by adjusting how much CO2 is exhaled
- Filtering, warming and humidifying inspired air
- Speech through the larynx and vocal cords
- Protection by coughing, mucus and cilia
Key structures
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Larynx (voice box)
The cartilage box at the top of the trachea that protects the airway and produces the voice.
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Trachea
The windpipe: a tube held open by C-shaped cartilage rings, from the larynx to the carina.
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Bronchi and bronchial tree
The branching airways that carry air from the trachea to every segment of the lungs.
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Lungs
The paired organs of gas exchange: three lobes on the right and two on the left.
Gas exchange in the alveoli
Inspiration is active: the diaphragm contracts and moves down, the external intercostals lift the ribs, chest pressure falls and air flows in. Normal expiration is passive as the muscles relax and the lungs recoil.
In the alveoli, oxygen diffuses from air into the capillary blood and binds to hemoglobin, while carbon dioxide diffuses out. The drive to breathe comes mainly from CO2 levels sensed in the brainstem; some clients with chronic CO2 retention rely more on low oxygen as their stimulus.
Nursing assessment
- Count the respiratory rate for 30–60 seconds without telling the client (normal adult 12–20 breaths per minute).
- Observe depth, rhythm, symmetry, accessory muscle use, nasal flaring and skin color.
- Auscultate anterior, lateral and posterior fields side to side; identify crackles, wheezes, rhonchi, stridor and diminished sounds.
- Check SpO2 (normal 95–100%) together with the clinical picture.
- Assess cough and sputum: amount, color and consistency.
Common conditions
| Condition | What happens | Key signs | Nursing priorities |
|---|---|---|---|
| Asthma | Reversible airway inflammation and bronchospasm | Wheezing, chest tightness, cough, prolonged expiration; a silent chest is an emergency | Short-acting bronchodilator first, then corticosteroids; teach inhaler technique and trigger avoidance |
| COPD | Chronic airflow limitation (emphysema and chronic bronchitis) | Dyspnea, barrel chest, pursed-lip breathing, chronic cough | Pursed-lip breathing, titrate oxygen to the prescribed target (often 88–92%), infection prevention, nutrition |
| Pneumonia | Infection of the lung tissue | Fever, productive cough, crackles, pleuritic pain; older adults may present with confusion | Obtain cultures before antibiotics, oxygen, fluids, cough and deep breathing, upright position |
| Pulmonary embolism | A clot blocks a pulmonary artery | Sudden dyspnea, pleuritic chest pain, tachycardia, anxiety, hypoxemia | High Fowler's, oxygen, notify the provider immediately, anticoagulation |
| Pneumothorax | Air in the pleural space collapses the lung | Sudden dyspnea, absent breath sounds on one side; tension pneumothorax shifts the trachea away | Prepare for chest tube; tension pneumothorax needs immediate decompression |
| Tuberculosis | Airborne Mycobacterium tuberculosis infection | Night sweats, weight loss, low-grade fever, hemoptysis | Airborne isolation with a negative-pressure room and N95 respirator, long-term multidrug therapy adherence |
Labs and normal values
| Test | Typical adult range | Why it matters |
|---|---|---|
| Arterial pH | 7.35–7.45 | Below 7.35 acidosis, above 7.45 alkalosis |
| PaCO2 | 35–45 mmHg | The respiratory component: high CO2 causes respiratory acidosis |
| HCO3− | 22–26 mEq/L | The metabolic component, regulated by the kidneys |
| PaO2 | 80–100 mmHg | Below 60 mmHg indicates significant hypoxemia |
| SpO2 | 95–100% | Lower targets may be prescribed in chronic CO2 retention |
Reference ranges differ between laboratories and textbooks. Use the values your program and facility use.
Exam tips
- ABG mnemonic ROME: Respiratory Opposite (pH and PaCO2 move in opposite directions), Metabolic Equal (pH and HCO3 move in the same direction).
- A sudden quiet chest in an asthma attack means almost no air is moving: it is an emergency, not an improvement.
- Suction for no longer than 10–15 seconds per pass and hyperoxygenate before and after.
Practice questions
8 NCLEX-style questions on the respiratory system. Pick an answer to see the rationale.
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An ABG shows pH 7.30, PaCO2 52 mmHg, HCO3 25 mEq/L. How does the nurse interpret it?
Show the answer and rationale
Answer A: Respiratory acidosis. The pH is low (acidosis) and PaCO2 is high in the opposite direction, so the cause is respiratory. HCO3 is normal, so it is not yet compensated.
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A client with COPD has an SpO2 of 89% on 2 L/min of oxygen. The prescribed target is 88–92%. What should the nurse do?
Show the answer and rationale
Answer B: Continue to monitor at the current setting. The saturation is within the prescribed target. Excess oxygen can worsen CO2 retention in some clients with COPD.
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During an asthma attack, the client's wheezing suddenly stops and he cannot speak. This most likely means:
Show the answer and rationale
Answer B: Airflow is severely obstructed. A silent chest means so little air is moving that wheezes cannot be produced. It is a sign of impending respiratory failure.
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Why do aspirated foreign bodies more often enter the right lung?
Show the answer and rationale
Answer B: The right main bronchus is wider, shorter and more vertical. The anatomy of the right main bronchus gives it a straighter path from the trachea.
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Which finding suggests a tension pneumothorax?
Show the answer and rationale
Answer A: Trachea deviated away from the affected side. Air under pressure pushes the mediastinum and trachea toward the opposite side, with absent breath sounds and hypotension.
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Which isolation is required for a client with suspected active pulmonary tuberculosis?
Show the answer and rationale
Answer C: Airborne precautions with an N95 respirator. TB spreads through airborne droplet nuclei. Use a negative-pressure room and a fitted N95 respirator.
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What is the maximum duration of each suction pass through an airway?
Show the answer and rationale
Answer B: 10–15 seconds. Longer suction removes oxygen and can cause hypoxemia and bradycardia. Hyperoxygenate before and after.
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Which muscle is the primary muscle of inspiration?
Show the answer and rationale
Answer B: Diaphragm. The diaphragm does most of the work of quiet breathing. Accessory muscles are recruited only when breathing is difficult.