2. The Respiratory System

Your lungs, airways and breathing

Bringing oxygen in. Removing carbon dioxide. Every breath, every cell.

The respiratory system brings oxygen into the body and removes carbon dioxide. It includes the airways, lungs and breathing muscles, and it works continuously from the first breath of life onward. Healthy breathing supports energy, exercise, sleep, speech, immunity and brain function.

1. What is the respiratory system?

The respiratory system includes the nose and nasal passages, throat, larynx, trachea, bronchi, lungs, alveoli and diaphragm. Its central job is gas exchange: oxygen moves from inhaled air into the bloodstream, while carbon dioxide moves from the blood into the lungs to be breathed out.

2. How it works

• Upper airways: Air enters through the nose or mouth. The nose helps filter, warm and humidify it before it travels through the throat.
• Lower airways: Air passes through the trachea, which divides into the right and left bronchi and then into progressively smaller bronchioles.
• Lungs and alveoli: At the ends of the smallest airways are millions of tiny air sacs called alveoli. Their very thin walls sit next to capillaries, allowing oxygen to enter the blood and carbon dioxide to leave it.
• Breathing muscles: The diaphragm is the main breathing muscle. When it contracts, the chest expands and air is drawn into the lungs; when it relaxes, air flows out.

3. What does it do?

4. Common respiratory conditions

Asthma – Long-term inflammation and sensitivity of the airways. Symptoms can include wheeze, cough, chest tightness and breathlessness.

COPD – Chronic obstructive pulmonary disease includes chronic bronchitis and emphysema. Smoking is the commonest cause, although other exposures can contribute.

Respiratory infections – Colds, influenza, COVID-19, bronchitis and pneumonia can affect the airways or lung tissue.

Allergic rhinitis (hay fever) – Inflammation of the nasal passages triggered by allergens such as pollen, dust mites or animal dander.

Obstructive sleep apnoea – Repeated narrowing or closure of the upper airway during sleep, causing disrupted breathing and poor-quality sleep.

Interstitial lung disease – A group of conditions causing inflammation and/or scarring of lung tissue, often leading to persistent breathlessness and dry cough.

Lung cancer – Can affect smokers, former smokers and people who have never smoked.

Tuberculosis (TB) – A bacterial infection that most often affects the lungs and requires specific antibiotic treatment.

5. Symptoms worth knowing

• Shortness of breath, especially if new, persistent or worsening

• Wheezing or whistling in the chest

• Persistent cough or coughing up mucus

• Chest tightness or pain

• Frequent chest infections

• Unusual fatigue or reduced exercise tolerance

• Long-standing nasal congestion or allergy symptoms

• Loud snoring, witnessed pauses in breathing or marked daytime sleepiness

6. What increases respiratory risk?

7. Protecting your respiratory health

• Do not smoke: Stopping smoking is one of the most effective ways to protect lung health. Avoid starting nicotine or tobacco use if you do not already use it.
• Stay active: Regular activity helps maintain cardiovascular fitness, breathing efficiency and respiratory muscle function.
• Vaccination: Keep recommended vaccinations up to date, including seasonal or risk-based respiratory vaccines where appropriate.
• Manage asthma and allergies: Use prescribed treatments correctly and review symptoms if control is poor.
• Reduce exposure: Limit avoidable exposure to dust, fumes, mould and indoor or outdoor pollutants where possible.
• Treat sleep apnoea: Persistent loud snoring, witnessed breathing pauses and severe daytime sleepiness should be assessed.
• Prevent infection: Hand hygiene, good ventilation and avoiding close contact when acutely unwell can reduce transmission of respiratory infections.

8. How doctors investigate respiratory symptoms

Clinical assessment – History, examination, breathing rate and oxygen saturation.

Spirometry – Measures how much air can be breathed out and how quickly; commonly used in asthma and COPD.

Peak-flow monitoring – Can help track variation in airflow, particularly in asthma.

Chest X-ray – A simple imaging test that can identify some infections, lung changes and other chest abnormalities.

Blood tests – May help assess infection, anaemia, inflammation, allergy or other causes of breathlessness.

Sleep study – Used when sleep apnoea or another sleep-related breathing disorder is suspected.

CT or other imaging – Provides more detailed assessment when clinically indicated.

9. Mind × Body

Breathing and emotion are closely linked. Anxiety and panic can cause rapid breathing, chest tightness and a powerful sensation of not getting enough air. Stress can also worsen asthma symptoms in some people, while chronic breathlessness can affect confidence, mood, sleep and activity.

Physical respiratory symptoms should not automatically be dismissed as anxiety. Mind and body interact, and both deserve appropriate assessment.

ADHD and the respiratory system

ADHD does not directly cause lung disease, but it can make respiratory care harder to manage. Difficulties may include remembering inhalers or other medication, attending appointments, maintaining routines, managing allergies and triggers, or stopping nicotine use.

Smoking and nicotine use are particularly relevant because ADHD is associated with higher rates of nicotine use in some populations. Sleep problems also matter: untreated obstructive sleep apnoea can worsen attention, memory, daytime alertness and executive functioning, sometimes overlapping with ADHD-like symptoms.

ADHD medication and breathing

Standard ADHD medicines do not usually impair lung function. However, stimulant medication can increase heart rate and may intensify awareness of breathlessness or anxiety in some people. Caffeine, nicotine and recreational stimulants can add to these effects.

People with asthma or other respiratory conditions should continue appropriate respiratory treatment and discuss significant new breathlessness, chest pain, fainting or persistent palpitations with a clinician.

When to get urgent help