Asthma
How type 2 inflammation makes the airways narrow too easily, why the narrowing is variable and reversible, why wheeze is loudest on breathing out, and how long-standing asthma can remodel the airway wall.
By the end, you can
- Describe the normal bronchiole, its smooth muscle and its control.
- Explain how Th2 cytokines, IgE and mast cells produce early and late airway responses.
- Relate bronchospasm, wall oedema and mucus to wheeze, air trapping and V/Q mismatch.
- Explain why a normal or rising PaCO2 in a severe attack is a warning sign.
- Distinguish reversible obstruction from the fixed component that remodelling can leave.
- Recognise the classic appearances, severity grades and tests of asthma, and explain how each main drug class acts on its mechanism.
What it is
Asthma is a chronic inflammatory disease of the airways in which hyperresponsive airways narrow in episodes, causing variable airflow obstruction that reverses, fully or largely, on its own or with a bronchodilator. Most asthma involves type 2 inflammation (often allergic); some does not.
2 types to tell apart
- Type 2 (T2-high) asthma
- Driven by Th2 cytokines (IL-4, IL-5, IL-13), with eosinophils, IgE and mast cells; often allergic and starting in childhood.
- T2-low asthma
- Fewer eosinophils and more neutrophils or few inflammatory cells; often adult-onset and linked with obesity or smoking. It responds less to treatments aimed at type 2 inflammation.
US spelling: fibres → fibers, adrenaline → epinephrine.
Normal function
Conducting airways and their smooth muscle
Air reaches the alveoli through a branching tree of conducting airways. Bronchi are held open by cartilage; the , under about 1 mm across, have none. A sheet of wraps the walls of both, and in the bronchioles it alone sets the width of the lumen. The terminal bronchioles open into , where gas exchange begins.
Parasympathetic (vagal) fibres release acetylcholine, which contracts the muscle; adrenaline acting on β2-adrenoceptors relaxes it. The larger airways are lined by a ciliated epithelium with mucus-secreting goblet cells: mucus traps particles and cilia sweep it upwards (the mucociliary escalator).
Width matters greatly for flow: in a simple tube, halving the radius raises resistance about sixteen-fold. In health most resistance lies in medium-sized bronchi, because the many small airways lie side by side; when thousands narrow together, as in asthma, resistance rises steeply.
Underlying change · Step 1 of 4
Type 2 inflammation: sensitisation and the early response
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 2 of 4
Three ways the airway narrows
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 3 of 4
Worse on breathing out: wheeze and air trapping
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 4 of 4
Reversible obstruction and airway remodelling
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Exam detail
Exam detail
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Treatment
How treatment works
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .