Disorders of Respiratory System

NCERT grounding

Chapter 14 of NCERT Class XI Biology closes with a tight three-sentence box on Section 14.6 followed by a brief side-note on occupational disorders. The wording is short enough to memorise verbatim — and NEET routinely lifts options straight from these sentences. NIOS Chapter 14 widens the same topic by tabulating bronchitis, pneumonia and tuberculosis alongside the two NCERT diseases.

"Asthma is a difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles. Emphysema is a chronic disorder in which alveolar walls are damaged due to which respiratory surface is decreased. One of the major causes of this is cigarette smoking."

NCERT Class XI · Chapter 14 · Section 14.6

Note how clinically minimal the chapter is. NCERT does not give pathophysiology, drug classes or radiological signs. It supplies one site of lesion (bronchi/bronchioles for asthma, alveolar walls for emphysema), one symptom (wheezing) and one cause (cigarette smoking, for emphysema). Occupational disorders are described in a single later paragraph that introduces silica and dust exposure as the cause and pulmonary fibrosis as the outcome. Everything else asked in NEET — chronic bronchitis, COPD, tuberculosis — comes either from NIOS or from cross-references to the Class XII Human Health and Disease chapter.

Three disorders, three lesions

The cleanest way to lock Section 14.6 into recall is to bind each disease to the part of the respiratory tree it attacks. Asthma attacks the conducting airways. Emphysema attacks the respiratory surface. Occupational disorders, with enough years of dust, attack the interstitial scaffold itself and replace it with fibrous tissue. The three lesions sit at three different points along the same anatomical pipeline.

Hold this map in mind when you read PYQs. Almost every NEET trap in this section asks you to identify which structure is involved. A wheezing patient with narrowed conducting airways is asthma. A breathless smoker with a shrinking exchange surface is emphysema. A stone-cutter with fibrotic patches on a chest X-ray is silicosis. Mixing up bronchi and alveoli is the single most common error.

Asthma — the airway disorder

NCERT defines asthma in exactly eighteen words: a difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles. NIOS adds the allergic mechanism — it is triggered by certain foreign substances in the air, with excess mucus secretion narrowing (clogging) the bronchioles. Wheezing, the audible whistle on expiration, is the symptom NEET prints in stem after stem. NEET 2016 even asked students to attribute asthma to "allergic reaction of the mast cells in the lungs", which is the immunological version of the same allergic story.

Mechanistically, an inhaled allergen binds IgE on mast cells lining the bronchioles. Mast cells degranulate, releasing histamine and leukotrienes that swell the airway wall, contract the smooth muscle and pour mucus into the lumen. The combination of bronchospasm, oedema and mucus plugging shrinks the radius of conducting airways. By the Hagen–Poiseuille relation, airway resistance scales with the inverse fourth power of the radius, which is why a modest swelling of the bronchiolar wall produces a dramatic increase in breathing effort. This biophysical detail is not in NCERT but explains why the symptom is "difficulty in breathing".

Emphysema — the alveolar wall disorder

Emphysema is NCERT's headline chronic disorder. The exact wording — "a chronic disorder in which alveolar walls are damaged due to which respiratory surface is decreased" — is the option that wins every match-the-column question on this disease. One sentence later, NCERT names the cause: cigarette smoking. NEET 2016 Q.68 literally asked which chronic disorder is caused mainly by cigarette smoking; the answer was emphysema. NEET 2025 Q.144 paired emphysema with "damaged alveolar walls and decreased respiratory surface" — a near-quotation of the textbook.

The smoking link is mechanistic. Cigarette smoke recruits neutrophils and macrophages into the alveolar wall; these release elastase, an enzyme that digests the elastin fibres holding the alveolar architecture together. Normally a serum protein called α1-antitrypsin neutralises elastase, but smoking inactivates the antitrypsin by oxidation. Elastase wins, elastin is destroyed, alveolar walls collapse and adjacent sacs coalesce into large bullae. The lung loses both surface area and recoil. NCERT does not require the biochemistry, but NEET examiners increasingly write distractors in that direction.

Unlike asthma, emphysema is not reversible. Once an alveolar wall is destroyed it does not regenerate. The patient's vital capacity falls, the residual volume rises, and the functional residual capacity drifts upward as more and more air gets trapped behind collapsed terminal bronchioles. This is the structural reason why emphysema is grouped under chronic obstructive pulmonary disease (COPD) in clinical medicine, although NCERT does not use that acronym.

Occupational respiratory disorders — silicosis and asbestosis

The NCERT paragraph on occupational disorders is one of the most asked snippets of the entire chapter. The textbook says that in industries involving grinding or stone-breaking, dust production overwhelms the body's defence mechanism; long exposure causes inflammation leading to fibrosis — defined right there as "proliferation of fibrous tissues" — and serious lung damage. Workers should wear protective masks. NEET 2018 Q.180 lifted "Which of the following is an occupational respiratory disorder?" directly out of this paragraph; the answer was silicosis.

Both diseases share the same NCERT-level pathology — long exposure, inflammation, fibrosis. The distinguishing detail is the inhaled species. Silicosis comes from silica dust in stone-related trades; asbestosis comes from asbestos fibres in insulation and ship-building. NEET will not split hairs over upper-versus-lower-lobe radiology, but it does expect you to recognise the term "occupational respiratory disorder" and to pick silicosis as the canonical example.

The mechanism, once dust crosses the mucociliary defence, is the same chain that NCERT lists in the chapter: inflammation precedes fibrosis. Phagocytic macrophages ingest the particles but cannot digest silicate-based dusts. The macrophages die, spill their lysosomal contents and recruit fibroblasts. Collagen accumulates around small airways and alveoli, stiffening the lung. The result is a restrictive pattern — the lung cannot expand fully — which is the opposite physiological signature from obstructive emphysema and asthma, where the problem is getting air out, not in.

COPD umbrella and tuberculosis

COPD — chronic obstructive pulmonary disease — is the clinical umbrella that groups chronic bronchitis and emphysema, both driven principally by cigarette smoking. NCERT Class XI never spells out "COPD"; the textbook treats emphysema as its representative. NIOS, in its table of common respiratory disorders, lists bronchitis separately as inflammation of the bronchi caused by infection, smoking and air pollution, with symptoms of cough and greenish-blue sputum. For NEET purposes the chain is: NCERT asks for emphysema and cigarette smoking; NIOS may ask for bronchitis as a smoker's disorder too; the clinical term COPD is a useful umbrella but rarely appears as an answer key word.

Tuberculosis (TB) deserves a quick mention because students sometimes expect it under Section 14.6. NCERT Class XI does not list TB in Chapter 14; the disease is covered in Class XII Chapter 8, Human Health and Disease, where it is described as a bacterial infection (caused by Mycobacterium tuberculosis) that primarily affects the lungs. NIOS Chapter 14, however, places TB in its respiratory-disorders table — a bacterial infection spreading through droplets, with cough and weight loss as core symptoms, prevented by the BCG vaccine and treated with a multi-month antibiotic regimen. For the NEET breathing chapter, restrict TB to a single line of recognition; the full immunology and epidemiology live under the human-health pages.

Worked examples

Common confusion & NEET traps