Human Lungs – Important Points

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 Human Lungs 

Lungs are the primary organ of the respiratory system, located in the thoracic cavity.

Humans have two lungs: Right lung (3 lobes) and Left lung (2 lobes) — left is smaller to accommodate the heart.

Covered by a double-layered membrane called Pleura (visceral & parietal), with pleural fluid reducing friction.

Main function: Gas exchange – oxygen intake and carbon dioxide removal.

Air pathway: Nose → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli.

Alveoli are tiny air sacs (~300 million) where actual gas exchange occurs via diffusion.

Alveolar walls are lined with a single layer of squamous epithelium for fast diffusion.

Surfactant (produced by Type II alveolar cells) reduces surface tension, preventing alveolar collapse.

Lungs are not muscular; breathing is driven by diaphragm and intercostal muscles.

Diaphragm contraction → lung volume increases → inhalation (negative pressure).

Diaphragm relaxation → lung volume decreases → exhalation.

Right lung is shorter, broader, and heavier than the left lung.

Blood supply: Pulmonary artery (deoxygenated blood in), Pulmonary vein (oxygenated blood out) — only vein carrying oxygenated blood.

Total lung capacity in adults: ~4–6 litres.

Tidal volume (normal breath): ~500 mL.

Vital capacity: max air exhaled after max inhalation (~4.8 L in males).

Residual volume: air remaining in lungs even after forced exhalation (~1.2 L).

Lungs are highly elastic and vascular, giving a spongy texture.

Common lung diseases: Asthma, Pneumonia, Tuberculosis, COPD, Lung Cancer, Pulmonary Fibrosis.

Lungs also help regulate blood pH by controlling CO₂ levels.

Cilia in bronchi trap dust/pathogens and move mucus upward (mucociliary escalator).

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