Source: Alveolus diagram — Wikimedia Commons
Key Labeled Structures
| Label | Structure | Key Function / NEET Fact |
|---|---|---|
| 1 | Alveolar wall (squamous epithelium) | Layer 1 of diffusion membrane; extremely thin for rapid diffusion |
| 2 | Shared/fused basement membrane | Layer 2 of diffusion membrane; shared between alveolar epithelium and capillary endothelium |
| 3 | Pulmonary capillary endothelium | Layer 3 of diffusion membrane; rich in carbonic anhydrase (inside adjacent RBCs) |
| 4 | Red Blood Cells (RBCs) | Carry O2 as oxyHb; convert CO2 to HCO3– via carbonic anhydrase |
| 5 | Alveolar air space | pO2 = 104 mmHg; pCO2 = 40 mmHg; site of O2 loading and CO2 unloading |
| 6 | Pulmonary capillary lumen | Deoxygenated blood: pO2 = 40 mmHg, pCO2 = 45 mmHg on arrival |
| 7 | Type II alveolar cells | Produce surfactant (reduces surface tension, prevents alveolar collapse) |
| 8 | Alveolar macrophages | Immune defence; remove inhaled particles in alveolar space |
| 9 | Bronchiole | Conducting airway leading to alveoli; no cartilage; smooth muscle walls |
| 10 | Pleural membrane | Double layer enclosing lungs; intrapleural fluid reduces friction |
Diffusion Arrows (Direction)
- O2: Alveolar air → blood (high pO2 104 → low pO2 40)
- CO2: Blood → alveolar air (high pCO2 45 → low pCO2 40)