Respiratory mechanics
Ventilation moves air because respiratory muscle activity changes thoracic volume and therefore pressure. Gas exchange occurs across the alveolar–capillary barrier.
Open interactive lesson & self-check ↗Alveolar gas exchange
Original conceptual SVG · scalablePartial-pressure gradients move O₂ into pulmonary capillary blood and CO₂ toward alveolar gas; schematic, not to scale.
Mechanics of inspiration
Contraction of the diaphragm increases thoracic volume and lowers alveolar pressure relative to atmospheric pressure, drawing air inward during quiet inspiration.
Gas exchange
Oxygen diffuses from alveolar air toward pulmonary capillary blood, while carbon dioxide diffuses in the opposite direction, according to partial-pressure gradients.
Separate terms
Ventilation is air movement, perfusion is blood flow, diffusion is gas transfer. Ventilation–perfusion mismatch can impair arterial oxygenation.
Reference and next reading
Explore the original curriculum and publisher-hosted resources for full-depth reading; this note is an original schematic introduction, not an exhaustive chapter.