Mechanics of breathing

Inspiratory muscles

Diaphragm: contracts, flattens, increases vertical dimension of chest

External intercostals: bucket handle action, increase AP and lateral dimensions of chest

Accessories (SCM, scalenes): pump handle action, increase vertical dimension of chest

Expiratory muscles

Abdominal muscles increase IAP -> increase ITP

Internal intercostals: decrease AP and lateral dimensions of chest

Pleura

Filled with incompressable fluid. -5cmH2O at rest. With inspiration, overcome the elastic recoil of lung.

Alveolus

Expands during inspiration. Alveolar pressure falls below atmospheric pressure, Flow from upper airways to alveolus. Inflates until pressure equalizes, then flow ceases.