Breathing Mechanics

Tidal Breathing

Normal breathing at rest; passive during both inhalation and exhalation.

Functional Residual Capacity

Volume of air remaining in the lungs after a normal exhalation.

Residual Volume

Amount of air remaining in the lungs after maximal exhalation; cannot be exhaled.

Mucus Elevator

Clears airways of debris and pathogens; uses acetylcholine (Ach) to cause bronchoconstriction.

Gas Diffusion

Movement of gases across membranes; governed by Fick’s Law.

Fick’s Law

Gas diffusion rate is proportional to surface area and pressure gradient, and inversely proportional to thickness.

Elasticity of Lungs

Determines how easily the lungs return to their original shape after being stretched.

Radius and Pressure

Smaller radius increases pressure required to keep alveoli inflated (per Laplace’s law).

Epinerphrine

A β-agonist that causes bronchodilation, increasing airway diameter.

Airway Cross-Section

Affects airflow; larger cross-sectional area means less resistance.

Fresh Air Measurement

Tidal volume and respiratory rate help determine how much fresh air reaches the alveoli.

Oxygen in Air

O2 composes about 21% of atmospheric air.