Respiratory System — Gas Exchange

Anatomy:

Nasal cavity → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli

Gas exchange occurs at the alveoli — thin walls, surrounded by capillaries

Mechanics of breathing:

Inhalation — diaphragm contracts (moves down), chest expands, pressure decreases, air flows in

Exhalation — diaphragm relaxes (moves up), pressure increases, air flows out

Negative pressure breathing (unlike positive pressure ventilators)

Gas exchange:

O₂ moves from alveoli into blood (high → low concentration)

CO₂ moves from blood into alveoli

Driven by partial pressure gradients (Fick's law)

CO₂ transport:

~70% as bicarbonate (HCO₃⁻)

~20% bound to hemoglobin

~10% dissolved in plasma

Lung volumes:

Tidal volume (TV) — normal breath (~500 mL)

Vital capacity (VC) — maximum breath

Residual volume — air remaining after maximum exhalation

Total lung capacity = VC + residual volume

Reference:

Wikipedia: Respiratory System

https://en.wikipedia.org/wiki/Respiratory_system