Lung–kidney system ↗Drive recruits breathing muscles
Brainstem networks, chemoreceptors, behavior, sleep state, and sensory feedback shape motor output to the diaphragm and other respiratory muscles.
LUNGS / 01
Move air.
Match blood.
Ventilation and gas exchange are related but distinct. Air must reach alveoli, blood must perfuse their capillaries, and gases must cross a thin barrier along partial-pressure gradients.
Thoracic pressure draws air inward
Inspiratory muscle contraction expands the chest, lowers alveolar pressure relative to atmosphere, and produces airflow through the conducting airways.
Resistance shapes flow
Airway caliber, smooth muscle, mucus, edema, dynamic compression, and gas properties determine resistance; small changes in radius can strongly affect flow.
Dead space does not exchange
Minute ventilation includes gas that remains in conducting regions. Alveolar ventilation reflects the fresh gas reaching exchange surfaces.
Partial pressures drive diffusion
Oxygen moves from alveolar gas toward venous blood while carbon dioxide moves in the opposite direction according to gradients and diffusion properties.
Barrier structure sets capacity
Exchange depends on surface area, membrane thickness, capillary transit, hemoglobin binding, and recruitment of pulmonary capillaries.
Ventilation and perfusion must align
Poor ventilation with preserved perfusion creates low-V/Q or shunt-like behavior; ventilation without perfusion creates dead-space behavior.
Whole-body delivery follows
Gas exchange loads arterial blood, but tissue oxygen delivery still depends on hemoglobin concentration, cardiac output, regional flow, and extraction.