Lung–kidney system ↗Alveolar oxygen sets a gradient
Inspired pressure, alveolar ventilation, water vapor, and carbon dioxide help determine alveolar oxygen partial pressure.
LUNGS + BLOOD / 02
Saturation is one part
of delivery.
Arterial oxygen content depends mainly on hemoglobin concentration and saturation, with a smaller dissolved component. Delivery then multiplies content by blood flow.
Oxygen crosses into plasma
Dissolved oxygen crosses the alveolar–capillary interface and establishes the partial pressure measured as PaO₂.
Hemoglobin binds most oxygen
Red-cell hemoglobin greatly increases blood oxygen content beyond the small dissolved fraction.
The binding curve is nonlinear
Cooperative binding creates a plateau that supports loading and a steeper region that supports unloading as tissue oxygen falls.
Affinity shifts with local context
Carbon dioxide, hydrogen ions, temperature, and red-cell 2,3-BPG can alter hemoglobin affinity and tissue unloading.
Anemia changes content
A person can have a normal saturation but lower oxygen content when hemoglobin concentration is reduced.
Cardiac output drives delivery
Whole-body oxygen delivery is arterial content multiplied by blood flow; regional vascular control then distributes it.
Tissues extract according to demand
Diffusion distance, microvascular flow, mitochondrial demand, and local regulation determine how much delivered oxygen is used.