Lungs
The right lung has three lobes (upper, middle, lower); the left has two (upper, lower). The functional unit is the acinus — terminal bronchiole, respiratory bronchioles, alveolar ducts, and alveoli. Each alveolus is surrounded by capillaries separated by an extremely thin membrane (0.5 μm) for efficient diffusion. Type I pneumocytes form the membrane; Type II pneumocytes produce surfactant.
Normal Function
Gas exchange: oxygen enters blood across the alveolar membrane; carbon dioxide exits. The lungs have a surface area of approximately 70 m² (the size of a tennis court) for efficient gas exchange. They also perform immune surveillance and filter small blood clots.
Lunar Adaptations
On Arrival (First Weeks)
Fluid redistribution may cause mild pulmonary congestion initially (cephalad shift). Mucus clearance may be impaired in the 1/6g environment — ciliary function continues but gravitational assistance with expectoration is reduced. HEPA-filtered habitat air is drier than outdoor air, affecting mucociliary clearance.
6-Month Resident
Pulmonary function largely maintained with regular exercise. However, chronic regolith dust exposure begins subclinical changes in early-exposed workers. Surfactant production changes noted in some residents. Pulmonary blood flow distribution changes from gravity-dependent to more uniform (similar to spaceflight).
Long-Term Resident (2+ Years)
Long-term residents show changes in lung ventilation-perfusion distribution (no longer gravity-dependent). Chronic regolith exposure history becomes the dominant pulmonary concern. Annual spirometry is essential to detect subclinical restriction from early dust deposition. Risk of irreversible lung fibrosis rises with cumulative dust exposure years.