Respiratory System

呼吸 · 看不见的传送带

Place · Level 3

3 亿肺泡 · 70 m² 交换面 · 每天 20000 次呼吸 ~ 12000 L 空气 · O₂/CO₂ + 酸碱 + 高原 HIF + 氧感受诺贝尔奖通路

Connected to · 6

cofactor · 2

Iron
Lungs load and tissues unload thanks to haemoglobin's cooperative binding curve plus the Bohr effect — and at the centre of every haemoglobin sits an iron atom. Short on iron, the lung is fine; the carriers are missing.
Vitamin D
Alveolar macrophages deal with pathogens crossing the mucus layer partly through the antimicrobial peptide LL-37, whose expression vitamin D upregulates — this is where the vitamin-D-and-airway association lands at cell level.

regulates · 4

Heart
Chronic hypoxia (COPD/OSA) → HIF-1α → pulmonary vasoconstriction → pulmonary hypertension → cor pulmonale. Cardiovascular events are the leading cause of death in respiratory patients.
Nervous
Respiration drives brainstem autonomic tone via chemoreceptors (pCO2/pH) + stretch receptors. Chronic hypercapnia (OSA, COPD) → cognitive decline + depression/anxiety. Chronic hyperventilation → mimics panic attacks.
Kidney
Acid-base homeostasis is co-regulated by lungs (CO₂ exhalation) and kidneys (HCO₃⁻ reabsorption). COPD-related CO₂ retention triggers renal base conservation; renal failure drives compensatory hyperventilation (Kussmaul breathing).
Vitamin A
Vitamin C, E and the carotenoids together form the lung's antioxidant net, but the effect is weak and dietary-pattern-level. The single-nutrient counter-example is hard: beta-carotene raised lung-cancer risk in smokers — the classic case of antioxidising too hard.

300 M alveoli · 70 m² exchange

Stop 1/6

3 亿肺泡 · 70 m² 交换面

The lung looks like a pair of fleshy blocks, but is actually a carefully folded tree — its total leaf-area is about 70 m² (roughly a tennis court), all packed inside your chest.

Lung geometry (Weibel 1963 classic measurement):

Airway branching: trachea → bronchus → 23 generations of bifurcation → 300 million alveoliAlveolus diameter ~0.2 mm, wall thickness ~0.5 μm (100× thinner than a hair)Total exchange surface ~70 m² (some estimates reach 100 m²; 70 is commonly cited)Total pulmonary capillary length ~1000 km — about 1/4 of all body capillaries are in the lungs
This design is up against physical limits: thin enough that any thinner would rupture, but any thicker would block diffusion (Fick's law has diffusion rate proportional to area / thickness); large enough that any larger wouldn't fit in the chest, but any smaller wouldn't keep up with cardiac output.

A day's workload: resting respiratory rate 12-16 breaths/min, ~20,000 breaths/day; resting tidal volume ~500 mL, ~12 m³ of air per day (about 1/5 of a bedroom); during exercise minute ventilation can spike 25× to 200 L/min.

The body has only two direct conduits to the outside world — the respiratory tract and the GI tract. The GI tract is relatively short, with mucus, gastric acid, and the liver layer-filtering it. The respiratory tract is directly exposed to ambient air — PM2.5, smoke, viruses, allergens — and is guarded by mucus + cilia + alveolar macrophages + IgA + antimicrobial peptides. This is why the vitamin-D / vitamin-A / zinc immune stories in the atlas land most directly here, in the respiratory tract.

Read story

Educational content, not medical advice — consult a clinician.

Back