Lesson 11 of 11 · 12 min
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Must-know facts
19 facts
- 01Trachea divides into primary bronchi at the level of the 5th thoracic vertebra.
- 02Incomplete cartilaginous rings give support to the trachea, the bronchi (primary to tertiary) and the initial bronchioles.
- 03Epiglottis covers the glottis during swallowing; the larynx is the sound box.
- 04Conducting zone ends at terminal bronchioles; the exchange zone is the alveoli and their ducts.
- 05Inspiration: diaphragm contracts (antero-posterior axis) and external intercostals contract (dorso-ventral axis); intra-pulmonary pressure falls below atmospheric.
- 06Normal breathing rate: 12–16 breaths per minute.
- 07TV ≈ 500 mL; IRV 2500–3000 mL; ERV 1000–1100 mL; RV 1100–1200 mL.
- 08VC = IRV + TV + ERV; TLC = VC + RV; FRC = ERV + RV; IC = TV + IRV; EC = TV + ERV.
- 09A healthy person breathes in or out roughly 6000–8000 mL of air per minute (about 500 mL per breath × 12–16 breaths).
- 10pO₂ (mm Hg): atmosphere 159, alveoli 104, deoxygenated blood 40, oxygenated blood 95, tissues 40.
- 11pCO₂ (mm Hg): atmosphere 0.3, alveoli 40, deoxygenated blood 45, oxygenated blood 40, tissues 45.
- 12CO₂ is 20–25 times more soluble than O₂.
- 13Diffusion membrane = alveolar squamous epithelium + capillary endothelium + basement substance; much thinner than 1 mm.
- 14O₂ transport: 97% as oxyhaemoglobin, 3% dissolved in plasma. One haemoglobin carries at most 4 O₂.
- 15CO₂ transport: about 70% as bicarbonate, 20–25% as carbamino-haemoglobin, about 7% dissolved.
- 16Per 100 mL blood: about 5 mL O₂ delivered to tissues; about 4 mL CO₂ delivered to alveoli.
- 17Oxygen dissociation curve is sigmoid.
- 18Rhythm centre = medulla; pneumotaxic centre = pons; chemosensitive area responds to CO₂ and H⁺; O₂ has an insignificant role.
- 19Emphysema = alveolar walls damaged, less exchange surface; occupational dust exposure leads to fibrosis.
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Key terms
18 terms
- Glottis
- The opening of the larynx, which the epiglottis closes during swallowing.
- Epiglottis
- A thin, elastic cartilage flap that stops food from entering the larynx.
- Alveoli
- Very thin, vascularised air sacs at the ends of terminal bronchioles where gas exchange occurs.
- Pleura
- The double membrane around each lung, with lubricating pleural fluid between its layers.
- Conducting part
- The airway from external nostrils to terminal bronchioles that carries air to the alveoli, clears it of particles, humidifies it and brings it to body temperature, without exchanging gases.
- Intra-pulmonary pressure
- The air pressure inside the lungs, whose difference from atmospheric pressure drives air movement.
- Spirometer
- An instrument for measuring volumes of air breathed in and out.
- Tidal Volume
- The volume of air moved in or out in one ordinary breath, about 500 mL.
- Residual Volume
- The air that stays in the lungs even after the strongest possible exhalation.
- Vital Capacity
- The largest volume a person can exhale after a maximal inhalation, or inhale after a maximal exhalation.
- Partial pressure
- The share of total pressure contributed by one gas in a mixture.
- Oxyhaemoglobin
- Haemoglobin with O₂ reversibly bound to it.
- Carbamino-haemoglobin
- Haemoglobin carrying bound CO₂.
- Carbonic anhydrase
- An enzyme, abundant in RBCs, that speeds up the interconversion of CO₂ + H₂O and HCO₃⁻ + H⁺.
- Oxygen dissociation curve
- The sigmoid graph of haemoglobin's percentage O₂ saturation against pO₂.
- Pneumotaxic centre
- A centre in the pons that moderates the medullary rhythm centre by shortening inspiration.
- Chemosensitive area
- A region beside the medullary rhythm centre that is highly sensitive to CO₂ and H⁺.
- Fibrosis
- Overgrowth of fibrous tissue in the lungs after long-term inflammation, as in dust exposure.