Anatomy and Mechanism of Breathing
High-Yield Summary
- Air travels one continuous path: external nares → nasal cavity → pharynx → larynx → trachea → bronchi → bronchioles → alveoli.
- Pharynx is a shared air/food pathway; larynx is air-only, protected during swallowing by the epiglottis folding over the glottis.
- Vocal cords (skeletal muscle + cartilage) sit in the larynx and produce sound.
- Cilia lining the bronchi/larger airways move trapped mucus + debris back up toward the throat.
- Alveoli are the gas-exchange site, wrapped in a dense capillary network.
- Visceral pleura (on the lung) + parietal pleura (chest wall lining) form a closed sac with a thin fluid-filled pleural cavity between them.
- Diaphragm: dome-shaped muscle that flattens/moves downward on contraction, increasing thoracic cavity volume.
The Path of Air
- 1External nares (nostrils) → nasal cavity — mucous membranes + vibrissae filter incoming air.
- 2Pharynx — shared pathway for air and food.
- 3Larynx — air-only; glottis opening protected by the epiglottis during swallowing.
- 4Trachea → bronchi (one per lung) — cilia-lined, sweep debris upward.
- 5Bronchioles — progressively smaller branching tubes.
- 6Alveoli — tiny sacs surrounded by capillaries; site of gas exchange.
Key Terms
- Epiglottis
- Flap that folds down over the glottis during swallowing, keeping food/liquid out of the airway.
- Visceral pleura
- Inner membrane layer, attached directly to the lung surface.
- Parietal pleura
- Outer membrane layer, lining the inside of the chest wall.
- Pleural cavity
- Fluid-filled space between visceral and parietal pleura; lubricates the layers and enables the pressure changes driving ventilation.
- Diaphragm
- Dome-shaped muscle separating thoracic and abdominal cavities; flattens/descends on contraction to expand chest volume.
Common MCAT Trap
- Pharynx = shared air/food route; larynx = air ONLY — don't mix these up when tracing the path of air vs. food.
- The pleural cavity isn't just structural support — it's central to generating the pressure differences that drive ventilation (covered further in Mechanisms of Breathing).
Quick Recall
What structure prevents food from entering the airway during swallowing?
What is the full path of air from nose to gas exchange?
What happens to thoracic cavity volume when the diaphragm contracts?