Structures & Zones
What are the two main structural divisions of the respiratory tract?
Upper (nose → pharynx) and lower (larynx → lungs).
According to Boyle’s Law, what happens to pressure when lung volume increases?
decreases
In external respiration, where does oxygen move to and from?
From alveoli → into blood (capillaries).
What type of epithelium lines most of the conducting zone?
Ciliated pseudostratified columnar epithelium.
What is tidal volume (TV)?
The amount of air inhaled or exhaled during normal breathing. (~500 mL)
What are the two functional zones of the respiratory system, and what is each responsible for?
Conducting zone (warms, humidifies, conducts air) and Respiratory zone (gas exchange).
During inspiration, what happens to the diaphragm and external intercostals?
They contract, causing the thoracic cavity to expand.
What drives gas exchange at the alveoli and body tissues?
Pressure gradients (partial pressures of O₂ and CO₂).
Which alveolar cells secrete surfactant?
Type II alveolar cells.
What is inspiratory reserve volume (IRV)?
Extra air inhaled after a normal inspiration.
What structure divides food and air into the correct pathways?
The larynx (via the epiglottis covering the trachea).
Which pressure keeps the lungs from collapsing? intrapulmonary or intrapleural?
Intrapleural pressure (it’s always slightly negative).
What are the three main ways CO₂ is transported in the blood?
7% dissolved in plasma, 23% bound to hemoglobin, 70% as bicarbonate (HCO₃⁻).
What is the function of alveolar macrophages?
They remove debris and pathogens from the alveoli.
What is expiratory reserve volume (ERV)?
Extra air exhaled after a normal expiration.
What happens to cartilage and smooth muscle as bronchi branch into bronchioles?
Cartilage decreases while smooth muscle increases.
What happens to intrapulmonary pressure during expiration?
It increases, pushing air out of the lungs.
What happens when the ventilation rate is higher than perfusion?
There’s not enough blood in alveolar capillaries for full gas exchange.
What is the main component of the respiratory membrane?
Alveolar epithelium + capillary endothelium + shared basement membrane.
What is vital capacity (VC)?
The maximum amount of air that can be moved in and out of the lungs (TV + IRV + ERV).
List the full pathway of airflow starting from the nose and ending at the alveoli.
Nose → nasal cavity → pharynx → larynx → trachea → bronchi → bronchioles → alveoli.
Why is pulmonary ventilation considered "bulk flow" while alveolar ventilation is "diffusion"?
Bulk flow moves large volumes of air via pressure changes; diffusion moves gases across membranes based on concentration gradients.
What molecule carries most oxygen in the blood?
Hemoglobin.
How does histology change from the trachea to the alveoli?
Epithelium becomes thinner (pseudostratified → simple cuboidal → simple squamous), cartilage disappears, and smooth muscle increases.
What is residual volume (RV) and why is it important?
Air that remains in the lungs after exhalation; prevents lung collapse.