Trachea Beneath the submucosa: C-shaped hyaline cartilages that keep the lumen permanently open Cartilages form an incomplete ring around the trachea Open on the posterior aspect where a thick layer of smooth muscle fibers (trachealis muscle) and fibroelastic ligament bridge the open ends of each cartilage

Lungs Pair of conical organs that occupy the greater part of the thoracic cavity – Right lung – 3 lobes – Left lung – 2 lobes

Pleura Double layer of fibrous tissue that envelopes the lungs – Parietal pleura – Visceral pleura – Pleural cavity Mesothelium (simple squamous epithelium)

Bronchial Tree The branching pattern of the main bronchi Main bronchi – Right main bronchus – Left main bronchus Secondary bronchi – Right – 3, Left – 2 Tertiary bronchi – Right – 10, Left – 8

Bronchopulmonary Segment Each tertiary bronchus and the area of the lung that it supplies These segments each have their own artery (thus, each segment is supplied by a bronchus and an artery) Each bronchopulmonary segment is a discrete anatomical and functional unit.

Bronchi Extrapulmonary – main bronchi (before they enter lung substance) – Same structure as trachea, but smaller caliber Intrapulmonary – all bronchi within the lung substance – Same structure as extrapulmonary, with exceptions

Intrapulmonary vs. Extrapulmonary Bronchi ExtrapulmonaryIntrapulmonary Hyaline cartilage C-shapedIrregular plates Big bronchi: completely encircle the lumen Smaller bronchi: incomplete rings or isolated plates Smooth muscle fibers Present only in the area where cartilage is deficient Occupy a recognizable layer between the mucous membrane and the cartilage plates

Intrapulmonary vs. Extrapulmonary Bronchi ExtrapulmonaryIntrapulmonary Mucous membrane Thrown into folds EpitheliumPseudostratified columnar Shorter Smaller bronchi: ciliated columnar Goblet cellsFewer

Bronchial Tree Bronchioles – 1 mm diameter, disappearance of cartilage – Terminal bronchioles – 0.5 mm diameter or less Respiratory bronchioles – Alveolar ducts

Bronchioles Smaller caliber than bronchi Wall: no cartilage, gland, lymph nodes Epithelium: respiratory epithelium but diminishes in height and transforms to cuboidal as bronchial tree goes distally, no goblet cells Smaller bronchioles: Clara cells

Clara Cells Non-ciliated, columnar cells Contain microvilli Rounded apices Contain dense secretory granules – protect the bronchiolar lining, form a non-sticky layer that helps keep the bronchioles patent