Trachea

• Beneath the submucosa: 16-20 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 BronchiExtrapulmonary Intrapulmonary

Hyaline cartilage

C-shaped Irregular platesBig bronchi: completely encircle the lumenSmaller 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 BronchiExtrapulmonary Intrapulmonary

Mucous membrane

Thrown into folds

Epithelium Pseudostratified columnar

ShorterSmaller bronchi: ciliated columnar

Goblet cells Fewer

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