P ulmonary
Aliya N. Husain, M.D.
II. Normal
A. Gross

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  1. Trachea has C-shaped cartilage

  2. Right bronchus is longer and more in line with trachea

  3. Accompanying the branching airways is the double arterial supply to the lung, i.e. the pulmonary and bronchial arteries. Thus infarctions rarely occur in the absence of significant cardiac failure.
B. Microscopic

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  1. The respiratory tree is lined by ciliated pseudostratified columnar epithelium from nose to terminal bronchioles except for the true vocal cords which are lined by stratified squamous epithelium. The true vocal cords do not have any lymphatics which is why early (T1) squamous cell carcinomas (SCC) have good prognosis.

  2. Bronchi have discontinuous cartilage and submucous glands.

  3. Bronchioleshave no cartilage or glands.

  4. Terminal bronchioles are less than 2 mm. in diameter.

  5. Alveoli are lined by type I (95%) and type II pneumocytes. There is no protective mucin or ciliary action in alveoli.

  6. Type I pneumocytes are flat. They do not divide.

  7. Type II pneumocytes are cuboidal. They synthesize surfactant and divide during repair. Eventually most of them flatten out to form type I pneumocytes.