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Normal histology

Reviewers: Elliot Weisenberg, M.D. (see Reviewers page)
Revised: 22 December 2011, last major update August 2011
Copyright: (c) 2003-2011, PathologyOutlines.com, Inc.


● Lung parenchyma consists of airways (bronchi/bronchioles) and alveoli
● The pulmonary lobule, also known as the acinus/terminal respiratory unit, contains 3-5 terminal bronchioles, alveolar ducts and alveoli; it is the smallest anatomic unit delineated by connective tissue
● In the bronchi, there is no clear distinction between the mucosa and submucosa
● The entire respiratory tree, except the vocal cords and alveoli, is lined by pseudostratified, tall, columnar, ciliated epithelial cells with neuroendocrine (Kultschitsky) cells, mucus secreting goblet cells in walls of trachea and bronchi, basal cells, brush cells, Clara cells and inflammatory cells
● The cells of the airways produce a mucociliary elevator protecting against particulate injury, providing immunologic protection, and provide moisture and warmth to inspired air
● In more distal airways, there are fewer goblet cells and more Clara cells

Alveolar capillary basement membrane: fuses with alveolar epithelium to form a single membrane for oxygen and carbon dioxide diffusion
Alveoli: lined almost exclusively by type I and II pneumocytes
Canals of Lambert: connections between non-respiratory bronchioles and adjacent alveoli; they function as a means of collateral ventilation and likely are origin of peribronchiolar metaplasis found during repair
Clara cells: increase towards terminal bronchiole, have secretory function, main progenitor cell after bronchiolar injury, and have apical PAS+ diastase resistant secretory granules
Lymphatics: present in pleura, septa and along pulmonary veins and bronchovascular bundles; not present in alveolar walls
Neuroendocrine cells: numerous in neonatal bronchial and bronchiolar epithelium; rare in adults except as clusters within epithelium of bronchi and bronchioles
Pores of Kohn: perforations in alveolar walls, normally function as means of collateral ventilation; in pneumonia permit passage of bacteria and exudate between alveoli
Pulmonary arteries: have internal and external elastic membrane, compared to a single elastic layer in pulmonary veins
Submucosal glands: contain serous and mucus cells with myoepithelial lining and may have oncocytic changes with age
Type I (squamoid) pneumocytes: 95%, flattened
Type II (cuboidal) pneumocytes: 5%, produce surfactant (lamellar bodies on EM); during repair, type II pneumocytes are able to give rise to type I cells

● Normal findings in alveoli: alveolar macrophages, corpora amylacea, blue bodies (calcium carbonate) and megakaryocytes
● Normal findings in interstitium: anthracotic pigment, scattered silica crystals

Micro images




Virtual slides

Fetal lung

Lung - baby

Normal lung

EM images

Type II pneumocyte

End of Lung-nontumor > Normal histology

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