Histology · MU Sofia

Lung + Developing lung

Covers the microscopic structure of the lung, moving from the bronchus through bronchioles and their cell types to the alveoli, with the pulmonary vessels, interlobular septa and anthracotic pigment. It then describes lung development in four stages: pseudoglandular, canalicular, terminal saccular and alveolar, with a developmental figure comparing mouse lung at each stage. The note includes a list of cell types and their features, which a general account may not give in such detail.

Inside: 1 section · 4 labelled pictures · 15 flashcards · 7 min

Topic 2 of 17 in the MU Sofia syllabus for Histology (Medicine, Year 2). The free AceMed note covers it in 1 section, about 994 words (7 min of reading), with 15 flashcards.

In this note

  1. Introduction

Introduction

Microscopic (histologic) description

  • Bronchus:
  • Airway lined by pseudostratified ciliated epithelium
  • Mucosal and submucosal layer are separated by elastic membrane confirmed by elastic staining (e.g. elastica Masson staining and elastica van Gieson staining), although it is not clearly observed by H&E staining alone
  • Bronchial glands exist in the submucosa; cartilage and annular muscular layer exist in the wall between submucosa and adventitia
  • References: Pawlina: Histology - A Text and Atlas, 8th Edition, 2018, Lowe: Stevens & Lowe's Human Histology, 4th Edition, 2014
  • Bronchiole:
  • Small airway, usually 1 mm in diameter or less, lined by single layer of ciliated epithelium
  • Lacks bronchial glands and cartilage
  • Ciliated cell:
  • Tall columnar epithelium, with cilia on the edge of airway side
  • Height becomes shorter as bronchiole heads toward periphery
  • Reference: Mills: Histology for Pathologists, 5th Edition, 2019
  • Mucous cell (goblet cell):
  • Tall columnar epithelium with clear cytoplasm containing mucin, lacking cilia
  • Basal cell:
  • Laying on the basal membrane of bronchus or bronchiole with high nucleocytoplasmic ratio (Lung Cancer 1994;10:S53)
  • Neuroendocrine cell (Kulchitsky cell):
  • Laying scattered on the basal membrane with granular scant cytoplasm and relatively high nucleocytoplasmic ratio
  • Usually difficult to distinguish from basal cell only by H&E staining
  • Club cell (formerly Clara cell):
  • Toll epithelial cell, no cytoplasmic mucin, no cilia
  • Number of club cells increase as bronchiole heads toward periphery
  • Bronchial gland:
  • Mixed gland composed of both serous and mucinous epithelium
  • Its duct opens to bronchial lumen
  • Interlobular septum:
  • Fibrous tissue separating Miller's secondary lung lobule, which contains pulmonary vein and lymphatic vessel
  • Note that not every secondary lobule is separated by this septum
  • Bronchovascular bundle:
  • Fibrous tissue connecting from pulmonary hilum, which contains bronchus, pulmonary artery, bronchial artery and lymphatic vessel
  • Alveolar duct:
  • Terminal airway opening to alveolus, of which alveolar entrance rings constitute the walls
  • Alveolar entrance rings contain elastic fibers and smooth muscles
  • Alveolus:
  • Sac-like structure lined by alveolar epithelium
  • Alveolar septum contains pulmonary capillaries
  • Strictly speaking, alveolar structure is not sac shaped but is a polyhedral architecture
  • Type I alveolar epithelium (pneumocyte):
  • Thin flat epithelium covering about 90 - 95% of alveolar lumen in area, about 40% of all alveolar epithelia in number
  • Type II alveolar epithelium (pneumocyte):
  • Cuboid epithelium covering 5 - 10% of the alveolar lumen in area, about 60% of all alveolar epithelia in number
  • Pulmonary artery:
  • Elastic artery in the central (hilar) side and muscular artery in the peripheral (alveolar) side

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