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Flashcards in Histology Deck (22):

What is the common histological plan of conducting airways?

Mucosa (epithelium and lamina propria)

Submucosa (loose CT with seromucous glands)

Adventitia (binds airway to adjacent structure)


What cells make up respiratory epithelium? What is the function of each?

Ciliated cells that are pseudostratified (i.e. the nuclei are at different levels, but the cells all contact the BM) (propel mucus up)

Goblet cells (mucus secreting, traps dust)

Basal cells (stem cells for goblet cells and ciliated cells)


"pseudostratified ciliated columnar epithelium with goblet cells"


Where does mucus in the airway come from?

Goblet cells and seromucous glands


When would metaplasia occur in the airway? -how does the airway respond to the irritant?

-when airflow is altered or forceful airflow (e.g. chronic coughing)

-first the airway makes more goblet cells to clear away particulate matter

-this extra mucus is difficult to clear away, so a chronic cough develops

-the columnar cells change to squamous cells which are hardier, but less functional (no cilia)


What are the layers of the trachea? What kind of epithelium does it have?

-mucosa (resp. epithelium + lamina propria) ,submucosa (seromucous glands) , cartilagenous C-rings (keep trachea from collapsing) ,adventia

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What is the histology of the main stem bronchi before they enter the lung? After they enter the lung?

  • Before they enter the lung it is the same as the trachea (mucosa, submucosa (with seromucous glands), cartilage, adventitia)
  • After they enter the lung: mucosa (resp. epithelium +lamina propria), muscularis, submucosa (with seromucous glands), irregular cartilage plates, adventitia

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What is the histology of intrapulmonary bronchi?

Same as for hilar bronchi (mucosa, muscularis,submucosa, cartilage plates, adventitia) but as you get further down in generations the cartilage, muscle and height of epithelium all decrease. In section, intrapulmonary bronchi will be surrounded by alveoli. 

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What is the histology of conducting bronchioles?

Mucosa (no goblet cells), muscularis, no seromucous glands, no cartilage, adventitia


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What epithelial changes happen as you move down in conducting bronchioles? 

Respiratory epithelium (Clara cells begin to replace goblet cells)--> simple columnar epithelium --> simple cuboidal with Clara cells


What are key features of Clara cells?

  • Clara cells progressively replace goblet cells
  • Secrete surfactant
  • Secrete enzyme that breaks down mucus
  • Ingest and digest toxins
  • Prevent luminal adesion if the airways collapse


Histology of bronchioles

  • Mucosa: Early: simple ciliated cuboidal +clara cells. Later: mostly clara cells (no cilia)
  • Muscularis
  • no glands
  • adventia


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Histology of pulmonary alveoli

-alveolar septa (collagen +elastin), network of capillaries, alveolar cells (Type 1 and Type 2), alveolar macrophages (dust cells)


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Contrast Type 1 and Type 2 pneumocytes

  • Type 1: thin squamous cell with large surface to faciliate gas exchange. Covers 95% of surface, but less numerous than type 2
  • Type 2: cuboidal cell that secretes surfactant. More numerous than type 1 (60%), but only covers 5% of alveolus. Often found at alveolar septae.

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Where does gas exchange occur in an alveolus? What are the components of the blood-air barrier?

  • In areas of minimal thickness
  • The blood air barrier is a Type 1 pneumocyte, and a capillary with fused basement membranes
  • Minimal interstitial space, minimal cytoplasmic content of the cells on either side 

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Alveolar macrophages: what do they do and how to identify them on LM and EM.

AKA dust cells: scavenge for foreign bodies

LM: brown dots- look like they've ingested a lot of foreign material

EM: lysosomes in cytoplasm


What is the dual blood supply of the lung?

Pulmonary arteries: Deoxy blood from RV enters lung at hila and travels down the bronchial tree to be oxygenated at alveoli.

Bronchial arteries: branch from the thoracic aorta and deliver oxygenated blood to the walls of airways

**Both return to the heart via the pulmonary veins 


Summarize the type of epithelium, the presence of smooth muscle and the presence of cartilage in the conducting airways

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Contrast normal airways to airways of an asthmatic

  • goblet cell hyperplasia--> lumen can be filled with mucin
  • more inflammatory cells  in the surrounding connective tissue
  • more regional changes in epithelium (e.g. metaplasia)


What is the role of elastin in the lung?

Elastin fibers form a continuum throughout the lung, along with collagen and proteoglycans, and function to return the lungs to their original volume following expiration and to diseminate any force exerted on the parenchyma throughout the entire organ.


What are the ultrastructural features of  alveolar macrophages?

Dust cells (pictured)

  • In the alveolar lumen, have lysosomes, pseudopodia all over edges 

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What are the ultrastructural features of type 1 and type 2 pneumocytes?

Type 1:


Will be right next to capillaries

Type 2:

Filled with lamellar bodies , edges studded with microvilli, euchromatic nucleus

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What are the main histopathological and pathological features of idiopathic pulmonary fibrosis?

  • Interstitial fibrosis
  • inflammation
  • honeycombing (end-stage)(dilatation of bronchioles to compensate for destruction of alveoli)

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