What is the histologic identity of the alveolar septa and what major cell types reside there?

What is the histologic identity of the alveolar septa and what major cell types reside there?

• A. Alveolar septa are thick walls containing capillaries; major cells are Type I and II pneumocytes, plus alveolar macrophages in alveolar spaces.
• B. Alveolar septa are thin walls containing capillaries; major cells are Type I and II pneumocytes, plus alveolar macrophages in alveolar spaces.
• C. Alveolar septa contain goblet cells and lymphocytes.
• D. Alveolar septa are lined by type III pneumocytes.

Answer: (B)

Alveolar septa are the extremely thin walls that separate neighboring alveoli, built to allow gas exchange. They contain a network of capillaries and a delicate connective tissue framework, and the epithelium here is made up mainly of two types of pneumocytes. Type I pneumocytes are the flat, expansive cells that form the thin barrier between the air in the alveolus and the blood in the capillary. Type II pneumocytes are fewer, cuboidal cells that secrete surfactant to reduce surface tension and can proliferate to replace Type I cells when needed. Alveolar macrophages reside in the alveolar airspaces to clear debris and pathogens; they are not contained within the septal walls themselves. So the septa are thin walls with capillaries, and the major resident cell types are Type I and Type II pneumocytes, with alveolar macrophages in the alveolar spaces.

Alveolar septa are the extremely thin walls that separate neighboring alveoli, built to allow gas exchange. They contain a network of capillaries and a delicate connective tissue framework, and the epithelium here is made up mainly of two types of pneumocytes. Type I pneumocytes are the flat, expansive cells that form the thin barrier between the air in the alveolus and the blood in the capillary. Type II pneumocytes are fewer, cuboidal cells that secrete surfactant to reduce surface tension and can proliferate to replace Type I cells when needed. Alveolar macrophages reside in the alveolar airspaces to clear debris and pathogens; they are not contained within the septal walls themselves. So the septa are thin walls with capillaries, and the major resident cell types are Type I and Type II pneumocytes, with alveolar macrophages in the alveolar spaces.