Thick section (alveolar-capillary complex)

The thick section of the alveolar capillary complex describes the histological features of a small percentage of the surface area of the alveoli where mainly type II pneumocytes are sited. In this region:

• the wall of the alveolus is relatively thicker than the thin sections
• the epithelial cell maintains its basement membrane
• the alveolar wall has a greater abundance of:
  • fibroblasts
  • mast cells
  • elastin fibres
  • reticulin fibres

The thick section may function as a potential space for storing exudate from the pulmonary capillaries when there is increased pressure within the pulmonary circulation. By this means, there is a 'buffer' before fluid enters the alveoli and restricts gaseous exchange at the thin portions of the alveolar-capillary complex.