The pleura: a combined light microscopic, scanning, and transmission electron microscopic study in the sheep. I. Normal pleura.

The structural features of the ovine pleura are described using light, scanning, and transmission electron microscopy. Extensive sampling of the visceral and parietal pleura revealed considerable variation in both surface morphology and pleural interstitial anatomy. Variations of mesothelial surface were encountered and these were due to microvillar density and length. The pleural interstitium varied considerably in thickness, being relatively sparse in the anterior lung lobes, where respiratory excursion is least, and much more robust in the caudal lung lobes, where respiratory excursion is greatest. A similar correlation was observed with regard to the abundance and extent of the elastic meshwork embedded in the interstitium. The parietal pleura had openings which connected directly with the lymphatics in the underlying interstitium, thus forming a direct channel between the pleural cavity and the lymphatic system.