MICROANATOMY OF THE RAT DIAPHRAGM - A SCANNING ELECTRON AND CONFOCAL LASER-SCANNING MICROSCOPIC STUDY

The present study demonstrated the three-dimensional microstructure of the rat diaphragm by scanning electron microscopy (SEM) of either int act or alkali-treated tissues, enzyme-histochemistry, and confocal las er scanning microscopy (LSM). The peritoneal and pleural surfaces of t he diaphragm were covered with mesothelial cells studded with microvil li. Many round gaps were formed between the mesothelial cells. The sub mesothelial connective tissue contained voluminous, irregularly shaped lymphatics. Some of these lymphatics extended many funnel-like projec tions of their endothelia towards the pored region of the mesothelium. On coming into contact with the mesothelium, many of the lymphatic pr ojections were perforated at their ends, thus giving rise to stomata c onnecting the peritoneal cavity and lymphatic lumen. Some projections ended blindly while plugging the mesothelial pores, thereby making vis ible some intercellular gaps in this contact. The subperitoneal sheet of the collagen fiber network possessed clusters of foramina which tig htly fit the passage of the lymphatic projections. Confocal LSM of the diaphragm after intraperitoneal injection of FITC-dextran demonstrate d the tracer both in the lymphatic lumina and in the connective tissue spaces. Our results indicate that peritoneal fluid is allowed to flow into the connective tissue spaces of the diaphragm through intercellu lar gaps and into lymphatics through stomata.