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The mammalian lung´s structural design is optimized to serve its main function: gas exchange. It takes place in the alveolar region (parenchyma) where air and blood are brought in close proximity over a large surface. Air reaches the alveolar lumen via a conducting airway tree. Blood flows in a capillary network embedded in inter-alveolar septa. The barrier between air and blood consists of a continuous alveolar epithelium (a mosaic of type I and type II alveolar epithelial cells), a continuous capillary endothelium and the connective tissue layer in-between. By virtue of its respiratory movements, the lung has to withstand mechanical challenges throughout life. Alveoli must be protected from over-distension as well as from collapse by inherent stabilizing factors. The mechanical stability of the parenchyma is ensured by two components: a connective tissue fiber network and the surfactant system. The connective tissue fibers form a continuous tensegrity (tension + integrity) backbone consisting of axial, peripheral and septal fibers. Surfactant (surface active agent) is the secretory product of type II alveolar epithelial cells and covers the alveolar epithelium as a biophysically active thin and continuous film. Here, we briefly review the structural components relevant for gas exchange. Then we describe our current understanding of how these components function under normal conditions and how lung injury results in dysfunction of alveolar micromechanics finally leading to lung fibrosis.

Meibomian glands are a modified type of sebaceous glands within the eye lid, which produce an oily secretion important for the stabilization and the prevention of evaporation of the tear film. The holocrine secretory mode of Meibomian glands is characterized by the centripetal movement, the maturation and finally degeneration of the acinar epithelial cells. The process of maturation and degeneration is paralleled by altered expression pattern of certain proteins and the intracellular accumulation of Meibomian gland lipids. In this study, we investigated the correlation between the differentiation status of Meibomian acinus cells and the presence of adhesive junctions. By ultrastructural analyses, we showed for the first time that the frequency of desmosomes increased with the degree of differentiation. Importantly, we detected a differentiation-dependent distribution pattern of desmosomes within the Meibomian gland cells of the acinus, whereas molecules of other cell junctions, e.g., adherens junctions, are equally distributed. Together, these findings provide new insights into the processes of Meibomian gland secretion and may be important for the interpretation of Meibomian gland dysfunction causing diseases like the dry eye syndrome.

By the use of a newly developed technique of ultrathin-layer electrophoresis, class I and class II alcohol dehydrogenase activity could be demonstrated in microdissected samples of the periportal, intermediate, and perivenous zones of the liver acinus in men and women. It could be demonstrated that both classes exhibit low activity in the periportal zone. From there, a rising gradient in the direction of the perivenous end was apparent. This increase, however, was found to be significant only in women. The analysis of class I alcohol dehydrogenase isoenzymes showed that the expression of alpha-, beta-, and gamma-containing isoforms did not differ in relation to the intraacinar position. The constant proportions of the isoenzymes to the maxima and minima of the total alcohol dehydrogenase activity support the view that the adult liver-specific isoenzyme pattern is determined during postnatal development.