Terebratulide brachiopod shell biomineralization by mantle epithelial cells.

To understand mineral transport pathways for shell secretion and to assess differences in cellular activity during mineralization, we imaged with TEM and FE-SEM ultrastructural characteristics of outer mantle epithelium (OME) cells. Imaging was carried out on Magellania venosa shells embedded/etched, chemically fixed/decalcified and high-pressure frozen/freeze-substituted samples from the commissure, central shell portions and from puncta. Imaging results are complemented with morphometric evaluations of volume fractions of membrane-bound organelles. At the commissure the OME consists of several layers of cells. These cells form oblique extensions that, in cross-section, are round below the primary layer and flat underneath fibres. At the commissure the OME is multi-cell layered, in central shell regions it is single-cell layered. When actively secreting shell carbonate extrapallial space is lacking, because OME cells are in direct contact with the calcite of the forming fibres. Upon termination of secretion, OME cells attach via apical hemidesmosomes to extracellular matrix membranes that line the proximal surface of fibres. At the commissure volume fractions for vesicles, mitochondria and lysosomes are higher relative to single-cell layered regions, whereas for endoplasmic-reticulum and Golgi apparatus there is no difference. FE-SEM, TEM imaging reveals the lack of extrapallial space between OME cells and developing fibres. In addition, there is no indication for an amorphous precursor within fibres when these are in active secretion mode. Accordingly, our results do not support transport of minerals by vesicles from cells to sites of mineralization, rather by transfer of carbonate ions via transport mechanisms associated with OME cell membranes.

[Association of work load and mental disorders: review of the data]. / Zusammenhang von Arbeitsbelastungen und psychischen Erkrankungen : Review der Datenlage.

Currently, the two faces of work as described by Kurt Lewin (The socialization of the Taylor system. A fundamental examination of work and vocational psychology 1920) are clearly pronounced. Thus, work can be beneficial to personal development and well-being as work is a possible source of learning opportunities, motivation and positive emotional states. On the other hand there are a growing number of complaints about stress and exhaustion because of high work load and working days lost due to incapacity to work because of mental ill health are increasing. The question arises whether there is a relationship between work load and mental health. This article presents information on the data and tries to clarify if the relationship between work load and mental health results more due to bad job design than a distorted response behavior due to mental illness.