No abstract is provided for this article.
Stem cells build our bodies during development, starting from a fertilized oocyte. Subsequently, they maintain and repair our organs for a lifetime. Thus, stem cells hold the promise of eternal life. While this may still be in the distant future, stem cells are rapidly changing the face of biomedical science and are finding applications in the clinic. In this article, I discuss the principles of stem cell biology and the mini-organs that can be grown from stem cells in a petri dish.
Central to the classical hematopoietic stem cell (HSC) paradigm is the concept that the maintenance of blood cell numbers is exclusively executed by a discrete physical entity: the transplantable HSC. The HSC paradigm has served as a stereotypic template in stem cell biology, yet the search for rare, hardwired professional stem cells has remained futile in most other tissues. In a more open approach, the focus on the search for stem cells as a physical entity may need to be replaced by the search for stem cell function, operationally defined as the ability of an organ to replace lost cells. The nature of such a cell may be different under steady state conditions and during tissue repair. We discuss emerging examples including the renewal strategies of the skin, gut epithelium, liver, lung, and mammary gland in comparison with those of the hematopoietic system. While certain key housekeeping and developmental signaling pathways are shared between different stem cell systems, there may be no general, deeper principles underlying the renewal mechanisms of the various individual tissues.
This chapter focuses on job stress in relation to workers’ physical and psycho logical health. We begin with an outline of job stress as a social problem, fol lowed by a discussion of the main perspectives on (job) stress, resulting in a process model of job stress that will be used as a frame of reference in the remainder of the chapter. In the next section, several leading models on job stress and health are presented and discussed. The role of individual differences as well as workplace social support in the relationship between job stress and health is discussed. Finally, an overview of organizational and individual inter ventions to reduce job stress is given.
In this study a social comparison model is constructed that predicts objectively recorded absence frequency among male Dutch blue‐collar workers from a metal factory in the Netherlands. By employing LISREL, the model is developed (tested and revised) in Plant North (N = 254), and successfully cross‐validated in Plant South (N= 199). The study demonstrates the impact of two social comparison processes upon absenteeism. Absenteeism is the result of: (a) the perception that one is less well‐off than one's colleagues on several job aspects, and (b) the adjustment of one's personal absence norm to that of the work group. In addition, our study reveals that, rather than being absent or having tolerant absence norms, employees may develop feelings of resentment in response to perceived inequity and a tolerant group absence norm. It is concluded that social comparison theory enhances our understanding of absenteeism.