Developmental Physiology

Abstract

The present review is concerned mainly with change-the physi ology of embryonic differentiation-rather than with functions more obviously of an operational nature. The writer is conscious of the difficulties involved in the assumption that embryonic func tions can, -in the first place, be segregated into categories of differ entiation versus operation. However space limitations have com pelled selection, and such topics as mechanics of heart action, trans port of gases, fetal muscular activity, and function of the nervous system have been left for future reviews. Fertilization.-Following up his earlier work on the cytolytic action of lecithinase, Ohman (1) has obtained data which indicate a decrease in the phosphatide content of the surface of the sea urchin egg as a result of fertilization. A decrease in susceptibility to cytolysis occurs shortly after fertilization, followed by a second period of increased susceptibility, and again a third period of de creased susceptibility, this last period coinciding with the time when the egg is preparing for cleavage' . One may only speculate on the possible relation between these findings and the shift in alkaline phosphatase as shown by the Comori method (2). In young oocytes of the sea urchin alkaline phosphatase is concen trated in the nucleolus and nuclear membrane, whereas in the mature egg it occurs in granules of the cortex and after fertilization is quite evenly distributed through the cytoplasm. Monroy & Montalenti (3) have related birefringence or its ab sence in the cortex of the sea urchin egg to the type of cellular shrinkage produced by hypertonic sea water. Uniform shrinkage (spherical plasmolysis) corresponds with the period of cortical birefringence, whereas irregular shrinkage (angular plasmolysis) corresponds with lack of birefringence. The interpretation is that radially oriented micelles characterize the cortex of the unfertilized egg, whereas a disorderly pattern occurs after fertilization. Mon roy (4) suggests that the cortex contains a lipid-protein -complex with the lipids arranged radially. Brooks (5), from a study of the activation of eggs by various redox dyes, finds marked agreement 1 Annu. Rev. Physiol. 1949.11:1-20. Downloaded from www.annualreviews.org Access provided by University of California -Davis on 02/04/15. For personal use only. Quick links to online content Further ANNUAL REVIEWS 2 SCHECHTMANbetween the rH values of the most effective dyes and of homologous sperm. This supports the suggestion previously made by the au thor that activation depends upon the establishment of appro priate redox potential. Cheney (14), from studies on caffeine inhi bition of oxygen upt�ke in Arbacia, finds that fertilization is inde pendent of a respiratory mechanism required shortly afterward. Barron et al. (132) have shown a similar difference in respiratory mechanism by the use of nitrogen mustards. The "myosin-like" protein obtained by Mirsky (134) from sea urchin eggs was found by Connors & Scheer (6) to be completely lacking in adenosinetriphosph...

Chapter VI: Physical Growth and Physiological Aspects of Development

“…It also included a very complete and excellent bibliography. Elsewhere splendid reviews of the literature dealing with specialized problems of growth (22,133,174) and physiological development (107,142,158,162) have been made available, and several general theoretical considerations of some of the basic problems involved have been published (27,45,113,120,163,165,166,170).…”