. The chemistry and physiology of growth. Growth; Biochemistry. 174 PAUL WEISS phology of inhabitant, as well as immigrating, cells. Potent as these effects are, they could not be a major factor in development if only tensions of extraneous origin were involved. But tensional stresses also arise within the developing organism as a result of shifts, growth, and chemical activity of its Figure i. Diagram illustrating the effect of graded stretching (in the direction of the arrows) of a reticular matrix on the shape of mesenchymal cells. Let us consider the two main intrinsic sources of m
. The chemistry and physiology of growth. Growth; Biochemistry. 174 PAUL WEISS phology of inhabitant, as well as immigrating, cells. Potent as these effects are, they could not be a major factor in development if only tensions of extraneous origin were involved. But tensional stresses also arise within the developing organism as a result of shifts, growth, and chemical activity of its Figure i. Diagram illustrating the effect of graded stretching (in the direction of the arrows) of a reticular matrix on the shape of mesenchymal cells. Let us consider the two main intrinsic sources of morphogenetic ten- sions—expansion and contraction. Their development is illustrated in Figure 2. On the left side (Ao, Bo) are sectors of a tissue possessing a continuous reticulated matrix and containing a circumscribed area (dark circle) in which some localized developmental process goes on, as follows. The lower half (Bo-^Be) represents a case in which the marked area expands relative to its surroundings, either by rapid proliferation or by deposition of large amounts of ground substance or, in the case of hollow organs, by distension. This local expansion creates in the sur- rounding continuum tensions that are oriented circumferentially, de- clining in strength with increasing distance from the border. The fibrous matrix assumes a corresponding pattern as depicted, and this in turn imparts itself to the cells. Cell movements and cell divisions will follow tangential courses. It is evident that the familiar concentric architecture of the mesenchymal sheaths, coats, tunics, and membranes around both solid organs and hollow ducts and vesicles finds a natural explanation on this basis. Essentially the same effect is observed if the surrounding tis- sue contracts against a rigid core, as in the formation of foreign-body capsules. A wholly different pattern results if a tissue contains a focal area that contracts. In this case, illustrated in the top row of diagrams (Ao-^Ac),
Size: 2764px × 904px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorprincetonuniversity, bookcentury1900, booksubjectgrowt
