摘要:

AbstractA light and electron microscopic study was conducted on the X cell of the normal dog pancreas. These cells were identified by their acidophilic cytoplasmic granules which do not stain with iron or phosphotungstic acid hematoxylin and also show a distinctive multilobate nucleus. They were found to be neither argyrophilic nor argentaffinic. Ultrastructurally, when fixed in osmium alone, the X cell cytoplasm contained numerous rounded, smooth membrane bound secretory granules with content of low electron density. However, after double fixation in glutaraldehyde and osmium the granules appeared irregularly round, ovoid or kidney shaped with content which may vary from electron lucent to homogeneously electron dense with gradations between. The functional significance of the X cell is unknown. However, its structure showed it to be a distinct, active secretory element, independent of other pancreatic exocrine and endocrine cell types.

ISSN:0003-276X    

DOI:10.1002/ar.1091690302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1971

数据来源: WILEY

摘要:

AbstractThe origin of the common cardinal veins (CCVs) in the chick embryo was traced by radioautographic mapping of the movements of tritiated thymidine‐labeled grafts excised from head process to three somite stage embryos and transplanted to the endoderm‐mesoderm layer of similarly staged recipient embryos.At the head process stage the CCV cells are migrating anteriorly and laterally from the streak in the lateral plate, posterolateral to the cells which will form the pulmonary veins and aortic arches, posterior to the cells destined for the ventricular septum, and dorsal to the liver mesoderm cells. At the 15–17 somite stage, the CCV cells are in the somatic mesoderm of the lateral mesocardium, where an anastomosis between the CCVs and heart establishes channels needed for the efficient return of blood from the various embryonic venous tributaries. This investigation suggests that during the stages studied, the cells which will form the anterior portion of each CCV are positioned anterior to the cells which will form the posterior portion of eac

ISSN:0003-276X    

DOI:10.1002/ar.1091690303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1971

数据来源: WILEY

摘要:

AbstractThe possibility of the formation of new lobules in rat liver during the course of compensatory growth has been investigated. Two methods inducing regeneration were used: the method of subtotal hepatectomy and the method of porcelain bead implantation. Observations were made at 28, 42, 56, 68, 84 and 112 days after subtotal hepatectomy, and at 28 and 42 days after implantation of the bead.The results obtained from subtotal hepatectomy were expressed as the lobular radius (or portal‐central vein distance) measured in micra. The values were 404 μ at the twenty‐eighth day after hepatectomy and 324 μ at the one‐hundred‐twelfth day. The results obtained from bead implantation were 352 μ at the twenty‐eighth day after implantation and 305 μ at the forty‐second day.It is concluded that regenerating rat liver undergoes structural changes involving new lobule formation between the fifty‐sixth and the one‐hundred‐twelfth day after subtotal hepatectomy, and sometime after the fourth week after bead implantation. The difference in times after which structural changes occur is explained by the difference in intensity of stimul

ISSN:0003-276X    

DOI:10.1002/ar.1091690304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1971

数据来源: WILEY

摘要:

AbstractType A spermatogonia in the mouse can be separated into five successive classes on the basis of nuclear morphology and stage of the cycle in which they occur. Enumeration of all types throughout the cycle of the seminiferous epithelium reveals that the Asspermatogonia are the stem cells. They divide throughout the cycle and, especially at stages IX to I, form chains of cells which then give rise to spermatogonia A1at stages II–VIII. The A1cells divide in IX to form the A2, which divide in XI to form A3, and the A3cells divide in I to form the class A4spermatogonia. Spermatogonia A4give rise only to the In type; there is no evidence for the formation of either Asor A1from A4spermatogonia. Repeated injections of3H‐thymidine and tracing the history of labeled cells to 15 days after labeling supported the conclusion obtained from morphological and numerical data that Asspermatogonia are the stem cells of the tes

ISSN:0003-276X    

DOI:10.1002/ar.1091690305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1971

数据来源: WILEY

摘要:

AbstractWhole mounted segments of seminiferous tubules from rat testes have been used to investigate the morphology and proliferative activity of the undifferentiated type A spermatogonial population. This has led to the formulation of a new model for spermatogonial stem cell renewal. Three groups of undifferentiated A spermatogonia were classified according to their topographical arrangements as isolated, paired, and aligned spermatogonia. It was proposed that the isolated (as well as a few paired) spermatogonia, which were always present throughout the seminiferous epithelium, are the functional stem cells and should therefore be designated as As. Through sporadic divisions, the Asspermatogonia both maintain their own numbers and give rise to pairs of cells which are destined to eventually differentiate. The latter undergo several synchronous divisions in succession, thereby forming increasingly longer chains of aligned spermatogonia. The proliferation of these chains, primarily in stages I–V, leads to a gradual expansion in the size of the undifferentiated type A population. When the population attains its maximal size in stage V, mitotic activity among the aligned cells ceases, and all of these cells morphologically transform without further division into typical A1spermatogonia. Subsequently, the cohort of A1cells synchronously divides in stage IX to begin the long process of spermatogonial maturation. The isolated (and a few paired) cells, which do not undergo this transformation and remain quiescent during the stage IX peak of mitosis, form a residual stock of stem cells, that, during the course of another cycle, rebuild the population of aligned A spermatogonia. In this way, a continual supply of type A1spermatogonia which will cyclically differentiate is insure

ISSN:0003-276X    

DOI:10.1002/ar.1091690306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1971

数据来源: WILEY

摘要:

AbstractThe structure of the organic matrix close to the mature enamel in 100 gm rat incisors was studied by light and electron microscopy using EDTA decalcified teeth.Under the light microscope, in 0.5 μ Epon sections, the enamel layer of cross sectioned upper incisors was about 60 μ thick. Theinner enamelwas about 40 μ thick and consisted of aninitial enamel layer(4 μ) adjacent to the dentin in which no rod profiles were seen, and aninner layer properwhich contained six to eight rows of oval‐shaped rod profiles set in a homogeneous background. The profiles in any given row were inclined mesially or laterally and alternated in adjacent rows. Theouter enamelwas about 20 μ thick and consisted of anouter enamel properand a 2–4 μ thickfinal enamel layerwhich smoothed out the enamel surface. The outer enamel proper contained smaller elliptical rod profiles in a more abundant background. These profiles were not arranged in rows and were oriented at right angles to the enamel surface. The final enamel layer contained no rod profiles and was lined on its outer surface by a PA‐Schiff positive layer resembling a basement membrane.Under the electron microscope the matrix ofrod profilesandinterrod materialcould be distinguished. This consisted of aggregated tubular (and filamentous)subunits, 250 Å in diameter, with empty space between them. Within the rod profiles the subunits ran parallel to the rod's long axis, whereas in the interrod material the subunits were again parallel but but running at right angles to the subunits of the rods. In addition to forming the material between the rods, the interrod material also formed the initial and final e

ISSN:0003-276X    

DOI:10.1002/ar.1091690307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1971

数据来源: WILEY

摘要:

AbstractA three‐dimensional reconstruction of the rod profiles seen in inner and outer rat incisor enamel was made from serial 1 μ cross sections of a decalcified upper incisor. The enamel rod was found to be an elongated structure which travelled incisally relative to its origin and ran continuously from the dentino‐enamel junction to the enamel surface. The rod was divisible into an inner and outer enamel portion. The inner enamel portion began at the dentinoenamel junction and travelled incisally for about 20 μ with either a mesial or lateral tilt towards the outer enamel. The outer enamel portion of the rod was straight and ran incisally for about 60 μ as it gradually approached the enamel surface.Inner enamel portions of rods were arranged in rows parallel to the cross sectional plane of the incisor. All the rods in each row were tilted either mesially or laterally such that individual rods of adjacent rows crossed each other at 90°. Outer enamel portions of rods were not arranged in rows but all passed incisally parallel to one

ISSN:0003-276X    

DOI:10.1002/ar.1091690308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1971

数据来源: WILEY

摘要:

AbstractAutoradiographic determination of the number and distribution of replicating mesenchymal cells in rabbit dermis was carried out using animals sacrificed between two hours and 21 days after a multiple‐dose‐pulse of3H‐thymidine. Initial labeling of mesenchymal cells occurred principally in a zone immediately subjacent to the germinative epithelium. This was confirmed byin vitrostudies of the uptake of3H‐Tdr by rabbit skin during one hour of incubation. Five days after thein vitropulse of3H‐Tdr there was a fifteen‐fold increase in the number of labeled cells, considerable dilution of label and migration of labeled cells so that they were evenly distributed throughout the full thickness of the dermis. At 21 days the number of labeled cells was similar to that found at five days, but there was further migration of labeled cells toward the deep dermis.This tissue provides an example ofappositional replication and divergent migrationof an epithelial‐mesen

ISSN:0003-276X    

DOI:10.1002/ar.1091690309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1971

数据来源: WILEY

ISSN:0003-276X    

DOI:10.1002/ar.1091690301

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1971

数据来源: WILEY