bluuebunny/crossref_metadata_2025_split huggingface dataset:
The ultrastructure of the enamel organ related to enamel formation
Authors: Elwood William K. , Bernstein Maurice H. 
Published: February 2005

AbstractThe ultrastructure of the cells of the enamel organ related to enamel formation was studied using the lower incisors of adult male rats. In the region of enamel deposition, stratum intermedium cells are stabilized by a system of intercellular bridges and intracellular fibrils. The mitochondria in these cells are positioned toward the extracellular channels through which any direct intercellular exchange between the capillaries and ameloblasts must occur. Tentatively, the mitochondrial arrangement is considered to be related to the movements of electrolytes and water across the capillary‐ameloblast interval.In the region of transition, enamel deposition ceases and the ergastoplasm of the ameloblasts is removed, apparently by cytosegresomes, with an accompanying reduction in the height of the ameloblasts. Here, vesicles containing stippled material are infrequent compared to their occurrence in ameloblasts concerned with enamel deposition. Other vesicles, characteristically found in ameloblasts related to maturing enamel, first appear in the transition region and seem to originate from the cell membrane abutting on the enamel.In the region of maturation, cytosomes are common in the Golgi region whereas vesicles and mitochondria predominate in the distal ends of the ameloblasts. The papillary cells contain an unusually large number of mitochondria, elaborate microvilli and vesicles, which suggests that these cells are extremely active, presumably in the movement of materials related to enamel maturation.The changes in structure of the papillary cells, which occur concomitantly with those of the ameloblasts during enamel formation, are indicative of interrelated functional changes and strongly support the concept of ameloblasts and papillary cells acting together as a functional unit.
Dense‐core microtubules in neurons and gliocytes of the toad Bufo arenarum Hensel
Authors: Echandía E. L. Rodríguez , Piezzi R. S. , Rodríguez E. M. 
Published: February 2005

AbstractNumerous microtubules of nerve cells and gliocytes in the toad are found, in electron micrographs, to contain a dense core. Such content is granular in nature, the granules being irregularly disposed in the lumen of the microtubules. Comparative observations on dense‐core microtubules in peripheral and central nerve cells indicate that they are consistent cell components in the entire nervous system of the toad. The functional significance of the granular content of the microtubles is discussed.
Changes in the fine structure of the parietal yolk sac of the rat placenta with increasing gestational age
Authors: Jollie William P. 
Published: February 2005

AbstractThe fine structure of the portion of the parietal yolk sac which extends across the fetal surface of the rat placenta (which is the only portion of the parietal yolk sac which persists after the sixteenth day of pregnancy) was examined sequentially on the even numbered days during the second half of gestation. The placental parietal yolk sac was seen to consist of two cellular layers, trophoblast and endodermal epithelium, which were separated by a thick, amorphous membrane (of Reichert). The trophoblast attenuated with increasing gestational age and, on day 18, became perforated by fenestrations which were closed by diaphragmata. By day 22, the attenuated trophoblast was patently perforate, and maternal blood was exposed to Reichert's membrane. Since throughout gestation, the cells of the parietal endoderm formed a discontinuous layer, at all stages Reichert's membrane was exposed to the vitelline cavity. When ferritin and thorotrast were injected i.v., both separately and together, the former passed readily from maternal blood through Reichert's membrane and was phagocytosed by cells of the parietal endoderm. Thorotrast, however, did not cross Reichert's membrane. Since the rodent yolk‐sac complex is known to serve as a placental route, selective permeability of Reichert's membrane may help regulate maternofetal exchange.
Histochemical and autoradiographic studies of the formation of the metrial gland in the pregnant rat
Authors: Larkin Lynn H. , Schultz Richard L. 
Published: February 2005

AbstractIt is shown in this study that cells of the mesometrial triangle proliferate at a high rate in the early formative period of the metrial gland. This, plus observations of sequential apperance of specific cell types during growth of this tissue, indicate that the metrial cells are formed in situ.Support for the hypothesis of in situ formation of metrial gland tissue also was obtained by observation of apparent differentiation of metrial cells from a precursor cell type. The precursor cells appear to arise from fibroblast‐like cells located in the mesometrial triangle throughout the formative period of the metrial gland. Quantitative autoradiographic studies indicate that the precursor cells accumulate glycogen, undergo division, and subsequently produce diastase‐resistant, PAS‐positive granules that are characteristic of metrial cells. These cells, which contain specific granules and glycogen, are an individual cell type and are referred to as mononucleate metrial cells. The experiments suggest that the mononucleate metrial cells undergo karyokinesis without cytokinesis resulting in typical binucleate metrial cells. Binucleate metrial cells synthesize DNA and appear to become polyploid rather than forming multinucleated cells or binucleate daughter cells. Some nuclei apparently attain a high ploidy, but the majority of binucleates are not highly polyploid.
A new cytoplasmic organelle, related to both lipid and glycogen storage materials in the yolk sac of the bat, Tadarida brasiliensis cynocephala
Authors: Stephens R. J. , Easterbrook N. 
Published: February 2005

AbstractThe gestation period of Tadarida is approximately four months long extending from late February to June. During the first half of gestation the yolk sac undergoes a complete collapse bringing two layers of endodermal cells into contact with one another and obliterating the cavity of the yolk sac. Both the endodermal and the mesodermal cells hypertrophy and develop into a glandular‐looking organ during the latter half of gestation. Approximately a month before parturition the endodermal cells become progressively laden with lipid and glycogen. Immediately before birth, however, both of these storage materials are depleted. This depletion is preceded by the formation of an extensive array of hexagonal membranous channels within the cytoplasm. Some of the membranes of this organelle are closely applied to lipid droplets and glycogen granules can be observed in linear patterns within the hexagonal channels. Tissues taken at term showed the membranes of the hexagonal channels continuous with a paracrystalline membranous structure. The close morphological association of the membranous organelle to both the lipid and glycogen storage materials indicates that it is involved in their metabolism in the yolk sac of the bat.
Eighteen hundred years of controversy: The paranasal sinuses,
Authors: Blanton Patricia L. , Biggs Norman L. 
Published: February 2005

AbstractThe reason for the presence of the paranasal sinuses has been a controversial subject since the time of Galen, 130–201 A.D. In a review of the literature, the diversity of the numerous functions ascribed to these air‐filled cavities was found to be astounding. Many functions were ascribed only on the basis of opinion rather than scientific investigation and recent studies have illustrated the fallacy of these opinions. To date, not one proposed function has been universally accepted to be the essential reason for their existence.This review of the literature deals mainly with those theories of anatomical and physiological significance of the paranasal sinuses having received the most consideration and many of which are currently considered tenable. These are, as follows: (1) impart resonance to the voice; (2) humidify and warm inspired air; (3) increase the area of the olfactory membrane; (4) absorb shock applied to the head for protection of sensory organs; (5) secrete mucus for keeping the nasal chambers moist; (6) thermally insulate the nervous centers; (7) aid facial growth and architecture; (8) exist as evolutionary remains and/or unwanted air spaces; and (9) lighten the bones of the skull for maintenance of proper balance of the head.
Sympathetic nerve pathways to the human heart, and their variations
Authors: Ellison Jeffrey P. , Williams Terence H. 
Published: February 2005

AbstractStimulated by the needs of surgery, common variations in the sympathetic pathways to the heart have acquired a practical significance. The cervical and upper thoracic sympathetic trunk was dissected on 24 sides in human fetuses at term, and the cardiac rami together with their communications studied and illustrated. To enable us to classify the cervical rami according to their sites of origin, the cervical sympathetic trunk was subdivided midway between ganglia into portions called ganglionic divisions; these divisions keeping the names applied to the ganglia in the Nomina Anatomica.Intermediate ganglia were found on the visceral outflow of the sympathetic trunk and are referred to as “distal intermediate ganglia” to distinguish them from the intermediate ganglia that have been described proximal to the sympathetic trunk.Thoracic cardiac rami were almost invariably present, the third and fourth thoracic ganglia most frequently providing substantial contributions. Some thoracic cardiac rami were traced as far as the left anterior descending coronary plexus.The question of bilateral symmetry was also examined. Whilst a variety of features are commonly present on both sides, the first dissection in a cervicothoracic sympathectomy is no reliable guide to the detailed anatomy of the second side. The sympathetic pathways to the heart are extremely variable in their topography, and the diversity of arrangements encountered accounts for the morphological contradictions in the literature. So numerous are the possible variations that the outcome of a sympathectomy is unpredictable. Where denervation is incomplete, collateral sprouting and regeneration of nerves could even lead to hyperstimulation via the sympathetic pathways.
Effects of cold on the skeletal growth of albino rats
Authors: Lee Marjorie M. C. , Chu P. C. , Chan H. C. 
Published: February 2005

AbstractTwo groups of male albino rats of 26 days old, were kept at 5°C and 28°C respectively. Their growth was studied by weekly gross measurements and biweekly radiographic investigations for 16 weeks. Compared with the controls at 28°C, the rats kept at 5°C showed the following effects of cold in their growth: (1) Smaller measurements at all ages; (2) Slower growth rates in the first two to four weeks; (3) Relatively shorter tail and shorter feet but body weight was the same as the controls of the same body lengths irrespective of age; (4) Shorter but relatively thicker bones; (5) A disto‐proximal stunting gradient was observed in the tail and limb bones, showing more severe effect in the distal segments and decreasing effect in the proximal segments; (6) Retardation of skeletal maturational status in the naked appendages (tail and foot); (7) Decreased number (1.4) of ossified caudal vertebrae.The above phenomena were discussed as results of possible reduction of blood flow to the skeletal tissue on cold exposure.
The prenatal development of the human humerus
Authors: Gray D. J. , Gardner Ernest 
Published: February 2005

AbstractForty pairs of humeri, from a series of embryos and fetuses ranging from 26 to 342 mm in crown‐rump length, were measured, radiographed, and sectioned for microscopic study.A primary bony collar was present before the end of the embryonic period, and in a 27 mm embryo it extended for nearly one‐third of the length of the humerus. Erosion of the collar occurred at the end of the embryonic period. By about 37 mm, endochondral ossification began, and cartilage canals were invading the proximal epiphysis.As endochondral ossification proceeded proximally and distally and growth zones became established, periosteal bone formation also proceeded longitudinally and, until about 18 weeks, extended about one millimeter beyond the zone of cartilage destruction in the growth zones. Subsequently the extents of periosteal and endochondral ossification were the same and at term occupied 79% of the length of the humerus.Trabeculation of the bony collar began in the embryonic period. Fusion of endochondral trabeculae with the inner aspect of the periosteal shell began by 61 mm. A central marrow cavity free of trabeculae was consistently present after 86 mm. Evidence of reconstruction appeared in the proximal end by 73 mm and in the distal end by 113 mm, and was always present after 97 and 125 mm respectively.
Unique aspects of reproduction in the female pronghorn (Antilocapra americana Ord)
Authors: O'gara Bart W. 
Published: February 2005

AbstractInvestigation of the reproductive tracts of 78 pregnant pronghorns (Antilocapra americana Ord) revealed that even though twin births were the rule, three‐seven ova were commonly ovulated, fertilized, and developed into expanded blastocysts. Some mortality occurred in the thread‐stage because of knotting and tangling of the blastocysts. When more than one embryo per uterine horn survived the thread‐stage, the one distal to the corpus uteri was displaced or its membranes were pierced by the necrotic tip of the proximal embryo. Thus, excess blastocysts and embryos were eliminated during the thread‐stage or at the time of implantation.The pronghorn uterus was bicornuate with an average of 92 caruncles which increased approximately 250 times in volume during gestation. The placenta was of the epitheliochorial type. Transuterine migration of ova occurred. When the embryos were 50–75 mm in length, their membranes met in the corpus uteri. The cervix had 4 or 5 muscular valves with papillae projecting caudally. During late gestation a cervical plug formed in the posterior valve.
Morphogenetic studies of the rabbit. XXXVIII. Epigenetic probing of the genome
Authors: Sawin P. B. , Muehlke Marjorie 
Published: February 2005

AbstractThis study is concerned with the use of the initial gradient of fusion of the neural arch lamellae of the vertebrae on days 31–34 postconception as epigenetic reference points for analysis of the growth retardation and malformation induced systemically by one specific gene, Da (chondrodystrophy), and the modification of such effect induced by the genomes of two different strains (DA and IIIDa). Although during this period the fusion process is confined to vertebrae 29–36, aproximately 10 to 14 days later it is extended throughout the vertebral column.Intra‐ and inter‐strain comparisons measured by incidence, range, and peak of neural arch fusion (NAF) confirm the same general nature of the growth effects resulting from the gene (Da) and genomes (DA, IIIDa) and from their interaction, i.e., Da and DA acting additively in retarding the growth (in this case fusion) process, whereas IIImo, IIIDa, and IIIep are in opposition. The study (1) increases knowledge of the generality or systemic nature of the Da retardation effect; (2) demonstrates a stronger effect of the polygenic genome in suppressing the effects of the major gene than previously found in the lumbar gradient; (3) reveals the usefulness of epigenetic reference points in defining the limits of endogenous (and possibly of exogenous) influences upon growth and developmental processes in time and locale; and (4) reveals the existence of at least one new genetic element within IIImo which has also been transferred to the IIIDa genome by the breeding procedure described.
The relation between human fetal mouth opening reflexes and closure of the palate
Authors: Humphrey Tryphena 
Published: February 2005

AbstractThe status of the palatal shelves of shelves of human fetuses (before, during and after palatal shelf elevation) was correlated with mouth opening reflexes recorded cinematographically by Doctor Davenport Hooker for many of the same fetuses. Some deductions and conclusions follow.Mouth opening reflexes begin before palatal shelf elevation and are a significant factor in tongue withdrawal from between the vertical shelves through traction resulting from mandibular depression. (2) The upward pull on the palatal shelves created by differences in pressure between the closed nasal area and the oral region when the tongue is withdrawn (epithelial plugs fill external nares completely) is an active force for palatal shelf elevation. (3) Palatal shelf movements are variable in character and closure sometimes results in the shelf borders enfolding each other. (4) On mouth closure, pressure on the shelves by the tongue and the amniotic fluid entering the mouth helps maintain shelf position before fusion. (5) Human palatal shelf elevation without shelf contact in the midline is not necessarily part of normal closure, but, especially if the shelves are far apart, a stage in cleft palate formation. (6) Increased mandibular growth follows rather than precedes tongue withdrawal. Other factors influencing closure are discussed.
Morphological and biochemical observations on the catecholamine‐storing vesicles of rat adrenomedullary cells during insulin‐induced hypoglycemia
Authors: D'anzi Francis A. 
Published: February 2005

AbstractThe purpose of this study is to demonstrate a structure – function relationship between the release of catecholamines and the depletion of catecholamine‐storing vesicles from cells of the adrenal medulla. The approach taken here is a comparative study of storage vesicle morphology and population, as determined electron microscopically, and of catecholamine concentration, as determined fluorometrically, in adrenomedullary cells at various times during the extrusion phase of the secretory process.To achieve an increased rate of catecholamine release from the gland, animals were made hypoglycemic by the administration of insulin. At one‐hour intervals following this injection and just prior to sacrifice, the severity of the imposed hypoglycemic state was determined from analysis of the blood serum glucose level. The fine structure alterations in adrenomedullary cells of one gland were then compared with the change in catecholamine content of the contralateral gland.The decline in blood serum glucose following insulin administration resulted in a decrease in both the adrenaline‐stroing vesicle population and adrenaline content of the gland.
Uptake and storage of thorotrast by the rodent yolk sac placenta: An electron microscopic study
Authors: Carpenter S. J. , Ferm V. H. 
Published: February 2005

AbstractElectron microscopy was used to investigate the uptake and storage of electrondense particulate matter by the rodent yolk sac placenta. Pregnant hamsters were given single intra‐uterine injections of Thorotrast on day 13, 14 or 15 of gestation and killed at intervals between 15 minutes and 48 hours thereafter. Electron microscopic examination of yolk sacs removed from the injected animals revealed the rapid and progressive uptake of the tracer particles by the visceral epithelial cells of these fetal membranes. Pinocytic vacuoles (phagosomes) containing Thorotrast were visible in the apical cytoplasm of epithelial cells as early as 15 minutes after injection and became increasingly abundant in these cells at later post‐injection intervals up to 18 hours. Epithelial cells which became fully engorged with Thorotrast vacuoles exhibited various pathologic changes, possibly caused by the interference of the metabolically inert metal particles with intracellular digestive mechanisms (the lysosome system). There was no evidence, however, of transport of Thorotrast particles through or between the yolk sac epithelial cells. The connective tissue spaces and blood vessels of the yolk sac, as well as underlying fetal compartments, were free of the tracer particles at all observed intervals after injection.
Rib development in chick embryos analyzed by means of tantalum foil blocks
Authors: Sweeney Robert M. , Watterson Ray L. 
Published: February 2005

AbstractRib development in chick embryos, with special emphasis on the origin of ribforming cells, has been analyzed by inserting tantalum foil blocks parallel to certain somites of the prospective rib‐forming level. Intact edges of bent pieces of foil the width of 4–6 somites were inserted through the somatopleure at stage 14–16 either (1) immediately lateral to the nephrotome, (2) between proximal and distal portions of the lateral plate or (3) within the distal lateral plate. Edges of similar pieces of foil containing a triangular notch the width of 2 somites were likewise inserted through the somatopleure of stage 14–16 embryos (4) immediately lateral to the nephrotome or (5) between proximal and distal portions of the lateral plate.On the basis of the modified rib pattersn studied in toto after 11 days of incubation it was concluded that the (1) original somatic mesoderm does not participate in formation of vertebral rib components, (2) original somatic mesoderm plays some role in formation of sternal rib components (ribs 3–7) but probably does not contribute chondroblasts for this purpose, and (3) distalmost somatic mesoderm is not involved in rib formation. Consistent types of modified wings are described and also modifications of the body wall, breast and ventral feather tracts of the right side.
Ultrastructure of the metrial gland cell in the pregnant rat
Authors: Larkin Lynn H. , Flickinger Charles J. 
Published: February 2005

AbstractThe metrial gland cells of the pregnant rat were studied with the electron microscope from day 12 through day 15 of pregnancy. Prominent features of their fine structure included abundant granular endoplasmic reticulum, a large Golgi complex, and numerous dense granules. These granules were bounded by a single membrane and contained a dense material, smooth vesicles, and membranous whorls. It is suggested that the dense material is aggregated in the mature granules by the coalescence of smaller progranules that are derived from the Golgi apparatus. The nature and fate of these granules is discussed in relation to the possible secretion of relaxin by metrial cells.