1,720,962 research outputs found
Plasticity of intercellular junctions of rat liver lymph capillaries in relation to functional conditions
No full textThe junctions between endothelial cells in lymph capillaries may have different degrees of complexity and have been classified as three types: "end to end" (EE), "overlapping" (OVL), and "interdigitating" (ID). Under normal conditions, the more complex junction types (ID and OVL) are more frequent than the simple type (EE). The authors' hypothesis was that not only the folds and digitations of the endothelial profile but also the prevalence of the more complex junction types under normal conditions impart plasticity and distensibility to the endothelial wall. To verify this hypothesis they performed a transmission electron microscope study of lymph capillaries of rat liver under normal conditions and after treatment with histamine, which induces natural filling of lymph vessels. In lymph capillaries of histamine-treated animals they found a significant prevalence of the simplest (EE) junctions (50 +/- 5% versus 20 +/- 4% in controls, p less than 0.001) over the more complex OVL (28 +/- 4% versus 57 +/- 4% in controls, p less than 0.001) and ID junctions (12 +/- 3% versus 19 +/- 4% in controls, NS). The overall trend in junction types showed a highly significant shift toward the simpler types after histamine treatment (p less than .0001). There was also a significant reduction in the mean length of adjoining cell borders from 1.5 +/- 0.1 m in histamine-treated animals (p less than 0.001). These findings indicate the participation of the junctions in variations in capacity of lymph vessels in rat liver. This mobilization of cell junctions may also favor the drainage of interstitial fluids into the absorbing lymph vessels
The structure of superficial lymphatics in the human thigh: precollectors
No full textBACKGROUND:
Little is known about the morphology of precollectors, the lymphatic vessels connecting the absorbing and the collecting vessels, which are regarded as the initial drainage routes of lymph. The aim of this study was to describe the structural features of human precollectors.
METHODS:
Samples of fat from around the saphenous veins were obtained from patients undergoing varicotomy, and serial sections were observed under light and transmission electron microscopy. Tridimensional reconstructions were also obtained by computer analysis.
RESULTS:
Precollectors were characterized by an irregular and discontinuous arrangement of smooth muscle cells in their wall. This arrangement was unrelated to the site of valves. When present, muscular elements were arranged helicoidally, as shown in tridimensional reconstructions. Under transmission electron microscopy, the endothelium of precollectors was similar to that of absorbing lymphatic vessels, irrespective of the presence of smooth muscle cells, and was thin, rich in pinocytotic vesicles, supported by a discontinous basal lamina, and connected by anchoring filaments to the surrounding connective tissue. Myoendothelial contacts were frequent. Valves were similar to those of collecting vessels, except for the presence of numerous zonulae adherentes connecting the characteristic "tip cells" of the free edge.
CONCLUSIONS:
Human thigh precollectors are characterized by the alternation of portions with a well-developed muscular coat and portions with an absorbing structure. These morphological features suggest that the precollectors contribute to fluid absorption and lymph propulsion. The frequent myoendothelial contacts suggest that smooth muscle contraction is regulated locally
Lymphatic vessels of the human heart: precollectors and collecting vessels. A morphostructural study
No full textOnly topographic and distributional data are available on the lymphatic outflow vessels of the human heart. Here we describe their structural and ultrastructural features. Fragments of the atria, ventricles and fat surrounding the major coronary branches were obtained from hearts of dilated cardiomyopathy patients. Serial semi-thin sections were observed under light microscopy and used for tridimensional reconstructions. Ultrathin sections were observed by transmission electron microscopy. Precollectors, the initial lymphatic outflow routes of the heart, are small valved vessels with irregular, discontinuous musculature. They originate in the subepicardial region from a network of epicardial, and from scattered myocardial absorbing lymphatic vessels and drain into the collecting vessels accompanying the major coronary branches. Collecting vessels are larger but structurally similar to precollectors. Wall musculature is independent of the size of the vessel. Their ultrastructure is the same as that of precollectors. Endothelial cells have many Weibel-Palade bodies, cytoplasmic filaments and focal adhesions. The basement membrane is discontinuous and anchoring filaments are frequent and conspicuous. The subendothelial layer contains much elastin. Human heart collecting vessels and precollectors may only be distinguished by their size. The scarcity of musculature suggests that lymph progression in this district is mainly ensured by cardiac revolutions. Their ultrastructural features are determined by adaptation to dynamic forces. The architecture of these vessels (random, disorderly, discontinuous, lacking any exact plan) and their large variations in caliber are in line with the ontogenetic hypothesis that peripheral lymphatic vessels originate from the coalescence of mesenchymal lacunae
Subendothelial nerve fibers in bovine mesenteric lymphatics: an ultrastructural and immunohistochemical study
No full textIn the lymphatic vessels of man and most animals the nerve fibers are confined to the adventitia. However, immunohistochemical studies suggest that acetylcholinesterase-positive and monoamine-containing fibers reach as far as the endothelium in bovines. The aim of this study was to verify the presence of subendothelial nerve fibers by transmission electron microscopy (TEM) in bovine mesenteric lymphatics and to determine whether typical sensory neurotransmitters such as Substance P (SP) and calcitonin gene related peptide (CGRP) could be detected in these fibers. TEM revealed numerous unmyelinated nerve fibers in the subendothelial connective environment in close association with endothelial cells. Their axons were devoid of Schwann cell sheath on the endothelial side and contained small clear vesicles and large nerve fibers were demonstrated to be SP and CGRP-immunoreactive with mouse monoclonal antibodies against SP and rabbit polyclonal antibodies against CGRP. It is hypothesized that these fibers act as mechanoceptors capable of detecting intraluminal pressure and vessel wall tension variations and of locally releasing SP and CGRP. Since SP, potentiated by CGRP, is known to be a vasoconstrictor in lymphatics, we propose that the contraction of bovine mesenteric lymphatics may also be neurogenic
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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