The Experts below are selected from a list of 168 Experts worldwide ranked by ideXlab platform

Karel Rakusan - One of the best experts on this subject based on the ideXlab platform.

John N. Maina - One of the best experts on this subject based on the ideXlab platform.

  • Implicit mechanistic role of the collagen, smooth muscle, and elastic tissue components in strengthening the air and Blood Capillaries of the avian lung
    Journal of anatomy, 2010
    Co-Authors: John N. Maina, Sikiru A. Jimoh, Margo Hosie
    Abstract:

    To identify the forces that may exist in the parabronchus of the avian lung and that which may explain the reported strengths of the terminal respiratory units, the air Capillaries and the Blood Capillaries, the arrangement of the parabronchial collagen fibers (CF) of the lung of the domestic fowl, Gallus gallus variant domesticus was investigated by discriminatory staining, selective alkali digestion, and vascular casting followed by alkali digestion. On the luminal circumference, the atrial and the infundibular CF are directly connected to the smooth muscle fibers and the elastic tissue fibers. The CF in this part of the parabronchus form the internal column (the axial scaffold), whereas the CF in the interparabronchial septa and those associated with the walls of the interparabronchial Blood vessels form the external, i.e. the peripheral, parabronchial CF scaffold. Thin CF penetrate the exchange tissue directly from the interparabronchial septa and indirectly by accompanying the intraparabronchial Blood vessels. Forming a dense network that supports the air and Blood Capillaries, the CF weave through the exchange tissue. The exchange tissue, specifically the air and Blood Capillaries, is effectively suspended between CF pillars by an intricate system of thin CF, elastic and smooth muscle fibers. The CF course through the basement membranes of the walls of the Blood and air Capillaries. Based on the architecture of the smooth muscle fibers, the CF, the elastic muscle fibers, and structures like the interparabronchial septa and their associated Blood vessels, it is envisaged that dynamic tensional, resistive, and compressive forces exist in the parabronchus, forming a tensegrity (tension integrity) system that gives the lung rigidity while strengthening the air and Blood Capillaries.

  • Study of the structure of the air and Blood Capillaries of the gas exchange tissue of the avian lung by serial section three-dimensional reconstruction.
    Journal of Microscopy, 2008
    Co-Authors: Jeremy D. Woodward, John N. Maina
    Abstract:

    We have previously reconstructed the gas exchange tissue of the adult muscovy duck, Cairina moschata using a method of manually aligning sections and tracing the contours of the components of the gas exchange tissue. This reconstruction method demonstrated that the air Capillaries are comprised of an expanded globular part interconnected by narrow air channels. The Blood Capillaries completely surround the air Capillaries forming an anastomosing meshwork of short segments. However, the resulting reconstruction was limited in scope because of the laborious process of tracing the profiles of each component through the sequence of micrographs. We have now reconstructed a larger proportion of the exchange tissue by using a cross-correlation based alignment strategy and have demonstrated that the staining intensity of each of the exchange tissue components is sufficiently different to allow them to be identified by simple filtering and thresholding. The resulting reconstructions sample a much larger proportion of the exchange tissue and demonstrate the heterogeneity of structures from different locations in the parabronchus. We have shown that a sheet-flow-type arrangement of Blood Capillaries surrounds the infundibulum; this represents an unexpected functional convergence with the arrangement of Blood Capillaries surrounding the mammalian alveoli. It is feasible, using this reconstruction strategy, to analyse the exchange tissue of a large number of avian species in order to determine structural correlates of function. The resulting reconstructions could be analysed in order to determine the basis of the functional efficiency and rigidity of the avian lung.

  • Sheet Flow Design in the Vasculature of Gas Exchangers
    Advances in Anatomy Embryology and Cell Biology, 2002
    Co-Authors: John N. Maina
    Abstract:

    The geometric arrangement and organization of the Blood capillary systems of the gas exchangers is remarkably different from those that appertain to the systemic circulation. Whereas, for example, the Blood Capillaries in the muscle tissue occur as long, loosely connected structures (e.g. Mathieu-Costello et al. 1992), the pulmonary Blood Capillaries form an extremely dense network. Rather than passing through a system of long tubes, the pattern of flow of Blood in a classic capillary system, in the gas exchangers, the Blood forms an expansive film, a ‘sheet’. Various investigators have analysed and mathematically modelled the size, shape and geometry of the Blood Capillaries of various gas exchangers to gain an insight into the Blood flow dynamics and the rate of gas transfer at the water/air-Blood (tissue) interface. The observations and inferences that have been made conflict even on certain fundamental aspects. For example, Guntheroth et al. (1982) regarded the mammalian pulmonary Blood Capillaries as ‘intersecting tubules’, whereas Weibel (1963) and Weibel and Gomez (1962) considered them to be ‘intersecting, short, circular, cylindrical tubules arranged predominantly in hexagonal arrays’. Hijiya and Okada (1978) suggested that the arrangement of the alveolar Blood Capillaries is ‘more frequently pentagonal in shape’. Schraufnagel et al. (1986) considered the shape of the alveolar Blood Capillaries to change from ‘ring’ to ‘square’ configurations between the inspiratory and expiratory phases. On the basis of what they considered to be ‘short and closely knit Blood Capillaries where the capillary segments were wider than they were long’ and the haemodynamic properties where the vascular compliance was such that ‘only sheet thickness increased when intravascular pressure was raised’, Fung and Sobin (1972) and Sobin et al. (1979) formulated what they named a ‘sheet-flow model’ to analyse the alveolar Blood volume and transit time. They considered the pulmonary capillary system to comprise of a construction made up of cellular/tissue ‘posts’ that traversed a vascular space.

David A. Silverman - One of the best experts on this subject based on the ideXlab platform.

Maxim E. Darvin - One of the best experts on this subject based on the ideXlab platform.

  • Two-photon autofluorescence lifetime imaging of human skin papillary dermis in vivo: assessment of Blood Capillaries and structural proteins localization
    Scientific Reports, 2017
    Co-Authors: Evgeny A. Shirshin, Yury I. Gurfinkel, Alexander V. Priezzhev, Victor V. Fadeev, Juergen Lademann, Maxim E. Darvin
    Abstract:

    The papillary dermis of human skin is responsible for its biomechanical properties and for supply of epidermis with chemicals. Dermis is mainly composed of structural protein molecules, including collagen and elastin, and contains Blood Capillaries. Connective tissue diseases, as well as cardiovascular complications have manifestations on the molecular level in the papillary dermis (e.g. alteration of collagen I and III content) and in the capillary structure. In this paper we assessed the molecular structure of internal and external regions of skin Capillaries using two-photon fluorescence lifetime imaging (FLIM) of endogenous compounds. It was shown that the Capillaries are characterized by a fast fluorescence decay, which is originated from red Blood cells and Blood plasma. Using the second harmonic generation signal, FLIM segmentation was performed, which provided for spatial localization and fluorescence decay parameters distribution of collagen I and elastin in the dermal papillae. It was demonstrated that the lifetime distribution was different for the inner area of dermal papillae around the capillary loop that was suggested to be due to collagen III. Hence, we propose a generalized approach to two-photon imaging of the papillary dermis components, which extends the capabilities of this technique in skin diagnosis.

Hemant Sarin - One of the best experts on this subject based on the ideXlab platform.

  • Physiologic upper limits of pore size of different Blood capillary types and another perspective on the dual pore theory of microvascular permeability
    Journal of Angiogenesis Research, 2010
    Co-Authors: Hemant Sarin
    Abstract:

    Background Much of our current understanding of microvascular permeability is based on the findings of classic experimental studies of Blood capillary permeability to various-sized lipid-insoluble endogenous and non-endogenous macromolecules. According to the classic small pore theory of microvascular permeability, which was formulated on the basis of the findings of studies on the transcapillary flow rates of various-sized systemically or regionally perfused endogenous macromolecules, transcapillary exchange across the capillary wall takes place through a single population of small pores that are approximately 6 nm in diameter; whereas, according to the dual pore theory of microvascular permeability, which was formulated on the basis of the findings of studies on the accumulation of various-sized systemically or regionally perfused non-endogenous macromolecules in the locoregional tissue lymphatic drainages, transcapillary exchange across the capillary wall also takes place through a separate population of large pores, or capillary leaks, that are between 24 and 60 nm in diameter. The classification of Blood capillary types on the basis of differences in the physiologic upper limits of pore size to transvascular flow highlights the differences in the transcapillary exchange routes for the transvascular transport of endogenous and non-endogenous macromolecules across the capillary walls of different Blood capillary types. Methods The findings and published data of studies on capillary wall ultrastructure and capillary microvascular permeability to lipid-insoluble endogenous and non-endogenous molecules from the 1950s to date were reviewed. In this study, the Blood capillary types in different tissues and organs were classified on the basis of the physiologic upper limits of pore size to the transvascular flow of lipid-insoluble molecules. Blood Capillaries were classified as non-sinusoidal or sinusoidal on the basis of capillary wall basement membrane layer continuity or lack thereof. Non-sinusoidal Blood Capillaries were further sub-classified as non-fenestrated or fenestrated based on the absence or presence of endothelial cells with fenestrations. The sinusoidal Blood Capillaries of the liver, myeloid (red) bone marrow, and spleen were sub-classified as reticuloendothelial or non-reticuloendothelial based on the phago-endocytic capacity of the endothelial cells. Results The physiologic upper limit of pore size for transvascular flow across capillary walls of non-sinusoidal non-fenestrated Blood Capillaries is less than 1 nm for those with interendothelial cell clefts lined with zona occludens junctions (i.e. brain and spinal cord), and approximately 5 nm for those with clefts lined with macula occludens junctions (i.e. skeletal muscle). The physiologic upper limit of pore size for transvascular flow across the capillary walls of non-sinusoidal fenestrated Blood Capillaries with diaphragmed fenestrae ranges between 6 and 12 nm (i.e. exocrine and endocrine glands); whereas, the physiologic upper limit of pore size for transvascular flow across the capillary walls of non-sinusoidal fenestrated Capillaries with open 'non-diaphragmed' fenestrae is approximately 15 nm (kidney glomerulus). In the case of the sinusoidal reticuloendothelial Blood Capillaries of myeloid bone marrow, the transvascular transport of non-endogenous macromolecules larger than 5 nm into the bone marrow interstitial space takes place via reticuloendothelial cell-mediated phago-endocytosis and transvascular release, which is the case for systemic bone marrow imaging agents as large as 60 nm in diameter. Conclusions The physiologic upper limit of pore size in the capillary walls of most non-sinusoidal Blood Capillaries to the transcapillary passage of lipid-insoluble endogenous and non-endogenous macromolecules ranges between 5 and 12 nm. Therefore, macromolecules larger than the physiologic upper limits of pore size in the non-sinusoidal Blood capillary types generally do not accumulate within the respective tissue interstitial spaces and their lymphatic drainages. In the case of reticuloendothelial sinusoidal Blood Capillaries of myeloid bone marrow, however, non-endogenous macromolecules as large as 60 nm in diameter can distribute into the bone marrow interstitial space via the phago-endocytic route, and then subsequently accumulate in the locoregional lymphatic drainages of tissues following absorption into the lymphatic drainage of periosteal fibrous tissues, which is the lymphatic drainage of myeloid bone marrow. When the ultrastructural basis for transcapillary exchange across the capillary walls of different capillary types is viewed in this light, it becomes evident that the physiologic evidence for the existence of aqueous large pores ranging between 24 and 60 nm in diameter in the capillary walls of Blood Capillaries, is circumstantial, at best.

  • physiologic upper limits of pore size of different Blood capillary types and another perspective on the dual pore theory of microvascular permeability
    Journal of Angiogenesis Research, 2010
    Co-Authors: Hemant Sarin
    Abstract:

    Much of our current understanding of microvascular permeability is based on the findings of classic experimental studies of Blood capillary permeability to various-sized lipid-insoluble endogenous and non-endogenous macromolecules. According to the classic small pore theory of microvascular permeability, which was formulated on the basis of the findings of studies on the transcapillary flow rates of various-sized systemically or regionally perfused endogenous macromolecules, transcapillary exchange across the capillary wall takes place through a single population of small pores that are approximately 6 nm in diameter; whereas, according to the dual pore theory of microvascular permeability, which was formulated on the basis of the findings of studies on the accumulation of various-sized systemically or regionally perfused non-endogenous macromolecules in the locoregional tissue lymphatic drainages, transcapillary exchange across the capillary wall also takes place through a separate population of large pores, or capillary leaks, that are between 24 and 60 nm in diameter. The classification of Blood capillary types on the basis of differences in the physiologic upper limits of pore size to transvascular flow highlights the differences in the transcapillary exchange routes for the transvascular transport of endogenous and non-endogenous macromolecules across the capillary walls of different Blood capillary types. The findings and published data of studies on capillary wall ultrastructure and capillary microvascular permeability to lipid-insoluble endogenous and non-endogenous molecules from the 1950s to date were reviewed. In this study, the Blood capillary types in different tissues and organs were classified on the basis of the physiologic upper limits of pore size to the transvascular flow of lipid-insoluble molecules. Blood Capillaries were classified as non-sinusoidal or sinusoidal on the basis of capillary wall basement membrane layer continuity or lack thereof. Non-sinusoidal Blood Capillaries were further sub-classified as non-fenestrated or fenestrated based on the absence or presence of endothelial cells with fenestrations. The sinusoidal Blood Capillaries of the liver, myeloid (red) bone marrow, and spleen were sub-classified as reticuloendothelial or non-reticuloendothelial based on the phago-endocytic capacity of the endothelial cells. The physiologic upper limit of pore size for transvascular flow across capillary walls of non-sinusoidal non-fenestrated Blood Capillaries is less than 1 nm for those with interendothelial cell clefts lined with zona occludens junctions (i.e. brain and spinal cord), and approximately 5 nm for those with clefts lined with macula occludens junctions (i.e. skeletal muscle). The physiologic upper limit of pore size for transvascular flow across the capillary walls of non-sinusoidal fenestrated Blood Capillaries with diaphragmed fenestrae ranges between 6 and 12 nm (i.e. exocrine and endocrine glands); whereas, the physiologic upper limit of pore size for transvascular flow across the capillary walls of non-sinusoidal fenestrated Capillaries with open 'non-diaphragmed' fenestrae is approximately 15 nm (kidney glomerulus). In the case of the sinusoidal reticuloendothelial Blood Capillaries of myeloid bone marrow, the transvascular transport of non-endogenous macromolecules larger than 5 nm into the bone marrow interstitial space takes place via reticuloendothelial cell-mediated phago-endocytosis and transvascular release, which is the case for systemic bone marrow imaging agents as large as 60 nm in diameter. The physiologic upper limit of pore size in the capillary walls of most non-sinusoidal Blood Capillaries to the transcapillary passage of lipid-insoluble endogenous and non-endogenous macromolecules ranges between 5 and 12 nm. Therefore, macromolecules larger than the physiologic upper limits of pore size in the non-sinusoidal Blood capillary types generally do not accumulate within the respective tissue interstitial spaces and their lymphatic drainages. In the case of reticuloendothelial sinusoidal Blood Capillaries of myeloid bone marrow, however, non-endogenous macromolecules as large as 60 nm in diameter can distribute into the bone marrow interstitial space via the phago-endocytic route, and then subsequently accumulate in the locoregional lymphatic drainages of tissues following absorption into the lymphatic drainage of periosteal fibrous tissues, which is the lymphatic drainage of myeloid bone marrow. When the ultrastructural basis for transcapillary exchange across the capillary walls of different capillary types is viewed in this light, it becomes evident that the physiologic evidence for the existence of aqueous large pores ranging between 24 and 60 nm in diameter in the capillary walls of Blood Capillaries, is circumstantial, at best.