Role Of Capillaries Research Articles

Capillary communication: the role of capillaries in sensing the tissue environment, coordinating the microvascular, and controlling blood flow.

Historically, capillaries have been viewed as the microvascular site for flux of nutrients to cells and removal of waste products. Capillaries are the most numerous blood vessel segment within the tissue, whose vascular wall consists of only a single layer of endothelial cells and are situated within microns of each cell of the tissue, all of which optimizes capillaries for the exchange of nutrients between the blood compartment and the interstitial space of tissues. There is, however, a growing body of evidence to support that capillaries play an important role in sensing the tissue environment, coordinating microvascular network responses, and controlling blood flow. Much of our growing understanding of capillaries stems from work in skeletal muscle and more recent work in the brain, where capillaries can be stimulated by products released from cells of the tissue during increased activity and are able to communicate with upstream and downstream vascular segments, enabling capillaries to sense the activity levels of the tissue and send signals to the microvascular network to coordinate the blood flow response. This review will focus on the emerging role that capillaries play in communication between cells of the tissue and the vascular network required to direct blood flow to active cells in skeletal muscle and the brain. We will also highlight the emerging central role that disruptions in capillary communication may play in blood flow dysregulation, pathophysiology, and disease.

On the role of capillary and viscous forces on wear and frictional performances of natural fiber composites under lubricated polishing

This paper aims to investigate the frictional and wear performances of natural flax fibers reinforced polypropylene composites subjected to lubricated mechanical polishing. Particularly, the interactions between the biocomposite surfaces and two different liquids (oil and water) are considered using a rotary tribometer where the counter-face is fed by silicon carbide (SiC) abrasive papers. Friction and wear at dry, water and oil-lubricated polishing are hence studied. The biocomposite worn surfaces are examined using a scanning electron microscope (SEM) and an atomic force microscope (AFM). Results show a significant influence of the lubricant type on the wear and frictional performances of flax fiber composites. The lubricated friction behavior is dependent on both the hydrophilic and oleophilic properties of flax fibers. In addition to the abrasive wear, while the thermal softening of the biocomposite controls the adhesive wear mechanism at dry polishing, changing the lubricant type from water to oil leads to modify the adhesive wear sources from only capillary forces to capillary and viscous forces, which contributes to increasing the wear of flax fiber composites under oil-lubricated polishing.

Experimental approbation of methodological and hardware-software speck-visualization in diagnosis of microcirculation of human surface biological tissues

In modern clinical practice, the assessment of the state of blood microcirculation and the diagnosis of microcirculatory disorders are extremely relevant in a variety of diseases: in cardiology, diabetology, oncology, dermatology, dentistry, surgery and resuscitation. Microcirculatory disorders are very diverse both in their pathogenesis and in clinical manifestations. Therefore, in the pattern of various diseases and extreme conditions, as well as in the correction of microcirculatory disorders the methods are needed for both operative assessment of the state of blood flow at tissue level and for its long-term monitoring. The interest in the study of the microvascular bed of the circulatory system is sparked by the significant role of capillaries in the implementation of the basic processes of the body's vital activity, in the trophic support of organs and their direct participation in tissue and cellular respiration. The health and life expectancy of a person depend on the coordinated work of the heart, large blood lines, and microcirculation vessels. The authors have studied modern optical methods for diagnosing microcirculation. The feasibility of using the speckle imaging method for noninvasive rapid assessment of the state of the microvasculature of human surface biological tissues has been substantiated. To implement the speckle-visualization method, methodological and software have been developed. The processing parameters that are most optimal from the point of view of the ratio of spatiotemporal resolution and computation time have been experimentally substantiated. The purpose of this work is the experimental testing of the developed methodological and hardware speckle imaging for the diagnosis of microcirculation of human surface biological tissues. The authors have carried out the studies of the state of microcirculation in the superficial blood vessels of the skin during physiotherapeutic procedures and in the imitation of pathology. The results of the studies have proved the feasibility of using the developed software for a high-quality diagnosis of the state of microcirculation of human surface biological tissues: primary changes in microcirculation are revealed, further changes to occur during physiotherapeutic procedures are visualized.

Keeping the Brain Well Fed: The Role of Capillaries and Arterioles in Orchestrating Functional Hyperemia

Cerebral blood flow increases in regions of increased brain activity. In this issue of Neuron, Rungta etal. (2018) characterize the contribution of different vascular compartments in generating this increase and outline the time course of arteriole and capillary dilation in generating functional hyperemia.

The Role of Capillaries in the Lesser Ailments of Old Age and in Alzheimer’s Disease and Vascular Dementia: The Potential of Pro-Therapeutic Angiogenesis

Apart from chronic diseases (arthritis, diabetes, etc.), old age is generally characterized by three lesser ailments: muscle weakness, minor memory lapses, and cold intolerance. This trio of complaints may have a common, underlying cause, namely, the age-associated reduced microcirculation in muscles, brain, skin, and elsewhere in the body. The Angiogenesis Hypothesis proposes that old age is in part a deficiency disease due to the decline in angiogenic (AG) factors, resulting in a reduced capillary density (CD) throughout the body. Over fifty published papers document waning levels of AG factors and/or decreased CD in various organ systems of aged animals and people, including those with Alzheimer's disease. The deficiency of AG factors is analogous to that of certain hormones (e.g., testosterone) whose blood levels also decline with age. In theory, therapeutic angiogenesis employing recombinant AG factors is a tenable treatment for the lesser ailments of old age and may improve the later years of human life. An optimal administration route may be intranasal.

Advances and challenges in skeletal muscle angiogenesis.

The role of capillaries is to serve as the interface for delivery of oxygen and removal of metabolites to/from tissues. During the past decade there has been a proliferation of studies that have advanced our understanding of angiogenesis, demonstrating that tissue capillary supply is under strict control during health but poorly controlled in disease, resulting in either excessive capillary growth (pathological angiogenesis) or losses in capillarity (rarefaction). Given that skeletal muscle comprises nearly 40% of body mass in humans, skeletal muscle capillary density has a significant impact on metabolism, endocrine function, and locomotion and is tightly regulated at many different levels. Skeletal muscle is also high adaptable and thus one of the few organ systems that can be experimentally manipulated (e.g., by exercise) to study physiological regulation of angiogenesis. This review will focus on the methodological concerns that have arisen in determining skeletal muscle capillarity and highlight the concepts that are reshaping our understanding of the angio-adaptation process. We also summarize selected new findings (physical influences, molecular changes, and ultrastructural rearrangement of capillaries) that identify areas of future research with the greatest potential to expand our understanding of how angiogenesis is normally regulated, and that may also help to better understand conditions of uncontrolled (pathological) angiogenesis.

Longitudinal Oxygen Tension Gradients in Small Cortical Microvessels in the Rat Brain on Development of Acute Anemia

Oxygen microelectrodes were used to study longitudinal oxygen tension gradients (pO2) in small arterioles (with lumen diameters in control conditions of 5–20 μm) and capillaries in the rat cerebral cortex during stepwise decreases in the blood hemoglobin concentration ([Hb]) from an initial 14.4 ± 0.3 g/liter to 10.1 ± 0.2 (step 1), 7.0 ± 0.2 (step 2), and 3.7 ± 0.2 (step 3) g/liter. All data are presented as mean ± error of the mean. Oxygen tension was measured at two points in arteriole segments, separated from each other by distances of ΔL = 265 ± 34 μm, n = 30. The mean diameter of arteriole lumens in controls was 10.7 ± 0.5 μm, n = 71. The magnitude of the longitudinal pO2 gradient (ΔpO2/ΔL) for the study arterioles was (mmHg/μm): 0.03 ± 0.01, n = 15 (controls), 0.06 ± 0.01, n = 16 (step 1), 0.07 ± 0.01, n = 14 (step 2), and 0.1 ± 0.01, n = 30 (step 3). In capillaries, ΔpO2/ΔL (with a segment length ΔL = 201 ± 45 μm, n = 18) was (mmHg/μm): 0.07 ± 0.01, n = 17 (controls), 0.09 ± 0.02, n = 16 (step 1), 0.08 ± 0.01, n = 15 (step 2), and 0.1 ± 0.02, n = 18 (step 3). The more than threefold decrease in oxygen content in arterial blood did not lead to significant changes (p > 0.05) in ΔpO2/ΔL in capillaries. Longitudinal hemoglobin oxygenation gradients (ΔSO2/ΔL) in capillaries (calculated using the animals' systemic blood oxyhemoglobin dissociation curve) was some three times greater than in arterioles, which provides evidence for the leading role of capillaries in supplying oxygen to the cerebral cortex in these conditions. These data include the first measurements of longitudinal pO2 gradients in arterioles and capillaries in the cerebral cortex on development of acute anemia.

Cellular and physiological mechanisms underlying blood flow regulation in the retina and choroid in health and disease

We review the cellular and physiological mechanisms responsible for the regulation of blood flow in the retina and choroid in health and disease. Due to the intrinsic light sensitivity of the retina and the direct visual accessibility of fundus blood vessels, the eye offers unique opportunities for the non-invasive investigation of mechanisms of blood flow regulation. The ability of the retinal vasculature to regulate its blood flow is contrasted with the far more restricted ability of the choroidal circulation to regulate its blood flow by virtue of the absence of glial cells, the markedly reduced pericyte ensheathment of the choroidal vasculature, and the lack of intermediate filaments in choroidal pericytes. We review the cellular and molecular components of the neurovascular unit in the retina and choroid, techniques for monitoring retinal and choroidal blood flow, responses of the retinal and choroidal circulation to light stimulation, the role of capillaries, astrocytes and pericytes in regulating blood flow, putative signaling mechanisms mediating neurovascular coupling in the retina, and changes that occur in the retinal and choroidal circulation during diabetic retinopathy, age-related macular degeneration, glaucoma, and Alzheimer's disease. We close by discussing issues that remain to be explored.

The role of capillary and surface forces in the crossover behavior of solid nanoparticles at liquid interfaces

We investigate the interaction between a nanoparticle and an oil–water interface with particular emphasis on the particle crossing through the interface. The formation of a three-phase contact line is investigated in two cases, namely in the presence and in the absence of surface forces. We carefully examine the interplay between capillary and surface forces in such systems. Two instabilities of the interface (snap-in/snap-out) as the particle is moved through the interface are identified and quantitatively described. While the snap-in instability was observed in some AFM studies, the precise interface position and configuration relative to the particle at the instability depends on the nature of the surface forces present in the system. After the snap-in, the particle is adsorbed and must overcome an energy barrier due to the interface deformation in order to cross-over to the other liquid. We make quantitative predictions on the interface configuration at the instabilities and the free energy barrier height. The roles of particle size and different interaction parameters characterizing the system in determining the magnitude of the energy barrier for crossing and in the formation of a three-phase contact line are discussed. Ultimately, this study will enable us to make quantitative predictions on capillary effects in nanoparticle-microemulsions mixtures and other colloidal systems. For particles in the micrometer range and larger the capillary forces dominate over the surface forces and dictate how the snap-in occurs. However, the situation becomes different for particle sizes smaller than about 100 nm. The presence of surface forces modifies the interface configuration and the free energy jump at the snap-in instability.

Role of Capillaries in Regulating Skeletal Muscle Fiber Size

Role of Capillaries in Regulating Skeletal Muscle Fiber Size

Microvasculature in acute myocardial ischemia: part I: evolving concepts in pathophysiology, diagnosis, and treatment.

Microvasculature in acute myocardial ischemia: part I: evolving concepts in pathophysiology, diagnosis, and treatment.

Usefulness of concomitant myoglobin and troponin elevation as a biochemical marker of mortality in non–ST-segment elevation acute coronary syndromes

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The role of capillaries in determining coronary blood flow reserve: Implications for stress-induced reversible perfusion defects

The role of capillaries in determining coronary blood flow reserve: Implications for stress-induced reversible perfusion defects

Normal perfusion pressure breakthrough: the role of capillaries.

Excision of human cerebral arteriovenous malformations (AVMs) can be complicated by postoperative edema and hemorrhage in adjacent brain tissue, despite the complete excision of the malformation. Various theories have purported to explain the hemodynamic basis for this predisposition, including disordered autoregulation causing "normal perfusion pressure breakthrough" and obstruction of venous drainage leading to "occlusive hyperemia." This study did not evaluate the arterial or venous circulations in this scenario, but rather examined the capillaries in adjacent brain parenchyma for any structural deficiencies that would predispose the brain to the postoperative formation of edema and hemorrhage. Arteriovenous fistulas (AVFs) were created surgically in the necks of 10 male Sprague-Dawley rats, which caused chronic cerebral hypoperfusion with a reduction in cerebral blood flow of between 25% and 50%. Ten age-matched animals were used as controls. Twenty-six weeks after AVF formation the animals were killed and perfusion fixed. Their brain tissue was prepared for light microscopic studies by staining for glial fibrillary acidic protein or for transmission electron microscopy. In the CA1 pyramidal cell region of the hippocampus, it was found that in the animals with AVFs there was increased capillary density and absent astrocytic foot processes in some of these vessels. It was concluded that these vessels had developed as a result of neovascularization in response to chronic cerebral ischemia and that their anatomical configuration made them prone to mechanical weakness and instability following the increase in perfusion pressure that occurs in adjacent brain parenchyma after AVM excision. The authors believe that this study pinpoints a structural accompaniment to the hemodynamic changes that occur in brain tissue in the vicinity of cerebral AVMs that predispose these areas to the formation of edema and hemorrhage after AVM excision.

2420 Co-culture of the female rat preoptic area and pituitary: Possible role of capillaries in the migration of lhrh neurons

2420 Co-culture of the female rat preoptic area and pituitary: Possible role of capillaries in the migration of lhrh neurons

An MRI study of drying in granular beds of nonporous particles

MRI is used to study the role of capillary and gravitational forces in controlling mass transport of water during isothermal drying of granular beds of nonporous particles. A new model is presented that shows how capillary and gravitational forces relate to Fickian diffusion driven by a chemical potential gradient. In granular beds, where capillary and gravitational forces dominate, the image profiles give direct information on the dependence of the degree of saturation on capillary suction pressure. The effects of changing particle size and surface tension on the profiles is investigated quantitatively, and it is shown that high capillary pressures create anomalies in the drying profiles.

Role of capillary and viscous forces in mobilization of residual oil

AbstractExperimental results are reported for a series of microemulsion displacement tests carried out in a consolidated core of medium permeability (1.75 μm2). The interfacial tension and viscosity were varied from 0.02 to 32.0 mN/m and 2.0 to 26.0 mN · s/m2, respectively. The amount of oil unrecovered is correlated as a function of capillary number, Nc. Results are compared with those obtained by other workers who used porous media of low permeability and the relative importance of capillary and viscous forces at various stages of oil mobilization is discussed.

Metabolic hyperemia in canine gut.

ARTICLESMetabolic hyperemia in canine gutW. W. Pawlik, J. D. Fondacaro, and E. D. JacobsonW. W. Pawlik, J. D. Fondacaro, and E. D. JacobsonPublished Online:01 Jul 1980https://doi.org/10.1152/ajpgi.1980.239.1.G12MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByCapillary communication: the role of capillaries in sensing the tissue environment, coordinating the microvascular, and controlling blood flowCoral L. Murrant and Nicole M. Fletcher9 November 2022 | American Journal of Physiology-Heart and Circulatory Physiology, Vol. 323, No. 5Nutrient-induced gastrointestinal hyperemia and specific dynamic action in rainbow trout (Oncorhynchus mykiss)—importance of proteins and lipidsHenrik Seth, Erik Sandblom, and Michael Axelsson1 February 2009 | American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, Vol. 296, No. 2 Video Abstract More from this issue > Volume 239Issue 1July 1980Pages G12-G17 Copyright & PermissionsCopyright © 1980 the American Physiological Societyhttps://doi.org/10.1152/ajpgi.1980.239.1.G12PubMed6994511History Published online 1 July 1980 Published in print 1 July 1980 Metrics