The cardiovascular system
C. Simon Herrington in Muir's Textbook of Pathology, 2020
The microcirculation is the capillaries, the arterioles that supply them, and the venules that drain the blood from the capillary bed. A capillary consists of a single endothelial cell encircling a lumen that only just admits the passage of red blood cells. Intercellular junctions join adjacent endothelial cells. The microcirculation is adapted to each organ and tissue. Thus, the liver sinusoids and kidney have a highly permeable fenestrated endothelium, whereas the capillaries in the brain are watertight and contribute to the blood–brain barrier. Capillary endothelial cells are surrounded by pericytes, which support them, synthesize basement membrane, and can differentiate into a variety of cell types including vascular smooth muscle cells. Capillaries act as a semipermeable membrane. They retain most of the protein but permit free exchange of fluid.
The Microcirculation and Clinical Disease
John H. Barker, Gary L. Anderson, Michael D. Menger in Clinically Applied Microcirculation Research, 2019
The microcirculation is usually defined as those vessels distal to the conduit arteries and before the veins; in addition, the prenodal lymphatics are conventionally also included. The blood microvessels comprise arterioles, the capillaries and venules, as well as specialized structures in some organ beds such as arteriovenous shunts. The lymphatics comprise terminal lymphatics, precollectors, and collectors. In certain animal models where detailed anatomical studies are possible, considerable attention has been paid to the size and branch order of the arterioles; as there is evidence that terminal arterioles may respond to a different range of stimuli than do more proximal resistance vessels,5 such a distinction may be important. The arteriole is characterized by the presence of vascular smooth muscle cells in its wall, which may be several layers thick in the case of proximal vessels. In contrast, as arterioles approach the capillary bed, vascular smooth muscle cells become more sparse. The precapillary sphincter, which in most microvascular beds is a functional concept rather than a demonstrable anatomical entity, comprises the last, single vascular smooth muscle cell encircling the endothelial tube that constitutes the capillary. Arterioles in general are characterized by relatively dense innervation that have nerve terminals possessing a wide range of neurotransmitters dependent upon the circulation studied.6
Diagnostics of Functional Abnormalities in the Microcirculation System Using Laser Doppler Flowmetry
Andrey V. Dunaev, Valery V. Tuchin in Biomedical Photonics for Diabetes Research, 2023
The main function of the microcirculation is to transport blood and substances to and from tissues. When the blood moves along the capillary, a huge number of water molecules and dissolved particles diffuse in one direction and in the other through the capillary wall, ensuring constant mixing of the tissue fluid and plasma. The permeability of capillaries for various substances is different and depends on the size of their molecules and the type of capillaries themselves. One of the most important purposes of delivering oxygen to the tissues is achieved by blood transport. Cells are constantly in need of oxygen, which they receive by diffusion from the blood through the interstitial fluid. The primary function of the blood is to deliver oxygen to tissues. The circulatory system pumps oxygen-rich blood through the capillary network. The microcirculatory system is organized in such a way that all cells have at least one adjacent capillary for diffusive oxygen exchange, and red blood cells deliver oxygen to the tissues as they pass through the capillaries [24].
Determination of baseline alveolar mucosa perfusion parameters using laser Doppler flowmetry and tissue spectrophotometry in healthy adults
Published in Acta Odontologica Scandinavica, 2020
Obada Barry, Ying Wang, Gerhard Wahl
Capillary microcirculation has also been studied using optical spectroscopic based microvascular imaging techniques. Orthogonal polarization spectral imaging and more recently sidestream dark-field (SDF) imaging, have demonstrated reproducible measurements of the capillary density of the gingiva [27,28]. Milstein and coworkers conducted measurements of microcirculation parameters to assess the differences between normal and alveolar cleft gingiva using the O2C device in addition to sidestream dark-field imaging [29]. The measurements showed significant differences in blood flow and velocity in areas of previous surgery. The SDF of the alveolar cleft gingiva demonstrated altered angiomorphology with notable large avascular zones [30] similar to the alveolar crest mucosa of edentulous jaws [26].
The effect of stiffened diabetic red blood cells on wall shear stress in a reconstructed 3D microaneurysm
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2022
Benjamin Czaja, Jonathan de Bouter, Morgan Heisler, Gábor Závodszky, Sonja Karst, Marinko Sarunic, David Maberley, Alfons Hoekstra
RBCs and platelets are initialized in the pre-inlet an approximate tube hematocrit of 3.7% and a platelet-to-RBC-ratio of 1/10. It is documented that the actual hematocrit in the microcirculation is much less than the systemic hematocrit, which has been measured to be 8–10% on average in the microciculation when the systemic hematocrit is reported at 35–40% (Johnson 1971; Lipowsky et al. 1978; Klitzman and Duling 1979). Additionally the hematocrit in the microcirculation can vary 6–10% between micro vessels (Lipowsky et al. 1978). Initializing hematocrits up to and above 10% in such small vessels without introducing un-physical spatial structure of cells is far from trivial. The force-bias model (Bargieł and Mościński 1991) of enclosing ellipsoids was applied to initialize a random hematocrit distribution that insured numerical stability for the entire run time of the simulations. We believe that the cell initializations in this study are lower than the expected physiological hematocrit but represents the current state of the art of such cell resolved blood flow models applied over such long timescales.
The beneficial effects of subcutaneous Allium cepa injection on random flap survival in rats
Published in Journal of Plastic Surgery and Hand Surgery, 2019
Dinçer Altınel, Merdan Serin, Havva Erdem, Burcu Biltekin, Mert Celikten, Sevgi Kurt Yazar, Gaye Toplu, Eymen Oruc
It has been shown in a previous study that A. cepa peel extract can have a positive effect on endothelial function in overweight and obese individuals [12]. We believe that this might be related to the enhanced capillary formation and increased microcirculation. In another study, Naseri et al. have shown the vasodilatation effect of A. cepa. This effect of A. cepa has been related to quercetin, antioxidant activity and inhibition vascular smooth muscle cells [8]. In our study A. cepa extract was shown to have a beneficial effect on flap survival and more prominent vessels were identified in the angiographic images of the A. cepa group. Despite this, there was no significant difference between the number of capillary formations in the A. cepa and the control group. These findings are consistent with previous studies which have shown that A. cepa has vasorelaxant effects.
Related Knowledge Centers
- Arteriole
- Tissue
- Vein
- Venule
- Capillary
- Circulatory System
- Blood
- Blood Vessel
- Metarteriole
- Lymph Capillary