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Diagnostics of Functional Abnormalities in the Microcirculation System Using Laser Doppler Flowmetry
Published in Andrey V. Dunaev, Valery V. Tuchin, Biomedical Photonics for Diabetes Research, 2023
Irina A. Mizeva, Elena V. Potapova, Elena V. Zharkikh
In the neutral state, the skin temperature is about 33 °C, but it varies in a wide range. The main regulator of heat exchange with the environment is papillary loops, which are located in the immediate vicinity of the dermoepidermal junction [19]. Even though the volume of capillaries is small, their surface area is large compared to other skin vessels, and the blood flow rate is quite small, which contributes to heat exchange. To a lesser extent, the vessels of the upper venous plexus, lying parallel to the surface of the skin, are involved in thermoregulation. These vessels are less efficient in terms of heat transfer than capillary loops, but they provide a useful backup mechanism when heat transfer through capillary loops is overloaded. AVAs lying deeper in the dermis are considered less effective for thermoregulation. When the body is close to thermoneutral conditions, AVAs play a large role in temperature control, as the body temperature is controlled exclusively by skin blood flow without changes in metabolism.
Cellular Adaptations to High-Intensity and Sprint Interval Training
Published in Peter M. Tiidus, Rebecca E. K. MacPherson, Paul J. LeBlanc, Andrea R. Josse, The Routledge Handbook on Biochemistry of Exercise, 2020
Martin J. MacInnis, Lauren E. Skelly
Capillaries are the site of gas, nutrient, and by-product exchange between muscles and blood. Growth of the capillary network within skeletal muscle (i.e., increased capillarization) provides a greater surface area for exchange and reduces the oxygen diffusion distance. The primary stimuli to increase capillary density in humans, which occurs in response to aerobic training over a period of weeks to months, are mechanical (i.e., shear stress and passive muscle stretch) and metabolic (i.e., muscle contractions). As described by Hellsten and Nyberg (50), capillary growth is regulated by transient changes in the concentration of pro-angiogenic (e.g., vascular endothelial growth factor [VEGF], angiopoietin-2) and anti-angiogenic (e.g., endostatin) compounds elicited by exercise.
Comparative Anatomy and Physiology of the Mammalian Eye
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
The vascular system of the retina varies greatly between species (Table 6). In those animals possessing retinal blood vessels, the arterial supply enters as either a central retinal vessel (human, primate) or via the short posterior ciliary arteries which give rise to the cilioretinal arteries.3 The number of larger arterioles and venules varies with the species, but all large vessels are contained in the nerve fiber layer. The arterioles are, in general, internal to the venules and are surrounded by a very large capillary-free zone.4 The smaller vessels extend deeper into the retina and the capillaries can extend as far as the middle limiting membrane. All structures external to this, the photoreceptor cell bodies, inner and outer segments, and the RPE are supplied by the choroid via the choriocapillaris.4 The capillaries have a single layer of endothelial cells surrounded by a basement membrane and an interrupted layer of pericytes which are, in turn, surrounded by their own basement membrane.4 The capillary endothelial cells are attached to each other by terminal bars and are, like the RPE, part of the blood-retinal barrier.
Heat distribution and the condition of hypothermia in the multi-layered human head: A mathematical model
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Ahsan Ul Haq Lone, M.A. Khanday, Saqib Mubarak, Feroze A. Reshi
Circulatory system also plays a pivotal role in the thermoregulation of body temperature in humans by regulating the temperature distribution throughout the body. Blood capillaries permeate almost every part of the body and perform the function of heat distribution within the body and also heat exchange with the environment. Figure 4 highlights the variation of temperature in human head in relation to the temperature at head-atmosphere interface. Head receives a number of arteries that deliver blood to brain and scalp and also facilitate the distribution and regulation of temperature in the head. The capillaries running through the head and reaching the surface of the head enable blood-mediated convective heat transfer from atmosphere to the core head (Coccarelli et al. 2017). When a human head exposed to cold environment, the blood capillaries present in the scalp exchange body heat with the external cold environment and consequently, experience lowering in the temperature of the blood in the scalp. Continued exposure to cold environment transmits the effect deep into the brain capillaries, wherein the temperature gradually lowers down below the normal body temperature. This decrease in arterial blood temperature in the head as function of the duration of exposure of the head to cold environment is reflected in Figure 4.
Selecting ideal drugs for encapsulation in thermosensitive liposomes and other triggered nanoparticles
Published in International Journal of Hyperthermia, 2022
Krishna K. Ramajayam, Danforth A. Newton, Dieter Haemmerich
We integrated the cell uptake and the cytotoxicity model in our 3-D model where we simulate a tumor capillary with surrounding tissue (Figure 1). We assumed ideal IV-DDS (e.g., TSL), where the drug is completely and instantaneously released from DDS upon entering the capillary. Specifically for TSL, we assume that the tumor is heated to 41 °C. TSL is carried to the capillary by plasma within a tumor-feeding artery. For larger vessels than capillaries, the blood may be at lower temperatures compared to surrounding tissue [55]. Due to the small diameter and low blood flow velocity within the capillary, we can assume that blood temperature immediately equilibrates with surrounding tissue temperature [36] and heats up to 41 °C, resulting in drug release from TSL at the capillary entrance. As drug and plasma move along the capillary, the drug is continuously extracted by the surrounding tissue, resulting in a longitudinal drug concentration gradient within the capillary (Figure 4). The amount extracted depends on the permeability of the vascular wall, which varies by drug (Table 2; Table S1). Therefore, the drugs with high permeability, such as IDA are extracted better (Figure 4).
Sub-acute oral toxicity study of aqueous extract of tobacco leaves (Nicotiana tabacum L.) on lipid profile, the tissue, and serum of the liver and kidney of male Wistar rats
Published in Biomarkers, 2021
Felix Atawal Andong, Ebele Augustina Orji, Ngozi Evelyn Ezenwaji, Augustine Okorie Nkemakolam, Temitope Dadewura Melefa, Antoinette Onyebuchi Chukwurah, Oguche Moses Ojonugwa, Faith Funmilayo Hinmikaiye, Arinze Ikechukwu Onwurah
The extract of tobacco leaves had a lesser effect on the treated groups of the kidney; for instance, the kidney experienced normal glomeruli and renal tubules in all treated groups (in Figures 1(b), 2(b), and 3(b)) compared with the control group (Figure 4(b)). Suggesting that the extract of tobacco may not have impacted the kidney cells and probably why the results from the biochemical analyses indicated that the urea and creatinine levels were non-signficantly influenced by the extract (Figure 1; Table 1). Notably, urea is a waste product removed from the body by the kidney; it is filtered by the glomerular capillaries, and then enters the renal tubule. However, around half of urea is largely reabsorbed passively by diffusion, while the rest is been removed as urine. Lower level or decreased level of urea in the blood may be indicative of increased glomerular filtration and excretion in the urine, or reduced reabsorption in the tubules (Sokal et al. 2013). On the other hand, creatinine is a larger molecule than urea and cannot pass through the tubular membrane. Increased creatinine levels or concentrations may arise from reduced kidney filtration, therefore, kidney malfunction is indicated by the accumulation of high levels of creatinine in the blood. An increase in both urea and creatinine in the blood may be indicative of the poorer kidney function or nephropathies (Hansen et al. 1996). However, the insignificant concentrations of urea and creatinine in this study, indicated that there may be no impairment caused by the extract of tobacco on the kidney.