Cardiovascular System
David Sturgeon in Introduction to Anatomy and Physiology for Healthcare Students, 2018
The final type of blood vessels are capillaries (from the Latin word capillaris for ‘hair-like’). These microscopic tubes consist of a single layer of endothelial cells through which plasma and other small molecules can pass. There is no tunica media or adventitia and the diameter of each capillary is only slightly larger than that of a single erythrocyte (remember how they can stack themselves like dinner plates to avoid blockage when travelling through these narrow vessels). Capillaries connect small arteries (arterioles) to small veins (venules) and the capillary network (or bed) between the two is the site of nutrient and waste exchange between the blood and interstitial fluid that surrounds the cells (Figure 7.3). The flow of blood through the capillary bed is known as microcirculation and takes place in two types of capillary. The first type of capillary is known as a metarteriole (or vascular shunt) and directly connects the arteriole to the opposing venule. True capillaries, on the other hand, branch from metarterioles and provide nutrient and waste product exchange between the plasma and interstitial fluid. The entrance to each true capillary is protected by a band of smooth muscle called a precapillary sphincter. This contracts or relaxes in order to control the flow of blood through the capillary bed. For example, when precapillary sphincters contract (close), blood flows directly through the metarteriole and bypasses the tissue. This occurs during vigorous exercise when blood is re-routed from the gastrointestinal tract to skeletal muscle in order to prioritise blood supply to the latter.
Ocular Blood Flow and Metabolism
Neil T. Choplin, Carlo E. Traverso in Atlas of Glaucoma, 2014
The eye offers a unique opportunity to study hemodynamics. It is the only location in the body where capillary blood flow may be observed in humans noninvasively. More than 100 years ago, Wagemann and Salzmann (1892) observed vascular sclerosis in many of their glaucoma patients. Through the years, numerous other researchers have uncovered pieces of the ocular blood flow puzzle: documenting reductions in the capillary beds, sclerosis of nutritional vessels, vascular lesions and degeneration, and other circulatory pathologies in many eye diseases, including glaucoma. A century of observation and circumstantial evidence suggesting a vascular component in the pathogenesis of glaucoma is now supported by direct experimental evidence with specialized measurements of hemodynamic function that are now readily available.
Bulk Diffusion Methods for Measuring Water Permeability of Biological Membranes
Gheorghe Benga in Water Transport in Biological Membranes, 1989
The self-diffusion of water is measured by using tritiated water (THO, 100 μCi/mℓ) as a tracer. Extracellular volume is determined by impermeable C14-sucrose (10 μCi/mℓ). The suspension medium for the experiments is prepared from an isotonic solution of NaCl (9.5 gNaCl/ℓ H2O) plus 10% (vol per vol) isotonic phosphate buffer (NaH2PO4/Na2HPO4, 125 mmol/ℓ, pH = 7.4). Osmolarity should be controlled and adjusted to about 330 mOsm/ℓ. High-precision microliter syringes like those used for gas-chromatographic injection are suitable as capillaries with variable length. This capillary length could be read to ±0.1 mm. The capillary diameter used in our studies was in the range of 0.802 ± .001 mm. The screw cap is cut away, and the face is carefully milled. The capillaries are filled with packed cells with a complete syringe.
Treatment of facial telangiectasia with narrow-band intense pulsed light in Chinese patients
Published in Journal of Cosmetic and Laser Therapy, 2018
Huihui Gan, Baishuang Yue, Yan Wang, Zhong Lu
Facial telangiectasia refers to superficial cutaneous vessels visible on the face. These vessels measure 0.1–1.0 mm in diameter and represent a dilated venule, capillary, or arteriole(1). They appear clinically as tiny erythematous to violaceous cutaneous vessels frequently accompanied with diffuse redness of face. Tens of millions of people worldwide are estimated to have facial telangiectasia, associated with various disorders, rosacea, photodamage, prolonged topical steroid use, hyperestrogenemic states, liver disease, radiodermatitis, connective tissue disease, hypertrophic scars, and various vascular genodermatoses such as hereditary hemorrhagic telangiectasia(2). These patients are sensitive to cold, heat, and sunlight, which induces discomfort not only physically, but also psychologically. The effect of traditional treatment methods including topical therapy and oral medication is acceptable, and long-term administration may cause certain adverse effects. Pulsed dye laser (595 nm or 585 nm) is effective for facial telangiectasia, but postoperative purpura usually causes downtime for about a week. Traditional IPL, on the other hand, causes hardly any downtime, but the results are varied. Recently, narrow-band intense pulsed light (DPL) provided new approaches for treating telangiectasia in hope of achieving long-term improvement with minimal downtime. In our study, 30 patients with facial telangiectasia were recruited and treated with DPL from August 2013 to December 2014. The objective of this study is to investigate the clinical efficacy and safety of DPL in treating facial telangiectasia.
Indocyanine green nanoparticles undergo selective lymphatic uptake, distribution and retention and enable detailed mapping of lymph vessels, nodes and abnormalities
Published in Journal of Drug Targeting, 2018
John C. Kraft, Piper M. Treuting, Rodney J. Y. Ho
The lymphatic vasculature is a distributed, whole-body network of vessels and nodes that converges toward the thoracic duct, which runs ventrally up the spine in the thoracic cavity. While blood capillaries deliver oxygen and nutrients to cells via the interstitial space, most of the interstitial fluid and its solutes are drained by lymphatic capillaries rather than being reabsorbed into the blood through venous capillaries [1]. As a whole, the lymphatic system is central to fluid homeostasis, immune function, fat absorption in the gut, reverse cholesterol transport and disease [2]. Blockages of lymph drainage and flow (e.g. due to surgical interventions such as mastectomy) can lead to peripheral oedema (lymphedema), which afflicts 4% of the world’s population [3]. Moreover, cancer and microbes exploit and block lymphatic pathways [4], and HIV infects cells of lymph nodes (LNs) throughout the body [5]. Despite the prevalence of occluded lymph flow and the lymphatic system being central to devastating diseases, there exists a gap in our ability to safely and efficiently visualise in detail and deliver drug to the extensive and distributed network of lymph vessels and nodes in the body. This is largely because current imaging and drug targeting agents do not widely distribute through and are not sufficiently retained within lymph vessels, nodes and overall lymphatic networks.
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.