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The Cause of Pressure Sores
Published in J G Webster, Prevention of Pressure Sores, 2019
The dermis is a vascular layer that lies beneath the epidermis. The surface between the dermis and the epidermis is usually uneven, because the epidermis has ridges projecting inward and the dermis has finger-like papillae passing into the spaces between the ridges (Hole 1987). These papillae increase the mechanical strength of the skin, binding the epidermis to the underlying tissues. The dermis is composed of mostly fibrous connective tissue that includes tough collagenous fibers and elastic fibers that are surrounded by a gel-like substance (Hole 1987). This also adds to the strength of skin. The dermis ranges from 0.5 mm thick in the eyelids to 3.0 mm on the soles, the average being 1.0 to 2.0 mm thick. It contains two kinds of sweat glands, the apocrine and eccrine glands. Eccrine glands are connected to pores on the surface of the epidermis. They respond throughout life by secreting sweat to cool the skin’s surface when the body’s temperature becomes elevated due to environmental heat or physical exercise. The apocrine glands are connected to hair follicles. They occur mostly in the armpits and groin. Other structures contained in the dermis include the lymphatics, nerves, hair follicles, smooth muscle fibers, and striated muscle fibers.
Behind the Scenes
Published in Ivana Špelić, Alka Mihelić-Bogdanić, Anica Hursa Šajatović, Standard Methods for Thermal Comfort Assessment of Clothing, 2019
Ivana Špelić, Alka Mihelić-Bogdanić, Anica Hursa Šajatović
The evaporative heat loss occurs independently of thermoregulatory control at the ambient temperature below 303.15 K (30°C). It accounts for 9 to 10 W/m2 and corresponds to evaporation of about 13 to 15 g/(m2h), one-half of which is moisture lost through breathing, and the other half is lost through insensible perspiration. As the ambient temperature increases, the body depends more and more on the evaporation of sweat to achieve heat balance. The two histologic types of sweat glands are eccrine (the dominant type in all human populations with about 2.5 million.) and apocrine sweat glands. The eccrine sweat glands are more important in human thermoregulation, and they are controlled by cholinergic stimulation through postganglionic sympathetic C fibres that release acetylcholine (ACh) rather than norepinephrine. This elicits secretion of the precursor fluid. The apocrine sweat is more viscous and produced in much smaller amounts than eccrine sweat although the exact function of the apocrine glands is unclear, though they are thought to represent scent glands. A healthy man unacclimatised to heat can secrete up to 1.5 L/h of sweat, and the secretion capacity of the individual glands can change due to heat acclimatisation (Witzmann, 2013).
How we experience indoor and outside climates
Published in Karl H.E. Kroemer, Fitting the Human, 2017
If heat transfer to the outside is still not sufficient, the body activates its sweat glands because the evaporation of the produced sweat cools the skin. Sweating reduces the water content of the body, which must be replenished by water° through drinking and eating. The recruitment of sweat glands from different areas of the body varies, and large differences in the ability to sweat exist among individuals: most adults have two to four million sweat glands in their skin, but some persons have fewer. During acclimation, the body learns to control its sweating. The amount of sweat developed and evaporated depends on the number of glands, the clothing, the environment, the work requirements, and the individual’s acclimatization. Reducing physical effort
An insight on topically applied formulations for management of various skin disorders
Published in Journal of Biomaterials Science, Polymer Edition, 2022
Amit K. Jain, Sakshi Jain, Mohammed A. S. Abourehab, Parul Mehta, Prashant Kesharwani
Various functions of human skin are summarized in Figure 1. Skin is the principal permeation barrier protecting humans both from excessive water loss and against various harmful microorganisms and foreign toxic materials. Briefly the keratinized epithelium of skin forms a waterproof layer to protect the deeper layers from attack by micro-organisms or any physical or chemical agents. To protect our skin from attack of various bacteria, virus and microorganism various specialized cells in the skin work closely with the immune system to fight against attack by these foreign pathogens. Those cells include epidermal dendritic cells, phagocytic cells and langerhans cells [3]. The sweat glands excrete perspiration through skin pores. Nitrogenous wastes (urea, uric acid), salts, and water make up perspiration. Skin is also involved in regulating body temperature in variable climatic conditions. There are four routes of heat loss through skin evaporation, convection, conduction and radiation. When skin temperature is higher than surrounding temperature it results in loss of heat through conduction and convection, and when surrounding temperature is higher than skin temperature it results in absorption of heat by conduction and convection. In both process of heat loss or heat gain, evaporation plays crucial role in controlling the body temperature.
Moisture transmission behaviour of individual component and multi-layered fabric with sweat and pure water
Published in The Journal of The Textile Institute, 2018
Arunangshu Mukhopadhyay, Agya Preet, Vinay Midha
Material constitution and structure of each layer in multilayer clothing system plays an important role in influencing the transmission of moisture from the fabric. The differences in the components of layered structure may alter thermoregulatory responses, thermal strain, and thermal comfort during work and rest periods (Atalay, KursunBahadir, & Kalaoglu, 2015). In order to improve the comfort of clothing, there is a need to investigate the liquid and moisture management properties of different layering component of outdoor apparels. An equally important aspect is composition of moisture as moisture stored by garment as a result of absorption of sweat or as result of absorption of moisture from humid environment, is not pure water but also contains other ingredients. Sweat is a clear colourless liquid secreted by the eccrine sweat glands which lie in dermal layer of the skin. It consists primarily of water (~99%) in addition to salts, fats, urea, lactic acid, carbohydrates and minerals such as potassium, calcium, magnesium, iron (Boguslawska-Baczek & Hes, 2014). During prolonged exercise or vigorous activity, two major solute excreted in sweat are lactate and ammonia whose respective concentrations are 10–15 and 80–150 times greater than in plasma. The lactate in sweat is derived mainly from anaerobic glycolysis within the sweat glands (Meyer, Laitano, Bar-Or, McDougall, & Heigenhauser, 2007). The high sweat ammonia may originate from the sweat glands itself or by diffusion from plasma. The widely reported variability in sweat lactate and ammonia may be accounted for their dependence on factors such as sweating rate, sweating acidity and transport of other ions in the duct of sweat gland. It is found that males have higher sweating rate than females because of difference in average skin surface area and fat content of the body. The sweating rate is also dependent on the body core temperature. In females the core temperature falls during the oestrogen phase of menstrual cycle (Zubieta-Calleja & Paulev, 2004).
Technical textiles for military applications
Published in The Journal of The Textile Institute, 2020
R. G Revaiah, T. M. Kotresh, Balasubramanian Kandasubramanian
Human body is governed by a complex, non-linear thermoregulatory mechanism. It is, therefore, important to know the thermal load under various workloads, environmental conditions and the type of clothing worn (Parsons, 2014). When exposed to extreme temperatures, humans exhibit physiological (Kurz, 2008) and behavioural response to the environmental conditions (McKinley, Martelli, Pennington, Trevaks, & McAllen, 2018); both interact systematically with the environmental condition to ensure survival and comfort of the stressed individual. The motivation for behavioural thermoregulation depends on the magnitude of change of mean skin temperature (Vargas et al., 2018). The powerful behavioural human thermoregulation (refers to addition and removal of cloths, seek shade/shelter, slowing down, discontinuation of strenuous work etc.) is lost in military operations (such as CBRN, environment) as there is a huge motivation and urgency to complete the assigned task at the earliest. The clothing cannot be removed and the combat positions cannot be changed in battle tank or helicopter, CBRN or ballistic environment. This leaves physiological thermoregulation as sole important mode of controlling the body temperature. The human body temperature, controlled by the hypothalamus, is divided into two regions; The core temperature refers to the temperature of the interior of the body, which always remains constant at 37 °C with a very small variation of 0.5 °C. The temperature of the tissue just below the skin, called shell temperature, varies greatly with the ambient temperature (Cooper, 1996). When the temperature of the skin reaches 37 °C, sweating begins (Wilusz, 2008). Cholinergic sympathetic nerves stimulate sweat glands to secret sweat onto the surface of the skin. About 1.5 L of sweat per hour is lost in case of a fresh inductee, while heat acclimatized person can lose up to 3.5 L of sweat (although for a short duration without pushing sweat glands towards fatigue mode). Baker, Barnes, Anderson, Passe, and Stofan (2016) have generated normative data for whole body sweating rate from 506 athletes. While preparing Alberto Salazar for 1984 hot summer marathon, Armstrong, Hubbard, Jones, and Daniels (1986) reported 3.71 L of sweat, the highest sweating rate ever measured in an individual (L. E.). During sweating, up to 0.5% of precious body salt is also lost. One gram of sweat evaporating at skin temperature takes away 580 calories of heat. However, the rate of evaporation of the sweat from skin surface depends on convection and relative humidity of air. Insensible sweating leads to physiological exertion and loss of important water (Kenefick & Cheuvront, 2016). The visualization of body thermoregulation by Infrared imaging is also reported in the literature (Bouzida, Bendada, & Maldague, 2009).