Temperature skin regulation

The temperatures monitored in Fig. 5.2 are used by the brain to regulate shivering, blood flow to the skin, and sweating. The sensed temperatures also contribute to our overall feelings of warmth and other thermal sensations. 7 hermal sensation (TS) can be predicted over a wide range of activities (0.8 to 4 met) from simple deviations in the mean body temperature (T j,) from the mean bodv temperature when the person feels neither warm or cool but neutral (Fig. 5.2). 

The thermal parameters for comfort should be relatively uniform both spatially and temporally. Variations in heat flow from the body make the physiological temperature regulation more difficult. Nonuniform thermal conditions can lead to nonuniform skin temperatures. The active elements of the regulatory system may need to make more adjustments and work harder in order to keep thermal skin and body temperatures stable. To avoid discomfort from environmental nonuniformities, the temperature difference between feet and head should be less than about 3 °C (Fig. 5.9) and the mean surface temperature or radiant difference from one side of the body to the other should not he greater then about 10 °C. 

The complex interplay of physicochemical and biological charactenstics that regulate the all important rate at which fluorocarbons may migrate within and finally leave the body, through the lungs and the skin, is not yet completely understood Certainly, variables are involved, such as vapor pressure, solubility m body tissues, molecular size and shape, lipid solubility, electron configuration, and critical soluQon temperatures [16, 17]... 

General functions of the skin are outlined in Table 1. These functions include containment of tissues and organs, multifaceted protections, environmental sensing, and body temperature regulation. Some skin functions are inextricably entwined. For instance, containment and the barrier functions are to some extent inseparable. Active sweating is accompanied by increased peripheral blood flow, which in turn is tied in with greater nourishment of the cells of the skin as needed to promote their proliferation, differentiation, and specialization. 

The veins of skin are organized along the same lines as the arteries in that there are both subpapillary and subdermal plexuses [11]. The main arteriole communication to these is the capillary bed. Copious blood is passed through capillaries when the core body is either feverish or overheated, far more than needed to sustain the life force of the epidermis, and this rich perfusion lends a red coloration to skin. When there is opposite physiological need, the capillary bed is short-circuited as blood is passed directly into the venous drainage by way of the arteriovenous anastomoses. Fair skin noticeably blanches when this occurs. These mechanisms act in part to regulate body temperature and blood pressure. 

Temperature influences skin permeability in both physical and physiological ways. For instance, activation energies for diffusion of small nonelectrolytes across the stratum corneum have been shown to lie between 8 and 15 kcal/mole [4,32]. Thus thermal activation alone can double the rate skin permeability when there is a 10°C change in the surface temperature of the skin [33], Additionally, blood perfusion through the skin in terms of amount and closeness of approach to the skin s surface is regulated by its temperature and also by an individual s need to maintain the body s 37° C isothermal state. Since clearance of percuta-neously absorbed drug to the systemic circulation is sensitive to blood flow, a fluctuation in blood flow might be expected to alter the uptake of chemicals. No clear-cut evidence exists that this is so, however, which seems to teach us that even the reduced blood flow of chilled skin is adequate to efficiently clear compounds from the underside of the epidermis. 

During a marathon, the rate of heat production can be more than tenfold greater than at rest and sufficient to raise the core body temperature by 1°C every eight minutes, if no cooling occurs. The core temperature is normally regulated so precisely that it does not rise more than about 1°C. The main mechanism for cooling is evaporation from the skin. Endurance runners can produce one litre of sweat per hour which removes about 2.4 MJ of heat. The energy used and therefore converted into heat in a marathon is about 12 MJ... 

If these processes produce too much heat, the body attempts to lose heat by vasodilation within the skin (via convection) and sweating (via evaporation of the water in the sweat). Both are well-known characteristics of fever. The patient s experience of alternate shivering and sweating (so well described by Hippocrates) probably represents an impairment of the thermorequlatory centre in the hypothalamus that regulates the balance between heat loss and heat production, resulting in fluctuations in body temperature. 

In air, temperature, relative humidity, barometric pressure, and air currents not only modulate the movement of molecules from the source but also affect odor reception once the molecules have arrived near the receptors. The evaporation of an odor from a surface such as animal skin, a scent mark, or vegetation is regulated by air temperature, relative humidity, the porosity of the surface, and other compounds present (Regnier and Goodwin, 1977 Figs. 1.1 and 1.2). 

Heat dissipation can also be achieved by increased production of sweat, because evaporation of sweat on the skin surface consumes heat (evaporative heat loss). Shivering is a mechanism to generate heat. Autonomic neural regulation of cutaneous blood flow and sweat production permit homeostatic control of body temperature (A). 

Besides covering and protecting the body, the other function of the skin are regulation of the body temperature (ca. 37°C) and also controlling penetration of the body by sunlight, liquids, solid materials, etc. The human skin is composed of four layers of different tissue ... 

In a sedentary state body temperature can be regulated by varying the amount of clothing worn or by adjusting the surrounding temperature. However, these mechanisms are inadequate when strenuous work is undertaken and temperature regulation must then be achieved by the evaporation of sweat from the surface of the skin. 

Alcohol produces dilation of the skin vessels, flushing, and a sensation of warmth. Alcohol also interferes with the normal cutaneous vasoconstriction in response to cold. The body heat is therefore lost very rapidly and the internal temperature consequently falls. At toxic alcohol levels, the hypothalamic temperature-regulating mechanism becomes depressed and the fall in body temperature becomes pronounced. For these reasons, consuming alcoholic beverages for the purpose of keeping warm in cold weather is obviously irrational. 

A classic example is the control of arterioles in the skin [7]. The arterioles participate in blood pressure control, and in case of acute cardiac failure or blood loss, the arterioles contract in order to reserve the cardiac output for the vital organs. But the arterioles also participate in temperature regulation [7]. When they contract, heat loss from the body is minimized, so a patient in shock risks getting hyperthermia, because the blood pressure control overrides the temperature control. Moreover, the same arterioles are fundamental for the regulation of local nutritional flow to the skin and also to the smooth muscle in the vessel walls [7]. So even if skin nutrition is given a low priority compared with blood pressure, the smooth muscle has to get some nutrition to keep up the same blood pressure control. This example shows not only the complexity of biological control, but also how difficult it is to intervene when a system is malfunctioning. 

Smart textiles from chemical finishing Temperature protection by coating with phase change materials (PCMs) foam, quicker healing/recovery of wounds by moisture regulation, release of drugs on demand by signals from the skin... 

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