Body Control Temperatures

Body temperatures are primarily sensed by temperature sensors in the hypothalamus near the center of the brain. Arterial blood flowing over and near the hypothalamus gives it information about the average thermal condition of 

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). 

During transients the rate of change of mean body temperature can have a strong effect on thermal sensation. 

T- Hypothalamus - center for temperature control (surrotmjed l y flov ing blood] 

FIGURE 5.2 Temperature sensors for ternperature regulation and thermal sensation. 

---

The manner in which the human body controls temperature is important not only under normal conditions but also during exercise, fever, and trauma induced by injury, bums, surgery, etc. Over longer periods of time, hormones, adaptation, and acclimatization can exert significant effects. Although the work reported here is limited to normal short-term regulation, it is possible that the other situations can be explained in terms of modifications of the basic mechanism. 

Disruption of these defense mechanisms can lead to bacterial colonization or viral infection. Mucus temperature is important in controlling respiratory infections because decreasing below central body core temperature not only impairs ciliary movement,hut also enhances viral replication,- greatly increasing the likelihood of respiratory infection. Drying of airway mucus also increases the possibility of respiratory infection by reducing mucus thickness and impairing mucociliary clearance, i- i--... 

A variety of assays are being reported in the literature which measure the interaction of cells with biomaterials, be they surfaces of various textures or micro or nano-particulates. While considerable attention has been paid to proper preparation of the materials and their surfaces, less has been paid to the cells used as probes in such assays. We suggest that where possible, primary human cell cultures at relatively low PD numbers from isolation are used, of a cell type directly relevant to the material application, or in toxicity studies, the exposed tissue. We suggest very significantly erroneous conclusions may be drawn from assays using inappropriate cells. If sufficient quantities of low PD primaries are not available, it may be possible to use telomerase transfected cells with extended lifespan, but these must first be verified against the non-transfected cells in the assay to be employed. Furthermore, care must be taken to conduct such assays at a controlled temperature, preferably at the temperature the material will be subjected to in the body. 

Controlled-release technology based on the external temperature-activated release can find application in diverse industrial fields. In the pharmaceutical area, for example, the deviation of the body temperature from the normal temperature (37°C) in the physiological presence of the pathogens or pyrogens can be utilized as a useful stimulus that induces the release of the therapeutic agents from a thermosensitive controlled-release system. Physically controlled temperature using a heat source such as the microwaves from outside the body can also be used for temperature-activated antitumor drug release combined with the local hyperthermic treatment of cancer. 

Evaporation, which requires energy, is the method by which your body controls its temperature. When you sit outside on a hot day or when you exercise, your body releases an aqueous solution called sweat from glands in your skin. Water molecules in sweat can absorb heat energy from your skin and evaporate. Excess heat is carried from all parts of your body to your skin by your blood. Evaporation of water also explains why a swim in cool ocean water is so refreshing. Not only is heat transferred from you to the cooler water while you are in the water, but water molecules left on your skin continue to cool you by evaporation once you come out of the water. The salts that remain when sea water evaporates often leave a white residue on your skin. To compare the rates of evaporation for different liquids, do the CHEMLAB at the end of the chapter. 

Operational Characteristics Feed enicis at higher saturation temperature than is maintained in the crystallizer body. Ciystallizer temperature, product recoveiy, and sluny density are regulated by vacuum control. Heat of ciystallization and the sensible hest of the feed are removed by evaporation and condensation of solvent. The condensate may either be removed or a portion or all returned. 

Perspiration Evaporation is one way your body controls its temperature. When you become hot, your body releases sweat from glands in your skin. Water molecules in sweat can absorb heat energy from your skin and evaporate. Excess heat is carried from all parts of your body to your skin by your blood. 

The skin protects the body from the environment, aids in controlling the body s temperature, and prevents the body s fluid loss. 

Animals and Study Design. This experimental protocol was approved by the Animd Care and Use Committee of the National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health. Time pregnant, female Long-Evans rats at d 3 of gestation were obtained firom Charles River (Portage, Ml) and maintained in our animal facility under conventional conditions with controlled temperature (23 1°C) and illumination (12 h 0600-1800 h). An n-3 adequate diet (maternal diet) containing 3.1% a-linolenic acid and water was consumed ad libitum (Table 1). Litters to be used in this experiment were selected on the basis of body weight and age so that they were within a 12-h time window. At postnatal d 2, three... 

A fabric sample measuring 300 x300mm is mounted on a square porous plate which is heated to a constant temperature that approximates body skin temperature (e.g. 35 °C).The plate temperature is measured by the sensor sandwiched directly underneath the plate surface. The whole apparatus is housed in a chamber so that the environmental conditions can be carefully controlled. Air speed above the specimen is regulated at 1 m/s. After steady state conditions are reached, the total evaporative resistance of the fabric is calculated by the following ... 

Passageways within the body of a mold through which a cooling or heating medium (e.g., chilled water, steam, hot oil, or other fluids) can be circulated to control temperature on the mold surface. 

SMPs have most notably been promoted because of their potential in minimally invasive surgery, where a compacted device could be passed through a smaller incision and deployed to its full shape once inside the body [40]. For biomedical devices, the heating of polymer to activate SMEs has been proposed by body, temperature, optical/laser heating, and remote inductive heating [41]. As each of these thermal activation methods is possible within the body, control over SMP geometry is possible with implantable devices. 

Snellen, Chang, and Smith (1983) described a special adiabatic whole-body calorimeter for humans. The calorimeter consists of three metal cylinders inside one another. The iimermost cylinder (157 cm high, 152 cm in diameter) serves as a radiation shield. The other two cylinders (183 and 193 cm high, 168 and 193 cm in diameter) form the adiabatic shield against the environment. The calorimeter works as follows. A continuous air flow (26m min ) with exactly controlled temperature and humidity is injected into the calorimeter, and half of the flow rate between the first and the second cylinder and via the proper inlet slots goes into the... 

The human body is itself is an automatic thermo-regulated organism. The body constantly generates heat, CO2 and HjO by the metabolism of food and muscle activity. The human body controls the release speed of heat by blood vessel dilatation or constriction, muscle and sweat gland activity, etc., and then regulates the body temperature. 

---