question: Why do cold drinks feel more hydrating than hot drinks?
comment: The further away from body temperature (98.6 degrees Fahrenheit) something is, the more obviously we can sense it. I imagine drinking boiling water would be equally as refreshing if our nerves didn’t send pain signals.
passages: Two laws governing the osmotic pressure of a dilute solution were discovered by the German botanist W. F. P. Pfeffer and the Dutch chemist J. H. van’t Hoff:
  
  BULLET::::1. The osmotic pressure of a dilute solution at constant temperature is directly proportional to its concentration.
  
  BULLET::::2. The osmotic pressure of a solution is directly proportional to its absolute temperature.
   The distribution of blood flow to the tissues is variable and subject to a variety of influences. When the flow is locally high, that area is dominated by perfusion, and by diffusion when the flow is low. The distribution of flow is controlled by the mean arterial pressure and the local vascular resistance, and the arterial pressure depends on cardiac output and the total vascular resistance. Basic vascular resistance is controlled by the sympathetic nervous system, and metabolites, temperature, and local and systemic hormones have secondary and often localised effects, which can vary considerably with circumstances. Peripheral vasoconstriction in cold water decreases overall heat loss without increasing oxygen consumption until shivering begins, at which point oxygen consumption will rise, though the vasoconstriction can persist.
   The distribution of blood flow to the tissues is variable and subject to a variety of influences. When the flow is locally high, that area is dominated by perfusion, and by diffusion when the flow is low. The distribution of flow is controlled by the mean arterial pressure and the local vascular resistance, and the arterial pressure depends on cardiac output and the total vascular resistance. Basic vascular resistance is controlled by the sympathetic nervous system, and metabolites, temperature, and local and systemic hormones have secondary and often localised effects, which can vary considerably with circumstances. Peripheral vasoconstriction in cold water decreases overall heat loss without increasing oxygen consumption until shivering begins, at which point oxygen consumption will rise, though the vasoconstriction can persist.
   Blood flow is directly influenced by the thermodynamics of the body. Changes in temperature affect the viscosity and surface tension of the blood, altering the minimum blood flow rate. At high temperatures the minimum flow rate will decrease and the capillary will expand. This allows heat transfer through the increased surface area of the inner capillary lining and through increased blood flow. At low temperatures the minimum flow rate will increase and the capillary will constrict. This restricts blood flow and decreases the surface area of the capillary, reducing heat transfer.
   The concentration of copeptin in the blood circulation ranges from 1 to 12 pmol/L in healthy individuals. The levels of copeptin are slightly higher in men than in women and are not influenced by age. In response to serum osmolality fluctuations, the kinetics of copeptin are comparable to those of vasopressin. For example, patients with an electrolyte disorders such as diabetes insipidus with very low vasopressin concentrations also show very low copeptin concentrations in blood plasma. On the other hand, patients suffering from syndrome of inappropriate antidiuretic hormone secretion show high concentrations of both vasopressin and copeptin.
   Taking advantage of the cooling properties of water may help attenuate the consequences of heat sensitivity. In a study done by White et al. (2000), exercise pre-cooling via lower body immersion in water of 16–17 °C for 30 minutes allowed heat sensitive individuals with MS to exercise in greater comfort and with fewer side effects by minimizing body temperature increases during exercise. Hydrotherapy exercise in moderately cool water of 27–29 °C water can also be advantageous to individuals with MS. Temperatures lower than 27 °C are not recommended because of the increased risk of invoking spasticity.
  
  Section::::History.
   For people who are alert and able to swallow, drinking warm sweetened liquids can help raise the temperature. Many recommend alcohol and caffeinated drinks be avoided. As most people are moderately dehydrated due to cold-induced diuresis, warmed intravenous fluids to a temperature of are often recommended.
  
  Section::::Management.:Cardiac arrest.
   A great deal of the bloodstream is made up of humor of “Blood” which is warm and wet. It is noteworthy that the body lives on “Blood” as it keeps the body warm and moist as warmth and humidity are indicatives of being alive.
  
  Section::::Humors.:Blood.:Excessive “Blood” symptoms.
   Blood flow to the muscles is lower in cold water, but exercise keeps the muscle warm and flow elevated even when the skin is chilled. Blood flow to fat normally increases during exercise, but this is inhibited by immersion in cold water. Adaptation to cold reduces the extreme vasoconstriction which usually occurs with cold water immersion.
   Section::::Thermodynamics.
  
  The ambient temperature of the body directly affects blood flow through microvasculature. Changes in temperature affect the viscosity of blood and the surface tension. Surface tension decreases with increasing temperature, decreasing the minimum flow rate (see Surface Tension). The decrease in minimum flow rate by higher temperatures allows more blood to flow and dissipate heat throughout the body. Temperature greatly affects blood flow by influencing the diameter of flow. Decreases and increases in temperature trigger vasoconstriction and vasodilation respectively.
  
  Section::::Thermodynamics.:Vasoconstriction.
   Because the ground coffee beans in cold-brewed coffee never come into contact with heated water, the process of leaching flavor from the beans produces a chemical profile different from conventional brewing methods. Coffee beans contain a number of constituent parts that are more soluble at higher temperatures, such as caffeine, oils and fatty acids. Brewing at a lower temperature results in lower acidity and lower caffeine content when brewed in equal volume. It is around 65 to 70 percent less acidic than hot drip coffee or espresso, per part. Although less caffeine is extracted with the cold brew method, a higher coffee-to-water ratio is often used, between 2 and 2 1/2 times. This may compensate for this difference in solubility, resulting in a brew with equal, if not more, caffeine (although this is unlikely).
   Another issue with aggressive fluid resuscitation is the potential for hypothermia if fluids that are stored at room temperature are used. If these fluids are not warmed prior to infusion (which sometimes time does not permit for), this can result in a significant drop in core body temperature. Hypothermia is associated with many problems including bleeding disorder, organ failure, and hypotension, and is one of the three components in the "Triad of Death" that is feared by all trauma specialists.
   The endocrine system is affected largely by many internal and external stimuli. One internal stimulus that causes hormone release is blood pressure. Hypotension, or low blood pressure, is a large driving force for the release of vasopressin, a hormone which causes the retention of water in the kidneys. This process also increases an individuals thirst. By fluid retention or by consuming fluids, if an individual's blood pressure returns to normal, vasopressin release slows and less fluid is retained by the kidneys. Hypovolemia, or low fluid levels in the body, can also act as a stimulus to cause this response.
   Conversely, when a tissue is less metabolically active, it produces fewer metabolites which are simply washed away in blood flow.
  
  Since most of the common nutrients in the body are converted to carbon dioxide when they are metabolized, smooth muscle around blood vessels relax in response to increased concentrations of carbon dioxide within the blood and surrounding interstitial fluid. The relaxation of this smooth muscle results in vascular dilation and increased blood flow.
   If the hot fluid had a much larger heat capacity rate, then when hot and cold fluids went through a heat exchanger, the hot fluid would have a very small change in temperature while the cold fluid would heat up a significant amount. If the cool fluid has a much lower heat capacity rate, that is desirable. If they were equal, they would both change more or less temperature equally, assuming equal mass-flow per unit time through a heat exchanger. In practice, a cooling fluid which has both a higher specific heat capacity and a lower heat capacity rate is desirable, accounting for the pervasiveness of water cooling solutions in technology—the polar nature of the water molecule creates some distinct sub-atomic behaviors favorable in practice.
   BULLET::::- After long-term of Jjimjil, body fat percentage of old woman decreased, but in case of old man, there was no effective change.
  
  BULLET::::- Every age of human, the heat-resisting ability has been increased. (Good Effect)
  
  BULLET::::- But, the cold-resisting ability has been decreased. However, if we control the time, power, and the repetition well, especially when we rest in the ice room during Jjimjil. It can reduce the decrease of cold-resisting ability and even we can increase it.
  
  Section::::Food.
  
  BULLET::::- Iced Sikhye () is a sweet rice beverage.
   BULLET::::- Arteriolar vasodilation occurs. The smooth muscle walls of the arterioles relax allowing increased blood flow through the artery. This redirects blood into the superficial capillaries in the skin increasing heat loss by convection and conduction.
  
  Section::::In hot and humid conditions.
   Normal blood plasma behaves like a Newtonian fluid at physiological rates of shear. Typical values for the viscosity of normal human plasma at 37 °C is 1.4 mN·s/m. The viscosity of normal plasma varies with temperature in the same way as does that of its solvent water; a 5 °C increase of temperature in the physiological range reduces plasma viscosity by about 10%.
  
  Section::::Blood.:Osmotic pressure of plasma.
   In fluids with relatively low viscosity there is an almost linear, inverse relationship between temperature and surface tension. The decrease in surface tension increases the wettability of the capillary walls, making it easier for the fluid to flow through the capillary.
   BULLET::::- Pressure Vessel - A sealed pressure vessel is filled at a lower pressure within the water cooler. As such, the water does not come into contact with the atmosphere, allowing a larger amount of cold water (depending on the size of the tank) to be dispensed at the expense of a slower cooling system.
   Section::::Cold-induced diuresis.
  
  Cold-induced diuresis, or cold diuresis, is a phenomenon that occurs in humans after exposure to a hypothermic environment, usually during mild to moderate hypothermia. It is currently thought to be caused by the redirection of blood from the extremities to the core due to peripheral vasoconstriction, which increases the fluid volume in the core. Overall, acute exposure to cold is thought to induce a diuretic response due to an increase mean arterial pressure.
   Section::::Physiological adaptations.:Heat.
  
  The only mechanism the human body has to cool itself is by sweat evaporation. Sweating occurs when the ambient air temperatures is above 28 °C (82 °F) and the body fails to return to the normal internal temperature. The evaporation of the sweat helps cool the blood beneath the skin. It is limited by the amount of water available in the body, which can cause dehydration.
   There are limitations in the use of cooling crystallization:
  
  BULLET::::- Many solutes precipitate in hydrate form at low temperatures: in the previous example this is acceptable, and even useful, but it may be detrimental when, for example, the mass of water of hydration to reach a stable hydrate crystallization form is more than the available water: a single block of hydrate solute will be formed – this occurs in the case of calcium chloride);
   BULLET::::- Destination spa
  
  BULLET::::- Enema
  
  BULLET::::- Finnish sauna
  
  BULLET::::- Halliwick
  
  BULLET::::- Hot tub
  
  BULLET::::- Mineral spring
  
  BULLET::::- Sebastian Kneipp
  
  BULLET::::- Spa
  
  BULLET::::- Spa bath
  
  BULLET::::- Spa town
  
  BULLET::::- Spotted Lake ("Kliluk")
  
  BULLET::::- Steam shower
  
  BULLET::::- Thalassotherapy
  
  Section::::Notes.
   Blood circulation transports heat throughout the body, and adjustments to this flow are an important part of thermoregulation. Increasing blood flow to the surface (e.g., during warm weather or strenuous exercise) causes warmer skin, resulting in faster heat loss. In contrast, when the external temperature is low, blood flow to the extremities and surface of the skin is reduced and to prevent heat loss and is circulated to the important organs of the body, preferentially.
  
  Section::::Physiology.:Rate of blood flow.
  