question: How and where does your body heats itself up and how does it carry the heat to every inch of your body?
comment: The metabolic activity within every cell, the use of chemical energy that makes every cell function, releases heat as a byproduct. This heats every living cell of the body, but also the blood flowing through our bodies tends to distribute this heat fairly well (less effectively to the extremities of course).
passages: Another commonly considered model is the heat pump or refrigerator. Again there are four bodies: the working body, the hot reservoir, the cold reservoir, and the work reservoir. A single cycle starts with the working body colder than the cold reservoir, and then energy is taken in as heat by the working body from the cold reservoir. Then the work reservoir does work on the working body, adding more to its internal energy, making it hotter than the hot reservoir. The hot working body passes heat to the hot reservoir, but still remains hotter than the cold reservoir. Then, by allowing it to expand without doing work on another body and without passing heat to another body, the working body is made colder than the cold reservoir. It can now accept heat transfer from the cold reservoir to start another cycle.
   Although Carathéodory himself did not state such a definition, following his work it is customary in theoretical studies to define heat, , to the body from its surroundings, in the combined process of change to state from the state , as the change in internal energy, , minus the amount of work, , done by the body on its surrounds by the adiabatic process, so that .
   The principles of heat transfer in engineering systems can be applied to the human body in order to determine how the body transfers heat. Heat is produced in the body by the continuous metabolism of nutrients which provides energy for the systems of the body. The human body must maintain a consistent internal temperature in order to maintain healthy bodily functions. Therefore, excess heat must be dissipated from the body to keep it from overheating. When a person engages in elevated levels of physical activity, the body requires additional fuel which increases the metabolic rate and the rate of heat production. The body must then use additional methods to remove the additional heat produced in order to keep the internal temperature at a healthy level.
   Section::::Heat transfer.
  
  Section::::Heat transfer.:Heat transfer between two bodies.
  
  Referring to conduction, Partington writes: "If a hot body is brought in conducting contact with a cold body, the temperature of the hot body falls and that of the cold body rises, and it is said that a "quantity of heat" has passed from the hot body to the cold body."
  
  Referring to radiation, Maxwell writes: "In Radiation, the hotter body loses heat, and the colder body receives heat by means of a process occurring in some intervening medium which does not itself thereby become hot."
   Section::::Gene structure.
   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.
   In order to ensure that one portion of the body is not significantly hotter than another portion, heat must be distributed evenly through the bodily tissues. Blood flowing through blood vessels acts as a convective fluid and helps to prevent any buildup of excess heat inside the tissues of the body. This flow of blood through the vessels can be modeled as pipe flow in an engineering system. The heat carried by the blood is determined by the temperature of the surrounding tissue, the diameter of the blood vessel, the thickness of the fluid, velocity of the flow, and the heat transfer coefficient of the blood. The velocity, blood vessel diameter, and the fluid thickness can all be related with the Reynolds Number, a dimensionless number used in fluid mechanics to characterize the flow of fluids.
   Section::::Control system.
  
  The core temperature of a human is regulated and stabilized primarily by the hypothalamus, a region of the brain linking the endocrine system to the nervous system, and more specifically by the anterior hypothalamic nucleus and the adjacent preoptic area regions of the hypothalamus. As core temperature varies from the set point, endocrine production initiates control mechanisms to increase or decrease energy production/dissipation as needed to return the temperature toward the set point (see figure).
  
  Section::::In hot conditions.
   In most cases, as the body is exposed to physical activity, the core temperature of the body tends to rise as heat gain becomes larger than the amount of heat lost. “The factors that contribute to heat gain during exercise include anything that stimulate metabolic rate, anything from the external environment that causes heat gain, and the ability of the body to dissipate heat under any given set of circumstances”. In response to an increase in core temperature, there are a variety of factors which adapt in order to help restore heat balance. The main physiological response to an increase in body temperature is mediated by the thermal regulatory center located in the hypothalamus of the brain which connects to thermal receptors and effectors. There are numerous thermal effectors including sweat glands, smooth muscles of blood vessels, some endocrine glands, and skeletal muscle. With an increase in the core temperature, the thermal regulatory center will stimulate the arterioles supplying blood to the skin to dilate along with the release of sweat on the skin surface to reduce temperature through evaporation. In addition to the involuntary regulation of temperature, the hypothalamus is able to communicate with the cerebral cortex to initiate voluntary control such as removing clothing or drinking cold water. With all regulations taken into account, the body is able to maintain core temperature within about two or three degrees Celsius during exercise.
   The resting human body generates about two-thirds of its heat through metabolism in internal organs in the thorax and abdomen, as well as in the brain. The brain generates about 16% of the total heat produced by the body.
   The human body has two methods of thermogenesis, which produces heat to raise the core body temperature. The first is shivering, which occurs in an unclothed person when the ambient air temperature is under 25 °C (77 °F). It is limited by the amount of glycogen available in the body. The second is non-shivering, which occurs in brown adipose tissue.
   BULLET::::- Eccrine sweat glands under the skin secrete sweat (a fluid containing mostly water with some dissolved ions), which travels up the sweat duct, through the sweat pore and onto the surface of the skin. This causes heat loss via evaporative cooling; however, a lot of essential water is lost.
   The CNS can be divided into the brain and spinal cord. The CNS processes many different kinds of incoming sensory information. It is also the source of thoughts, emotions, and memories. Most signals that stimulate muscles to contract and glands to secrete originate in the CNS. The spinal cord and spinal nerves contribute to homeostasis by providing quick reflexive responses to many stimuli. The spinal cord is the pathway for sensory input to the brain and motor output from the brain. The brain is responsible for integrating most sensory information and coordinating body function, both consciously and unconsciously.
   Heat also effects the viscosity of a fluid inside a capillary. An increase in heat decreases the viscosity of the lumenal fluid. A good example of this action can be observed in the human body during exercise. When a human is exercising, there is an increase in the metabolic rate inside the muscles, creating an increase in heat production. The increase in heat is detected by thermoreceptors, a type of sensory receptor located at various points in body. These receptors send a signal to the brain that tells the body to dilate the blood vessels, including capillaries. This creates a visible change in the number of vessels on the skin. This allows for heat transfer via convection to occur.
   Body heat is generated by metabolism. This refers to the chemical reactions cells use to break down glucose into water and carbon dioxide and, in so doing, generate ATP (adenosine triphosphate), a high-energy compound used to power other cellular processes. Muscle contraction is a type of metabolic process that generates heat energy, and heat is also generated through friction when blood flows through the circulatory system.
   The neural activation mechanisms involved in the regulation of body temperature are largely undefined. It is known that sympathetic pathways are involved in increasing heat production and reducing heat loss and are activated by neurons in the rostal medullary raphe (RMR). These neurons were identified as playing an important role in the elevation of body temperature during both cold exposure and induced fever by observation that hyperpolarization prior to exposure to these conditions inhibits the elevation of body temperature in response.
  
  Section::::Role in thermoregulation.:Febrile response.
   When an energy transfer to or from a body is only as heat, the state of the body changes. Depending on the surroundings and the walls separating them from the body, various changes are possible in the body. They include chemical reactions, increase of pressure, increase of temperature, and phase change. For each kind of change under specified conditions, the heat capacity is the ratio of the quantity of heat transferred to the magnitude of the change. For example, if the change is an increase in temperature at constant volume, with no phase change and no chemical change, then the temperature of the body rises and its pressure increases. The quantity of heat transferred, , divided by the observed temperature change, , is the body's heat capacity at constant volume:
   The square root of the product of thermal conductivity, density, and specific heat capacity is called thermal effusivity, and tells how much heat energy the body absorbs or releases in a certain amount of time per unit area when its surface is at a certain temperature. Since the heat taken in by the cooler body must be the same as the heat given by the hotter one, the surface temperature must lie closer to the temperature of the body with the greater thermal effusivity. The bodies in question here are human feet (which mainly consist of water) and burning coals.
   Section::::Controls of variables.
  
  Section::::Controls of variables.:Core temperature.
  
  Mammals regulate their core temperature using input from thermoreceptors in the hypothalamus, brain, spinal cord, internal organs, and great veins. Apart from the internal regulation of temperature, a process called allostasis can come into play that adjusts behaviour to adapt to the challenge of very hot or cold extremes (and to other challenges). These adjustments may include seeking shade and reducing activity, or seeking warmer conditions and increasing activity, or huddling.
   Section::::Interactome.
   Heat spontaneously flows from a hotter to a colder body. For example, heat is conducted from the hotplate of an electric stove to the bottom of a saucepan in contact with it. In the absence of an external driving energy source to the contrary, within a body or between bodies, temperature differences decay over time, and thermal equilibrium is approached, temperature becoming more uniform.
   BULLET::::- The hair on the skin lie flat, preventing heat from being trapped by the layer of still air between the hair. This is caused by tiny muscles under the surface of the skin called arrector pili muscles relaxing so that their attached hair follicles are not erect. These flat hairs increase the flow of air next to the skin increasing heat loss by convection. When environmental temperature is above core body temperature, sweating is the only physiological way for humans to lose heat.
   Section::::Pathophysiology.
  
  Heat is primarily generated in muscle tissue, including the heart, and in the liver, while it is lost through the skin (90%) and lungs (10%). Heat production may be increased two- to four-fold through muscle contractions (i.e. exercise and shivering). The rate of heat loss is determined, as with any object, by convection, conduction, and radiation. The rates of these can be affected by body mass index, body surface area to volume ratios, clothing and other environmental conditions.
   Section::::Definitions of transfer of heat.:Thermodynamic stream of thinking.
  
  In the thermodynamic stream of thinking, the specified mechanisms of heat transfer are conduction and radiation. These mechanisms presuppose recognition of temperature; empirical temperature is enough for this purpose, though absolute temperature can also serve. In this stream of thinking, quantity of heat is defined primarily through calorimetry.
   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.
  
presuppositions: Body heat is generated at a specific body location.
corrections: Body heat is generated throughout the body due to cells which generate heat existing nearly everywhere within the body.
raw_presuppositions: Body heat is generated at a specific body location. Body heat is generated at a specific body location.
raw_corrections: Body heat is generated throughout the body due to cells which generate heat existing nearly everywhere within the body. Body heat is generated throughout the body.