Body temperature regulation is controlled by a balance between heat generation and heat loss. If the rate of body heat generation is greater than the rate of heat loss, heat will be generated in the body and body temperature will increase. On the other hand, if heat dissipation is greater, body heat and body temperature will decrease (Guyton & Hall, 2014).
Heat Generation
Heat generation is the main product of metabolism. What determines the rate of heat generation is called the body's metabolic rate. The most important factors in this regard:
- The basal metabolic rate of all body cells.
- Additional metabolic rate caused by muscle activity, including muscle contraction caused by shivering.
- Additional metabolism affected by the effect of thyroxine on cells.
- Additional metabolism caused by the influence of epinephrine.
- Additional metabolism caused by increased chemical activity within the cells themselves, especially when the temperature inside increases.
- Additional metabolism required for digestion, absorption and storage of food.
Heat Discharge
Most of the heat generated in the body is generated in the internal organs, especially in the liver, brain, heart, and skeletal muscles during work. This heat is then transferred from deeper organs and tissues to the skin, which is then discharged into the air or the surrounding environment. The rate of heat dissipation is almost entirely influenced by factors:
- How quickly heat can be conducted from where the heat is generated, i.e. from the core of the body to the skin.
- How quickly heat can then be transferred from the skin to the environment?
There are four mechanisms of heat removal, namely (Sherwood, 2009):
1. Radiation
Radiation is the emission of heat energy from the surface of a warm object in the form of electromagnetic waves or heat waves that propagate in space. The human body emits (a source that loses heat) and absorbs a source that gains radiant energy. The net transfer of heat by radiation is always from a warmer object to a cooler one, so the body derives heat from an object that is warmer than the clitoral surface. In contrast, the body loses heat through radiation to objects in the environment whose surface is cooler than the surface of the skin.
2. Conduction
Conduction is the transfer of heat between objects of different temperatures that are in direct contact with each other, with heat flowing down a temperature gradient from a warmer object to a cooler object by transfer from molecules to molecules. When molecules with different heat contents come into contact with each other, the warmer, faster moving molecules trigger the colder molecules to move faster so the colder molecules get warmer. The rate of heat transfer by conduction depends on the temperature difference between the objects in contact and the thermal conductivity of the materials involved.
3. Convection
Convection is the transfer of heat energy by air currents. As the body loses heat by conduction to the cooler ambient air, the air in direct contact with the skin becomes warmer. Because warm air is lighter than cold air, the warmed air rises while cooler air moves closer to the skin to replace the warm air. This process repeats itself, and this movement of air, known as convection currents, helps carry heat away from the body. If there is no convection current, then there is no release of heat anymore after the temperature of the air layer that is right around the body equals the temperature of the skin.
4. Evaporation
Evaporation is the last method of heat transfer used by the body. When air evaporates from the skin's surface, the heat needed to change water from a liquid state to a gas is absorbed from the skin, making the body cooler. An example of evaporation is sweating. Sweating is an active evaporative heat loss process under sympathetic nerve control.
Body temperature regulation center
The part of the brain that regulates body temperature is the hypothalamus. The hypothalamus is able to respond to changes in blood temperature as small as 0.01 0C. The response rate of the hypothalamus to deviations in body temperature is adjusted in a very careful manner, so that the heat generated or released is very much in accordance with the need to restore the temperature to normal (Sloane, 2003).
- Peripheral thermoreceptors, located within the skin, monitor skin temperature throughout the body and transmit information about changes in surface temperature to the hypothalamus.
- Central thermoreceptors, located between the anterior hypothalamus, spinal cord, abdominal organs and other internal structures also detect changes in blood temperature.
Shivering is the main involuntary way to increase heat production. The body can derive heat from internal heat production generated by metabolic activity or from the external environment if it is warmer than body temperature. Since body temperature is usually higher than ambient temperature, metabolic heat production is the main source of body heat. In a resting state, some of the body's heat is generated by the thoracic and abdominal organs. In changes in skeletal activity is the main heat production line that is controlled for temperature regulation.
Reference :
Guyton, A.C., Hall, J.E. (2014).
Sherwood, Lauralee. (2009).
Sloane, Ethel. (2003).
