Not mentioned in the above excerpt is the role of the hypothalamus in thermoregulation. Sensory receptors, called thermoreceptors, are fine-tuned sensory machines that can detect changes in body temperature and instantly relay said messages to the hypothalamus gland. In response to the thermoreceptor?s incoming messages, the hypothalamus activates mechanisms that regulate internal body temperature. The hypothalamus has a type of internal memory bank where the optimal body temperature is stored. If this temperature has not been reached, the hypothalamus will act to see that it is. The smallest deviation from the optimal body temperature will trigger the thermoregulatory center of the hypothalamus to initiate these mechanisms.
Any changes in body temperature will be picked up by two different sets of thermoreceptors: central receptors and peripheral receptors. Central thermoreceptors are located within the hypothalamus, and are thus ?central? to the thermoregulatory system. Central thermoreceptors monitor the temperature of the blood as it circulates throughout the brain. The central receptors are sensitive to temperature changes as little as .018°F. Peripheral receptors are located in the skin. These receptors provide the hypothalamus and cerebral cortex with information about external temperature, thus allowing the individual to consciously perceive temperature so that the individual can voluntarily control exposure to heat and cold environments. During massive sweat evaporation, however, the skin can feel cold while the interior of the body is hyperthermic (overheated). In this case, the peripheral receptors would incorrectly notify the hypothalamus and cerebral cortex that the individual is cold, when in fact the body may be nearing a critically high temperature.
When body temperature fluctuates, it can be restored to normal levels via the actions of four effector mechanisms.
Sweat glands: When either the skin or the blood is heated above normal equilibrium levels, the hypothalamus will initiate impulses to the sweat glands, instructing them to actively secrete sweat that moistens the skin. The hotter the internal temperature, the more sweat is produced. Evaporation will take over once the sweat reaches the surface, as discussed earlier in this journal entry.
Smooth muscle around arterioles: When the skin or the blood is heated, the hypothalamus will not only send impulses to sweat glands, but also to smooth muscle tissue in the walls of the arterioles that supply the skin with blood, causing them to vasodilate (increase in diameter). This reaction will subsequently increase local blood flow to the skin. The blood carries heat from the deep interior of the body, and is more able to release that heat if blood flow to the surface of the skin is increased.
Skeletal muscle: When more body heat needs to be generated, skeletal muscle can be called into play. In a cold environment, the peripheral thermoreceptors will relay the signal to the hypothalamus. The central thermoreceptors will also notify the hypothalamus if blood temperature drops below normal. In response to this neural input, the hypothalamus activates the brain centers that control muscle tone. These centers will stimulate small and rapid neuromuscular reactions (shivering). This increased muscle activity will generate heat (as noted before, heat is a byproduct of the energy producing pathways).
Endocrine glands: The effects of several hormones can cause groups of cells to increase their metabolic rates. Increased metabolism affects heat balance because it also increases heat production. Cooling the body stimulates the release of thyroxine from the thyroid gland. Thyroxine can elevate the metabolic rate throughout the body by more than 100%. Catecholamines (such as epinephrine and norepinephrine) have the capacity to mimic and enhance the activity of the sympathetic nervous system. Thus, they can directly affect the metabolic rate of virtually all of the body?s cells.
doesn't answer your quesiton, but thought i would throw that out
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