Fever signals sent to the DMH and rRPa lead to stimulation of the sympathetic output system, which evokes non-shivering thermogenesis to produce body heat and skin vasoconstriction to decrease heat loss from the body surface. It is presumed that the innervation from the POA to the PVN mediates the neuroendocrine effects of fever through the pathway involving pituitary gland and various endocrine organs. = Management= =
Fever does not necessarily need to be treated, and most people with a fever recover without specific medical attention. Although it is unpleasant, fever rarely rises to a dangerous level even if untreated. Damage to the brain generally does not occur until temperatures reach 42.0 °C (107.6 °F), and it is rare for an untreated fever to exceed 40.6 °C (105.1 °F). Treating fever in people with sepsis does not affect outcomes. Small trials have shown no benefit of treating fevers of 38.5 °C (101.3 °F) or higher of critical ill patients in ICUs, and one trial was terminated early because patients receiving aggressive fever treatment were dying more often.According to the NIH, the two assumptions which are generally used to argue in favor of treating fevers have not been experimentally validated. These are that (1) a fever is noxious, and (2) suppression of a fever will reduce its noxious effect. Most of the other studies supporting the association of fever with poorer outcomes have been observational in nature.
Norepinephrine increases thermogenesis in brown adipose tissue, and muscle contraction through shivering raises the metabolic rate.If these measures are insufficient to make the blood temperature in the brain match the new set point in the hypothalamus, the brain orchestrates heat effector mechanisms via the autonomic nervous system or primary motor center for shivering. These may be:
Increased heat production by increased muscle tone, shivering (muscle movements to produce heat) and release of hormones like epinephrine; and
Prevention of heat loss, e.g., through vasoconstriction.When the hypothalamic set point moves back to baseline—either spontaneously or via medication—normal functions such as sweating, and the reverse of the foregoing processes (e.g., vasodilation, end of shivering, and nonshivering heat production) are used to cool the body to the new, lower setting.This contrasts with hyperthermia, in which the normal setting remains, and the body overheats through undesirable retention of excess heat or over-production of heat. Hyperthermia is usually the result of an excessively hot environment (heat stroke) or an adverse reaction to drugs. Fever can be differentiated from hyperthermia by the circumstances surrounding it and its response to anti-pyretic medications.In infants, the autonomic nervous system may also activate brown adipose tissue to produce heat (non-exercise-associated thermogenesis, also known as non-shivering thermogenesis).Increased heart rate and vasoconstriction contribute to increased blood pressure in fever. Pyrogens
A pyrogen is a substance that induces fever. In the presence of an infectious agent, such as bacteria, viruses, viroids, etc., the immune response of the body is to inhibit their growth and eliminate them.