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Part I
Symptoms
Chapter I Fever
The core body temperature is kept constant (36.3-37.2o). Under normal circumstances, it is tightly regulated, with circadian variations over a range that usually does not exceed 1oC and a mean value of 37oC (the normal “set point”). Fever is defined as an elevation of core body temperature above the normal range.
Pathogenesis
It is important to realize that fever is not equivalent to an elevated core temperature but to an elevated set-point. The neuropathys responsible for thermoregulation originate in the hypothalamus. A local sensing mechanism exists wherein the temperature of blood is coupled to the development of autonomic discharge.
Two types of pyrogen: exogenous pyrogen and endogenous pyrogen
1. Exogenous pyrogen: various microorganisms (such as endotoxin), mostly are polysaccharides, can cause muscle contraction and rigor.
2. Endogenous: polymorphonuclear myelocytes and monocytes, activated by exogenous pyrogen, synthesize cytokines, which cause liberation of PGE from hypothalamus. The PGE is believed to reset the hypothalamic thermoregulatory center by prompting an elevation in core body temperature.
Etiology and classification
1. Infective fever: After infection, metabolites from organism or pyrogen from WBC cause fever.
2. Non-infective fever:
1). Absorption of necrotic substances: injury; ischemic necrosis; cell necrosis
2). Allergy
3). Endocrine and metabolic disturbances: hyperthyroidism and dehydration
4). Decreased elimination of heat from skin: heat failure
5). Dysfunction of central heat regulation:
a: Physical, as heat stroke;
b: chemical , as barbiturate poisoning;
c: Mechanical, as cerebral hemorrhage.
6). Dysfunction of vegetative nervous system; as the cases of sympathetic overactivity.
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