Hypothalamus, temperature regulation

The balance between heat production and heat loss, determine body temperature

Heat production From all vital process in the body, endocrine, muscular exercise & foods intake

Heat loss Radiation, conduction & evaporation

Normal body temperature 36.3 - 37.1 C Core temperature undergo regular circadian fluctuation of 0.5 - 0.7 C

Temperature regulating mechanisms Skin, deep tissues, spinal cord, extrahypothalamic region of the brain & hypothalamus (send information about body temperature through sensory receptors (cold receptors)) Hypothalamus integrate information, then produce integrated body temperature

Temperature regulating mechanisms Heat conserving mechanisms: Shivering Hunger Increased voluntary activity Increase secretion of A & NA Cautious vasoconstriction Curling up horripilation

Temperature regulating mechanisms Heat loosing mechanisms Coetaneous vasoconstriction Sweating Increased respiration Anorexia Apathy & inertia

Fever During fever the thermoregulatory mechanism behave as if they were adjusted to maintain body temperature at higher levels Resetting of the thermostat to new temp. above 37C temp. receptors then signals that the actual temp. is below the new set point Temp. raising mechanisms activated

Pathogenesis of fever Indotoxins (from bacteria), inflammation »»»»» act on monocytes, kupffer cells & macrophages to produces cytokines (act as endogenous pyrogens) »»»»» activation of preoptic area of hypothalamus »»»»» prostaglandin release in hypothalamus »»»»»raise temp. set point »»»»» Fever

Benefit of fever Inhibit microrganisms growth Antibody production increase when temp. elevated Slow growth of some tumours (lymphoma)

High temp. is harmful Permanent brain damage if rectal temp. above 41C Above 43C heat stroke develop & death

Malignant hyperthermia (gene mutation) Excess Ca released during muscle contraction »»»»» contracture of muscle »»»»» increased muscle metabolism »»»»» increased heat production »»»»» increased body temp. which it is fatal if not treated

Hypothermia Decreased body temp. »»»»» slow metabolic rate & physiological process (low HR, RR, PB & loss of consciousness) If temp. below 28C loss of spontaneous return to normal state but if warmed externally »»»»» individual survive

If care is taken in preventing the formation of ice crystals in tissues, then no damage is produced after subsequent warming Human can tolerate body temp. of 21-24C during which it is possible to perform open-heart surgery & brain surgery