Body Temperature Regulation Flashcards
Why is it important for core temperature to be regulated?
Cannot survive if not functioning
What influences the rate of hear production?
Basal rate metabolism
Metabolism inc by muscular activity
Metabolism inc by sympathetic stimulation
Metabolism inc by hormonal effect on cells
Metabolism inc by inc chemical production
Inc digestion, absorption and storage of food
Where is most heat lost?
Through the skin
What are some barriers to heat transfer?
Insulation
Skin
SubQ tissue
Fat - conducts 1/3 more heat than other tissues
Where are the temperature regulating centers?
Preoptic and anterior hypothalamic nuclei
What is the main mediator of fever when there is an infection?
Pyrogenic
What regulates homeostatic mechanisms to maintain a body temp set point?
Hypothalamus
What ate the mechanism to increase body temp?
Vasconstriction
Thermogenesis
Piloerection
What is vasoconstriction?
Tightening of vasculature in the skin
What is vasoconstriction mediated by?
Tonic sympathetic control - noradrenergic
Nonglabrous (hairy) glabrous (palm, soles), skin all have sympathetic inn
What is thermogenesis?
Shivering to inc heat production
Chemical by sympathetic stimulation and thyroxin
What are the chemical thermogenesis agents?
Norepinephrine and epinephrine
How is thermogenesis stimulated?
By the uncoupling oxidative phosphorylation in mitochondria so heat, not ATP, is released
Where does the most uncoupling oxidative phosphorylation occur?
In brown fat
What does thyroxin do as a chemical thermogenesis?
Increases the rate of cellular metabolism
When does thyroxin being working?
After a prolonged amount of time (weeks) in exposure to low temps
What is piloerection?
Sympathetic stimulation which causes contraction of arrector pili muscles creating a later of insulating air
What is hypothermia?
Heat loss occurring from radiation, conduction, convection, evaporation or respiration
What are some causes of hypothermia?
Extensive exposure to cold
Endocrine dysfunction
Drugs
Neurologic injury
What are some mechanisms to dec body temp?
Vasodilation
Sweating
Dec heat production
What is vasodilation?
Opening of the vasculature of the skin
Sympathetically controlled - cholinergic receptors cotransmission with roles for nitric oxide, vasoactive intestinal peptide, protoglandins and substance P
Raynaud’s syndrome
Hyperreactive vasoconstriction of periphery (vasospasm) activated by cold or emotional stimulus
Severe - ischemia-reperfusion injury
Erythromelalgia
Rare disorder that is characterized by burning pain, warmth and redness of extremities
What is hyperthermia and what are its causes?
Core temp higher than 38C
Thermoregulatory failure from drugs or severe brain injury
What is hyperpyrexia?
Core temperature above 41.5
What is malignant hyperthermia?
A genetic disorder, mutation of ryanodine receptor (RYR1)
In response to anesthetics/succinylcholine, intracell Ca2+ release is elevated so muscle metabolism inc and become rigid
Acidosis
What is fever?
Controlled inc in core temperature
What is the main cause fever response?
Pyrogen (any substance that causes a fever)
What are exogenous pyrogens?
Microbial product, toxin or whole microbe
Gram neg (all) - LPS
Gram pos - enterotoxin (S. aureus), group A & B step toxin
What are endogenous pyrogens?
Cytokines
IL-1, IL-6, TNF, ciliary neurotrophic factor (CNTF), interferon alpha
What is hypertermia?
Uncontrolled elevation in core body temp that exceeds the body’s ability to lose heat
Pyrogens not involved
What are some possible causes for hypertermia?
Heat stroke Drug induced (MAOIs, tricyclic antidepress, SSRIs etc)
