Thermoregulation, Pyrexia, Hypothermia Flashcards
what is a poikilotherm
cold blooded
temperature flucuates with environment
activity levels related to body/environment temp
what is homeotherm
maintian steady body temp
can increase/decrease their body temp
remain active at all temps
what are the regional variations in the body temperature
core body temp organs: in cranium, thoracic cavity, abdominal cavity (very narrow range)
shell temp: oral and skin temp
what causes variations in hemeotherm temp
- seasonal
- environment
- exercise
- digestion
- gender
what ways can heat be transferred by
- radiation: energy in the infrared portion of the spectrum given off or absorbed by an object
- conduction: energy transferred between an object and the material next to the object by direct passage
- evaporation: loss of water from an organism in the form of water vapour requires significant heat input
how is thermogenesis controlled
regulated at level of preoptic area of the hypothalamus
peripheral and central temp sensors sends info to POA
acts as integrating centre
what info does POA send to the heat promoting centre
more posterior region
promotes shivering, peripheral vasoconstriction
what info does POA send to the heat losing centre
more anterior region
promotes sweating, panting, behavioural changes
what are physiological changes for heat production/promotion (5)
1. cutaneous vasoconstriction: sympathetic nervous system, peripheral vasoconstriction a1 adrenoreceptors –> divert blood to core, periodic vasodilation
2. countercurrent exchange system: occurs in mammals between main arteries and adjacent larger veins deep within tissues
3. heat production/promotion: piloerection/horripilation
4. shivering: spinal reflex muscle movement
5. non-shivering thermogenesis: SNS (via B adrenoreceptors) and T4 stimulate Na/K ATPase which increases metabolic rate, heat production (brown fat in fetal animals not linked to ATP –> uncoupling protein thermogenin, in adults increase food intake)
what are complications of vasoconstriction
hypovolemia
frost bite
what are physiological changes to promote heat loss (2)
1. altering conductance: cutaneous vasodilation increases skin temperature (conduction and convection decrease as ambient temp increases)
2. evaporative heat loss: works even at high temps (sweating, panting, spreading saliva on fur)
how do animals sweat
not all have sweat glands and less effective if you have fur
what are the two types of sweat glands
- apocrine: developed from hair follicles, produce membrane bound secretions and watery sweat –> thermoregulatory in horses and cattle. respond to adrenaline
- eccrine glands: thermoregulatory in man, cholinergic sympathetic innervation
what are sweat glands stimulated by
increase in central and skin temp
how does panting help with heat loss
movement of air in “non-resp” zone of airways “forced convection:
cools blood going to the brain via the nasal passages
dogs, sheep, goats, gazelles
what are adjustments to chronic cold temperatures
- increase thermal gradient: increased level of surface insulation (summer vs. winter fur)
- increased metabolic rate
- decrease core temperature (hibernation –> decrease body temp, heart rate, resp rate, metabolic rate –> fat used as energy source)
how do animals adjust to chronic hot temperatures
- decrease thermal gradient: decrease level of surface insulation (summer vs. winter fur)
- increase in core temp
- decrease the metabolic rate
what are thermoregulatory disorders
- pyrexia
- heat stress (hyperthermia, heat stroke, heat exhausiton, heat fatigue)
- cold stress (hypothermia)
what is the purpose of pyrexia (3)
- promotes interferon activity
- increases metabolic rate and accelerates tissue repair
- decreases bacteria and viral replication
how does pyrexia occur (6)
- neutrophils and macrophages secrete pyrogen IL1 –> stimulates the anterior hypothalamus to secrete PGE
- PGE raises the set point
- individual shivers and peripheral vasoconstriction increase body temp
- body temp osscilates around new set point. liver and spleen hoard zinc and iron depriving bacteria of the minerals needed to reproduce
- when infection is gone, pyrogen secretion decrease and the set point is reset
- heat loss mechanisms activated
what are heat cramps
excessive electrolyte loss (often after exercise and heavy sweating) –> muscle spasms
what is heat stroke (hot and humid)
gain heat by radiation and conduction but can’t loose by evaporation
delirium, convulsions, coma, tachycardia, hyperventilation, inflammation, multiorgan dysfunction
what are the stages of cold stress (3)
- BT decrease to 35-37: shivering, vasoconstriction, breathing quick and shallow, nausea, muscles becomes less responsive
- 33-35: shivering more violent, muscle miscoordination, confusion, surface blood vessels contract further, extremities become blue
- <32: shivering stops, cognitive impairement and physical inability present, metabolic processes shut down. <30 exposed skin, blue and puffy, muscle coordination very poor, incoherent/irrational behaviour
