Thermoregulation, Pyrexia, Hypothermia

Question 1

what is a poikilotherm

Answer 1

cold blooded

temperature flucuates with environment

activity levels related to body/environment temp

Question 2

what is homeotherm

Answer 2

maintian steady body temp

can increase/decrease their body temp

remain active at all temps

Question 3

what are the regional variations in the body temperature

Answer 3

core body temp organs: in cranium, thoracic cavity, abdominal cavity (very narrow range)

shell temp: oral and skin temp

Question 4

what causes variations in hemeotherm temp

Answer 4

1. seasonal
2. environment
3. exercise
4. digestion
5. gender

Question 5

what ways can heat be transferred by

Answer 5

1. radiation: energy in the infrared portion of the spectrum given off or absorbed by an object
2. conduction: energy transferred between an object and the material next to the object by direct passage
3. evaporation: loss of water from an organism in the form of water vapour requires significant heat input

Question 6

how is thermogenesis controlled

Answer 6

regulated at level of preoptic area of the hypothalamus

peripheral and central temp sensors sends info to POA

acts as integrating centre

Question 7

what info does POA send to the heat promoting centre

Answer 7

more posterior region

promotes shivering, peripheral vasoconstriction

Question 8

what info does POA send to the heat losing centre

Answer 8

more anterior region

promotes sweating, panting, behavioural changes

Question 9

what are physiological changes for heat production/promotion (5)

Answer 9

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)

Question 10

what are complications of vasoconstriction

Answer 10

hypovolemia

frost bite

Question 11

what are physiological changes to promote heat loss (2)

Answer 11

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)

Question 12

how do animals sweat

Answer 12

not all have sweat glands and less effective if you have fur

Question 13

what are the two types of sweat glands

Answer 13

1. apocrine: developed from hair follicles, produce membrane bound secretions and watery sweat –> thermoregulatory in horses and cattle. respond to adrenaline
2. eccrine glands: thermoregulatory in man, cholinergic sympathetic innervation

Question 14

what are sweat glands stimulated by

Answer 14

increase in central and skin temp

Question 15

how does panting help with heat loss

Answer 15

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

Question 16

what are adjustments to chronic cold temperatures

Answer 16

1. increase thermal gradient: increased level of surface insulation (summer vs. winter fur)
2. increased metabolic rate
3. decrease core temperature (hibernation –> decrease body temp, heart rate, resp rate, metabolic rate –> fat used as energy source)

Question 17

how do animals adjust to chronic hot temperatures

Answer 17

1. decrease thermal gradient: decrease level of surface insulation (summer vs. winter fur)
2. increase in core temp
3. decrease the metabolic rate

Question 18

what are thermoregulatory disorders

Answer 18

1. pyrexia
2. heat stress (hyperthermia, heat stroke, heat exhausiton, heat fatigue)
3. cold stress (hypothermia)

Question 19

what is the purpose of pyrexia (3)

Answer 19

1. promotes interferon activity
2. increases metabolic rate and accelerates tissue repair
3. decreases bacteria and viral replication

Question 20

how does pyrexia occur (6)

Answer 20

1. neutrophils and macrophages secrete pyrogen IL1 –> stimulates the anterior hypothalamus to secrete PGE
2. PGE raises the set point
3. individual shivers and peripheral vasoconstriction increase body temp
4. body temp osscilates around new set point. liver and spleen hoard zinc and iron depriving bacteria of the minerals needed to reproduce
5. when infection is gone, pyrogen secretion decrease and the set point is reset
6. heat loss mechanisms activated

Question 21

what are heat cramps

Answer 21

excessive electrolyte loss (often after exercise and heavy sweating) –> muscle spasms

Question 22

what is heat stroke (hot and humid)

Answer 22

gain heat by radiation and conduction but can’t loose by evaporation

delirium, convulsions, coma, tachycardia, hyperventilation, inflammation, multiorgan dysfunction

Question 23

what are the stages of cold stress (3)

Answer 23

1. BT decrease to 35-37: shivering, vasoconstriction, breathing quick and shallow, nausea, muscles becomes less responsive
2. 33-35: shivering more violent, muscle miscoordination, confusion, surface blood vessels contract further, extremities become blue
3. <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