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ZOOL 463 > Thermoregulation > Flashcards

Thermoregulation Flashcards

1
Q

endotherm

A

an organism that generates heat to maintain its body temperature typically above the temperature of surroundings

includes birds and mammals

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2
Q

ectotherm

A

AKA poikilotherm
an organism that regulates its body temperature largely by exchanging heat with its surroundings

includes fish, reptiles, etc

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3
Q

downside of endothermic regulation

A

physiological costly to maintain body temperature

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4
Q

a study found that mitochondrial density and cytochrome oxidase activity is larger in endotherms or ectotherms?

A

endotherms

ATP is produced in mitochondria and ATP is used to produce heat as a byproduct
(oxidative phosphorylation produces ATP + heat)

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5
Q

which animals are closest to being true endotherms

A

humans, primates and felines (cats)

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6
Q

benefit of ectothermic regulation

A

it is easier to be “compliant” with ambient environment than having to work against it (by producing body heat or using cooling mechanisms)

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7
Q

4 overall types of body temperature regulation

A

homeotherm ectotherm
heterotherm ectotherm
homeotherm endotherm
heterotherm endotherm

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8
Q

2 types of heterothermy

A

temporal and regional

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9
Q

temporal heterothermy

A

certain endotherms (bats, hummingbirds) when at rest (short term or long term - torpor/hibernation) reduce metabolism and body temperature drops close to surrounding environment

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10
Q

regional heterothermy

A

certain endothermic and ectothermic animals are able to maintain different temperature “zones” in different regions of the body

core temperature is usually constant though

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11
Q

normal body temperature (mammals)

A

close to 37° Celsius or 98.6° Fahrenheit

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12
Q

body temperature may increase to ____ during heavy exercise

A

38.3-40°C

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13
Q

body temperature can be as high as _____ during febrile illness/pyrexia

A

42°C

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14
Q

long exposure to cold may reduce body temperature to

A

36.1°C

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15
Q

is oral or rectal temperature more similar to core body temperature?

A

rectal

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16
Q

core temperature

A

temperature of internal organs

remains constant at 36.7-37°C even when the environment fluctuates between 13-60°C for a short period at rest

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17
Q

skin tempertaure

A

changes with the temperature of the surrounding

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18
Q

fluctuations in body temperature occur when

A

the rate of heat loss does not balance the rate of heat gain

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19
Q

thermal neutral zone

A

comfortable temperature (room temperature) where there is no sweating/not feeling cold

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20
Q

hypothermia

A

core temperature much below thermal neutral zone

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21
Q

hyperthermia

A

core temperature above thermal neutral zone

body unable to cool down - feels hot and humid

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22
Q

metabolic rate

A

rate of energy expenditure (usually per hour)

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23
Q

how is metabolic rate measured?

A

either directly by direct calorimetric methods (using chamber) or indirectly by measuring oxygen consumption (easier)

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24
Q

the body produces ____ cal of heat/L of oxygen

A

4.8 (metabolic rate)

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25
Q

basal metabolic rate (BMR)

A

rate of energy expenditure in a post absorptive condition (has not eaten ~12 hr), following a rest period at room temperature (22-23°C)

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26
Q

BMR reflects the energy the body needs for what?

A

to perform its most essential activities, such as breathing and maintaining resting levels of neural, cardiac, liver and kidney function (i.e., the energy cost of living)

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27
Q

average BMR in a 70 kg adult

A

60-72 Kcal/hr (~1500-1700 Kcal/day)

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28
Q

factors influencing BMR

A

surface area/mass ratio, age, gender, muscle, stress/hormones

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29
Q

most important factor for BMR

A

surface area/mass ratio

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30
Q

surface area/mass ratio in small animals

A

very high

surface area is larger compared to mass (very small)

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31
Q

mass-specific MR

A

whole animal MR divided by body weight

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32
Q

do small or large animals have lower mass specific MR?

A

much lower MR in large animals (decreased SA:mass)

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33
Q

do small/large animals burn more calories?

A

small

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34
Q

how does age affect BMR?

A

BMR is higher in a younger age - declines significantly in old age

this is why it’s harder to lose weight as you age

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35
Q

how does gender affect BMR?

A

BMR is higher in males than in females

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36
Q

how does muscle/fat affect BMR?

A

BMR is higher in muscular than in fatty people

muscle burns more energy while fat stores energy

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37
Q

total metabolic rate (TMR)

A

total rate of energy expenditure during ongoing involuntary and voluntary activities

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38
Q

average TMR for 70 kg adult with no activities

A

approximately 2000 cal/day

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39
Q

highest energy expenditure activity

A

mountain climbing

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40
Q

TMR is affected by

A

exercise, hormones

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41
Q

how does exercise affect TMR?

A

mechanothermogenesis - moving muscles increases heat production and burns calories

can increase heat production 20-50x than normal for a few seconds/minutes depending on physical fitness

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42
Q

difference in heat production between Olympic athletes and unathletic person

A

Olympic athlete: extent of heat production is lower + they can endure for long period of time
Unathletic person: extent of heat production increases + can only endure for short time

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43
Q

hormones that affect TMR

A

thyroid hormones (more so BMR), catecholamines (epinephrine/norepinephrine), sex hormones, growth hormones and certain growth factors

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44
Q

why is MR higher in children?

A

more growth hormones

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45
Q

hormone-mediated increase in TMR contributes to

A

non-shivering thermogenesis (increase in heat production not associated with muscle activity)

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46
Q

thyroid hormones can increase/decrease TMR by how much?

A

increase by 50-100% above the normal and low thyroid secretion reduces TMR by 40-60% below the normal

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47
Q

What causes long-term hormone-mediated change in TMR?

A

thyroid hormones

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48
Q

What causes short-term hormone-mediated change in TMR?

A

sympathetic pathway (epinephrine and norepinephrine)

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49
Q

brown fat

A

metabolically active tissue containing large number of mitochondria

chemicalthermogenesis is much greater in animals with brown fat

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50
Q

maintenance of a constant temperature requires

A

a balance between heat loss and heat production

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51
Q

heat production

A

byproduct of metabolism primarily in the liver, muscle, heat, etc. (chemical thermogenesis)

increase in thyroid hormones (long-term) and sympathetic activity (short-term)

increase in muscle activity such as shivering (mechanical thermogenesis)

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52
Q

heat loss

A

primarily through the skin

increased rate of heat conductance from core to skin - heat loss by vasodilatation of subcutaneous blood vessels

increase rate of heat transfer from the skin to surroundings

increase rate of sweating (cools down the skin)

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53
Q

effective means of heat production

A

muscle contraction (mechanical thermogenesis)

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54
Q

muscle has energy efficiency of

A

~25% (i.e., for 1 cal of chemical energy converted into mechanical work, 3 cal are degraded to heat)

low efficiency but great for heat production

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55
Q

effective means of maintaining normal core temperature

A

skin insulation (fur, blubber)

subcutaneous fat is an important insulator (heat conductance of fat is 1/3 of other tissues)

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56
Q

how does fur decrease heat conductance?

A

by creating a temperature gradient (reducing sharp gradient)

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57
Q

vasoconstriction of capillaries limits blood flow to

A

epidermis

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58
Q

vasoconstriction

A

limits blood flow to skin so blood flows through shunt

low heat conductance

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59
Q

vasodilation

A

decreased blood flow to shunt vessels and increased blood flow to skin

high heat conductance

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60
Q

the rate of blood flow to the subcutaneous venus plexus (SHUNT) could vary between

A

1-30% of cardiac output (significant change)

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61
Q

subcutaneous venus plexus

A

shunt vessel

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62
Q

what is blood flow in the shunt vessel controlled by?

A

arteriovenous anastomosis opening/closing

connections between arteries and veins that are not capillaries

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63
Q

increased temperature leads to

A

vasodilation of vessles > increased blood flow > increased conductance from core to skin > increased heat loss

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64
Q

decreased temperature

A

vasoconstriction of vessels > decreased blood flow > decreased conductance from core to skin > decreased heat loss

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65
Q

conductance in which areas of the body is most effective?

A

exposed/vascularized areas like ears, face, hands

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66
Q

heat loss by skin is affected by

A

radiation, conductance, evaporation

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67
Q

heat loss by radiation

A

~60% of the total heat lost by infrared rays

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68
Q

heat loss by conductance is influenced by

A

temperature gradient (cannot be controlled)

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69
Q

conductance of heat to _____ is much greater than _____

A

water; air

water is 23.5 times more efficient in transferring heat than air

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70
Q

normal evaporation rate from skin and lungs amounts to

A

~600 mL/day (heat loss of 12-16 cal/h)

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71
Q

what is evaporation increased by?

A

greater air current (i.e., convection)

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72
Q

what is an important regulatory mechanism of heat loss?

A

evaporation through sweating

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73
Q

how can heat loss via radiation be reduced?

A

insulation

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74
Q

when are radiation and conduction effective mechanisms of heat loss?

A

when skin temp > surrounding temp

but the body will gain heat when skin temp < surrounding temp

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75
Q

how is sweat carried to the surface of skin?

A

through sweat ducts - moistens surface of skin

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76
Q

tonicity of sweat vs plasma

A

isotonic (excluding proteins in plasma) but most of ions in sweat are reabsorbed during passage through the duct to minimize ion loss

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77
Q

what happens when rate of sweating is high

A

~1/2 of constituents (Na+ and Cl-) may be lost - this is why skin becomes salty

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78
Q

what reduces the secretion of Na+ and Cl-

A

aldosterone - involved in osmoregulation of kidney and reabsorption of ions

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79
Q

acclimatization to sweating

A

increases ability to sweat from 700 mL/hr to 2000 mL/hr

increased efficiency (reduces ion loss, higher volume, earlier onset = improved ability to cool down faster)

80
Q

environmental factors influencing temperature control

A

movement of air/moisture and temperature gradient

81
Q

control of sweating

A

cholinergic sympathetic pathway in the subdermal region of the sweat gland

82
Q

what increases sweating but is NOT related to the cooling mechanism

A

circulating epinephrine - related to nervousness (cold sweat) but not thermoregulated

83
Q

cholinergic and adrenergic neurons are part of which system

A

parasympathetic system; sympathetic system

84
Q

the sympathetic fibre of the sweat gland, piloerector muscle and some blood vessels have which hormone?

A

cholinergic (exceptional case bc sympathetic system is usually adrenergic)

85
Q

which hormone causes goosebumps/hair to stand up

A

adrenaline (via piloerector muscles)

86
Q

how do animals that lack skin sweat glands and have skin covered in thick fur lose heat?

A

panting is an effective mechanism of heat loss - shallow breath that does not increase alveolar ventilation (not related to rate of breathing)

87
Q

temperature regulatory centre

A

located in the posterior hypothalamus

88
Q

where does the posterior hypothalamus receive nervous feedback signals from?

A

sensory thermoreceptors located peripherally and in the anterior hypothalamus

89
Q

how are thermal signals relayed?

A

to the brain stem, thalamus, somatic sensory cortex and then relayed to posterior hypothalamus

90
Q

where are thermoreceptors located?

A

skin and body tissues (peripheral system and anterior hypothalamus)

91
Q

type of sensory receptors

A

4 types: cold pain, cold, warm, heat pain

92
Q

what temperatures can thermoreceptors distinguish between?

A

freezing cold, cold, cool, indifferent, warm, hot, burning hot

93
Q

the peak optimal firing rate for each type of thermoreceptor is

A

different for each type

94
Q

cold and warm receptors are located

A

immediately under the skin at discrete points and varying densities

95
Q

peripheral vs deep temperature receptor location

A

peripheral: around the skin region
deep: present around spinal cords, abdominal viscera and the great veins in the upper abdomen and thorax

96
Q

which are more abundant: peripheral cold or warm receptors?

A

there are 10 times more peripheral cold

97
Q

when are pain receptors stimulated?

A

by extreme cold or heat

98
Q

when do peripheral thermoreceptors increase rate of firing?

A

when exposed to temperature change

99
Q

adaptation of peripheral thermoreceptors

A

strongly stimulated when subjected to abrupt changes in temperature

e.g. when jumping into a cold pool, it’s initially very cold but the response fades away gradually

100
Q

spatial summation of peripheral thermoreceptors

A

thermal sensation is proportional to the number of thermoreceptors stimulated

101
Q

which has a greater effect: a small temp change over a large area or a large temp change over a small area?

A

a small temp chance over a large area (more thermoreceptors stimulated)

102
Q

which area of the hypothalamus contains thermoreceptors

A

preoptic area (temperature sensor area) - specifically the anterior hypothalamus

mainly warm receptors

103
Q

what does the temperature sensor area (preoptic area) of the anterior hypothalamus detect?

A

mainly core body temperature - gets alerted to changes in core temperature

104
Q

number of heat-sensitive receptors vs cold-sensitive in the anterior hypothalamus

A

3 times more heat-sensitive receptors (opposite to peripheral thermoreceptors)

105
Q

how is the critical temperature set point determined?

A

by the degree of activity of temperature receptors in the hypothalamus

106
Q

what is the set point analogous to?

A

thermostat - set to a specific temperature and gain or lose heat to maintain that temperature

107
Q

what provides a physiological mechanism for altering the hypothalamic set point?

A

feedback from peripheral temperature receptors

108
Q

increase in skin temperature results in?

A

a decrease in set point in anticipation of a warming trend

109
Q

decrease in skin temperature results in?

A

an increase in set point in anticipation of a cooling trend

110
Q

in humans, there is a _____°C change in body temperature for each 25-30°C change in environmental temperature

A

~1

111
Q

increased body temperature results in ______ of thermoregulatory centres in the posterior hypothalamus

A

inhibition

112
Q

what specific responses occur to heat?

A

increased sweating, vasodilation, decreased body heat production (decreased shivering - mechanical and metabolism - chemical thermogenesis)

result of INHIBITION of thermoregulatory centres in posterior hypothalamus

113
Q

a temperature rise of _____°C results in a significant increase in sweating

A

0.5 - very efficient mechanism

can be enhanced by factors like convection (sitting in front of fan)

114
Q

decreased body temperature results in ______ of thermoregulatory centres in the posterior hypothalamus

A

stimilation

115
Q

what specific responses occur to cold?

A

vasoconstriction, piloerection, increased shivering, increased chemical thermogenesis

result of STIMULATION of thermoregulatory centres in posterior hypothalamus

116
Q

piloerection involves

A

sympathetic stimulation (via cholinergic pathway) > contraction of arrector pili muscle attached to hair > upright stance of hair > insulation (minimizes temperature gradient)

117
Q

shivering

A

excitation of the primary motor centre for shivering in the posterior hypothalamus through brain stem > increased tone of skeletal muscle (excitation of motor system) > shivering

118
Q

chemical thermogenesis

A

increased sympathetic stimulation (adrenergic - short term) > increased NE/E levels > increased metabolic rate > increased chemical thermogenesis

increased TMR but not BMR

119
Q

prolonged (long term) exposure to cold leads to increased

A

thyroid hormone production

this increases overall BMR

120
Q

which hormone increases overall BMR?

A

thyroid hormone

121
Q

acclimatization to cold in some animals (like gophers and true hibernators) leads to what?

A

increased chemical thermogenesis by ~500%

(only 10-15% in humans bc no brown fat)

122
Q

thyroid hormone-induced increase in BMR in a consequence of

A

long term exposure to low temperature

123
Q

prolonged exposure to cold

A

increased TRH > increased TSH > increased thyroid hormone secretion (T3/T4) > increased metabolic rate (chemical thermogenesis)

124
Q

how does long term exposure to low temperature affect the thyroid gland?

A

increase in size (up to 40%)

125
Q

subconscious mechanisms for body temperature control are complemented by

A

behavioural aspects resulting from discomfort (either feeling too hot or too cold)

animals do this too (seek shelter, hibernate, etc.)

126
Q

pyrexia

A

state of increased body temperature beyond normal range - could result from infection, allergic reaction, CNS injuries and cancer

127
Q

what do leukocytes release in response to pyrogens?

A

macrophages and neutrophils release cytokines (IL-I, IL-6, TNF tumor necrosis factor)

128
Q

most common pyrogens

A

bacterial lipopolysaccharides toxins (LPS)

viral polyribonucleptide pyrogen (Poly I: PolyC)

cytokines released from injured cells

129
Q

pyrogens acts through the

A

Toll family of membrane receptors

initiates cellular innate immune responses; evolutionary conserved in many species

130
Q

pyrogens such as cytokines (IL-I, IL-6, TNF) act through

A

specific hypothalamic membrane receptors resulting in activation of Cox-II which results in production of prostaglandins

(remember Cox-II pathway to produce thromboxane-A2)

131
Q

what do prostaglandins do?

A

increase the hypothalamic set point and increase temperature (fever)

132
Q

what is the pathway of pyrogens increasing fever?

A

leukocytes release cytokines in response to pyrogens, which act through specific hypothalamic membrane receptors to activate Cox2 which results in production of prostaglandins and increases set point (fever)

133
Q

how does aspirin reduce the degree of fever?

A

by blocking prostaglandin production from arachidonic acid (inhibits Cox2)

134
Q

during fever, the person experiences

A

chills and feels cold even with above normal body temperature

set point is higher now so body thinks you are cold and starts shivering to produce heat

135
Q

vasodilation and sweating during drop in fever is known as

A

flush (trying to lose heat)

136
Q

2 phases of a fever

A

pyresis (increasing temperature - body activates responses to cold which increases heat production)

antipyresis (after crisis and set point is suddenly reduced)

137
Q

what happens when body temperature reaches its upper limit

A

thermoregulatory process may be disrupted

heatstroke, brain lesion, febrile disease

138
Q

what happens in a fever induced by infections like malaria?

A

dangerously high temperature - temperature regulation seriously impaired

139
Q

what happens when the pyrogen is removed?

A

set point now reduced to a lower level which stimulates the hypothalamic preoptic area resulting in the onset of response to reduce body temperature such as sweating, vasodilation, etc.

STARTS ANTIPYRESIS

140
Q

why did we evolve to have fever?

A

sign of disease and evidence that an increase in temperature can improve body defense response

141
Q

examples of experimental evidence that an increase in temperature can improve body defence response

A

neutrophil migration and movement significantly increased when the temperature is higher

a number of genes important for immunity are activated by heat shock proteins

in lower vertebrates (poikilotherms), survival from infection significantly increases at higher temperatures

142
Q

hyperthermia (heat stroke)

A

if cooling mechanism is not efficient (high humidity or excessive heat gain), an upper limit is reached

143
Q

what happens beyond the upper limit of body temperature

A

loss of ability to regulate temperature

results in further increase of body temperature and symptoms of heat stroke: extreme weakness, headache, dizziness, nausea, eventually unconsciousness

144
Q

sustained hyperthermia results in

A

hemorrhages (comprised integrity of endothelial layer), degeneration of cells especially neurons, irreversible damage to liver, kidney, and neurons leading to death

145
Q

how can certain mammls manage sustained running without being affected by heat stroke?

A

anatomical adaptation (in animals like sheep, goats, gazelles, cats, dogs)

146
Q

how do hoofed animals prevent overheating of the brain?

A

special counter-current heat exchange

147
Q

how does the counter-current heat exchange process happen in hoofed animals?

A

head carotid artery supplying the brain passes through a venous blood sinus which contains blood returning from the nasal cavity and respiratory passages (2-3 degrees cooler than normal blood)

therefore brain temperature is cooler than core temperature when animal is running

148
Q

which animals do not have counter-current system to reduce heat stroke

A

rodents and primates

they have to manage physical activity to prevent heat stroke

149
Q

hypothermia

A

sustained exposure to extreme cold will result in decreased body temperature

a lower limit will be reached if the heating mechanism is inefficient

150
Q

which is greater: the lower or upper range of body temperature?

A

lower range

151
Q

what happens in hypothermia?

A

loss of ability to regulate temperature; symptoms include sleepiness, coma and eventually death

152
Q

frostbite

A

ice crystal formation - leads to tissue damage (kills cell membrane on contact)

153
Q

why does your face turn red when cold?

A

natural response to cold is vasoconstriction (pale skin due to decrease blood flow near surface) BUT in skin exposed to extreme cold, smooth muscle is paralyzed and cannot vasoconstrict anymore which allows blood flow (prevents frostbite short term)

154
Q

how do wild animals survive the extreme cold?

A

by physiological and anatomical adaptation

155
Q

how do marine mammals cope with extreme cold?

A

blubber to increase insulation (conductance in water is 3x air)

circulatory anatomical adaptation - blood flow to extremities is through counter-current fashion to minimize heat loss

156
Q

counter-current blood flow in marine mammals

A

warm blood goes through centre then cools down and returns closer to surface - doesn’t fully prevent heat loss but minimizes it by creating a heat graident

157
Q

regional heterothermy to protect from extreme cold

A

part of body (like extremities) maintained at lower temperature

in some arctic animals, tissues in legs and feet are close to freezing

158
Q

how do membranes survive in extremities of regional heterothermic animals?

A

change in lipids - less saturated (more unsaturated fats) which is more oily and less viscous to maintain fluidity and allow adequate functioning of cell membrane at low temperatures

159
Q

how does fur thickness change in summer vs winter?

A

winter: fur grows
summer: shed fur and don’t grow as much

160
Q

examples of temporal heterothermy

A

dormancy: sleeping through bad weather or lack of food

deep sleep, torpor, hibernation

161
Q

dormancy

A

advantageous to allow body temp to drop to avoid energy loss and excessive catabolism

162
Q

how does the temperature rise to normal after a period of dormancy?

A

increased metabolism (esp in animals with brown fat) - generates heat

163
Q

why can’t all animals go through torpor and hibernation?

A

large animals: too large mass - impossible to bring temp back up
very small animals: high metabolic rates - have to constantly eat to survive

164
Q

difference in temp of deep sleep and hibernation

A

deep sleep: falls by 3-5 degrees
hibernation: falls by 25-35 (almost freezing)

165
Q

torpor

A

short term change in body temperature for a few hours to help animal survive cold climate

(birds like hummingbirds, some mammals like bats and mice)

166
Q

what causes the physiological changes and characteristics of torpor?

A

photoperiod and drop in temperature (environmental cues) cause a reduction in set point

167
Q

what are the physiological changes and characteristics of torpor?

A

reduction in core temperature, decrease in MR, heart rate, breathing rate and O2 consumption, low blood supply to limbs - restricted to vital organs

168
Q

a greater reduction in body temp is seen in torpor or hibernation?

A

hibernation (about 2-3 degrees above freezing)

169
Q

hibernation

A

setpoint reduced to a very low level but thermoregulation is not suspended (if temp falls below freezing, metabolism increases) and body function slowed

mammals like rodents and insectivores store enough energy to hibernate

lasts up to weeks or months but animals wake to empty bladder

170
Q

why is urine produced during hibernation?

A

water is a byproduct of metabolism (BMR because they don’t eat during hibernation)

171
Q

which body functions are slowed during hibernation?

A

cardiac output and reduced blood flow (10% of normal)

blood flow mainly to vital organs (selective vasoconstriction)

BMR drops to 7% of normal

respiration reduced

almost functioning like a poikilotherm

172
Q

what is analogous to hibernation + temporal heterothermy in mammals/birds but in ectotherms?

A

snakes and frogs remain dormant and inactive in winter

(but not hibernation bc they have no setpoint)

173
Q

why is poikilothermy an energy efficient way of life?

A

do not need to maintain a constant body temperature

174
Q

rate of metabolism in poikilotherms depends on

A

environmental temp (q10 effect), developmental stage and species

q10: rate of O2 consumption increases 2x for every 10 degree increase in ambient temperature

175
Q

at which developmental stage do poikilotherms generate the most heat?

A

early growth stage (embryo) - growth hormone levels are high so MR is high

inverse relationship between body size and MR

176
Q

do poikilotherms generate heat?

A

yes

177
Q

problems with low temperatures with poikilotherms

A

enzymes are less effective at low temp (Q10 effect)

membranes become more viscous

178
Q

how can poikilotherms adapt to low temps?

A

biochemical adaptation - change in membrane composition to increase fluidity

acclimatization - increased MR over time

179
Q

what is an energy-efficient way of thermoregulation for poikilotherms?

A

control of temp conductance - making the most out of environment

e.g. iguanas control rate of heat exchange by controlling rate of heart rate/blood flow to skin + behavioural adaptation

180
Q

at higher temp, affinity of hemoglobin for O2 is

A

significantly less

ability to supply tissues with O2 decreases by half

181
Q

upper critical temperature (UCT)

A

all ectotherms have a UCT - beyond this, there is a breakdown in physiological processes and can be lethal

182
Q

UCT within the same species is the same or different

A

can be very different

183
Q

behaviour as a mechanism of thermoregulation in poikilotherms

A

honeybees fly and swarm differently depending on environmental temp - flying generates heat

form packs/fly close together in cold weather (inside of swarm can be as hot as 35 degrees) vs form loose swarms in hot weather

184
Q

regional heterothermy in poikilotherms

A

flying insects use heterothermy to increase the temp in the thorax region in order to fly

185
Q

regional heterothermy in poikilotherms (insects)

A

flying insects use heterothermy to increase the temp in the thorax region in order to fly

shivering increases thoracic muscle temp prior to flight and circulation in the abdomen assists in cooling to prevent overheating

186
Q

regional heterothermy in poikilotherms (pythons)

A

female pythons generate heat by shivering and muscle contraction to help brood their eggs

heat generation is greater when ambient temp is lower than at high temps

187
Q

regional heterothermy in poikilotherms (tuna)

A

certain fish able to increase MR in the darker muscle tissue and increase body temp 10 degree above ambient

aorta pumps blood from heart through centre of body which minimizes heat loss

188
Q

what classification are tuna?

A

heterotherm (regional heterothermy) and poikilotherm

189
Q

rete region

A

muscle + brown fat in tuna that can produce heat via mechanical and chemical thermogenesis

temp here is significantly higher

190
Q

poikilotherms survive cold temperatures by

A

freeze avoidance by super cooling or production of antifreeze

partial freeze tolerance by freezing ECF or production of cryoprotectants

191
Q

freezing avoidance by super cooling

A

body fluids are cooled below their freezing temps but remain unfrozen bc ice crystals fail to form by preventing the presence of ice nucleating centres

some fish avoid the surface and areas containing ice crystals to prevent the mechanical seeding of ice (ice nuclei) - stay still

PREVENT ICE CRYSTAL FORMATION

192
Q

freeze avoidance by production of antifreeze

A

adhere to growing ice crystals and prevent the crystals from growing to hazardous sizes which prevents tissue damage and allows free flow of blood

alpha helix of antifreeze interrupts lattice of ice from growing

LOWER FREEZING POINT

193
Q

examples of antifreeze production

(glycoprotein, sorbitol, glycerol)

A

flounder + arctic cod have glycoprotein antifreeze protein which lowers freezing point

certain insects (mites) increase sorbitol and glycerol concentration which increases osmotic pressure and lowers freezing point

194
Q

partial freezing - freezing of extra cellular fluid compartment (ECF)

A

some beetles produce nucleating proteins which accelerate and regulate freezing in ECF outside cells

freezing of ECF increases osmotic pressure in ECF and results in dehydration of cells - solute concentration in tissues and loss of water increases which reduces freezing point

LOSS OF WATER FROM CELL TO PREVENT CELL FREEZING BUT ECF FROZEN

195
Q

partial freezing - freeze tolerance

(cryoprotectants: trehalose, proline)

A

many invertebrates can survive partially frozen at extreme temps bc of cryoprotectants such as trehalose and proline which form a gel phase as cells dehydrate and prevents disruption of internal cell organelles by stabilizing the membrane

FORM GEL TO PREVENT ICE CRYSTAL DAMAGE TO MEMBRANE + STABILIZE MEMBRANE

ZOOL 463 (4 decks)

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