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
2
Q
ectotherm
A
AKA poikilotherm
an organism that regulates its body temperature largely by exchanging heat with its surroundings
includes fish, reptiles, etc
3
Q
downside of endothermic regulation
A
physiological costly to maintain body temperature
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)
5
Q
which animals are closest to being true endotherms
A
humans, primates and felines (cats)
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)
7
Q
4 overall types of body temperature regulation
A
homeotherm ectotherm
heterotherm ectotherm
homeotherm endotherm
heterotherm endotherm
8
Q
2 types of heterothermy
A
temporal and regional
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
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
11
Q
normal body temperature (mammals)
A
close to 37° Celsius or 98.6° Fahrenheit
12
Q
body temperature may increase to ____ during heavy exercise
A
38.3-40°C
13
Q
body temperature can be as high as _____ during febrile illness/pyrexia
A
42°C
14
Q
long exposure to cold may reduce body temperature to
A
36.1°C
15
Q
is oral or rectal temperature more similar to core body temperature?
A
rectal
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
17
Q
skin tempertaure
A
changes with the temperature of the surrounding
18
Q
fluctuations in body temperature occur when
A
the rate of heat loss does not balance the rate of heat gain
19
Q
thermal neutral zone
A
comfortable temperature (room temperature) where there is no sweating/not feeling cold
20
Q
hypothermia
A
core temperature much below thermal neutral zone
21
Q
hyperthermia
A
core temperature above thermal neutral zone
body unable to cool down - feels hot and humid
22
Q
metabolic rate
A
rate of energy expenditure (usually per hour)
23
Q
how is metabolic rate measured?
A
either directly by direct calorimetric methods (using chamber) or indirectly by measuring oxygen consumption (easier)
24
Q
the body produces ____ cal of heat/L of oxygen
A
4.8 (metabolic rate)
25
basal metabolic rate (BMR)
rate of energy expenditure in a post absorptive condition (has not eaten ~12 hr), following a rest period at room temperature (22-23°C)
26
BMR reflects the energy the body needs for what?
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)
27
average BMR in a 70 kg adult
60-72 Kcal/hr (~1500-1700 Kcal/day)
28
factors influencing BMR
surface area/mass ratio, age, gender, muscle, stress/hormones
29
most important factor for BMR
surface area/mass ratio
30
surface area/mass ratio in small animals
very high
surface area is larger compared to mass (very small)
31
mass-specific MR
whole animal MR divided by body weight
32
do small or large animals have lower mass specific MR?
much lower MR in large animals (decreased SA:mass)
33
do small/large animals burn more calories?
small
34
how does age affect BMR?
BMR is higher in a younger age - declines significantly in old age
this is why it's harder to lose weight as you age
35
how does gender affect BMR?
BMR is higher in males than in females
36
how does muscle/fat affect BMR?
BMR is higher in muscular than in fatty people
muscle burns more energy while fat stores energy
37
total metabolic rate (TMR)
total rate of energy expenditure during ongoing involuntary and voluntary activities
38
average TMR for 70 kg adult with no activities
approximately 2000 cal/day
39
highest energy expenditure activity
mountain climbing
40
TMR is affected by
exercise, hormones
41
how does exercise affect TMR?
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
42
difference in heat production between Olympic athletes and unathletic person
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
43
hormones that affect TMR
thyroid hormones (more so BMR), catecholamines (epinephrine/norepinephrine), sex hormones, growth hormones and certain growth factors
44
why is MR higher in children?
more growth hormones
45
hormone-mediated increase in TMR contributes to
non-shivering thermogenesis (increase in heat production not associated with muscle activity)
46
thyroid hormones can increase/decrease TMR by how much?
increase by 50-100% above the normal and low thyroid secretion reduces TMR by 40-60% below the normal
47
What causes long-term hormone-mediated change in TMR?
thyroid hormones
48
What causes short-term hormone-mediated change in TMR?
sympathetic pathway (epinephrine and norepinephrine)
49
brown fat
metabolically active tissue containing large number of mitochondria
chemicalthermogenesis is much greater in animals with brown fat
50
maintenance of a constant temperature requires
a balance between heat loss and heat production
51
heat production
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)
52
heat loss
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)
53
effective means of heat production
muscle contraction (mechanical thermogenesis)
54
muscle has energy efficiency of
~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
55
effective means of maintaining normal core temperature
skin insulation (fur, blubber)
subcutaneous fat is an important insulator (heat conductance of fat is 1/3 of other tissues)
56
how does fur decrease heat conductance?
by creating a temperature gradient (reducing sharp gradient)
57
vasoconstriction of capillaries limits blood flow to
epidermis
58
vasoconstriction
limits blood flow to skin so blood flows through shunt
low heat conductance
59
vasodilation
decreased blood flow to shunt vessels and increased blood flow to skin
high heat conductance
60
the rate of blood flow to the subcutaneous venus plexus (SHUNT) could vary between
1-30% of cardiac output (significant change)
61
subcutaneous venus plexus
shunt vessel
62
what is blood flow in the shunt vessel controlled by?
arteriovenous anastomosis opening/closing
connections between arteries and veins that are not capillaries
63
increased temperature leads to
vasodilation of vessles > increased blood flow > increased conductance from core to skin > increased heat loss
64
decreased temperature
vasoconstriction of vessels > decreased blood flow > decreased conductance from core to skin > decreased heat loss
65
conductance in which areas of the body is most effective?
exposed/vascularized areas like ears, face, hands
66
heat loss by skin is affected by
radiation, conductance, evaporation
67
heat loss by radiation
~60% of the total heat lost by infrared rays
68
heat loss by conductance is influenced by
temperature gradient (cannot be controlled)
69
conductance of heat to _____ is much greater than _____
water; air
water is 23.5 times more efficient in transferring heat than air
70
normal evaporation rate from skin and lungs amounts to
~600 mL/day (heat loss of 12-16 cal/h)
71
what is evaporation increased by?
greater air current (i.e., convection)
72
what is an important regulatory mechanism of heat loss?
evaporation through sweating
73
how can heat loss via radiation be reduced?
insulation
74
when are radiation and conduction effective mechanisms of heat loss?
when skin temp > surrounding temp
but the body will gain heat when skin temp < surrounding temp
75
how is sweat carried to the surface of skin?
through sweat ducts - moistens surface of skin
76
tonicity of sweat vs plasma
isotonic (excluding proteins in plasma) but most of ions in sweat are reabsorbed during passage through the duct to minimize ion loss
77
what happens when rate of sweating is high
~1/2 of constituents (Na+ and Cl-) may be lost - this is why skin becomes salty
78
what reduces the secretion of Na+ and Cl-
aldosterone - involved in osmoregulation of kidney and reabsorption of ions
79
acclimatization to sweating
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
environmental factors influencing temperature control
movement of air/moisture and temperature gradient
81
control of sweating
cholinergic sympathetic pathway in the subdermal region of the sweat gland
82
what increases sweating but is NOT related to the cooling mechanism
circulating epinephrine - related to nervousness (cold sweat) but not thermoregulated
83
cholinergic and adrenergic neurons are part of which system
parasympathetic system; sympathetic system
84
the sympathetic fibre of the sweat gland, piloerector muscle and some blood vessels have which hormone?
cholinergic (exceptional case bc sympathetic system is usually adrenergic)
85
which hormone causes goosebumps/hair to stand up
adrenaline (via piloerector muscles)
86
how do animals that lack skin sweat glands and have skin covered in thick fur lose heat?
panting is an effective mechanism of heat loss - shallow breath that does not increase alveolar ventilation (not related to rate of breathing)
87
temperature regulatory centre
located in the posterior hypothalamus
88
where does the posterior hypothalamus receive nervous feedback signals from?
sensory thermoreceptors located peripherally and in the anterior hypothalamus
89
how are thermal signals relayed?
to the brain stem, thalamus, somatic sensory cortex and then relayed to posterior hypothalamus
90
where are thermoreceptors located?
skin and body tissues (peripheral system and anterior hypothalamus)
91
type of sensory receptors
4 types: cold pain, cold, warm, heat pain
92
what temperatures can thermoreceptors distinguish between?
freezing cold, cold, cool, indifferent, warm, hot, burning hot
93
the peak optimal firing rate for each type of thermoreceptor is
different for each type
94
cold and warm receptors are located
immediately under the skin at discrete points and varying densities
95
peripheral vs deep temperature receptor location
peripheral: around the skin region
deep: present around spinal cords, abdominal viscera and the great veins in the upper abdomen and thorax
96
which are more abundant: peripheral cold or warm receptors?
there are 10 times more peripheral cold
97
when are pain receptors stimulated?
by extreme cold or heat
98
when do peripheral thermoreceptors increase rate of firing?
when exposed to temperature change
99
adaptation of peripheral thermoreceptors
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
spatial summation of peripheral thermoreceptors
thermal sensation is proportional to the number of thermoreceptors stimulated
101
which has a greater effect: a small temp change over a large area or a large temp change over a small area?
a small temp chance over a large area (more thermoreceptors stimulated)
102
which area of the hypothalamus contains thermoreceptors
preoptic area (temperature sensor area) - specifically the anterior hypothalamus
mainly warm receptors
103
what does the temperature sensor area (preoptic area) of the anterior hypothalamus detect?
mainly core body temperature - gets alerted to changes in core temperature
104
number of heat-sensitive receptors vs cold-sensitive in the anterior hypothalamus
3 times more heat-sensitive receptors (opposite to peripheral thermoreceptors)
105
how is the critical temperature set point determined?
by the degree of activity of temperature receptors in the hypothalamus
106
what is the set point analogous to?
thermostat - set to a specific temperature and gain or lose heat to maintain that temperature
107
what provides a physiological mechanism for altering the hypothalamic set point?
feedback from peripheral temperature receptors
108
increase in skin temperature results in?
a decrease in set point in anticipation of a warming trend
109
decrease in skin temperature results in?
an increase in set point in anticipation of a cooling trend
110
in humans, there is a _____°C change in body temperature for each 25-30°C change in environmental temperature
~1
111
increased body temperature results in ______ of thermoregulatory centres in the posterior hypothalamus
inhibition
112
what specific responses occur to heat?
increased sweating, vasodilation, decreased body heat production (decreased shivering - mechanical and metabolism - chemical thermogenesis)
result of INHIBITION of thermoregulatory centres in posterior hypothalamus
113
a temperature rise of _____°C results in a significant increase in sweating
0.5 - very efficient mechanism
can be enhanced by factors like convection (sitting in front of fan)
114
decreased body temperature results in ______ of thermoregulatory centres in the posterior hypothalamus
stimilation
115
what specific responses occur to cold?
vasoconstriction, piloerection, increased shivering, increased chemical thermogenesis
result of STIMULATION of thermoregulatory centres in posterior hypothalamus
116
piloerection involves
sympathetic stimulation (via cholinergic pathway) > contraction of arrector pili muscle attached to hair > upright stance of hair > insulation (minimizes temperature gradient)
117
shivering
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
chemical thermogenesis
increased sympathetic stimulation (adrenergic - short term) > increased NE/E levels > increased metabolic rate > increased chemical thermogenesis
increased TMR but not BMR
119
prolonged (long term) exposure to cold leads to increased
thyroid hormone production
this increases overall BMR
120
which hormone increases overall BMR?
thyroid hormone
121
acclimatization to cold in some animals (like gophers and true hibernators) leads to what?
increased chemical thermogenesis by ~500%
(only 10-15% in humans bc no brown fat)
122
thyroid hormone-induced increase in BMR in a consequence of
long term exposure to low temperature
123
prolonged exposure to cold
increased TRH > increased TSH > increased thyroid hormone secretion (T3/T4) > increased metabolic rate (chemical thermogenesis)
124
how does long term exposure to low temperature affect the thyroid gland?
increase in size (up to 40%)
125
subconscious mechanisms for body temperature control are complemented by
behavioural aspects resulting from discomfort (either feeling too hot or too cold)
animals do this too (seek shelter, hibernate, etc.)
126
pyrexia
state of increased body temperature beyond normal range - could result from infection, allergic reaction, CNS injuries and cancer
127
what do leukocytes release in response to pyrogens?
macrophages and neutrophils release cytokines (IL-I, IL-6, TNF tumor necrosis factor)
128
most common pyrogens
bacterial lipopolysaccharides toxins (LPS)
viral polyribonucleptide pyrogen (Poly I: PolyC)
cytokines released from injured cells
129
pyrogens acts through the
Toll family of membrane receptors
initiates cellular innate immune responses; evolutionary conserved in many species
130
pyrogens such as cytokines (IL-I, IL-6, TNF) act through
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
what do prostaglandins do?
increase the hypothalamic set point and increase temperature (fever)
132
what is the pathway of pyrogens increasing fever?
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
how does aspirin reduce the degree of fever?
by blocking prostaglandin production from arachidonic acid (inhibits Cox2)
134
during fever, the person experiences
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
vasodilation and sweating during drop in fever is known as
flush (trying to lose heat)
136
2 phases of a fever
pyresis (increasing temperature - body activates responses to cold which increases heat production)
antipyresis (after crisis and set point is suddenly reduced)
137
what happens when body temperature reaches its upper limit
thermoregulatory process may be disrupted
heatstroke, brain lesion, febrile disease
138
what happens in a fever induced by infections like malaria?
dangerously high temperature - temperature regulation seriously impaired
139
what happens when the pyrogen is removed?
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
why did we evolve to have fever?
sign of disease and evidence that an increase in temperature can improve body defense response
141
examples of experimental evidence that an increase in temperature can improve body defence response
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
hyperthermia (heat stroke)
if cooling mechanism is not efficient (high humidity or excessive heat gain), an upper limit is reached
143
what happens beyond the upper limit of body temperature
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
sustained hyperthermia results in
hemorrhages (comprised integrity of endothelial layer), degeneration of cells especially neurons, irreversible damage to liver, kidney, and neurons leading to death
145
how can certain mammls manage sustained running without being affected by heat stroke?
anatomical adaptation (in animals like sheep, goats, gazelles, cats, dogs)
146
how do hoofed animals prevent overheating of the brain?
special counter-current heat exchange
147
how does the counter-current heat exchange process happen in hoofed animals?
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
which animals do not have counter-current system to reduce heat stroke
rodents and primates
they have to manage physical activity to prevent heat stroke
149
hypothermia
sustained exposure to extreme cold will result in decreased body temperature
a lower limit will be reached if the heating mechanism is inefficient
150
which is greater: the lower or upper range of body temperature?
lower range
151
what happens in hypothermia?
loss of ability to regulate temperature; symptoms include sleepiness, coma and eventually death
152
frostbite
ice crystal formation - leads to tissue damage (kills cell membrane on contact)
153
why does your face turn red when cold?
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
how do wild animals survive the extreme cold?
by physiological and anatomical adaptation
155
how do marine mammals cope with extreme cold?
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
counter-current blood flow in marine mammals
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
regional heterothermy to protect from extreme cold
part of body (like extremities) maintained at lower temperature
in some arctic animals, tissues in legs and feet are close to freezing
158
how do membranes survive in extremities of regional heterothermic animals?
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
how does fur thickness change in summer vs winter?
winter: fur grows
summer: shed fur and don't grow as much
160
examples of temporal heterothermy
dormancy: sleeping through bad weather or lack of food
deep sleep, torpor, hibernation
161
dormancy
advantageous to allow body temp to drop to avoid energy loss and excessive catabolism
162
how does the temperature rise to normal after a period of dormancy?
increased metabolism (esp in animals with brown fat) - generates heat
163
why can't all animals go through torpor and hibernation?
large animals: too large mass - impossible to bring temp back up
very small animals: high metabolic rates - have to constantly eat to survive
164
difference in temp of deep sleep and hibernation
deep sleep: falls by 3-5 degrees
hibernation: falls by 25-35 (almost freezing)
165
torpor
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
what causes the physiological changes and characteristics of torpor?
photoperiod and drop in temperature (environmental cues) cause a reduction in set point
167
what are the physiological changes and characteristics of torpor?
reduction in core temperature, decrease in MR, heart rate, breathing rate and O2 consumption, low blood supply to limbs - restricted to vital organs
168
a greater reduction in body temp is seen in torpor or hibernation?
hibernation (about 2-3 degrees above freezing)
169
hibernation
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
why is urine produced during hibernation?
water is a byproduct of metabolism (BMR because they don't eat during hibernation)
171
which body functions are slowed during hibernation?
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
what is analogous to hibernation + temporal heterothermy in mammals/birds but in ectotherms?
snakes and frogs remain dormant and inactive in winter
(but not hibernation bc they have no setpoint)
173
why is poikilothermy an energy efficient way of life?
do not need to maintain a constant body temperature
174
rate of metabolism in poikilotherms depends on
environmental temp (q10 effect), developmental stage and species
q10: rate of O2 consumption increases 2x for every 10 degree increase in ambient temperature
175
at which developmental stage do poikilotherms generate the most heat?
early growth stage (embryo) - growth hormone levels are high so MR is high
inverse relationship between body size and MR
176
do poikilotherms generate heat?
yes
177
problems with low temperatures with poikilotherms
enzymes are less effective at low temp (Q10 effect)
membranes become more viscous
178
how can poikilotherms adapt to low temps?
biochemical adaptation - change in membrane composition to increase fluidity
acclimatization - increased MR over time
179
what is an energy-efficient way of thermoregulation for poikilotherms?
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
at higher temp, affinity of hemoglobin for O2 is
significantly less
ability to supply tissues with O2 decreases by half
181
upper critical temperature (UCT)
all ectotherms have a UCT - beyond this, there is a breakdown in physiological processes and can be lethal
182
UCT within the same species is the same or different
can be very different
183
behaviour as a mechanism of thermoregulation in poikilotherms
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
regional heterothermy in poikilotherms
flying insects use heterothermy to increase the temp in the thorax region in order to fly
185
regional heterothermy in poikilotherms (insects)
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
regional heterothermy in poikilotherms (pythons)
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
regional heterothermy in poikilotherms (tuna)
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
what classification are tuna?
heterotherm (regional heterothermy) and poikilotherm
189
rete region
muscle + brown fat in tuna that can produce heat via mechanical and chemical thermogenesis
temp here is significantly higher
190
poikilotherms survive cold temperatures by
freeze avoidance by super cooling or production of antifreeze
partial freeze tolerance by freezing ECF or production of cryoprotectants
191
freezing avoidance by super cooling
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
freeze avoidance by production of antifreeze
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
examples of antifreeze production
(glycoprotein, sorbitol, glycerol)
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
partial freezing - freezing of extra cellular fluid compartment (ECF)
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
partial freezing - freeze tolerance
(cryoprotectants: trehalose, proline)
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
