Thermoregulation Flashcards
endotherm
an organism that generates heat to maintain its body temperature typically above the temperature of surroundings
includes birds and mammals
ectotherm
AKA poikilotherm
an organism that regulates its body temperature largely by exchanging heat with its surroundings
includes fish, reptiles, etc
downside of endothermic regulation
physiological costly to maintain body temperature
a study found that mitochondrial density and cytochrome oxidase activity is larger in endotherms or ectotherms?
endotherms
ATP is produced in mitochondria and ATP is used to produce heat as a byproduct
(oxidative phosphorylation produces ATP + heat)
which animals are closest to being true endotherms
humans, primates and felines (cats)
benefit of ectothermic regulation
it is easier to be “compliant” with ambient environment than having to work against it (by producing body heat or using cooling mechanisms)
4 overall types of body temperature regulation
homeotherm ectotherm
heterotherm ectotherm
homeotherm endotherm
heterotherm endotherm
2 types of heterothermy
temporal and regional
temporal heterothermy
certain endotherms (bats, hummingbirds) when at rest (short term or long term - torpor/hibernation) reduce metabolism and body temperature drops close to surrounding environment
A bat in torpor (temporal heterothermy) lowers its body temperature overnight to conserve energy but actively warms up when needed.
regional heterothermy
certain endothermic and ectothermic animals are able to maintain different temperature “zones” in different regions of the body
core temperature is usually constant though
normal body temperature (mammals)
close to 37° Celsius or 98.6° Fahrenheit
body temperature may increase to ____ during heavy exercise
38.3-40°C
body temperature can be as high as _____ during febrile illness/pyrexia
42°C
long exposure to cold may reduce body temperature to
36.1°C
is oral or rectal temperature more similar to core body temperature?
rectal
core temperature
what + remains at what
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
skin tempertaure
changes with the temperature of the surrounding
fluctuations in body temperature occur when
the rate of heat loss does not balance the rate of heat gain
thermal neutral zone
comfortable temperature (room temperature) where there is no sweating/not feeling cold
hypothermia
core temperature much below thermal neutral zone
hyperthermia
core temperature above thermal neutral zone
body unable to cool down - feels hot and humid
metabolic rate
rate of energy expenditure (usually per hour)
how is metabolic rate measured?
either directly by direct calorimetric methods (using chamber) or indirectly by measuring oxygen consumption (easier)
the body produces ____ cal of heat/L of oxygen
4.8 (metabolic rate)
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)
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)
average BMR in a 70 kg adult
60-72 Kcal/hr (~1500-1700 Kcal/day)
factors influencing BMR
surface area/mass ratio, age, gender, muscle, stress/hormones
most important factor for BMR
surface area/mass ratio
surface area/mass ratio in small animals
very high
surface area is larger compared to mass (very small)
mass-specific MR
whole animal MR divided by body weight
do small or large animals have lower mass specific MR?
much lower MR in large animals (decreased SA:mass)
do small/large animals burn more calories?
small
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
how does gender affect BMR?
BMR is higher in males than in females
how does muscle/fat affect BMR?
BMR is higher in muscular than in fatty people
muscle burns more energy while fat stores energy
total metabolic rate (TMR)
total rate of energy expenditure during ongoing involuntary and voluntary activities
average TMR for 70 kg adult with no activities
approximately 2000 cal/day
highest energy expenditure activity
mountain climbing
TMR is affected by
exercise, hormones
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
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
hormones that affect TMR (5)
- thyroid hormones (more so BMR)
- catecholamines (epinephrine/norepinephrine)
- sex hormones
- growth hormones
- certain growth factors
why is MR higher in children?
more growth hormones
hormone-mediated increase in TMR contributes to
non-shivering thermogenesis (increase in heat production not associated with muscle activity)
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
What causes long-term hormone-mediated change in TMR?
thyroid hormones
What causes short-term hormone-mediated change in TMR?
sympathetic pathway (epinephrine and norepinephrine)
brown fat
chemicalthermogenesis?
metabolically active tissue containing large number of mitochondria
chemicalthermogenesis is much greater in animals with brown fat
maintenance of a constant temperature requires
a balance between heat loss and heat production
heat production (3)
What + can be due to x2
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)
heat loss (4)
Primarily thru + caused by x3
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)
effective means of heat production
muscle contraction (mechanical thermogenesis)
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
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)
how does fur decrease heat conductance?
by creating a temperature gradient (reducing sharp gradient)
vasoconstriction of capillaries limits blood flow to
epidermis
vasoconstriction
heat conductance?
limits blood flow to skin so blood flows through shunt
low heat conductance
vasodilation
heat conductance?
decreased blood flow to shunt vessels and increased blood flow to skin
high heat conductance
the rate of blood flow to the subcutaneous venus plexus (SHUNT) could vary between
1-30% of cardiac output (significant change)
subcutaneous venus plexus
shunt vessel
increased temperature leads to
vesell + BF + Conductance + heat loss
vasodilation of vessles > increased blood flow > increased conductance from core to skin > increased heat loss
decreased temperature
vesell + BF + Conductance + heat loss
vasoconstriction of vessels > decreased blood flow > decreased conductance from core to skin > decreased heat loss
conductance in which areas of the body is most effective?
exposed/vascularized areas like ears, face, hands
heat loss by skin is affected by (3)
radiation, conductance, evaporation
heat loss by radiation
~60% of the total heat lost by infrared rays body generated
heat loss by conductance is influenced by
temperature gradient (cannot be controlled).
conductance of heat to —– is much greater than ——
water; air
water is 23.5 times more efficient in transferring heat than air
normal evaporation rate from skin and lungs amounts to
~600 mL/day (heat loss of 12-16 cal/h)
what is evaporation increased by?
greater air current (i.e., convection)
what is an important regulatory mechanism of heat loss?
evaporation through sweating
how can heat loss via radiation be reduced?
insulation
when are radiation and conduction effective mechanisms of heat loss? What occurs the opposite?
when skin temp > surrounding temp
but the body will gain heat when skin temp < surrounding temp
how is sweat carried to the surface of skin?
through sweat ducts - moistens surface of skin
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
what happens when rate of sweating is high in terms of ions
~1/2 of constituents (Na+ and Cl-) may be lost - this is why skin becomes salty
mineral in blood lost in sweat
what reduces the secretion of Na+ and Cl-
aldosterone - involved in osmoregulation of kidney and reabsorption of ions
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)
control of sweating
cholinergic sympathetic pathway in the subdermal region of the sweat gland
what increases sweating but is NOT related to the cooling mechanism
circulating epinephrine - related to nervousness (cold sweat) but not thermoregulated
There are receptor for EP/NE on sweat gland
cholinergic are part of ——-, adrenergic neurons are part of ——– system
parasympathetic system; sympathetic system
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)
which hormone causes goosebumps/hair to stand up
adrenaline (via piloerector muscles)
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)
Increase convection and heat exchange
temperature regulatory centre
located in the posterior hypothalamus
Where does the posterior hypothalamus receive nervous feedback signals from?
sensory thermoreceptors located peripherally and in the anterior hypothalamus
How are thermal signals relayed (4)?
to the brain stem, thalamus, somatic sensory cortex and then relayed to posterior hypothalamus
where are thermoreceptors located?
skin and body tissues (peripheral system and anterior hypothalamus)
Four type of sensory receptors:
4 types: cold pain, cold, warm, heat pain
What temperatures can thermoreceptors distinguish between (7)?
freezing cold, cold, cool, indifferent, warm, hot, burning hot
The peak optimal firing rate for each type of thermoreceptor is
different for each type
cold and warm receptors are located
immediately under the skin at discrete points and varying densities
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
which are more abundant: peripheral cold or warm receptors?
there are 10 times more peripheral cold
when are pain receptors stimulated?
by extreme cold or heat
When do peripheral thermoreceptors increase rate of firing?
when exposed to temperature change
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
spatial summation of peripheral thermoreceptors
thermal sensation is proportional to the number of thermoreceptors stimulated
More response to 3-4 degree change whole body then dipping hand in 25 degree change water
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)
Which area of the hypothalamus contains thermoreceptors and which kind?
preoptic area (temperature sensor area) - specifically the anterior hypothalamus
mainly warm receptors
what does the temperature sensor area (preoptic area) of the anterior hypothalamus detect?
mainly core body temperature - gets alerted to changes in core temperature
Number of heat-sensitive receptors vs cold-sensitive in the anterior hypothalamus
3 times more heat-sensitive receptors (opposite to peripheral thermoreceptors)
how is the critical temperature set point determined?
by the degree of activity of temperature receptors in the hypothalamus
what provides a physiological mechanism for altering the hypothalamic set point?
feedback from peripheral temperature receptors
increase in skin temperature results in?
Set point
a decrease in set point in anticipation of a warming trend
decrease in skin temperature results in?
Set point
an increase in set point in anticipation of a cooling trend
in humans, there is a ——°C change in body temperature for each 25-30°C change in environmental temperature
~1
increased body temperature results in ——- of thermoregulatory centres in the posterior hypothalamus
inhibition
what specific responses occur to heat (3)?
- increased sweating,
- vasodilation in almost all area of the bidy particularly skin and ears and hand
- decreased body heat production (decreased shivering - mechanical and metabolism - chemical thermogenesis)
result of INHIBITION of thermoregulatory centres in posterior hypothalamus
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)
decreased body temperature results in —— of thermoregulatory centres in the posterior hypothalamus
stimilation
what specific responses occur to cold (4)?
- vasoconstriction
- piloerection
- increased shivering
- increased chemical thermogenesis
result of STIMULATION of thermoregulatory centres in posterior hypothalamus
piloerection involves
sympathetic stimulation (via cholinergic pathway) > contraction of arrector pili muscle attached to hair > upright stance of hair > insulation (minimizes temperature gradient)
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
how to increase chemical thermogenesis (2)
Increase what MR?
increased sympathetic stimulation (adrenergic - short term) > increased NE/E levels > increased metabolic rate > increased chemical thermogenesis
- increased TMR but not BMR
Prolonged (long term) exposure to cold leads to increased —–
thyroid hormone production
which hormone increases overall BMR?
thyroid hormone
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)
thyroid hormone-induced increase in BMR in a consequence of
long term exposure to low temperature
the hormone pathway long term for prolonged exposure to cold
increased TRH > increased TSH > increased thyroid hormone secretion (T3/T4) > increased metabolic rate (chemical thermogenesis)
how does long term exposure to low temperature affect the thyroid gland?
increase in size (up to 40%)
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.)
pyrexia
state of increased body temperature beyond normal range - could result from infection, allergic reaction, CNS injuries and cancer
what do leukocytes release in response to pyrogens?
macrophages and neutrophils release cytokines (IL-I, IL-6, TNF tumor necrosis factor)
most common pyrogens
bacterial lipopolysaccharides toxins (LPS)
viral polyribonucleptide pyrogen (Poly I: PolyC)
cytokines released from injured cells
pyrogens acts through the
Toll family of membrane receptors
initiates cellular innate immune responses; evolutionary conserved in many species
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)
what do prostaglandins do?
increase the hypothalamic set point and increase temperature (fever)
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)
how does aspirin reduce the degree of fever?
by blocking prostaglandin production from arachidonic acid (inhibits Cox2)
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
vasodilation and sweating during drop in fever is known as
flush (trying to lose heat)
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)
what happens when body temperature reaches its upper limit
thermoregulatory process may be disrupted
heatstroke, brain lesion, febrile disease
what happens in a fever induced by infections like malaria?
dangerously high temperature - temperature regulation seriously impaired
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
why did we evolve to have fever?
sign of disease and evidence that an increase in temperature can improve body defense response
examples of experimental evidence that an increase in temperature can improve body defence response (3)
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
hyperthermia (heat stroke)
if cooling mechanism is not efficient (high humidity or excessive heat gain), an upper limit is reached
what happens beyond the upper limit of body temperature
Body + sympt
loss of ability to regulate temperature, body ni longer try to regulate temp
results in further increase of body temperature and symptoms of heat stroke: extreme weakness, headache, dizziness, nausea, eventually unconsciousness
sustained hyperthermia results in (3):
- hemorrhages (comprised integrity of endothelial layer)
- degeneration of cells especially neurons
- irreversible damage to liver, kidney, and neurons leading to death
how can certain mammls manage sustained running without being affected by heat stroke?
anatomical adaptation (in animals like sheep, goats, gazelles, cats, dogs)
how do hoofed animals prevent overheating of the brain?
special counter-current heat exchange
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
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
hypothermia
sustained exposure to extreme cold will result in decreased body temperature
a lower limit will be reached if the heating mechanism is inefficient (6-7 degree)
which is greater: the lower or upper range of body temperature?
lower range
what happens in hypothermia?
loss of ability to regulate temperature; symptoms include sleepiness, coma and eventually death
frostbite
ice crystal formation - leads to tissue damage (kills cell membrane on contact)
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)
how do wild animals survive the extreme cold (2)?
by physiological and anatomical adaptation
how do marine mammals cope with extreme cold (2)?
- 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
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
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
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
How does fur thickness change in summer vs winter?
winter: fur grows
summer: shed fur and don’t grow as much
examples of temporal heterothermy
dormancy: sleeping through bad weather or lack of food
deep sleep, torpor, hibernation
dormancy
advantageous to allow body temp to drop to avoid energy loss and excessive catabolism
how does the temperature rise to normal after a period of dormancy?
increased metabolism (esp in animals with brown fat) - generates heat
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
difference in temp of deep sleep and hibernation
deep sleep: falls by 3-5 degrees
hibernation: falls by 25-35 (almost freezing)
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)
what causes the physiological changes and characteristics of torpor?
photoperiod and drop in temperature (environmental cues) cause a reduction in set point
what are the physiological changes and characteristics of torpor (5)?
- reduction in core temperature
- decrease in MR
- decrease in heart rate
- Decrease in breathing rate and O2 consumption
- low blood supply to limbs: restricted to vital organs
a greater reduction in body temp is seen in torpor or hibernation?
hibernation (about 2-3 degrees above freezing)
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
why is urine produced during hibernation?
water is a byproduct of metabolism (BMR because they don’t eat during hibernation)
which body functions are slowed during hibernation (5)?
- 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
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)
why is poikilothermy an energy efficient way of life?
do not need to maintain a constant body temperature
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
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
do poikilotherms generate heat?
yes
Problems with low temperatures with poikilotherms (2)
enzymes are less effective at low temp (Q10 effect)
membranes become more viscous
how can poikilotherms adapt to low temps (2)?
biochemical adaptation - change in membrane composition to increase fluidity
acclimatization - increased MR over time
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
at higher temp, affinity of hemoglobin for O2 is
significantly less
ability to supply tissues with O2 decreases by half
upper critical temperature (UCT)
all ectotherms have a UCT - beyond this, there is a breakdown in physiological processes and can be lethal
UCT within the same species is the same or different
can be very different
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
regional heterothermy in poikilotherms
flying insects use heterothermy to increase the temp in the thorax region in order to fly
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
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
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
Tuna, despite being classified as poikilotherms, exhibit regional endothermy—maintaining higher temperatures in specific body regions (e.g., swimming muscles, brain, and eyes) while allowing other parts to match the surrounding water temperature. This adaptation gives them physiological advantages in active swimming, predation, and extended habitat range.
what classification are tuna?
heterotherm (regional heterothermy) and poikilotherm
rete region
muscle + brown fat in tuna that can produce heat via mechanical and chemical thermogenesis
temp here is significantly higher
poikilotherms survive cold temperatures by
freeze avoidance by super cooling or production of antifreeze
partial freeze tolerance by freezing ECF or production of cryoprotectants
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
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
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
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
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
