Cold Physiology - Exam 2

Lecture 9

cellular lysis

freezing and thawing tissue can cause damage via (blank)

intracellular; extracellular

(Blank) freezing is very destructive, but not (blank) freezing

"freeze intolerant" strategies

poikilothermic strategies for extreme cold that are basically just to avoid freezing

antifreeze compounds

production is "freeze intolerant" strategy; dissolved substances added to body fluid; serve function of lowering freezing point of body fluids

colligative antifreezes

lower freezing point by increasing concentration of solutes in body fluids; common in terrestrial arthropods; can compose 15-25% of arthropod's biomass during winter

non-colligative antifreezes

lower freezing point via specific chemical properties of solutes in body fluids, not by altering their concentration

polyols

most common types of colligative antifreezes; type of sugar alcohol; ex: mannitol, glycerol, sorbitol, erythritol, etc.

Antifreeze proteins (AFP)

non-colligative antifreezes; bind with weak bonds to form ice crystals, preventing water molecules from joining them; can be effective even when very dilute; most well-studied in fish and insects; can be up-regulated seasonally or produced year-round, depending on environmental selection pressures

certain Antarctic fish

In (blank) AFP-coding genes are derived from those involved in digestive enzyme production

Supercooling

"freeze intolerant" strategy; reducing concentration of "ice-nucleating agents" in body to reduce probability of spontaneous ice formation; used by many types of animals, though best studied in insects; allows some insects to remain unfrozen at temps as low as -60 degrees C

freeze tolerant strategies

poikilothermic strategies for extreme cold in which tissues freeze, but in less damaging way; synthesize ice-nucleating agents and keep them in higher concentration in extracellular fluid to promote extracellular freezing early in winter; ex: high-latitude barnacles, muscles, snails, insects, and wood frogs

freeze tolerance

ability to survive freezing and thawing

homeothermic endotherms

Strategy to avoid freezing is to just not get cold; deep body temps don't vary much with climate

~37 degrees C

most placental mammals maintain deep body temps of (blank)

~39 degrees C

most birds maintain deep body temps of (blank)

chemical processes to be very thermally specialized/more efficient; sense and regulate temperature at system level and has high energy cost in very col or hot

Extreme endothermic thermoregulation of homeothermic endotherms is both beneficial, as it allows (blank) to be (blank)/(blank), and costly, as it necessitates ways to (blank) and has (blank) in (blank) environments

thermoneutral zone

range of temps in homeotherms at which oxygen consumption per unit time is minimized

Shivering

strategy for increasing heat production when below thermoneutral zone; unsynchronized, high-frequency contraction and relaxation of skeletal muscle, mediated by motor neurons of somatic nervous system

Non-shivering thermogenesis

strategy for increasing heat production when below thermoneutral zone; increased heat production unrelated to shivering; due to multiple mechanisms

brown adipose tissue / brown fat

high mitochondrial density; metabolize fats, producing fatty acids, specialize in heat production via uncoupling; after days-long acclimation to low temps, mammals can produce extra heat in this way

regional heterothermy

mammals and birds commonly lose heat via legs, tails, and ears, so reducing appendage temperature reduces heat lost to environment; increaed blood flow - lower core Tb, decreased blood flow = higher core Tb; ex: hare losing temperature in ears and healthy human adult losing temperature in fingers, ears, and nose in cold environments

vasoconstriction

constriction of blood vessels; adjusting blood flow in limbs via this is one way to thermoregulate

vasodilation

dilation of blood vessels; adjusting blood flow in limbs via this is one way to thermoregulate

perfusion

passage of blood through blood vessels

countercurrent heat exchange

reduces heat loss in limbs; more permanent strategy for regional heterothermy used by cold specialized animals; centralized and adjacent large arteries and veins in limbs allow for "short circuiting flow of heat into appendage", without restricting blood flow

homeoviscous adaptation

Some regional heterotherms have (blank) across different regions of their body; this is the adjustment/adaptation of the level of fatty acid saturation in cell membranes to maintain necessary membrane fluidity; ex: elk have higher proportions of monosaturated fatty acids in their feet so that they can afford to not have the temperature so high in these extremities

1. tissues in elk's shoulder

2. tissues in elk's foot

label the two performance curves

controlled hypothermia

homeothermic strategy for dealing with winter; simply not thermoregulating when it's too cold out

hibernation

controlled hypothermia strategy; Tb approximates Ta seasonally, for days to months in winter; trend shown in picture 3

estivation

strategy related to controlled hypothermia; Tb approximates Ta seasonally, for days to months in summer

Daily torpor

controlled hypothermia strategy; Tb approximates Ta for hours of a day for multiple days; trend shown in picture 2

endothermic homeotherms

Insects with flight muscles can generate enough heat to be, at least temporarily, (blank), which is useful in cold environments

eusocial insects; their nest at group level

By clustering and shivering flight muscles, (blank) can also thermoregulate (blank)

endotherms; thermally sensitive

At group level, honeybees are (blank), which benefits (blank) brood

baby reindeer

must thermoregulate on their own from birth in very cold climates, so milk they receive is energy dense (20% lipid); by the time they're 14 days old, they have far lower energy costs to thermoregulate in cold air than when they're newborn

polyunsaturated fatty acids (PUFAs)

mammals can't synthesize these; eating more appears to enable deeper, more efficient hibernation

Omega-6

mammals consuming (blank)-rich diets before hibernation provides greatest benefits (type of PUFA)

Understand what type of damage freezing does to animal tissues.

-Intracellular ice damage: rapid freezing, small ice crystals form inside cells, destroying internal structures and membranes.
-Extracellular ice damage: water escapes the cell to freeze in extracellular spaces, causing the cell to shrink and triggering harmful dehydration.
-Denaturation of protein and lipids
-As ice crystals grow and expand, they rupture cell-to-cell connections.

Be able to explain the costs and benefits of thermoregulation and thermoconformation in cold environments.

-Thermoregulators (endotherms) has the benefits of optimal performance, more geographical range, and reduced predation risk. Meanwhile, the costs are high energetic demand, increased foraging time/risk, and structural costs (such as insulation like fur and blubber and shivering)

-Thermoconformers (ectotherms) has the benefits of extremely low energy expenditure, energy savings, and is energy efficient (no energetic cost is spent on internal heating). Cons are limited performance, vulnerability (cannot forage or flee from predators), and limited niche.

Learn the different strategies that poikilotherms and endothermic homeotherms use to survive in extremely cold environments.

-Poikilotherms survive the cold by entering dormant states, utilizing antifreeze compounds, or employing behavioral changes to manage body temperature, allowing them to lower their metabolism.

-Endothermic homeotherms survive the cold by having insulation, metabolic heat generation (shivering, non-shivering thermogenesis), torpor/hibernation, circulatory adjustments, behavioral adaptations (huddling), etc.

Be able to give examples of the type of animals that use each strategy. (Pay especially close attention to the different strategies for regional heterothermy)

-Countercurrent heat exchanges in limbs (endotherms)

-Specialized heat retention/exchange in core (fish)… uses a complex network of veins and arteries to maintain a higher core temperature than the surrounding cold water, improving muscle function.

-Thermal separation of body segments (insects)… they use countercurrent exchange mechanism at the constriction between their thorax and abdomen. This retains heat in the thorax and allows heat to be lost from the abdomen.

Know the difference between hibernation, estivation, and daily torpor.

-Hibernation is prolonged winter dormancy
-Estivation is long-term summer dormancy
-Daily torpor is a short-term (under 24 hours) energy-saving pause.

Understand the relationship between cold-adaptation and consumption of lipids (in general and of specific types)

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