ECO PHYS UNIT 3 EXAM (LECTURE NOTES)

What are issues with freezing?

Intracellular freezing can be fatal due to ice crystals damaging internal structures and rupturing membrane and extracellular freezing can sometimes be tolerated.

Why is freezing a problem?

The formation of ice outside of the cell can result in dehydration of the cell. As extracellular water turns to pure ice, the remaining extracellular liquid becomes hypertonic (higher solute concentration), drawing water out of the cell via osmosis and causing severe cellular shrinkage or dehydration

Why? How could freezing be circumvented?

Osmotic pressure increases and becomes higher outside the cell as water freezes into ice. Freezing is circumvented by using cryoprotectants that lower freezing point, reduce ice crystal formation, and limit osmotic shock.

Define freezing point?

The highest temperature capable of inducing freezing.

What are increasing solutes due to freezing point?

Decreasing in freezing point

What is ectotherm’s response to freezing in physiological mechanisms?

Colligative antifreeze and noncolligative antifreeze

Colligative antifreeze?

Lowers freezing point by increasing solute concentration. Examples are salts, glucose, glycerol, and urea.

Non-colligative antifreeze?

Molecules suppress ice growth by interfering with chemical bonding (e.g hydrogen bonds) between water molecules. Prevents ice formation/growth by interacting directly with ice crystals; antifreeze proteins/glycoproteins bind to surface of ice crystals; preventing additional water molecules from joining the cells. Examples antifreeze glycoproteins, antifreeze proteins.

What is an example of colligative antifreeze and non-colligative antifreeze use?

A study compared the freezing points of black perch and polar fish. Polar fish had much lower freezing points but also expressed antifreeze glycoproteins (AFGP). After dialysis, the freezing point of the black perch increased from -0.7 to 0.01. Illustrates effects of colligative antifreeze. After dialysis, the freezing point of the polar fish increased, but was comparatively lower due to the AFGP. Has both colligative and non-colligative antifreeze effects.

Thermogenesis define?

the physiological process by which organisms generate heat internally to regulate their body temperature, adapt to changing environmental conditions, and maintain metabolic function.

If thermogenesis is based upon the rate at which molecular bonds are broken (exergonic reactions), then how can cell respiration be modified to heat production? What is this process called?

This process is called non-shivering thermogenesis. Non shivering thermogensis is when cell respiration can be modified for heat production by using uncoupling proteins (UCP 1)  to insert protein channels in the mitochondrial membrane. Kinetic energy (movement down gradient) of the protons generate heat; this is uncoupled from ATP synthesis. As the H+ cross the gradient, the energy in the electrochemical gradient is released as heat rather than being passed through ATP synthase to make ATP.  Consequently, factors that typically drive cellular respiration—such as an increased metabolic rate, higher mitochondrial enzyme concentrations, and the activation of brown adipose tissue will now result in increased heat production instead of increased ATP synthesis

What are other thermogenetic mechanisms?

Shivering thermogenesis and non-shivering thermogenesis

Shivering thermogenesis?

Rapid unsynchronized muscle contraction and relaxation. Evolved independently in birds and mammals and some brooding pythons.

Brown adipose tissue in non-shivering thermogenesis?

Rapid lipolysis of brown adipose tissue (BAT) releases heat. “BAT” is brown because it is highly vascularized (increased blood flow); also had a greater mitochondrial density. BAT is typically located in body regions to maximize heat production where most needed.

How does uncoupling proteins in non-shivering thermogenesis increase heat production?

Uncoupling proteins (UCP 1) inserts protein channels in the mitochondrial membrane. Kinetic energy (movement down gradient) of the protons generate heat; this is uncoupled from ATP synthesis. As the H+ cross the gradient, the energy in the electrochemical gradient is released as heat rather than being passed through ATP synthase to make ATP.

What are phenotypic differences (anatomical and cellular adaptations) associated with endothermy?

Higher mitochondrial abundance, higher mitochondrial membrane surface area, and larger visceral organs (upregulated oxygen consuming processes)

Why is the negative mass-specific relationship between body size and metabolic rate more prominent in endotherms?

Endotherms have a higher surface area/volume ratio which increases heat exchange.

What is thermal neutral zone (TNZ)?

A range of temperatures a homeotherm can maintain normal body temperature.

What are lower or higher critical temperatures?

Ambient temperatures at which metabolic rates increase.

Lower Critical Temperature (LCT)?

The ambient temperature at the bottom of the thermoneutral zone. Below this point, an endotherm's metabolic rate increases through shivering or non-shivering thermogenesis to produce extra body heat.

Upper Critical Temperature (UCT)?

The ambient temperature at the top of the thermoneutral zone. Above this point, an organism's metabolic rate increases due to active cooling mechanisms (like panting, sweating, or evaporative cooling) and elevated cellular activity caused by the heat.

Thermoneutral Zone (TNZ)?

The temperature range sitting between the LCT and UCT where an animal maintains a steady resting metabolic rate without needing extra energy to warm up or cool down.

How do organisms physiologically regulate heat exchange?

Regional heterothermy, countercurrent heat exchange, and countercurrent exchange for cooling.

What is regional heterothermy?

A difference in temperature from one body region to another. Achieved by vasomotion (vasoconstriction, and vasodilation).

Vasomotion?

Helps regulate heat transfer. Types include vasoconstriction and vasodilation.

Vasoconstriction?

Decreases diameter of blood vessels, keeps heat away from surface; heat retention.

Vasodilation?

Increases diameter of blood vessels, of blood vessels, move heat to the surface to cool.

How does the latter save energy?

Heat loss from arterial blood is exchanged with venous blood, warmer venous blood acquires less energy to heat.

Why are birds allowed to have their feet drop so low in body temperature?

Connective tissue has a low metabolic rate, so it has lower energy requirements. Muscle tissue has a high metabolic rate so it has higher energy requirements.

Countercurrent heat exchange to cool?

Countercurrent heat exchange is used to cool arterial blood to the brain. Rete mirable allows a larger surface area for countercurrent heat exchange(increases). Brain is less tolerant to temperature changes because nervous tissue is not tolerant to changes. Nasal passage are moist and have a high surface area which results in evaporative cooling.

Countercurrent heat exchange?

Arterial and venous blood act as the two fluid streams. In cold conditions, heart can move from warm arterial blood to cooler returning venous blood. This minimizes heat loss to environment and reduces energy needed to replace lost heat.

Adaptions for high temperatures using thermoregulation in homeotherms?

Active evaporation cooling

Active evaporation cooling?

Increasing the rate at which evaporation occurs. Sweating, panting, gular fluttering. The cost is water loss, will need alternative strategies in water limited habitats.

What do placental mammals also have in relation to non-shivering thermogenesis?

High mitochondrial density and high mitochondrial surface areas.

In high temperatures, how do homeotherms use thermoregulation?

Cycling of body temperatures and hyperthermia.

What is cycling of body temperatures?

Allowing the body temperature to rise and fall within a day.

What is hyperthermia?

Allowing the body to rise to high temperatures.

How is hyperthermia advantageous?

Decreases rate of heat gain by decreasing differences between ambient and body temperatures (creating a smaller thermal gradient). Heat stored during day is released at night through non evaporative cooling (energy conserved by not heating on cold nights).

How do homeotherms acclimatize seasonally?

Insulation acclimatization, increase peak metabolic rate, increase metabolic endurance, and decreased lower critical temperatures.

Insultation acclimatization?

Change in pelage or peripheral blood flow reduces heat loss.

Increase peak metabolic rate?

Increase in rate of heat production through metabolism.

Metabolic endurance?

Increase duration that a high metabolic rate can be maintained.

What are adaptations to the cold in thermoregulation of homeotherms?

Higher basal metabolic rates, lower low critical temperatures, and they increase metabolic rate proportionally less above BMR when below TNZ.

Basal metabolic rates?

The measure of metabolism when the animal is at rest, fasted, and within its thermal neutral zone.

What is lower critical range difference in arctic species vs tropical species?

Arctic species have lower critical temperatures (point at which MR increases) that are lower than tropical species.

What is Q10 in relation to how arctic species increase metabolic rate proportionally less above BMR when below TNZ?

Q10 is lower in cold adapted homeotherms when below lower critical temps.

How are each of these adaptations to the cold? In other words, how do they improve fitness?

Maintaining a constant body temperature in cold temperatures is very energetically expensive. These adaptations help homeotherms save vast amounts of energy. Because homeotherms don’t have to spend as much energy to stay warm, they can allocate more energy towards survival and reproduction of genes which improves fitness.

What is solution to surface area to volume ratio creating heat loss in appendages in homeotherms?

Regional heterothermy

Regional heterothermy?

Some animals allow appendages to cool to conserve or release heat. Achieved by countercurrent heat exchange to retain heat. Minimizes differences between surface temperature and ambient temperature to minimize heat loss. Tissues in appendages typically have low metabolic demands (i.e tendons, ligaments, bone).

Countercurrent heat exchange?

 

Depends upon two, close fluid streams flowing in opposite directions. In this heat exchange, venous and arterial blood are the “fluid streams”. Regarding heat conservation, this method both minimizes heat loss to environment while warming venous blood (returning to heart).

How does the former minimize heat loss to environment?

Minimizes differences between body and ambient temperatures.