Lecture 13- Living systems and temperature Flashcards
Why can most living cells generally only live within a narrow range of temperatures?
- Too hot: proteins denature
- Too cold: ice crystals damage the cell
What does Q10 describe?
The temperature sensitivity of a reaction or process
How is Q10 calculated?
Dividing the rate of a process or a reaction at a certain temperature by the rate of that reaction or process 10 degrees Celsius lower
What is the Q10 value of a reaction that is not temperature sensitive?
1
Within what range of Q10 values do most biochemical reactions and physiological processes fall within?
2-3
Why does changes in temperature disrupt an animals physiology?
Not all component reactions that constitute the metabolism have the same Q10 values- this disrupts the balance and integration
What must animals be able to do in order to maintain homeostasis?
Compensate for or prevent changes in body temperature
Animals whose body temperature is tightly coupled to the environment are able to continue to function in the different season by…
acclimatizing
How do fish acclimatize to different seasons?
The fish expresses a number of different isozymes that operate at different optimal temperatures
What type of acclimatization is most commonly seen?
Partial compensation- most animals cannot compensate completely for seasonal change
What animals have a constant body temperature?
Homeotherms
What animals have variable body temperatures?
Poikilotherms
What is the thermal classification system based on?
The source of heat that predominantly determines the temperature of the animal
What name is given to animals that have their body temperature determined primarily by external sources of heat?
Ectotherms
What name is given to animals who regulate their body temperature by producing heat metabolically or by using active mechanisms of heat loss?
Endothemrs
What name is given to animals that behaves sometimes like an endotherm and other times like an ectotherm?
Heterotherm
What animals are endotherms?
Most mammals and birds
Give an example of a heterotherm.
A mammal that hibernates over the winter
How is heat produced by animals?
Inefficient transfer of energy in biological systems produces heat energy
Why do endotherms produce more heat than ectotherms?
Endotherms have less efficient cells- the transport of ions across membranes requires energy and endotherms have more ‘leaky’ membranes
Endotherms therefore expend more energy
Why did endothermy evolve?
A mutation in a small ecotherm produced enough heat to remain active longer after the sun went down
What are the three major differences between endotherms and ectotherms?
- Resting metabolic rate
- Total energy expenditure when resting
- Response to changes in environmental temperatures
Define isozymes
Enzymes that differ in amino acid sequence but catalyse the same reaction
How do endotherms react to cold conditions?
Increasing their metabolic rate to maintain body temperature
What mechanisms do both endo and ectotherms use to maintain body temperature?
Behavioral regulation (such as moving into the sun)
Give an example of complex thermoregulatory behavior.
Huddling, nest construction
What are the 4 avenues of heat exchange between an animals body and its environment?
- Radiation
- Conduction
- Convection
- Evaporation
How does radiation exchange heat?
Heat transfers from warmer objects to cooler ones via the exchange of infrared radiation
How does conduction exchange heat?
Heat transfers directly when objects of two different temperatures come into contact
How does convection exchange heat?
Heat transfers to a surrounding medium such as air or water as that medium flows over a surface
How does evaporation exchange heat?
Heat transfers away from a surface when water evaporates on that surface
What can the balance of heat production and heat exchange be expressed as?
An energy budget
What is the energy budget equation?
Heat in (metabolism, radiation absorbed)= heat out(radiation out, convection, conduction, evaporation)
How does heat get exchanged between the internal environment and the skin?
Blood flow
What two areas do marine iguana’s on the Galapagos islands alternate between?
Hot black larva rocks on the shore to bask
Cold ocean water to feed on seaweed
Why do marine iguana’s alternate between two areas?
The ocean water cools them- their metabolism slows and they become vulnerable to predators and incapable of digestion.
How do the marine iguana’s on the Galapagos islands control their body heat?
Changing their heart rate and rate of blood flow to their skin
How do mammals maintain a constant temperature by controlling their blood flow?
Fur acts as insulation
Special blood vessels transports heat to their hairless skin surfaces
How is heat loss in skin controlled?
Opening and closing of special blood vessels
Why do fish have difficulty retaining heat produced by their metabolism?
Blood pumped from the heart goes directly to the gills where it is in very close contact with surrounding water
How do some large, rapidly swimming fishes maintain temperature differences of 10-15 degrees Celsius from their surrounding water?
-Powerful swimming muscles produces heat
-Arrangement of blood vessels conserves heat
Example:great white sharks, bluefin tuna
Describe the typical ‘cold’ fish circulatory system.
Oxygenated blood from gills connect to a large dorsal vessel, the aorta,
The aorta travels through the centre of the fish
The aorta distributes blood to all organs and vessels
Describe the typical ‘hot’ fish circulatory system.
Hot fish have a smaller central dorsal aorta
Most oxygenated blood is transported to large vessels beneath the skin
Cold blood from the gills is kept close to their surface
The smaller vessels transporting this blood into muscle mass runs parallel to vessels transporting warm blood from muscle mass back to the heart.
What is the name of the heat exchange that occurs in some large, fast swimming fish?
Countercurrent heat exchanger
How does the countercurrent heat exchanger work?
Vessels carrying cold blood into the muscle are in close contact with vessels carrying warm blood to the heart- heat flows from the warm to the cold blood
Why is the system in ‘hot’ fish circulatory systems named ‘countercurrent heat exchanger’?
Heat is exchanged between blood vessels carrying blood in opposite directions
Why is it advantageous to maintain heat within fish?
Each 10 degrees Celsius rise in body temperature increases fish’s sustainable power output by almost 3 fold
What temperature must some insects flight muscles reach before they can fly?
35-40 degrees celsius
How do insects maintain high temperatures in their flight muscles?
Contracting their heat muscles in a manner analogous to shivering mammals
Give an example of ectotherms regulating heat production. (Beetle)
Underground scarab beetles in mountains north of LA
Mating- they come above ground at night, in winter, during snowstorms.
Give an example of ectotherms regulating body heat as a group.
Honeybees
How do honey bees regulate their body heat during the winter?
Workers cluster around the brood of larvae- adjusting individual metabolic rates and density of clustering so brood temperature remains constantly 34 degrees C.
How is metabolic rate determined?
Measuring rate at which an animal consumes oxygen and produces carbon dioxide
When is the metabolic rate of endotherms low and independent of temperature?
A narrow range of environmental temperatures- the thermoneutral zone
What is the metabolic rate of a resting organism within the thermoneutral zone?
Basal metabolic rate
What is the basal metabolic rate
The rate at which a resting animal is consuming just enough energy to carry out its minimal body functions
What is the relationship between BMR per gram of tissue and animal size?
BMR per gram of tissue increases as animals get smaller
What initial theory was put forwards to explain why BMR per gram of tissue increases as animals get smaller?
Larger animals cannot dissipate heat as easily but have a larger volume to produce metabolic heat in (avoid overheating)
Why is the explanation put forwards to explain why BMR per gram of tissue increases as animals get smaller?
The relationship is seen in very small animals and ectotherms where overheating is not a problem
A mouse uses energy at how many times greater than an elephant per gram of tissue?
20x
What is the thermoneutral zone bound by?
Upper and lower critical temperature
What do animals do below the lower critical temperature?
Produces metabolic heat to compensate for increased heat loss to the environment
What do animals do above their upper critical temperature?
The animal expends energy to lose heat by panting or sweating, which makes the metabolic rate increase
How is body temperature regulated in the thermoneutral zone?
Altering heat loss through the skin, fluffing fur, changing posture
How do mammals increase their metabolic rate in response to cold temperatures? What about birds?
Shivering and nonshivering heat production
Birds use only shivering
How does shivering raise body temperature?
Contractile machinery of skeletal muscle consumes ATP - shivering muscles pull against each other so a temor results.
Energy of ATP to ADP conversion is released as heat
Where does nonshivering heat production occur?
Specialized adipose tissue called brown fat
What is brown fat brown?
Abundant mitochondria and rich blood supply
Explain how brown fat produces metabolic heat.
A protein called thermogenin uncouples proton movement from ATP production, protons leak across the inner mitochondrial membrane (do not pass ATP synthase)- metabolic fuels are used without producing ATP- heat is released
In which organisms is brown fat most abundant?
Newborn infants of many mammalian species
Some small adult mammals acclimatized to the cold
Animals that hibernate
What are the most important adaptations to endotherms in cold environments?
Those that reduce heat loss
What are some of the adaptations endotherms in cold environments have?
- Smaller surface area than warm-climate cousins (rounder body, shorter appendages)
- Thermal insulation- thicker fur, feathers or fat
- Decreased blood flow to the skin (countercurrent heat exchange in appendages)
What cold environment animals show adaptation in their fur?
Arctic fox, northern sled dog, arctic hare (Lepus arcticus)
Why do some species secrete oil in their fur and feathers by grooming?
So air trapped close to the skin is not displaced by water- maintains high level of insulation
Name large mammals that wallow in water when temperatures rise.
Elephants, rhinoceroses, water buffaloes
Why does water dissipate heat?
Heat absorbing capacity of water is greater than air
Evaporation of water cools endotherms
How many calories of heat can a gram of water absorb when it evaporates?
580 calories
Why is some sweating/salivating not advantageous?
- If it drips/falls, it does not provide cooling benefits, but water is lost- bad in arid environments.
- Sweating/panting is an active process and uses energy and generates heat.
What can the regulatory system of body temperature control be thought of?
A thermostat
Where is the vertebrate thermostat?
The hypothalamus - an integrative center at the bottom of the brain
In many species, what is the source of feedback information in the regulatory system?
The hypothalamus
What happens when the hypothalamus of fish is cooled?
The fish seeks warmer water
What happens when the hypothalamus of mammals is cooled?
The blood vessels constrict
Increase in metabolic rate
Body temperature rises
Where is the set point generated?
The hypothalamus
Hypothalamic temperature is what type of signal?
Negative feedback signal
What does experimental warming and cooling of the hypothalamus show about mammal thermoregulatory responses?
Mammals have separate set points for activating different thermoregulatory responses (vasoconstriction, then shivering at low temperatures etc.)
What other sources of information does the thermoregulatory system also integrate?
Temperature sensors in the skin: Change in skin temperature (feedforward information)
Other than skin temperature, what other factors can shift hypothalamic set points?
- Set point higher during wakefullness than during sleep
- Higher during active part of the day
- Cycle is controlled by a circadian rhythm
Why do fever’s exist?
They are adaptive responses to help fight pathogens
What substance rise body temperature to bring about a fever?
Pyrogens
What are the two types of pyrogens?
Exogenous pyrogens- foreign substances coming from bacteria or viruses invading the body
Endogenous pyrogens- produced by immune system cells in response to an infection
How does the presence of a pyrogen effect the body?
Raise the hypothalamic set point, body temperature rises in response
What is hypothermia?
A state of below normal body temperature.
What can cause hypothermia?
- Turning down thermostat
- Starvation (lack of metabolic fuel)
- Exposure to extreme cold
- Serious illness
- anesthesia
What do many species of birds and mammals use to survive periods of cold and food scarcity?
Regulated hypothermia
Give an example of regulated hypothermia.
Hummingbirds- high metabolic rate, small.
Extend the period over which they can survive without food by dropping their body temperature when inactive
What is the name given to regulated hypothermia in hummingbirds?
Daily torpor
How much can body temperature drop during daily torpor?
10-20 degrees C
What is hibernation?
Regulated hypothermia that lasts days or weeks- thermostat is dropped very low to conserve energy
When does an animal become aroused from their hibernation?
When the hypothalamic set point returns to the normal level for a mammal
Give examples of animals that hibernate.
Mammals- bats, bears, ground squirrels
Birds- (only one species) poorwill
