Lecture 22 - Thermoregulation Flashcards
Do different ages of species have different thermoregulation needs?
Yes - ie adults can handle more than babies
What is an endotherm?
Animals who use metabolic heat to maintain a stable internal temperature, often one different than the environment
Examples of endotherms?
Birds and mammals
What is an ectotherm?
Animals that do not use metabolic heat to maintain their body temperature but take on the temperature of the environment
Examples of ectotherms
Lizards and snakes
Do endotherms and ectotherms have strategies to let them live in different environments
Yes, even some that are extreme
What is diurnal temperature
Variations in body temperature related to the time of day - ie colder in the morning, warmer as day goes on
The core temperature of a human body is
37°C
The core of the human body includes the
Thorax, abdomen, and the head
Where are the vital organs located in the human body
In the core
In the core, the enzyme systems must operate in
Optimum conditions
Can the periphery of the body withstand some deviation from the core temperature?
Yes
What is the effect of temperature on enzyme reaction rate
When temperature increases, rate of rxn increases as molecules gain kinetic energy
Temperature increases & hits optimum temperature
After optimum temperature, enzyme begins denaturing & rate of rxn
Is there a relationship between body weight and heat production?
Yes - as body weight increases (kg), so does heat production (kcal/day)
Temperature is regulated by
Nervous feedback mechanisms
Thermoregulatory responses include
Behavioural, anatomical, or physiological ones
Endotherms can use some of these responses to alter heat production when it’s cold
Endotherms and ectotherms use other methods (not neural control) to increase or decrease exchange with the environment such as
Conduction, convection, radiation, and evaporation
Feedback system for thermoregulation strategies
1) receptor
2) Control Center - sets range of values, evaluates input, and sends input
3) effector - receives output from control centre & produces a response
Hypothalamus acts as
A thermostat
The hypothalamus receives nerve impulses from
Peripheral thermoreceptors for both cold and heat
Hypothalamus also has thermoreceptors called central thermoreceptors - these detect
Changes in blood temperature
Core temperature is in dynamic equilibrium as a result of
Balance between heat gain and heat loss
Things that contribute to thermal balance
Heat input
Core temperature
Heat output
Things that contribute to heat input
Conduction, radiation
things that contribute to core temperature
Basal metabolism, muscle activity, thyroxine, catecholamines, sympathetic output
Things that contribute to heat output
Conduction
Radiation
Convection
Evaporation
Heat is gained by
Chemical reactions in the cells
By the body’s metabolic activity which generates heat (eg when muscles move)
By conduction and radiation from environment
Heat is lost by
Conduction and radiation to the environment
By evaporation from the body surface
animals can also affect their body temperature by
Changing their behaviour
Conduction is
The direct transfer of heat through a liquid, solid, or gas from one molecule to another
A small amount of body heat moves by conduction directly through deep tissues to
Cooler surfaces. Heat exchange involves changing the temperature of air molecules and surfaces in contact with the skin
The rate of conductive heat exchange depends on
Thermal gradient
In an attempt to reduce heat loss, animals instinctively
Curl up when they lay down. This behavioural response reduces the surface area exposed to the cold
What is heat exchange of radiation
Objects emit electromagnetic heat waves without molecular contact with other objects
when temperature of things in environment exceeds the skin temperature, radiant heat energy is
Absorbed from the surroundings without direct contact
What is heat exchange by evaporation
When sweat or water is vaporized from either skin surface of respiratory passages, heat is taken away from the surface.
For each litre of water vaporized , _____ kcal is transferred to the environment
580
For water to be vaporized from the liquid to the gaseous stage, _____________ is required
Lots of energy
Heat transferred as water is vaporized from
Respiratory passages and skin surfaces
Land animals often lose water from
Their skin, mouth, and nose by evaporation into the air
What is the primary means of cooling the body during exercise
Sweating
In panting, an animal breathes rapidly and shallowly with its mouth open to
Increase evaporation from the surfaces of the mouth
What animals use panting
Mammals and birds
Dogs have sweat glands on the undersides of their paws and within their ears. Do they help cooling?
No - these glands only have minimal cooling capabilities
Panting allows a dog to
Rapidly inhale, humidify, then exhale the air, which lead the evaporation of water and loss of heat across the moist surfaces of the upper respiratory system, tongue, and surfaces within the mouth
Is there a relationship between body temperature and hydration
Yes - when a Camel is dehydrated, it’s body temperature is much more variable than when the camel is hydrated & water is available for evaporation
Jackrabbits have large ears with an extensive network of blood vessels that allow
Rapid heat loss
Furry mammals often have special networks of blood vessels for
Heat exchange located in areas of bare skin - this adaptation helps them live in hot desert environments
What’s the body’s main site for heat exchange with the environment
The body’s surface
Because tissues are poor conductors, heat is most effectively transferred in
The blood
What is an important way to control the rate of heat loss to or gain from the surroundings?
Controlling the flow of blood to the skin
In endotherms, warm blood from the body’s core typically loses heat to the environment as
It passes near the skin
Vasoconstriction reduces
Blood flow and helps retain heat
Opposite adaptation to jackrabbits
Arctic hares have shortened ears and thick, white fur to hep survive in harsh, frozen tundra
What happens when core body temp is <37°C?
Thermoreceptors detect & send signal to hypothalamus
Hypothalamus send nerve impulses to muscles and sweat glands
Muscles -> shiver & muscles of skin arteriole walls constrict
- more heat generates, less water covers skin, less radiation & conduction of heat
Diagram on slide 29 if this isn’t clear!!
What happens when core body temperature >37
Thermoreceptors detect & send signals to hypothalamus
Hypothalamus sends impulses to muscles, and sweat glands
Muscles - reduce activity & muscles of skin arteriole walls relax
-> less heat generated, more evaporation, and more radiation& conduction of heat
Thermogenesis
Heat production
Anatomical features for thermogenesis
Shivering & non shivering
Shivering is
Muscle contractions to generate heat
Very effective short term
30-50% of the energy of muscle contraction is converted to heat
What is non-shivering thermogenesis
Brown fat contains many mitochondria with special proteins that let them release energy from fuel molecules directly as heat instead of channeling it into formation of the energy carrier ATP
Is shivering or non shivering thermogenesis more effective
Brown fat is more effective to generate heat
What is insulation
Another way to minimize heat loss to the environment. Birds use feathers, and most mammals use hair or fur, to trap a later of air next to the skin and reduce heat transfer to the environment
Marine mammals insulation
Blubber - a thick layer of fat
In cold weather, birds
Fluff feathers and animals raise their fur to thicken the insulating layer
Examples of behavioural regulations animals perform
Lizards sunbathing, elephants soaking themselves with water, seeking shade, etc
What is hibernation
A dormant, inactive state in which normal body activities slow. They need little energy to stay alive and can live off fat stored in their body during long periods of hibernation
What do animals do to get ready for hibernation
Eat more, and find or build shelter to hibernate in
Hibernation heartbeats/breathing
Heartbeats slow & breathing almost stops - slow down metabolism to conserve energy
What are light sleepers
Animals who do not truly hibernate, and are easily awakened during their winter slumbers. The animals breathe a little more slowly and lower their body temperature a few degrees.
Migration is
The movement of animals in a group from one place to another and back
Animals migrate for different reasons
Some to look for more food, or better climate & animals have specific times during the year that they migrate
How do animals know where to migrate
Animals use their senses to determine direction
Some make mental maps using scent, sight, and/or hearing
Others use stars or sun
At high ambient temperatures, effectiveness of heat loss via conduction and radiation
Decreases
when ambient temperature exceeds body temperature by a lot, heat is
Gained
The only effective mechanism for heat loss at high temperatures is
Evaporation of sweat and respiratory tract vaporization of water
Total sweat vaporized from skin depends on
Surface area exposed to environment
Temperature and humidity of ambient air
Air currents about the body
- most important factor is relative humidity
Increasing steps of heat illness
Heat cramps -> heat syncope -> heat exhaustion -> heat stroke
Hypothermia
Lowering of core body temperature
In humans, below 35°C
It is important to monitor body temperature during and after procedures requiring anesthesia because of
The depressed hypothalamic response
- external heat sources are often fitted to surgical tables for the maintenance of body temperature
- when these are used, there must be assurance that injury to skin doesn’t occur
When animals do not recover quickly after anesthesia, monitoring body temperature and provision of external heat is
Extremely important
