L7 Flashcards
Temperature vs Heat
temperature - a measure of the speed of the random motions of the atoms or molecules in a substance (degrees)
heat - the total energy that a substance possess by virtue of the sum of random motions of its atoms or molecules (calories)
body temperature regulation
At temperatures much higher than optima, proteins denature, losing the structure
necessary for function
even a few degrees deviation from optima can be lethal
sources of body heat
Internal to the body - Biochemical reactions.
* The sum of our biochemical reactions lead to heat gains.
* External to the body - Environmental.
* Gains or losses.
metabolic heat is always…
positive
Due to the inefficiency of biochemical reactions.
- 35% of the energy to generate ATP from glucose is lost in heat, if we are active or at rest.
- 70% of muscle use of ATP is lost in heat, when we are active
heat exchange equation: sums each gain and loss of heat
Tbody = f(T ambient + H metabolism +/- H radiation +/- H conduction +/- H convection -H evaporation)
H metabolism is highly variable
heat can be measured by…
direct calorimetry
Put someone in an insulated water bath,
known starting temperature and volume.
Measure the water temperature increase over time
indirect calorimetry
Breathe into a device that measures air flow, CO2 levels, O2 levels.
- Calculate calories from this reaction, based on CO2 produced and O2 consumed
endotherms
Consistent high metabolic rates are a major source of energy that contributes to body temperature.
- Endo – internal to
- Therm – heat sources
- Examples: Most mammal
Heterotherms
Endotherms with variable metabolic rates that are a major source of energy that contributes to body temperature.
- Hetero – Other, different
- Often change metabolic rates in response to food or temperature stresses
ectotherms
Lower metabolic rates provide much less energy contributing to body temperature. Environment more significant.
* Ecto – external to
regulators
Use physiology or behavior to adjust temperature
non-regulators
No temperature adjusting processes
categories of organisms: their Hmetabolism behavior & physiology
other heat quation terms: heat exchange occurs across surfaces
slide 17 - explain
radiation
heat can be gained or lost
energy is lost/gained as infrared electromagnetic waves
depends on: surface area, emissivity of the surfaces, does not require contact between source
conduction
can be gained/lost
requires physical contact of the object w/ a s/l/g
depends on diff in temp of 2 surfaces, area of contact, how well surfaces conduct heat
convection
heat can be gained/lost
mass flow within a fluid medium
deoends on surface area, temp diff, rate of flow of medium
evaporation
always takes heat away from the body
depends on ambient temp, wolume of h20 evaporated, humidity of ambient air
importance of organism size on thermoregulation
smaller animals have higher metabolic rates per gram than larger animals
anatomic features that limit heat loss
insulation
animals may evolutionaruly modify conductivity and/or distance to vital organs
counter current exchange
regional heterothermy: different regions of the body have diff temp; allows to keep core temp more stable
arrangement of blood vessels in some mammals and birds allows for countercurrent exchange, generating regional heterothermy
physiologic responses that regulate body temperature
heat gain from increased metabolic rates (BMR, exercise)
heat loss from evaporative cooling and radiation
insulation (hairs at an angle of upright)
uncoupling oxidative phosphorylation (BAT)
control of blood flow regulates…
heat exchange
vasodilation
increased flow in distal loop exposes blood to exterior
-> increases heat exchange with environment
vasoconstriction
Decreased blood flow can shunt flow inside insulating subcutaneous fat
-> reduces heat exchange
cooling feedback loop
heating feedback loop
heterothermy
conserves energy
Heterotherms:
* Reduce metabolic rate, food and water intake, activity
* Do not maintain constant body temperature like homeotherms
* Are tolerant of lower body temperatures
- Hibernation – Seasonal, voluntary, lasts weeks to months
(Bears, bats, several rodent species. Some non-heterotherms hibernate, e.g. several insect, amphibia, reptiles) - Torpor – Seasonal, involuntary, lasts hours
(Bats, hummingbirds, reindeer)
benefits of being a homeothermic endotherm
Activity levels can be kept higher
Greater independence from external thermal conditions
More flexibility in exploiting different habitat
costs being a homeothermic endotherm
Energetically expensive, especially in colder habitats where Ta < Tb
Regulatory machinery, e.g., sensors, receptors, hormones, effector
benefits of being a poikilothermic ectotherm
Energetically cheap
No regulatory mechanisms, which cost energy to build and operate
costs of being a poikilothermic ectotherm
No independence from external thermal conditions
Limited flexibility in exploiting different habitat
activity levels are subject to environment
smaller metabolic rate
rely on behavioral responses to thermoregulate
