Exam 2 Flashcards
Mammalian endothermy results from
High metabolic heat production, insulation
Body size role
As body mass increases, total metabolic rate increases. As body mass increases, mass specific metabolic rate decreases.
BMR
Basal Metabolic Rate, energy used as body preforms basic metabolic functions. Measured as oxygen use over time. Also known as resting metabolic rate.
MSMR
Mass Specific Metabolic Rate, amount of energy used for basic metabolic function per each gram of tissue, BMR/ body weight
Why does MSMR show a negative slope as body mass increases?
All about surface area to volume ratio. Small mammals have a large SA:V and large mammals have a small SA:V. Large mammals have ‘thermal inertia’ due to small SA:V. Small mammals see rapid heat loss to the environment due to a large SA:V.
Role temperature has on metabolic rate
Each mammalian taxa has a range of Tb where no additional energy is expended on temp regulation the TNZ (Thermal Neutral Zone). Mammals can vary their thermal conductance (C) in an energetically inexpensive way to maintain Tb within TNZ.
How do mammals vary C?
Fluffing fur, posture shifts, timing of activity
Interpreting Scholander Diagrams
Range of TNZ, contrast the position of LCT and UCT, interpret the slope of the line below and above the TNZ.
Body size (Maintaining)
A large body size favors heat conservation and a small body size favors heat dissipation.
Bergman’s Rule
Colder climates should support large mammals and warmer climates should support smaller mammals. “Races” from colder climates tend to be larger than “races” of the same species living in a warmer climate.
Allen’s Rule
Mammals in colder climates will have smaller external appendages to reduce surface area and in turn reduce heat loss.
Insulation
Lowers thermal conductance (C) by reducing heat loss from body surface. Thickness, color and density of fur all play a role.
Blubber
In cetacea and pinnipods, up to 50% of animal body mass may be in the form of blubber. Does not compress under pressure, allows for a smooth surface.
Behavioral Thermoregulation
Energetically inexpensive ways of expending the TNZ and manipulating C. Curling up, nest building, group thermoregulation, finding favorable microclimate.
Regional heterothermy
RH = allowing certain parts of the body to become much cooler, particularly the extremities where SA:V ratio is high.
Mechanisms for regional heterothermy
- Vasoconstriction (blood shunt), a transverse blood vessel detours blood from entering close to the skin, heat is conserved rather than lost to the environment. 2. Counter current exchange, arterial blood is warm and venous blood is substantially cooler. Arterial blood passes next to venous blood returning from extremities, arterial blood gives up heat to venous blood.
Consequences of counter current exchange
arterial blood is pre-cooled and venous blood is pre-warmed therefore reducing the potential for heat loss and regulation.
Increasing metabolic heat production
- Elevating metabolic capacity of skeletal muscles, shivering and locomotion, requires energy investment. 2. metabolize brown fat
Brown fat vs white fat
Numerous small fat vacuoles, glycogen present in cell to fuel mitochondria, eutheria only, production of heat 10x skeletal contractions. LOTS of mitochondria.
Adaptive hyperthermia
A continuum of responses that allows energy to be saved by temporarily abandoning homeothermy on a circadian or seasonal basis.
Shallow hyperthermia
period of inactivity, Tb drops but is regulated within 10 degrees (c) of normal, sometimes called “daily torpor”
Profound hyperthermia
Torpor or hibernation, Tb approaches Ta, oxygen consumption is reduced and aprea occurs
Torpor
Stimuli: variable on species, may be lack of resources or temp but typically is photoperiod. Preparation: increase feeding and energy storage, particularly in terms of fat intake. Entrance: decrease in heart rate, metabolic, oxygen uptake and body temp. Other: periodic arousal, bouts increase in duration and length then decrease as spring apporaoches.
Strategies to get water
Periodic drinker: drink large amounts of water when available. Dietary moisture: obtaining water via food. Metabolic water: water formed as a byproduct of the oxidation of energy containing substances in food.
Strategies to conserve water
Concentration of feces and urine: increases water retention via long loop of Henle. Concentration of milk: production of highly concentrated milk, reclamation of water lost in lactation by consuming urine and feces of young.
Strategies for maintaining a thermodynamic equilibrium in a xeric environment
- Behavioral thermoregulation: avoid extreme heat and finding a suitable microhabitat and adhering to defined periods of activity. 2. Evaporative cooling: the major mechanism employed by mammals to decrease Tb, panting and sweating. 3. Adaptive hyperthermia: tolerating high Tb to as a way to conserve energy and water. 4. Dormancy: passing through unfavorably warm periods by becoming dormant, torpor- dormancy in the cold, estivation- dormancy during hot or dry (rare in mammals, dwarf lemur, east African hedgehog)
Sweating vs panting
Sweating: convection may be limited in certain situations, results in loss of electrolytes, passive. Panting: Animal provides own airflow, minimal loss of salt, active muscle contraction.
Hyperthermia
Advantage: water saving strategy. Disadvantage: mammalian brain fries at temps 4-5 C above resting temp. To survive desert mammals have evolved circulatory systems to cool the brain (counter current exchange).
