Lecture 25 And 26: Thermoregulation Flashcards
Give definition of heat and temperature
Heat= total kinetic energy of all molecules in system
Temperature= mean kinetic energy of molecules in a system
-detainees direction of heat flow
Total heat is the sum of all
Total heat= metabolic h + conduction h + convection h + radiation h + evaporation h + stored h
Conduction:
Movement of heat from high to low temperatures by interaction of adjacent molecules Influenced by: -thermal conductivity (k) -area (a) through which heat flows -temperature gradient -separation distance
Convection:
Movement of heat through a fluid (liquid or gas) by mass transport of currents
Influences by:
-temperature gradient
-convection coefficient -dependant on body shape (surface area), wind speeds (or water current) - free convection vs forced convection
Radiation
Energy transfer by means of electromagnetic energy-travels at speed of light and needs no medium of propagation
Influenced by:
-absolute temp
-surface area
Evaporation
Evaporation of water requires loss of heat Influenced by: -temp gradients -vapour pressure gradients -surface area -wind speeds
How is heat exchanged in the body?
Because tissues are poor conductors, heat is most effectively transferred in the blood
-countercurrent mechanisms are used to both conserve and lose heat
Heat transfer
Effect of size and shape on heat loss
Body size affects heat exchange: (thermal inertia)
-elephant: high thermal inertia
Mouse: low thermal inertia
-elongated shapes increases heat loss/gain
Heat transfer:
Bergmanns rule
“Animals from cooler climates tend to be of larger body size and hence have smaller SA to Vol ratios than animals of the same species living in Warner climates.
Heat transfer:
Alleys rule
“Animals adopted to cold have smaller and shorter limbs and protruding body parts”
From the northern arctic hare to to southern desert jackrabbit
Refer to slide 16 for image
Thermal strategies:
Based on the stability of Tb (body temp)
Poikilotherm
Homeotherm
Based on the source of thermal energy
Ectotherm
Endotherm
Based on the stability of Tb (body temp)
Poikilotherm: body temp changes with ambient temp
Homeotherm: regulates body temp by physiological means (not just behaviour)
Based on the source of thermal energy
Ectotherm: thermal balance depends on external source of heat
Endotherm: thermoregulation depends on metabolic heat production
Most animals are best described by a combination of terms
Refer to slide 21 for picture
Explain
Temporal heterotherms:
Regional heterotherms:
Temporal heterotherms undergo prolonged changed in body heat
- hibernating animals
- pythons after large meal
regional heterotherms retain heat in specific regions of the body
- billfish with heater organs in near their eyes
- tu a retain heat within red muscles
Thermal strategies
Humans
Maintains a near constant core temperature, but the extremities (hands, feet, testicle) may be colder.
Core Tb may vary during the reproductive period for females and increases as a result of a fever
For a human what is the temp that indicates you have a fever?
> 38 degrees Celsius
The vertebrate thermostat- Amphetamines
Amphetamines (eg ecstasy, speed, ice) are associated with significant morbidity and mortality, largely due to the disturbances caused in thermoregulation.
- effects range from mild tremor, headache, excessive sweating, blurred vision and muscle cramps
- to severe and hypothermia, seizures, multi-organ failure and death
What are the three things we can change for thermoregulation
- Heat production
- Insulation
- Body temp
Cold: heat production. What are some coping strategies?
- Shivering: using locomotion to generate heat
- Non shivering thermogenesis:
- enzyme systems for fat metabolism activated to produce energy (heat) occurs in both regular fat and ‘brown fat’ - Increased basal metabolic rate
- Insulation: different for arctic and tropical animals
Cold: increase insulation
Explain
A layer of material that reduces thermal exchange
Types:
Internal insulation: blubber
External insulation: hair, feathers, air, water
Effectiveness of insulation depends on thickness
Piloerection:
- hair and feathers act as insulation
- efficiency of insulation depends on its thickness
- animals get fluffier when it is cold
- hair on feathers are pulled perpendicular by smooth muscle (erector muscles) attach at their bases
Comparison of blubber and fur for insulation
Insulation of fur cannot be bypassed
Cold: behaviour
Hibernation
Huddling eg emperor penguins
Hibernation: seasonal
Body temperature and metabolism
Poikilotherm VO2
Homeotherm
Poikilotherm: VO2 increases with increase in Ambient temp
Homeotherm: VO2 decreases with ambient temp, then is independant after critical point
Homeotherms: Thermal zones Thermoneutral zone Upper critical temperature Lower critical temperature Eurythermic Stenothermic
Thermoneutral zone: range of temperatures that are optimal for physiological processes; metabolic rate is minimal (basal metabolic rate)
Upper critical temperature: metabolic rate increases to induce a physiological response to recent overheating
Lower critical temperature: metabolic rate increases to increase heat production
Eurythermic: have a wide thermoneutral zone
Stenothermic: have a narrow thermoneutral zone
Poikilotherms vs homeotherms
- Source of heat
- Anaerobic vs aerobic activity
Amphibians and reptiles are ectotherms = low energy approach to life. Low metabolic rate (VO2)
Birds and mammals are endotherms = high metabolic rate (VO2) and is independant of Ta
Where is the internal thermostat located on mammals? Send birds?
Mammals:
-information from the central and peripheral thermal sensors are integrated in the hypothalamus
Birds:
-the thermostat is located in the spinal cord
Sends signals to the body to alter the rates of heat production and dissipation.
Negative feedback information ie a homeostatic process
All animals have a critical thermal maximum, above which long-term exposure can be fatal
Eg protein denaturation, and decreased affinity for Hb for O2
Hot: effect of size
- Height of the ground
- Ability to move to a more suitable habitat
- More efficient locomotion
- Thermal inertia (also thick of their body shape)
Larger animals have advantage of size in the dessert
Small mammals in hot environment rely most on behavioural thermoregulation eg retreat to burrows, eg become nocturnal.
Hot:
a) increased conductance (inverse of insulation)
b) evaporative cooling
A) a rise in 0.5 degrees causes peripheral vasodilation eg flushed skin after activity
-in the rabbit, heat loss is through ears (more blood flow there)
B) evaporative cooling
-1g of water removes 2,4 kJ of heat
Hot: temporal heterothermy
Diurnal heterothermy
Eg antelope and camel
Have massive changes in body temp thought the day depending on the temp
Hot: selective brain cooling
Carotid rete- countercurrent heat exchange
Eg the brain of a gazelle can be kept at Lowe temp than body core coz arterial blood, before it reaches the brain, passes in small arteries through a pool of cooler venous blood that drains from the nasal region, where evaporation takes place .
Selective brain cooling can save evaporative water loss
