Regulation Of Body Temperature Flashcards
Ectotherm
An organism that regulates its body temperature by exchanging heat with its surroundings
Endotherm
An organism that generates heat to maintain its body temp at constant level
Temperature regulation and mitochondria surface area
Larger mitochondria surface area permits larger cytochrome oxidase activity to produce more ATP
Perfect ectotherm
Lizard
Perfect endotherm
Cat
Temporal heterothermy
Reducing metabolic rate by being at rest, allowing body temp to drop close to surrounding environment
Regional heterothermy
Maintain different temperature zones in the body
Core temperature
Temperature of internal organs, should remain at constant rate (37C)
Can fluctuate between 13-60Cat rest
Skin temperature
Changes with temp in the surrounding
Metabolic rate
Rate of energy expenditure (usually per hour)
Measured by calorie consumption (direct) or oxygen consumption (indirect)
4.8 ca, of best/L of oxygen
Basal metabolic rate
Rate of energy expenditure in a post absorptive condition (following a rest period)
Surface area : Volume ratio and BMR
Increase ratio = higher BMR
Lower ratio = low BMR
Factors affecting BMR
Surface area to mass ratio Age Gender Build Stress
Total metabolic rate
Total rate of energy expenditure during ongoing involuntary and voluntary activities
What affects total metabolic rate
Exercise
Hormones (thyroid, catecholamines, sex, growth)
Both increase TMR
Non shivering thermogenesis
Hormone mediated increase in TMR
Heat production
Heat is byproduct of metabolism
Hormones
Sympathetic activity
Muscle activity
Heat loss
Though the skin
Heat conductance
Ability to control amount of heat loss or gain between core and skin
Skin insulation
Blubber reduce best conductance via vasoconstriction.
Fur reduces heat conductance because it disrupts the heat gradient.
How does altering blood flow help thermoregulation?
Decrease external temp = vasoconstriction = reduce heat loss
Increase external temp = vasodilation = increase heat loss
Areas of highest heat conductance
Ears, face, hands
Heat loss by skin is affected by…
Radiation
Conductance (heat gradient)
Evaporation (breathing, sweating, increased via convection)
Why is sweating an important cooling mechanism?
Sweat is carried to surface of skin through duct
Sweat is isotonic to blood plasma excluding proteins
Most ions are reabsorbed
Keeps body cool because water is cool
Aldosterone and sweat
Reduces Na Cl excretion
Control of sweating
Cholinergic sympathetic pathway
Piloerector muscle
Surround hair follicles
Temperature regulatory center
Posterior hypothalamus
Receives negative feedback signals from sensory thermo receptors at skin that relay stimulus to anterior hypothalamus
Thermo receptors
Cold pain
Cold
Warm
Hot pain
Ratio of cold to hot receptors
10:1
Adaptation of thermo receptors
Response of receptors fades gradually if exposed to same temperature continuously
Spatial summation of thermo receptors
Thermal sensation is proportional to number of thermo receptors stimulated
Hyoothalamus thermo receptors
Hot to cold = 3:1
Set point
Determined by degree of activity of temp receptors in the hypothalamus.
Temperature deviating from set point elicit response
How does skin temp affect set point
Increase skin temp = decrease set point
Decrease skin temp = increase set point (reduce heat loss)
Change in set point is to initiate thermo response sooner
Specific response to heat
Inhibit thermo receptors in posterior hypothalamus
Sweating
Vasodilation
Decreased heat production
Specific response to cold
Stimulate thermo receptors in posterior hypothalamus
Vasoconstriction
Piloerection (related to fur)
Shivering
Chemical thermogenesis
Prolonged exposure to cold
Increase thyroid releasing hormone
Increase thyroid stimulating hormone
Increase secretion of thyroid
Increase metabolic rate
May enlarge thyroid gland
Cold stimulate thermo center in posterior pituitary
True
Heat stimulate thermo center in post pituitary
False
Pyrexia
Fever
State of increased body temp beyond normal range due to infection or injury or cancer
Caused by response to pyrogens
Most common pyrogens
Bacterial lipopolysaccharide toxin (LPS)
Viral polyribonucleotide pyrogen (poly I or C)
Cytokines from injured cells
What receptors do pyrogens act on?
Toll receptors
Conserved cross species
What do pyrogens activate?
Cyclo oxygenase 2 which produces prostaglandins
Function of prostaglandins
Increase hypothalamic set point
Increase body temp
Inhibited by arachidonic acid like aspirin
Hypothermia
Extreme cold causes decrease in body temp
Extreme hypothermia
Can disrupt thermo system
Resist sleep to survive because you can enter comatose
Frost bites cause tissue damage by killing cells
Vasodilation causes momentary to permananent paralysis.
Why is vasodilation important during extreme cold?
Blow flow to skin increase heat to prevent frost bite
Why does the body raise set point due to infection?
Raising set point makes person feel colder so they shiver to generate heat rich raises their temp that is associate with a fever. This rise in body host is suppose to kill infections.
Increase neutrophil migration
Activate genes via heat shock
Survival is better when warm
Why are fevers dangerous?
Can cause body to reach temp beyond critical range which can cause brain damage
Hyperthermia
Extreme heat that causes body to reach upper temp limit due to insufficient cooling mechanisms
Sustained hyperthermia results in…
Hemorrhage
Degeneration of cells
Damage to vital organs like liver, kidney, etc.
How do mammals manage to sustain running while preventing heat stroke?
Anatomical adaptions
Counter current best exchange: carotid artery pass sinus with blood returning from nasal cavity. Close proximity cause exchange of heat. Cool blood moves to brain.
Adaptations of marine mammals to extreme cold
Blubber increase insulation.
Counter current blood flow to extremities reduce heat loss.
Adaptation of land mammals to extreme cold
Counter current heat exchange of blood moving to brain
Regional heterothermy
Low temp lipids
Fur
Heat shock enzymes make polyunsaturated lipids
Temporal heterothermy: Dormancy
Deep sleep
Torpor
Hibernation
Allows body to drop to lower temp during times of non feeding to avoid energy lost
Large animals and very small animals cannot hibernate, they exhibit deep sleep
True
Marmots, ground squirrels, and some ectotherms hibernate
True
Torpor
Short term change in body temp to help body survive in cold climate
Reduce core temp Decreased metabolic rate Decreased heart rate Decrease breathing rate Decrease O2 consumption Blood supply restricted to vital organs
Hibernation
Set point set really low
Maintain temp 1C above environment
Metabolism keeps temp above freezing
Poikilotherm
Ectotherm
Q10 effect
For every 10 degrees reaction rate doubles
Biochem response in poikilotherms
Acclimatization increase O2 consumption
Heat shock change metabolic rate
Freezing extracellular compartment
Poikilotherm survive cold by frees if their extracellular fluid compartment
Increases osmotic pressure in extracellular compartment which dehydrates cells
Increase intracellular concentration reduce freezing point so cells do not freeze.
Super cooling
Prevent ice nucleating centres to prevent ice formation in cold temps
Partial freeze tolerance
Produce cyroprotectants: trehalose and proline
Forms gel that stabilize cell membranes
Prevent formation of ice crystals
Freeze avoidance
Produce antifreeze
Ie. glycoprotein prevent ice crystals from growing
Ie. sorbitol, glycerol increase osmotic pressure of fluid and decrease freezing point
Behavioural and Physical mechanisms
Ex. Honey bees
Cold cause condensed swarming to reduce heat loss. Bees circulate from inside to outside of swarm to keep warm.
Heat cause loose swarm
Others: shivering, brown fat, circulation
