ENI - thermoregulation Flashcards
Define thermoregulation
The ability of an organism to maintain a relatively constant body temperature despite fluctuations in external environmental temperature
Define endotherm
Heat geenrated by heat production from body
Define homeotherm
Temperature maintained within narrow limits
Define ectotherm
Heat from external sources
Define poikilotherm
Body temperature across wide range of environmemtal temperatures i.e. lots of variation in temperature dependig on environment
Define thermoneutral zone
- The range of temperatures where basal metabolic rate is enough to maitnain the body temperatuer within normal limits
- either side will increase metabolic rate to maintain body in normal range
What components are within the thermoregulatory system?
- Sensory component
- Integrating component
- Motor component
Describe the sensory component of the thermoregulatory system
Neurons with nerve endings that have thermoreceptors continuously monitor body temperature and transmit to the integrating centre
Describe the integrating centre in the thermoregulatory system
- Hypothalamus
- Compares temperature information with internal reference or set point
- Like a thermostat
Describe the motor component in the thermoregulatory centre
- Neurons that send command signals to alter heat production or loss
- Move animal to warmer/cooler area or stimulate shivering
- Travel via somatic motor system and affect heat production in skeletal muscles
- Or sympathetic system to chenge
- Physiological and behavioural changes
What changes can be made by the thermoregulatory signals travelling in sympathetic nerve fibres?
- Alter blood flow to skin
- Activity of sweat glands
- Activity of smooth muscles that regualte thickness of fur or plumage
What is the function of the anterior hypothalamus in thermoregulation?
Cooling centre (cools body)
What is the function of the posterior hypothalamus in thermoregulation?
Heating cente (warms the body)
Outline the thermoregulatory pathway in cold
- Skin thermoreceptors detect reduction in temperature, sent to cerebral cortex and hypothalamic thermostat
- Cooled blood reaches hypothalamus
- Information from cerebral cortex to the hypothlamus
- Cerbral cortex causes voluntary responses e.g moving from cold to warm place
- Hypothalamus stimulates SNS stimulation, TRH release and shivering
What is the effect of TRH release from hypothalamus?
- To anterior pituitary
- Stimulates TSH release
- To thyroid
- Stimualtes T4/T3 release
- Increased basal metbaolic rate leading to heating
What are the effects of SNS stimulation?
- Piloerection
- Stimualtes adrenal medulla, release of adrenaline and noradrenaline
- Adrenaline increases BMR
- Noradrenaline leads to skin vasoconstriciton
- SNS stimulates brown adipose tissue thermogenesis
Outline the thermoregulatory pathway in heat
- Skin thermoreceptors detect increase, signal to cerebral cortex and hypothalamic thermostat
- Warmer blood to hypothalamus
- Cerebral cortex sends to (and receives signals from) hypothalamus
- Cerebral cortex stimulates voluntary responses e.g. move somewhere cooler
- Hypothalamus causes adrenergic inhibition and stimulates cholinergic nervous system
What are the effects of adrenergic inhibition?
- Decreased BMR
- Skin vasodilation
What is the effect of cholinergic stimulation in thermoreguation?
Sweating
What is the functionof the thermoregulatory feedback mechanism?
- Allows clsoe regulation of body temperature
- I.e. if cools self too farm sends signal to stop and increase heat production
What causes the fever response?
- Exposure to pyrogens
- Increase hypothalamic set point - New “normal” set for body to be regulate to
What are pyrogens?
products from bacteria or cytokines from inflammation etc that stimulate an animal to have a fever
What is the function of fever?
- Defence mechanism
- Improved T-cell and immune function
- May limit invading organsism growth (body can cope but pathogen cannot)
- HOWEVER some invading organsims may evolve to adapt and benefit from fever
What is brown adipose tissue?
- Specialised adipose tissue found in most mammals, particularly neonates
- In large mammals may still be present in adulthood
- In rodents can be switched on and off throughout life
- Switched on upon arousal in hibernating mammals
Where is brown adipose tissue commonly found?
- Perirenal
- Interscapular
- Abdominal
Describe the structure of brown adipose tissue compared to white adipose tissue
- Small cells with central nucleus
- Multilocular TAG droplets, greater SA for lipid metabolism (only 1 or 2 in white)
- Abundant mitochondria richly endowed with respiratory chain enzymes, spread throughout cell (in white are fewer and pushed to side)
- Higher degree of vascularisation
How does brown adipose tissue generate heat?
- Uses uncoupling protein 1 (UCP1)
- Eists in inner mitochondrial memrbane
- Uncouples mitochondrial energy production to generate heat (in normal tissues, mitochondria gerenate with minimial heat loss)
Compare normal and uncoupled cellular respiration
- Electron transport chain pumps H+ into intermembrane space of mitochondria
- Creates concentration gradient
- In coupled: H+ pass through ATP-synthase, with each passage producing one ATP molecule
- In uncoupled: H+ pass throguh UCP1, generating heat as flood through
What are the stimulatory factors for UCP1 activity in BAT?
- Most switched on at birth
- Cortisol
- Sympathetic NS
- Cold temeprature
- Leptin
- Prolactin
- Thyroid hormones
What factors make neonates more susceptible to cold than adults?
- Higher ratio of body surface to body volume
- Higher proportional surface area of head (significant heat loss)
- Lack of musculature and inability/reluctance to shiver
- Poor thermal insulationdue to lack of subcut fat, also wet
- Inability to move away from cool areas
What is meant by altricial?
- Immobile
- Lack of hair/down
- Closed eyes (not all)
- Immature HPA axis at birth
What is meant by precocial?
- Mobile after birth
- Hair/down present
- Eyes open
- Mature HPA axis at birth
What is the function of melanophores in amphibian and lizard thermoregulation?
- Contain dark melanin pigment
- Makes skin darker
- Able to absorb more solar radiation in order to increase temperature
What are some cardiovascular adaptations fo birds for shedding or conserving heat?
- No sweat glands, lose heat via blood shunts
- Dilate large vascular plexus on back of neck
- Large proportion of blood from left ventricle to legs to increase heat loss during stress
Why is it important for reptiles to be maintained in the preferred optimal temperature zone?
- Affects metabolism
- Digestion is temperature dependent
Why should reptiles be starved 1 week before hibernation?
- Digestion is temperature dependent
- A temperature drop is what triggers hibernation
- If enter hibernation before all food has been digested, will rot and lead to death
What are some respiratory mechanisms of the bird used for thermoregulation?
- Panting
- Gular fluttering
- Air sacs
- Panting and gular fluttering for evaporative heat loss
Outline some thermoregulatory measures of rodents
- Shivering
- Huddling together
- lots of born fat
- Peripheral vasoconstriction/dilation of ears and tail
- Tunnel underground (cooler/warmer depending on environment)
- Stretching out to increase heat loss
- Seek shade
- Evaporative heat loss via saliva
