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
