Topic 1: Homeostasis - Case of Thermoregulation
Homeostasis: maintenance of a constant internal environment
- Coordinated responses of organs/systems that automatically compensate for environmental
changes
- Body temp, BP, O2/CO2 levels
- Coordinated system = more than 1 system
- Automatically: involves autonomic nervous system (reflexes)
Body Temperature
- Mammals and birds are homeotherms
- Warm blooded animals, maintain body temp within narrow limits
- Low and high temp not tolerated
- Core body temp
- Protects vital organs
- Measured by rectal insertion of thermometer
- Influenced by environment, exercise, metabolism
- Core stays the same, outer extremities fluctuate in temp
- Thermoneutral zone
- Ambient temp at which no adjustment is needed (no additional energy needed to maintain
body temp)
- Critical temp = energy required to maintain homeothermic condition
- Easier to produce heat than to dissipate heat
- Hyperthermia (heat stress): generally fatal, cells cannot function
- Hypothermia (cold stress): cells can survive freezing however blood circulation and
respiration fail = death
- Balance between heat production and heat loss
- In mammals and birds, heat comes mainly from body production
- Metabolism = conversion of nutrient to energy
, - Growth and production
- Exercise
- Heat transported by the blood needs to be released in the environment through these 4
physical processes
- Radiation
- Conduction
- Convection
- Evaporation/condensation
- How is extra heat produced?
- Muscle activity → shivering (involuntary rhythmic muscle contractions)
- Non shivering thermogenesis: increased metabolism
- Sympathetic nervous system results in secretion of catecholamines
(adrenalin) stimulate increase in metabolism in brown fat
- Thyroid hormone
- How is extra heat lost?
- Metabolic heat is removed from the core by the blood through the skin
- Insulation property of the skin inversely proportional to the blood flow
, - Mechanisms of heat transport
- Gradient physical laws = transfer from high
to low
- Radiation: electromagnetic
radiation is emitted and absorbed
relative to the surface and
temperature of the object/animal
- Conduction: transfer through
contact; depends on the
conductivity. Animal → ground
- Convection: transfer via moving
air or water
- Evaporation: very efficient, requires
energy to break water molecules apart.
Through skin and airways
- Passive evaporation: normal water
loss
- Sweating: active process under
sympathetic nervous system
- Panting: rapid shallow breathing
- Bathing: water absorb
energy before evaporating
But HOW???
Thermoregulation: System Components
- Involves participation of numerous physiological
systems
- Automatic = reflex = sensor + integration +
effectors
- Thermoreceptors = nerve cells
- Integration center = hypothalamus: information
compared to internal reference set points
- Effectors
- Neurons connected to muscles
- Sympathetic nervous system for blood
flow, sweat gland and metabolism
- Hormones: hypothalamo-pituitary axis
- Voluntary component:
- Hypothalamus connected to the cortex
= exchange of information
- Change of behavioural response =
cognitive behaviour
Homeostasis: maintenance of a constant internal environment
- Coordinated responses of organs/systems that automatically compensate for environmental
changes
- Body temp, BP, O2/CO2 levels
- Coordinated system = more than 1 system
- Automatically: involves autonomic nervous system (reflexes)
Body Temperature
- Mammals and birds are homeotherms
- Warm blooded animals, maintain body temp within narrow limits
- Low and high temp not tolerated
- Core body temp
- Protects vital organs
- Measured by rectal insertion of thermometer
- Influenced by environment, exercise, metabolism
- Core stays the same, outer extremities fluctuate in temp
- Thermoneutral zone
- Ambient temp at which no adjustment is needed (no additional energy needed to maintain
body temp)
- Critical temp = energy required to maintain homeothermic condition
- Easier to produce heat than to dissipate heat
- Hyperthermia (heat stress): generally fatal, cells cannot function
- Hypothermia (cold stress): cells can survive freezing however blood circulation and
respiration fail = death
- Balance between heat production and heat loss
- In mammals and birds, heat comes mainly from body production
- Metabolism = conversion of nutrient to energy
, - Growth and production
- Exercise
- Heat transported by the blood needs to be released in the environment through these 4
physical processes
- Radiation
- Conduction
- Convection
- Evaporation/condensation
- How is extra heat produced?
- Muscle activity → shivering (involuntary rhythmic muscle contractions)
- Non shivering thermogenesis: increased metabolism
- Sympathetic nervous system results in secretion of catecholamines
(adrenalin) stimulate increase in metabolism in brown fat
- Thyroid hormone
- How is extra heat lost?
- Metabolic heat is removed from the core by the blood through the skin
- Insulation property of the skin inversely proportional to the blood flow
, - Mechanisms of heat transport
- Gradient physical laws = transfer from high
to low
- Radiation: electromagnetic
radiation is emitted and absorbed
relative to the surface and
temperature of the object/animal
- Conduction: transfer through
contact; depends on the
conductivity. Animal → ground
- Convection: transfer via moving
air or water
- Evaporation: very efficient, requires
energy to break water molecules apart.
Through skin and airways
- Passive evaporation: normal water
loss
- Sweating: active process under
sympathetic nervous system
- Panting: rapid shallow breathing
- Bathing: water absorb
energy before evaporating
But HOW???
Thermoregulation: System Components
- Involves participation of numerous physiological
systems
- Automatic = reflex = sensor + integration +
effectors
- Thermoreceptors = nerve cells
- Integration center = hypothalamus: information
compared to internal reference set points
- Effectors
- Neurons connected to muscles
- Sympathetic nervous system for blood
flow, sweat gland and metabolism
- Hormones: hypothalamo-pituitary axis
- Voluntary component:
- Hypothalamus connected to the cortex
= exchange of information
- Change of behavioural response =
cognitive behaviour
