Week 4: Body energy homeostasis Flashcards
Give the overview of how humans maintain their body temperature within the optimal range.
Are endotherms - so able to generate own heat by metabolism
Can then stabilise core temperature by loss or gain of heat by exchange with the environment.
Are homeotherms - so remain at a relatively constant body temperature goal range
How does heat production compare to heat dissipation in humans?
Equal
How do humans generate their own heat? (endotherm)
Sum of all metabolic processes release heat (exothermic)
Increasing metabolic rate releases heat
Increasing activity = increases heat generation by ATP hydrolysis
Which in turn increases the rate of ATP production
What are the two different differentiations of temperature in the human body?
Core temperature
Peripheral temperature
What are the features of humans core body temperature?
Kept within tightly regulated limits (presever metabolism of brain, heart and organs)
Prioritised maintenance over peripheral temperature
Consists of major thoracic and abdominal organs and brain
2/3 of body heat content
What are the features of humans peripheral core body temperature?
Peripheral temp can vary widely
Includes the skin, extremities of body (limbs) and subcutaneous tissue
1/3 of body heat content
Is less important in maintenance than core body temp
What is the target range for core body temperature?
36.6 to 37.4 degrees
What is the target range for peripheral body temperature?
30-32 degrees
What mechanism allows there to be a difference between core and peripheral body temperature?
Vasoconstriction and/or vasodilation of blood vessels
What factors contribute to heat production in a human?
Basal metabolic rate
Skeletal muscle activity
Metabolic factors
Thyroid disease
Medications
Convulsions
Fever
Environmental heat
Menopause
What does basal metabolism contribute to heat production?
Is overall exothermic
Contributes 100kcal/hour - this would raise temperature by one degree per hour if there was no dissipation mechanism
How does skeletal muscle activity contribute to heat production?
ATP hydrolysis releases heat
Can raise heat by 20 fold
What are the different ways in which the CNS can influence body temperature?
Shivering thermogenesis
Non-shivering thermogenesis
Metabolic Control
Vasomotor control
Sweating control
What are the different ways that heat can be carried from the core to the skin?
By blood (greater in vasodilation)
By fixed tissue conductance (this is minimal)
What are the different ways that heat is lost from the skin to the ambient environment?
Evaporation _ by sweat
Radiation
Convection
Conduction
What is conduction as a method of heat loss?
Transfer of heat by direct contact
Minimal in air by significant in water
What is convection as a method of heat transfer?
Transfer of heat by air circulating the body
Varies with wind velocity
What is radiation as a method of heat transfer?
Transfer of heat via electro-magnetic waves
Bidirectional - gain or loose heat
Can result in heat gain
What is evaporation as a method of heat transfer?
Transfer of feat via conversion of liquid to gas
Evaporation of 1cc of sweat consumes 0.58kcal
Dominant mechanism of heat loss in hot environments
What makes up the central thermoregulatory network?
Afferent neurons that realy info from the peripheral and core thermoreceptors
Thermal afferent pathway within the CNS
Thermoregulatory integration centre in the preoptic anterior hypothalamus
Efferent pathway providing autonomic and somatomotor inputs to effectors
Thermal effectors that control heat transfer to the environment and heat production in the body.
What is the passive poikilothermic system in humans?
How the circulatory system and laws of physics determine heat transfer between the environment and core body temperature.
Is superimposed on by the central thermoregulatory network
How might acclimatisation occur to a hot temperature?
Requires repeated exposure to same temperature
- increased sweat volume and decrease Na conc
- increased plasma volume and cardiac stoke volume
How might acclimatisation occur to a cold temperature?
Requires repeated exposure to the same temperature
- increased body hair
- decreased sweat volume
- decreased plasma volume and cardiac stroke output
What class of receptors is considered thermosensitive?
TRP channel members
Different receptors detect different temperatures from freezing cold (cold-pain) to burning hot (heat-pain)
What is the role of TRMP8 receptor?
Expressed on cutaneous afferent neurons are skin cold receptors - function demonstrated in dorsal root ganglia and trigeminal ganglia
Peak activation at 25 degrees, but ranges from 7 to 42 degrees.
Is known as the menthol receptor - stimulated by mint
What is the TRPV3 and TRPV4 receptor?
Found in keratinocytes when activates triggers paracrine signals that are responsible for skin warmth sensation and activate melanin production.
Activate from 30 to 50 degrees peak activation at 42 degrees.
What is the TRPM2 receptor?
Expressed in neurons in the pre-optic area of the hypothalamus act as central warm sensation neurons.
What receptors detects cold-pain?
TRPA1
What receptor detects heat-pain?
TRPV1 and TRVP2
also called the capsaicin receptor ( activated by capsaicin component in chilli)
What are the two different classes of thermosensory neurons found in the periphery?
What are there characteristic features?
1.Activated by innocuous warmth (34 to 42 degrees)
2.Activated by innocuous cold (14 to 30 degrees)
Both have cell bodies in the trigeminal ganglion (if innervating head and face) or cell bodies in the dorsal root ganglion for rest of body.
Are pseudounipolar - one axon projecting to skin or visceral, other to the ganglion
What are the different types of input for the thermoregulatory system?
Afferent sensory neurones that detect temperature in the periphery
Sensory neurons located within the brain that detect the temperature of the hypothalamus
What areas in the brain are associated with temperature discrimination?
Insula cortex
Somatosensory cortex
Ventral posterior thalamus
What parts of the brain are involved in temperature homeostasis?
POA - preoptic area of the hypothalamus
LPB - lateral parabrachial nucleus
Spinal Trigeminal Nucleus
What external factors can cause the body to increase in temperature?
Environmental thermal changes influence skin temperature, recognised by TRP channel family receptors and sends afferents to the POA
Infection triggers the immune response causes the release of pyrogenes which act on the POA
What internal factors influence body temperature?
Brain temperature
Spinal cord temperature
Visceral temperature
Detected by TRP channel family receptors and relayed to the POA by afferent neurons
What is the function of the POA in thermoregulation?
Integration of different afferent signals, central and peripheral.
To determine the most appropriate efferent signal in order to keep body temperature within the optimal range.