Thermoregulation Flashcards
What are the costs and benefits of thermoregulation mechanisms in poikilotherms?
- Cold blooded
Benefits:
- Reduced food requirements
Costs:
- Depend on absorbing heat from the environment for function (ECTOTHERMIC)
- inactive in cold
- seek shelter in heat
What are the costs and benefits of thermoregulation in homeotherms?
- Warm blooded
Benefits
- Function in wide range of temperatures by producing own heat through metabolism (ENDOTHERMIC)
Costs:
- Maintaining constant temp requires higher energy consumption –> more food
Identify areas of the body where temperature gradients exist.
- Rectal = core body temp
- Oral = 0.6C lower
- Underarm and oral are both lower
- Skin temp varies widely up to 20C
- Viscera:
> Rumen is 2-3C higher because of fermentation
> Liver is 1-2C higher to filter blood
> the brain generates the most heat (consumes glucose) - Testes = lower temp by 4-7C
Explain how body temperature is regulated and describe normal variations
Negative Feedback Control:
Effector > (Afferent pathway) > Control Centre > (Efferent pathway) > Responses
e. g. Cells want to increase BMR > (peripheral thermoreceptors) > Cerebral Cortex & Hypothalamus > (Behavioural changes & Sympathetic nerves, respectively) > Skeletal muscle & Adrenal medulla/ sweat glands / vasoconstriction / Skeletal muscle
- Main mechanisms for retaining temp are by vascular controls, counter-current exchange, vasodilation/constriction and by arterio-venous anastomoses.
Homeothermy is:
A pattern of temperature regulation characterised by small variation in body temperature, usually less than +/- 2C
Trace the pathways for transmitting information on thermal sensation and explain how temperature is perceived
Spinothalamic pathway: - 3 neuron pathway - Input to thalamus - reticular formation A. Perception = somatosensory cortex B. Thermoregulation = hypothalamus
- Peripheral thermoreceptors (skin and mucous membranes, bare nerve endings) detect warmth/cold
- -> Info. on temp carried by small myelinated fibres in the lateral spinothalamic tract -> travels along spinal cord -> synapses in thalamus -> projects to sensory cortex & hypothalamus
- Central thermoreceptors (anterior hypothalamus, spinal cord/other centres, dominate over peripheral)
- -> sensors detect changes in temp of blood in brain
- Hypothalamus, receives thermal afferents
- > determines Set point (normal range)
- Produces integrated response (neural effectors/humoral effectors)
What are the mechanisms for heat gain/ production?
Intrinsic heat gain:
- BMR (thyroid hormones, sympathetic stimulation, temperature)
- Breakdown of nutrients
- By-product of chemical reactions
- Fermentation in rumen/hindgut
- Cellular rate of heat production is increased by hormones T3/T4, A, NA
Extrinsic:
- Radiation (infrared)
- Conduction/Convection
- Muscle-exercise, shivering
- Heat uptake from environment
What are the mechanisms for heat loss?
- Radiation (via infrared rays, emitted from warm body)
- Conduction (direct transfer from the body to a cooler object, most sig. in small animals)
- Convection (movement of warm air/water from a body and replacement with cool air/water, reduced by insulation, Piloerection traps air, wetting accelerates conduction & convection)
- Evaporation (increase with sweating, panting/gular flutter, salivation, air current/movement; decreased by humidity)
- Vasodilation
- Blood shunted from deep to superficial vessels
- Counter-current heat exchange occurs between arteries and veins
What permits heat transfer?
Perfusion with blood efficiently transfers heat from muscle, liver (production sites) to skin, lungs (loss sites).
What is the “Thermoneutral Zone”?
“Comfort” zone.
Animal does not need to actively lose or gain heat but can maintain temperature at its basal metabolic rate through variations in insulation (vasomotor responses and piloerection).
The upper and lower limits of ambient temperature for each animal’s thermoneutral zone are the upper and lower critical temperatures.
Outside these temps the animal must expend energy to maintain core temperature at the set point.
What is an apocrine gland?
- adrenaline sensitive, dual autonomic innervation
- important in cattle and horses
- minor in pigs, goats, dogs and cats
- Structure: Glands at hair follicles, shed apical cytoplasm during secretion
What is an eccrine gland?
- ACH innervation
- Ad & NAd sensitive in footpads and nasal plane
- Composition of sweat is similar to urine, varies rate of sweating
What are the responses to cold in domestic species?
Immediate Responses: - Passive - shelter, vascular - Active - evaporative cooling - Species specific responses Longer term: - Environmental acclimitisation - Developmental responses Genetic: - Heat tolerance
Use the thermoneutral zone concepts to describe what happens in heat exhaustion and hyperthermia as well as cold response and hypothermia
Hyperthermia= Elevated body temperature due to failed thermoregulation.
Heat Stroke:
- Production/gain of heat > loss of heat and evaporative cooling fails
- Effects: High temp induces an increase in metabolic rate +/- protein degradation
- 44-45C –> death
- > 42C –> cell damage and CNS lesions
How do reptiles regulate their temperature?
Heliothermy - absorbed radiated heat from sun
Thigmothermy - conducted heat from the environment
Panting - evaporative cooling
Inertial homeothermy - thermal inertia of large mass of body or its environment
Counter-current exchange, shunt heat away from extremities
