Download - Thermoregulation 2012(1)
Learning Outcomes1. Demonstrate an understanding of
the mechanisms by which heat may be gained or lost by the body
2. Distinguish between core and shell temperature and describe the effects f circadian variations, menstrual cycle and exercise on core temperature
3. Describe how the body uses a negative feedback homeostatic loop to maintain normal core temperature
4. Outline the particular probnlems associated with thermoregulation in neonates and the elderly
5. Define the term pyrexia and outline the causes and effects of pyrexia
Introduction to Thermoregulation
Heat gain Heat LossBody Temp = 37oC
•The control centre for temp regulation is the HYPOTHALAMUS in the brain•Warm blooded and we generate heat and lose heat constantly•A very good example of HOMEOSTASIS
• APYREXIA (Normal) = 35.6 - 37.8 C (ave = 36.2 C)• PYREXIA (Above norm) = 38 C (41 C can cause fitting)• Hypothermia < 35 C
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Thermoregulation• This is the regulation of body
temperature• Normal body temperature
range: _____________ • During the day the temp
fluctuates by 1C (lowest in early am, highest in late pm)
• A constant body temperature is needed for body enzyme function
• We need to balance the heat gained and lost
• Heat is lost through the lungs, urine, faeces and the skin
• The loss through skin is the only route of heat loss we can be control
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Core and Shell temperatures
Core temperature: • temp within the centre of the
cavities• Core temp is higher than shell
temp • Body controls this• Rectal thermometer is the best
for measurement of core temp
Shell temperature: – temp at the surface e.g.
skin
‘Thermoregulation’Heat is a type of energy –
also expressed in units of calories
1 calorie = the amount of heat energy need to raise the temp of 1g of water by 1C (1000 calories = 1 kilo calorie(kcal)
Heat is measured as temperature and expressed in degrees centigrade or C The temperature of the body is an index registering the amount of heat in the tissues
Heat GainVia cell metabolism –heat is
produced as a ‘by product’ eg.liver, brain, heart, muscles which use food to create energy in the form of heat
Some hormones also important to increase metabolism and increase heat gain eg.thyroxine and adrenalin
Heat gain from environment also important ie. radiation, convection and conduction
Heat Loss (1) via skin (~ 90%)
(perspiration)(2) expiration (~ 9%)
(breathing)(3) micturition/defecation
(~1%)
Radiation (60%) - from a warmer object to a cooler one - without physical contact, e.g. sunlight
Evaporation (22%) - conversion of a liquid to a gas results in heat loss. e.g.sweating and evaporation of perspiration
Conduction - (3%) - heat transfer by direct contact from a warm surface to a cooler one. e.g.hot water, cold chair
Convection (15%) - heat transfer from hot to cold through gas/liquid e.g.warm air rises away from body
Gains Losses
Trmprt
Temperature ControlHypothalamus is the
temperature control centre in the brain
It works by responding to messages sent from ‘thermoreceptor’ cells in skin and to the temp of blood circulating
Here there are 2 centres concerned with maintaining body temperature
Heat Loss CentreHeat Promoting Centre
When temperature increases above normal the nerve cells in the ‘heat loss centre’ stimulated to initiate;
Dilation of skin blood vessels or VASODILATION so that blood flows to surface of body and heat lost via radiation
Increased activity of sweat glands and increased perspiration and heat loss via evaporation
When Body temperature decreases below normal range the ‘heat promoting’ centre swings into action and initiates:Narrowing of blood vessels
(VASOCONSTRICTION) so that blood does not flow to body’s surface and less heat lost
Activation of skeletal muscles to generate heat via shivering
Goosebumps (traps warm air), BMR, and thyroxine release enhance heat production
Factors Influencing Temperature ControlStage of development/Age
Babies – immature nervous system and large surface area for losses
Elderly - degeneration gf nervous system, reduced BMR
Environment - local climate, winD, humidity
Exdrcise/sleepFood - availability, dietingDiurnal rhythm
Temp lower between "am - 6amTemp higher between 5pm and
8pmHormones - Female temperatube
increased before ovulation - temperature is important in the rhythm method of birth control
QUIZ
Which part of the brain is responsible for thermoregulation?
Name the types of heat transfer which occur in man
Is thermoregulation dependent on the nervous system?
Would vasoconstriction increase or decrease the volume of blood in the capillaries of the skin?
How does sweat cool us down?Which hormones can increase our
metabolic rate and increase heat gain and body temperature?
HomeworkState 3 of the functions of the
skinName the 2 regions of the skin.The upper layer is composed of
which type of cells?Does the epidermis contain blood
vessels?What are the functions of the skin
pigment melanin?Name the 2 layers of the dermisHow come the epidermis remains
attached to the dermis?Which dermal layer is more
involved in temp. control and why?
What is produced from a sebaceous gland?
What is the function of the hair?What does the ‘core temp.’ refer
to ?What is ‘pyrexia’?