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

3

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

4

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

Core 37oC

Forehead 34oC

Hands & Feet 28oC

Toes 27oC

Legs 31oC

Skin 33-34oC

‘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

Summary of Mechanisms

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’?