Temperature regulation -I year 2022.pptx

Dr. Sayyada Humaira Masood
DR. SAYYADA HUMAIRA MASOOD
ASSOCIATE PROFESSOR
PHYSIOLOGY
ATMC

 Define thermoregulation and body temperature.
 Describe skin and core temperature of body.
 Know the temperature measured at different sites of body.
 Explain the physiological variations in body temperature.
 Explain various mechanisms of heat production and heat
loss

 Guyton and Hall, Medical Physiology, 13th edition, chapter
74. pages 911- 915.
 Sherwood’s Human Physiology, 9th edition, chapter 17.pages
627-630.

THERMOREGULATION
The maintenance of body temperature within a range
that enables cells to function efficiently

 A term used to describe the processes which
maintain the balance between heat production
and heat loss.
 It is the measure of body's ability to generate &
loss heat in same proportion.

٨
It is the degree of heat maintained by the body
 Humans are warm-blooded animals or homeotherms.
 Humans are able to regulate their internal body
temperatures within a narrow range near 37°C, despite
of wide variations in environmental temperature.

 Normal Body Temperature (NBT) --- 98.60F(370C)
 Range of NBT ----- (960F to 99.90F)(35.5 to 37.70C )
 Core Body Temperature remain almost constant
 Skin Temperature -----Variable

CORE TEMPERATURE
 The temperature within the central core remains constant, which
consists of the abdominal and thoracic organs, the central nervous
system and skeletal muscles.
 This internal core temperature is precisely regulated to maintain its
homeostatic constancy.
 The core tissues function best at a relatively constant temperature of
around 100°F (37.8°C).
SKIN TEMPERATURE
 The skin and subcutaneous fat constitute the outer shell.
 The temperature within the shell is generally cooler and may vary
substantially.
 Skin temperature may fluctuate between 68°F and 104°F (20°C and 40°C)
without damage.
 The temperature of the skin is deliberately varied as a control measure to
help maintain the core’s thermal constancy.

 Temperature > 41 to 43.50C (ULT) Deterioration
of enzymes, block metabolic pathways, nerve
malfunction, convulsions, irreversible brain
damage by denaturation of enzymes.
 Temperature < 260C (LLT)
Inhibit enzymes, slow down metabolism ,
cardiac arrhythmia & death due to cardiac
failure .

 Oral Temp.:36 to 37.50C
 Axillary Temp. : < 0.50C
 Rectal Temp :> 0.50C
 Skin Temp.: varies with environment.
 Extremities: Surface temp. cooler than rest of body.

1. Diurnal variation: 10C ,the lowest level early in the morning before rising
(6 to 7 a.m.) and the highest point in late afternoon (5 to 7 p.m.). This
variation is the result of an innate rhythm driven by the master biologic
clock.
2. Age: Infants , older are colder
3. Sex: female < Males, but in female the core temperature averages 0.9°F
(0.5°C) higher during the last half of the cycle from the time of ovulation
to menstruation & in pregnancy
4. Exercise: 2 to 30C increases during exercise because of the tremendous
increase in heat production by the contracting muscles
5. Sleep: decrease by 0.5 ℃
6. Emotions: increase 20C
7. Posture & clothing:

Body temperature is
controlled by balancing
heat production and heat
loss
Heat loss is
called as
thermolysis
Heat
production is
called
thermogenesis

HEAT GAIN-PRODUCTION
1. Metabolic activity or basal rate of metabolism: Major portion of heat
produced in the body is due to the metabolism of foodstuffs. Liver is the
organ where maximum heat is produced due to metabolic activities.
2. Specific dynamic action of protein or thermogenic effect of food.
3. Muscular activity : Heat is produced in the muscle both at rest and during
activities. During rest, heat is produced by muscle tone. Heat produced
during muscular activity is called heat of activity. About 80% of heat of
activity is produced by skeletal muscles.
4. Non-shivering thermogenesis - Hormones (T3,T4, Adrenaline)
5. Shivering
6. Brown fat tissue

 Heat loss from Skin:-
Transfer of heat from the skin to the Surrounding by
Radiation, conduction, convection, Evaporation of sweat
& insensible perspiration.
 Heat loss from lungs & in excreta

1)Radiation:60 %
 The transfer of heat energy from a warmer object to cooler
object in the form of electromagnetic waves which travel
through space.
 Objects are not in contact.
 Heat loss depends upon temp. difference & Surface Area.
 60% of the total heat loss from a nude person occurs by
radiation.
 Color of skin has no effect on radiation

 The transfer of heat from a warmer to a cooler
object that is in direct contact with the warmer
one.
 The heat is transferred through the movement of
thermal energy from molecules to adjacent
molecule.
 Only minute amount (3-5%)
 Conduction to other objects such as a chair or bed.

 The transfer of heat energy by air currents. Cool air
warmed by the body through conduction rises and is
replaced by more cool air.
 This process is enhanced by the forced movement of air
across the body surface.
 About 15% convection.
 When temp. of surrounding is low.
 Cooling effect of wind
 Conduction and convection of heat from a person
suspended in water is better than air

 Conversion of a liquid such as sweat into a gaseous vapor, a process that
requires heat, which is absorbed from skin.
 Evaporation of 1g water removes about 0.58 Kcal. of heat.
 Evaporation: (up to 3L)- Sweat evaporation.
 when the temperature of surrounding is more, body gains heat by
radiation, conduction & convection, the only means by which heat loss
can occur is evaporation.
 Insensible water loss 600-700 ml/day, 16 -19 cal / hour through
epidermis, in absence of sweating, independent of environmental temp.

Three processes:
 Evaporation of water-300ml/day(200 Kcal)
 Warming of inspired air(2%)
 Panting
 Small amounts of heat are removed in the urine and
Feces.(1%)

Mechanism Heat loss in calories Percentage
Radiation 1500 50 %
Conduction and
convection
600 20 %
Evaporation
Skin
lungs
690
210
20
7= 27%
Warming inspiration 60 2 %
Excreta(U & F) 30 1 %
Total 3000 100%
Mechanisms of Heat Loss from Body

 Gradient between the temp. of skin & environmental temp. heat loss
maximally by RCC
 Heat loss from skin depends upon radiator system of body
 Radiator system of body: formed by cutaneous circulation,
arteriovenous anastomoses underneath.
by varying rate of Blood Flow to skin as per environmental
temperature.
 Insulator system: skin and subcutaneous fat, females have better
insulator system.
 Piloerector muscle: in response to cold, erection, reduce heat loss
 Clothing: woolen clothes reduce heat loss

 Skin serve as a heat exchanger for
thermoregulation.
 Skin blood flow is adjusted to keep
deep body at 37 ℃.
 By arterial dilation or constriction and
activity of arteriovenous
anastomoses. Which control the
blood flow through surface
capillaries.

Temperature regulation -I year 2022.pptx

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