BODY TEMPERATURE BODY TEMPERATURE REGULATIONREGULATION

DR. ZAHID MAHMOODDR. ZAHID MAHMOOD

M.B.B.S (Pb),M.B.B.S (Pb),

R.M.P (P.M.D.C)R.M.P (P.M.D.C)

NORMAL BODY TEMPERTURENORMAL BODY TEMPERTURE

CORE TEMPERATURE:CORE TEMPERATURE:Temperature of deep tissues of body.Temperature of deep tissues of body.

.very constant in nature.very constant in nature

.orally 98-98.6 °F (±0.6 °C / ± 1°F ).orally 98-98.6 °F (±0.6 °C / ± 1°F )

SKIN TEMPERATURE:SKIN TEMPERATURE:Rises and fall very frequently.Rises and fall very frequently.

BODY TEMPERATURE COTROL:BODY TEMPERATURE COTROL:It is controlled by balance between heat production It is controlled by balance between heat production

and heat loss.and heat loss.Heat production = Heat lossHeat production = Heat loss

HEAT PRODUCTION:HEAT PRODUCTION:It is the by-product of metabolism.It is the by-product of metabolism.

Factors determining rate of heat production:Factors determining rate of heat production:1.Basal rate of metabolism1.Basal rate of metabolism2.Extra rate of metabolism caused by muscle 2.Extra rate of metabolism caused by muscle

activityactivity

3.Extra rate of metabolism caused by effect of 3.Extra rate of metabolism caused by effect of thyroxine.thyroxine.

4.Extra rate of metabolism caused by 4.Extra rate of metabolism caused by epinephrine/nor-epinephrine/sympathetic epinephrine/nor-epinephrine/sympathetic stimulationstimulation

5.Extra rate of metabolism caused by chemical 5.Extra rate of metabolism caused by chemical activity in cells.activity in cells.

6.Extra rate of metabolism needed for digestion, 6.Extra rate of metabolism needed for digestion, absorption and storage of food.absorption and storage of food.

HEAT LOSS:HEAT LOSS:Heat produced in deeper tissues of body is Heat produced in deeper tissues of body is

transferred to skin and is lost to air.transferred to skin and is lost to air.

Factors determining the rate of heat loss:Factors determining the rate of heat loss:1.How rapidly heat is conducted from where it is 1.How rapidly heat is conducted from where it is

produced in body core to skin.produced in body core to skin.

2.How rapidly heat is transferred from skin to 2.How rapidly heat is transferred from skin to surroundings.surroundings.

●●increased blood flow to skin increases the rate of increased blood flow to skin increases the rate of heat transfer.heat transfer.

METHODS OF HEAT LOSS:METHODS OF HEAT LOSS:1.RADIATION:1.RADIATION:. 60% of total heat loss. 60% of total heat loss

.in the form of infrared rays of wavelength 5-20µm.in the form of infrared rays of wavelength 5-20µm

2.CONDUCTION:2.CONDUCTION:a) To solid objects 3% of total heat lossa) To solid objects 3% of total heat loss

b) To air 15% of total heat lossb) To air 15% of total heat loss

3.CONVECTION:3.CONVECTION:. Loss of heat by convection air currents.. Loss of heat by convection air currents.

.It is first conducted to air and then carried by .It is first conducted to air and then carried by convection air currents.convection air currents.

.EFFECT OF WIND: it increases heat loss by .EFFECT OF WIND: it increases heat loss by conductionconduction

.EFFECT OF SUSPENSION IN WATER:.EFFECT OF SUSPENSION IN WATER:Rate of heat loss in water > rate of heat loss in air.Rate of heat loss in water > rate of heat loss in air..EFFECT OF CLOTHING:.EFFECT OF CLOTHING:Increases the thickness of private zone of air and Increases the thickness of private zone of air and

decreases conductiondecreases conductionDecreases the flow of convection air currents and Decreases the flow of convection air currents and

decreases convectiondecreases convection

4.EVAPORATION:4.EVAPORATION:0.58 kcal of heat loss with each gram of water0.58 kcal of heat loss with each gram of water1)By sweating1)By sweating2)By insensible loss from skin and lungs(600-2)By insensible loss from skin and lungs(600-

700ml/day)700ml/day)1)1)BY SWEATING:BY SWEATING:MECHANISM OF SWEAT SECRETION:MECHANISM OF SWEAT SECRETION:1)Coiled portion1)Coiled portion2)Duct portion2)Duct portion.Primary secretion is similar to plasma except it .Primary secretion is similar to plasma except it

does not contain plasma proteins.does not contain plasma proteins.

.Na ion 142mEq/L.Na ion 142mEq/L

.K ion 103mEq/L.K ion 103mEq/LIF SWEAT GLANDS ARE STIMULATED SLIGHTLY:IF SWEAT GLANDS ARE STIMULATED SLIGHTLY:.secretion pass through duct slowly.secretion pass through duct slowly.almost all sodium and potassium ions are .almost all sodium and potassium ions are

reabsorbedreabsorbed.sodium and potassium ions almost 5mEq/l.sodium and potassium ions almost 5mEq/l.water is also reabsorbed..water is also reabsorbed..uric acid, lactic acid and potassium ions are very .uric acid, lactic acid and potassium ions are very

concentratedconcentrated

. . IF SWEAT GLANDS ARE STIMULATED IF SWEAT GLANDS ARE STIMULATED STRONGLY:STRONGLY:

.Secretion pass through ducts quickly..Secretion pass through ducts quickly.

.Only slight reabsorption of ions.Only slight reabsorption of ions

.sodium and potassium ions 50-60mEq/l.sodium and potassium ions 50-60mEq/l

.little water reabsorption.little water reabsorption..●●IN UNACCLIMITIZED PERSON:IN UNACCLIMITIZED PERSON:Sweat 1L/day salt loss 15-30g/daySweat 1L/day salt loss 15-30g/day

●●IN ACCLIMITIZED PERSON:IN ACCLIMITIZED PERSON:Sweat 2-3L/day salt loss 3-5g/daySweat 2-3L/day salt loss 3-5g/day

HEAT LOSS BY PANTING:HEAT LOSS BY PANTING:.In lower animals.In lower animals

.turned on by thermo-regulatory centres of brain.turned on by thermo-regulatory centres of brain

.when animals pants, they breathe in and out .when animals pants, they breathe in and out rapidly and large quantities of new air comes in rapidly and large quantities of new air comes in contact with upper respiratory passages and contact with upper respiratory passages and cools the blood in respiratory passagescools the blood in respiratory passages

REGULATION OF BODY REGULATION OF BODY TEMPERATURETEMPERATURE

1)ROLE OF ANTERIOR HYPOTHALAMUS-1)ROLE OF ANTERIOR HYPOTHALAMUS-PREOPTIC AREA:PREOPTIC AREA:

.Contains heat and cold sensitive neurons..Contains heat and cold sensitive neurons.

.heat sensitive neurons > cold sensitive neurons.heat sensitive neurons > cold sensitive neurons

.when this area is stimulated it causes:.when this area is stimulated it causes:

●●profuse sweatingprofuse sweating

●●vasodilation of blood vesselsvasodilation of blood vessels

..acts as THERMOSTSAT body temperature control acts as THERMOSTSAT body temperature control center.center.

2)ROLE OF POSTERIOR HYPOTHALAMUS2)ROLE OF POSTERIOR HYPOTHALAMUS::.Located at the level of bodies..Located at the level of bodies.

.Receives sensory signals from mamillary peripheral .Receives sensory signals from mamillary peripheral receptors as well as from anterior hypothalamus.receptors as well as from anterior hypothalamus.

ROLE OF PERIPHERAL RECEPTORS IN ROLE OF PERIPHERAL RECEPTORS IN TEMPERATURE REGULATION:TEMPERATURE REGULATION:

1) SKIN RECEPTORS:1) SKIN RECEPTORS:.Cold receptors > warmth receptors.Cold receptors > warmth receptors

.mainly detect cold.mainly detect cold

.when skin is chilled.when skin is chilled

●●causes shiveringcauses shivering

●●inhibits sweatinginhibits sweating

●●increases vasoconstrictionincreases vasoconstriction

2) DEEP TISSUE RECEPTORS:2) DEEP TISSUE RECEPTORS:.Found in:.Found in:

1)spinal cord1)spinal cord

2)abdominal viscera 2)abdominal viscera

3)around great veins3)around great veins

.mainly detect cold.mainly detect cold

NEURONAL EFFECTOR MECHANISMNEURONAL EFFECTOR MECHANISM

●●TEMPERATURE DECREASING MECHANISM TEMPERATURE DECREASING MECHANISM WHEN BODY IS TOO HOT:WHEN BODY IS TOO HOT:

1)Vasodilation:1)Vasodilation:

.caused by inhibition of the sympathetic centers in the posterior hypothalamus that causes vasoconstriction..Cutaneous vasodilatation increases the rate of heat tranfer to the skin.

2)Sweating:2)Sweating: When the anterior hypothalamus-preoptic area is When the anterior hypothalamus-preoptic area is

stimulated by heat, impulses are transmitted to stimulated by heat, impulses are transmitted to the spinal cord and then through the sympathetic the spinal cord and then through the sympathetic cholinergic fibers to the sweat glands to increase cholinergic fibers to the sweat glands to increase their secretion.This is turn increases the their secretion.This is turn increases the evaporative heat loss.evaporative heat loss.

Sweat gland can also be stimulated by Sweat gland can also be stimulated by epinephrine or nor epinephrine circulating in the epinephrine or nor epinephrine circulating in the blood. This is important during exercise. blood. This is important during exercise.

3)Decrease heat production3)Decrease heat production

..Strong inhibition of mechanisms which cause Strong inhibition of mechanisms which cause excess heat production.excess heat production.

.Anorexia..Anorexia.

.Apathy and inertia.Apathy and inertia

●●TEMPERATURE INCREASING MECHANISM TEMPERATURE INCREASING MECHANISM WHEN BODY IS TOO COLD:WHEN BODY IS TOO COLD:

1)Vasoconstriction:1)Vasoconstriction:.Caused by stimulation of the posterior hypothalamus sympathetic centers.

.This decreases the rate of heat transfer to the skin.

2)Piloerection:2)Piloerection: .caused by sympathetic stimulation of the erector .caused by sympathetic stimulation of the erector

pili muscles.pili muscles. .This mechanism is not important in the human .This mechanism is not important in the human

beings but in lower animals ,upright projection of beings but in lower animals ,upright projection of the hairs allows them to entrap a thick layer of “ the hairs allows them to entrap a thick layer of “ insulator air” next to the skininsulator air” next to the skin. .

3)Increase heat production:3)Increase heat production:.by shivering .by shivering .by sympathetic excitation.by sympathetic excitation.by thyroxine secretion.by thyroxine secretion

..BY HYPOTHALAMIC STIMULATION OF SHIVERING:BY HYPOTHALAMIC STIMULATION OF SHIVERING:

.Primary motor center for shivering is located in .Primary motor center for shivering is located in dorsomedial portion of posterior hypothalamus.dorsomedial portion of posterior hypothalamus.

.Normally inhibited by heat center in anterior .Normally inhibited by heat center in anterior hypothalamus-preoptic areahypothalamus-preoptic area

.excited by cold signals from skin and spinal cord.excited by cold signals from skin and spinal cord

activation of shivering centeractivation of shivering center

transmit signals through bilateral tracts transmit signals through bilateral tracts down the brain stemdown the brain stem

through lateral column of spinal cordthrough lateral column of spinal cord

anterior motor neuronsanterior motor neurons

increases tone of skeletal musclesincreases tone of skeletal muscles

shivering beginsshivering begins

BY SYMPATHETIC STIMULATION:BY SYMPATHETIC STIMULATION:.can cause an immediate increase in the rate of .can cause an immediate increase in the rate of

cellular metabolism. This effect is called cellular metabolism. This effect is called “chemical thermogenesis”.“chemical thermogenesis”.

. it results mainly from uncouple oxidative . it results mainly from uncouple oxidative phosphorylation. This process occurs in brown fatphosphorylation. This process occurs in brown fat

. Adults do not have a significant amount of this . Adults do not have a significant amount of this type of fat, therefore chemical thermo genesis type of fat, therefore chemical thermo genesis increases the rate of heat production only 10%.increases the rate of heat production only 10%.

. infants have some brown fat in the interscapular . infants have some brown fat in the interscapular space & chemical thermo genesis can increase space & chemical thermo genesis can increase the rate of heat production as much as 100% the rate of heat production as much as 100%

THYROXINE SECRETION:THYROXINE SECRETION:

.Exposure to cold increases the production of .Exposure to cold increases the production of thyrotropin-releasing hormone by the thyrotropin-releasing hormone by the hypothalamus which stimulates the secretion of hypothalamus which stimulates the secretion of the thyroid stimulating hormone (TSH) from the the thyroid stimulating hormone (TSH) from the anterior pituitary gland.anterior pituitary gland.

.TSH in turn stimulates increased output of thyroid .TSH in turn stimulates increased output of thyroid gland. Thyroxine increases the rate of cellular gland. Thyroxine increases the rate of cellular metabolism throughout the body.metabolism throughout the body.

SET POINT OF TEMPERATURE SET POINT OF TEMPERATURE CONTROLCONTROL

.Core body temperature is set at a critical point of .Core body temperature is set at a critical point of about 37.1°C (98.8 °F).about 37.1°C (98.8 °F).

.At temperature above this level, rate of heat loss is .At temperature above this level, rate of heat loss is greater than rate of heat production so body greater than rate of heat production so body temperature falls and approaches set point.temperature falls and approaches set point.

.At temperature below this level, rate of heat .At temperature below this level, rate of heat production is greater than rate of heat loss so production is greater than rate of heat loss so body temperature rises and again approaches set body temperature rises and again approaches set point.point.

.temperature control mechanisms attempts to bring .temperature control mechanisms attempts to bring body temperature back to the set pointbody temperature back to the set point

FEEDBACK GAIN FOR TEMPERATURE FEEDBACK GAIN FOR TEMPERATURE CONTROL:CONTROL:

.It is the measure of effectiveness of control system..It is the measure of effectiveness of control system.

.it is equal to the ratio of change in environmental .it is equal to the ratio of change in environmental temperature to the change in change in body temperature to the change in change in body core temperature minus one.core temperature minus one.

feedback gain =feedback gain =change in environmental temp. -1change in environmental temp. -1

change in core temp.change in core temp.

=27=27

SKIN TEMPERATURE SLIGHTLY ALTERS SET POINT SKIN TEMPERATURE SLIGHTLY ALTERS SET POINT FOR TEMPERATURE CONTROL:FOR TEMPERATURE CONTROL:

.Set point increases as the skin temperature decreases .Set point increases as the skin temperature decreases e.g hypothalamic set point increased from 36.7C when e.g hypothalamic set point increased from 36.7C when skin temperature was higher than 33C to a set point of skin temperature was higher than 33C to a set point of 37.4C when skin temperature had fallen to 29 C ,thus 37.4C when skin temperature had fallen to 29 C ,thus when skin temperature was high, sweating begins at when skin temperature was high, sweating begins at lower hypothalamic temp.lower hypothalamic temp.

.similar effect occurs in shivering. When skin becomes .similar effect occurs in shivering. When skin becomes cold, it drives hypothalamic centers to shivering cold, it drives hypothalamic centers to shivering threshold even when hypothalamic temp. itself is still threshold even when hypothalamic temp. itself is still on hot side of normal.on hot side of normal.

ABNORMALITIES OF BODY ABNORMALITIES OF BODY TEMPERATURE REGULATIONTEMPERATURE REGULATION

FEVER:FEVER:Body temperature above usual range of normal.Body temperature above usual range of normal.Caused by:Caused by:

a) brain itselfa) brain itselfb) toxic substancesb) toxic substances

PYROGENS:PYROGENS:Proteins and breakdown products of proteins Proteins and breakdown products of proteins

released from bacterial cell membranes, causes released from bacterial cell membranes, causes causes set point of hypothalamic thermostsat to causes set point of hypothalamic thermostsat to rise.rise.

MECHANISM OF ACTION OF PYROGENS:MECHANISM OF ACTION OF PYROGENS:Bacteria present in bloodBacteria present in blood

phagocytized by leucocytes,macrophages phagocytized by leucocytes,macrophages and and lymphocyteslymphocytes

release of interleukin-1release of interleukin-1

production of PG-E2production of PG-E2

Acts in hypothalamus to cause feverActs in hypothalamus to cause fever

CHARACTERISTICS OF FEBRILE ILLNESS:CHARACTERISTICS OF FEBRILE ILLNESS:

1)1) CHILLS:CHILLS:

set point suddenly changed to high value set point suddenly changed to high value causes following changes to increase body causes following changes to increase body temp. :temp. :

a) feeling of extreme colda) feeling of extreme cold

b) skin vasoconstrictionb) skin vasoconstriction

c) shiveringc) shivering

2)CRISIS OR FLUSH:2)CRISIS OR FLUSH:

when factor causing high temperature is when factor causing high temperature is removed,hypothalamic set point is reduced to removed,hypothalamic set point is reduced to normal value but body temperature is still higher normal value but body temperature is still higher so it responds by intense vasodilation which so it responds by intense vasodilation which causes flush.causes flush.

HEATSTROKE:HEATSTROKE:When body temperature increases beyond a critical When body temperature increases beyond a critical

level usually in range of 105°C to 108°C ,person level usually in range of 105°C to 108°C ,person is likely to develop heatstroke.is likely to develop heatstroke.

SIGN AND SYMPTOMS:SIGN AND SYMPTOMS:

.dizziness.dizziness

.abdominal distension.abdominal distension

.Vomiting.Vomiting

.Delerium leading to unconsciousness.Delerium leading to unconsciousness

.circulatory shock.circulatory shock

MANAGEMENT:MANAGEMENT:

11)Placing person in cold water bath)Placing person in cold water bath

2)Sponge or spray cooling of skin2)Sponge or spray cooling of skin

HARMFUL EFECTS OF HIGH TEMPERATURE:HARMFUL EFECTS OF HIGH TEMPERATURE:

1)Local hemorrhages1)Local hemorrhages

2)Parenchymal degeneration of cells throughout the 2)Parenchymal degeneration of cells throughout the bodybody

ACCLIMITIZATION TO HEAT:ACCLIMITIZATION TO HEAT:

Mostly seen in soldiers and minersMostly seen in soldiers and miners

Changes seen in body:Changes seen in body:

.2 fold increase in rate of sweating.2 fold increase in rate of sweating

.increase in plasma volume.increase in plasma volume

.minimal loss of salt in sweating and urine.minimal loss of salt in sweating and urine

FROSTBITE:FROSTBITE:When body is exposed to extremely low When body is exposed to extremely low

temperature, surface area can freeze.temperature, surface area can freeze. .especially seen in lobes of ear and digits of hand .especially seen in lobes of ear and digits of hand

and feet.and feet.ARTIFICIAL HYPOTHERMIA:ARTIFICIAL HYPOTHERMIA:.done by first administrating strong sedative to .done by first administrating strong sedative to

depress the reactivity of hypothalamus and then depress the reactivity of hypothalamus and then cooling the person with ice or cool blanket.cooling the person with ice or cool blanket.

.procedure is used in heart surgery so that heart .procedure is used in heart surgery so that heart can be stopped for many minutes at a time.can be stopped for many minutes at a time.