Temperature dpt

BODY TEMPERATURE REGULATION
Dr. Misbah-ul-Qamar

Definitions:
• CORE BODY TEMPERATURE:
• The temperature of the deep tissues of the body which
remains nearly constant under physiological conditions
(within ±1˚F or ±0.6˚C).
• Average core body temperature is taken to be around
98.6 ˚F orally and 1˚F higher when measured rectally.
• It is measured from tympanic membrane, pulmonary
artery, distal esophagus & nasopharynx
• The core thermal component is composed of highly
perfused tissues whose temperature is kept uniform &
high compared with rest of body
• It gradually decreases with age
Dr. Misbah-ul-Qamar

• SKIN TEMPERATURE:
• The skin temperature rises and falls with the
temperature of the surroundings or ambient
temperature.
• It can be measured by placing temperature
sensors (thermistors) at skin at various locations
• Mean skin temperature can be calculated by
measuring skin temperature at several locations
and computing the average across these locations
(forehead, chest, thigh, calf, abdomen & back)
Dr. Misbah-ul-Qamar

• Ambient temperature:
• At which there is no active heat loss and heat
gain mechanism operated by the body. It is
27+ 2oC
• Average Body Temperature:
• Used when one wishes to calculate the total
amount of heat stored in the body
• =(0.33 x surface temp ) + (0.67 x internal
temp)
Dr. Misbah-ul-Qamar

Thermal gradient
• Within the body, there is a difference between
core temperature and the shell temperature,
called thermal gradient
• Ideal difference between core & skin
temperature is approximately 4oC
• Even within the core, temperature varies from
one organ to another
• In extreme circumstances, the core
temperature can be 20oC higher than the skin
Dr. Misbah-ul-Qamar

Thermoregulation:
• The ability to maintain nearly constant internal body
temperature i.e, the core temperature, is called
thermoregulation.
• HOMEOTHERMIC(Warm blooded) endotherms: The
animals who can maintain nearly constant core body
temperature despite wide variation in the surrounding
temperature.
• POIKILOTHERMIC(Cold blooded) ectotherms: Animals
having rudimentary thermoregulation and their core
body temperature changes with the change in the
ambient temperature.
Dr. Misbah-ul-Qamar

Recording temperature:
Sites for temperature recording are
• Mouth
• Axilla
• Rectum
• Skin
• Lower one third of esophagus
• Tympanic membrane
• Rectal temperature is not the same as the temperature
in the brain, where temperature is regulated
• Tympanic temperature is a good estimate of actual
brain temperature
Dr. Misbah-ul-Qamar

Devices used to measure temperature
• Mercury thermometers
• Thermocouples
• Thermistors
• Ingestible core temperature pills (use low
power radio frequency transmissions to
communicate with temperature monitor)
Dr. Misbah-ul-Qamar

Relationship of body heat to body
temperature
• The temperature of an object is a measure of
the kinetic activity of its molecules
• This is proportional to the amount of heat
stored in the object
• Body temperature is directly proportional to
the heat in the body
Dr. Misbah-ul-Qamar

Heat capacity or specific heat
• A measurement of the changes in body heat
stores utilized to characterize temperature
regulation quantitatively
• Defined as the ratio of heat supplied (or
removed) to the corresponding temperature
rise(or decrease)
• Specific heat of tissues is said to be 0.83
calorie/kg/degree centigrade
Dr. Misbah-ul-Qamar

Constancy of internal body
temperature
Dr. Misbah-ul-Qamar

Heat balance
• When the rate of heat production is exactly
equal to the rate of heat lost= heat balance
Dr. Misbah-ul-Qamar

The insulator system of the body
• Skin
• Subcutaneous tissues
• Fat in subcutaneous tissues
Dr. Misbah-ul-Qamar

The radiator system of the body
• Flow of blood to the skin
• Skin temperature is important in heat transfer
to the environment
• Delivery of heat to the surface is blood flow
dependent
Dr. Misbah-ul-Qamar

Heat production
• Body produces internal heat due to metabolic
processes
– At rest or during sleep, metabolic heat production
is small
– During intense exercise, heat production is large
• Heat production can be classified as
– Voluntary muscular exercise
– Involuntary shivering & non shivering
(hormonal action) thermogenesis
Dr. Misbah-ul-Qamar

Heat production factors:
• Basal metabolism of all the cells of the body
• Extra metabolism caused by
1. increased chemical activity of all the cells eg,
fever
2. shivering and muscle contraction
3. thyroxine and growth hormones
4. epinephrine, norepinephrine and sympathetic
stimulation
5. digestion and absorption of food
Dr. Misbah-ul-Qamar

Mechanisms of Heat production:
• Basal metabolism BMR: The minimum amount of heat
produced when a person is physically and mentally relaxed.
• Most of the heat is produced by liver , heart , muscle, skin,
brain, endocrine organs and other tissues.
• With each degree rise in temperature there is 13 %increase
in BMR.
• Muscular exercise or shivering produce much more heat.
• During exercise around 90% of heat is produced by
muscles.
• Shivering starts when the surrounding temperature falls to
around 23˚C.It is controlled by somatic division of nervous
system.
Dr. Misbah-ul-Qamar

• Diet induced thermogenesis: Food intake
increases the basal metabolic rate and heat
production.
• Diet induced thermogenesis is more marked with
protein diet.
• Skin exposure causes absorption of heat when
the ambient temperature is higher than the body
temperature.
• Brown fat in some animals and infants only, can
be mobilized to produce heat when needed.
Dr. Misbah-ul-Qamar

Heat loss:
• Heat is lost in two steps:
• From body core to skin
• From skin to atmosphere
Dr. Misbah-ul-Qamar

Blood flow to skin from core provides
heat transfer
• A high rate of skin flow causes heat to be
conducted from core to skin with great
efficiency
• Blood is very effective in this function because
of its high capacity to store heat
• Therefore skin is an effective controlled “heat
radiator’’ system
Dr. Misbah-ul-Qamar

• Blood vessels are distributed profusely
beneath the skin, specially important is a
continuous venous plexus that is supplied by
inflow of blood from skin capillaries
• In most exposed areas of body (hands, feet,
ears) blood is also supplied to the plexus
directly from small arteries through highly
muscular arterio-venous anastamosis
Dr. Misbah-ul-Qamar

Heat radiator –the skin
Dr. Misbah-ul-Qamar

Basic physics of how heat is lost from
skin surface
• Through following mechanisms:
• Radiation
• Conduction
• Convection
• Evaporation
• the first 3 of these require a temperature
gradient to exist between skin & environment
Dr. Misbah-ul-Qamar

• Radiation is a mode by which heat can be lost
from a hot to a cold object in the form of
infrared rays (60% of the total heat loss).
• It can take place in vacuum as well.
• Example: sun transferring heat to earth
• On a hot sunny day, body can also gain heat
via radiation
Dr. Misbah-ul-Qamar

• Conduction means loss of heat from body to the
solid objects due to direct contact(3% of body
heat loss).
• Conduction from the solid object to air constitute
around 15% of heat loss.
• Convection causes the heat loss by the
movement of air.
• Whatever heat is lost by the body ,it is taken
away by convection currents.
• If the surrounding air is cooler than the body
,heat can be lost very easily.
Dr. Misbah-ul-Qamar

Conduction and convection in water
• a)Specific heat of water is far greater , so per unit
volume of water can absorb much more amount of
heat
• b)Heat conductivity in water is far greater so it is
impossible to heat the thin layer of water next to body.
• c)If the temperature of water is below body
temperature , heat loss from the body is rapid .
• Water’s effectiveness in cooling is about 25 times
greater than that of air at same temperature
Dr. Misbah-ul-Qamar

• Clothing can increase the thickness of private
zone of air adjacent to skin.
• Heat loss can be reduced by decreasing rate of
conduction and convection.
• The effectiveness of clothing in maintaining
body temperature is almost completely lost if
the clothing becomes wet.
Dr. Misbah-ul-Qamar

Evaporation
• Only way to lose heat when the the temperature of the surrounding is
greater than the temperature of the body.
Evaporation produces cooling.
For each gram of water that evaporates,0.58 kcal are lost.
Some heat is being continuously lost by the skin in low ambient
temperature and it is called INSENSIBLE LOSS.
Mild evaporation continues from the respiratory tract during the process of
respiration
Heat production:
At rest= 1.5kcal/min
At exercise= 15kcal/min
Humidity:
High– limits sweat evaporation & heat loss
Low– ideal for sweat evaporation & heat loss
Dr. Misbah-ul-Qamar

Evaporation of sweat from skin is dependent on
following factors
• Ambient conditions
– Air temperature
– Relative humidity
• Convection currents around the body
• Amount of skin surface exposed to
environment
Dr. Misbah-ul-Qamar

Relative humidity
• It indicates how moist the air is
• the amount of water vapor present in air is
expressed as a percentage of the amount
needed for saturation at the same
temperature
• High relative humidity reduces the rate of
evaporation as in this situation vapor pressure
gradient between skin & environment is
reduced
Dr. Misbah-ul-Qamar

Effectors altering body temperature
• Sweat glands
• Smooth muscles around arterioles
• Skeletal muscles
• Endocrine glands releasing thyroxine &
epinephrine
Dr. Misbah-ul-Qamar

Regulation of sweating:
• Autonomic nervous system controls the sweat glands .
• Cholinergic nerve fibers supply the sweat glands.
• Primary secretions are rich in electrolytes.
• Secondary secretions are the secretions in which very
little amount of electrolytes is present.
• In an acclimatized person ,very little amount of NaCl is
lost in sweat due to release of Aldosterone which is
responsible for salt and water conservation.
• Heat loss by panting is more effective in lower animals.
Dr. Misbah-ul-Qamar

Mechanism of sweat secretion
• Cholinergic sympathetic nerve fibers ending on or
near the glandular cells elicit the secretion
• Secretory portion of the sweat gland secretes a
fluid called primary secretion or precursor
secretion
• The precursor secretion is an active secretory
product of the epithelial cells lining the coiled
portion of the sweat gland
• Then the concentrations of the constituents in
the fluid are modified as the fluid flows through
the duct
Dr. Misbah-ul-Qamar

Acclimatization of the sweating
mechanism
Dr. Misbah-ul-Qamar

REGULATION OF BODY TEMPERATURE
Temperature regulating centers are located in
hypothalamus.
Temperature detectors are present throughout
the body .
Nervous feedback mechanisms help to
regulate body temperature .
Dr. Misbah-ul-Qamar

Why regulation of body temperature is
required?
• The enzymes of body work in optimal
temperature
• Speed of chemical reaction varies with
temperature
• Temperature spikes above the normal range
denature proteins & depress neuronal activity
• Very low temperature leads to cardiac fibrillation
& failure ( lower lethal core temp is 26C
• Very high temperature leads to heat stroke
(upper lethal core temp is 43.5C
Dr. Misbah-ul-Qamar

Advantage of thermoregulation
Dr. Misbah-ul-Qamar

Disadvantage of thermoregulation
Dr. Misbah-ul-Qamar

Thermal sensations
• The humans can perceive different gradations of cold &
heat progressing from freezing cold– to cold– to cool–
to indifferent– to warm– to hot– to burning hot
Thermal gradations are discriminated by at least 3 types
of sensory receptors
• Cold receptors
• Warmth receptors
• Pain receptors
Pain receptors are stimulated only by extreme degrees of
heat or cold
Dr. Misbah-ul-Qamar

Thermal receptors
• Cold & warmth receptors are located immediately
under the skin at discrete points
• Each point have a stimulatory diameter of 1mm
• In most areas of body, there are 3-10 times as many
cold receptors as warmth receptors
• Number in different areas of body varies from 15-25
cold points/cm2 in lips to 3-5 in fingers
• Less than 1 cold point/cm2 in some broad surface areas
of trunk
• There are correspondingly fewer numbers of warmth
points
Dr. Misbah-ul-Qamar

Working of thermoceptors
• Cold & warmth receptors are stimulated by
changes in their metabolic rates as temparature
alters the rates of intracellular chemical reactions
more than twofold for each 10oC change
• It is difficult to judge gradations of temperature
when small areas of surface are stimulated
• When a large area of body is stimulated all at
once, thermal signals from the entire area
summate
Dr. Misbah-ul-Qamar

Skin and deep tissue receptors:
• Skin contains 10 times more cold receptors as
compared to warmth receptors.
• Peripheral temperature detection is primarily
responsible for cold detection.
• When skin receptors are cooled , reflexes try to
increase body temperature and conserve heat
immediately by
– Causing shivering
– Inhibiting sweat formation
– Promoting skin vasoconstriction
Dr. Misbah-ul-Qamar

Deep receptors for temperature
detection:
• Present in spinal cord, near deep viscera and
around great veins .
• These deep tissue receptors are responsible
for detecting core body temperature.
• Both the skin and deep tissue receptors are
responsible for preventing hypothermia.
• All types of receptors function by showing
transient change in the receptor potential.
Dr. Misbah-ul-Qamar

• Warmth signals are received by free nerve
endings & transmitted by type C nerve
fibers@ 0.4- 2 m/sec
• Cold signals are transmitted via A delta nerve
fibers @ 20m/sec
• Some cold sensations are transmitted in type
C nerve fibers
• Afferents reach hypothalamus through
spinothalamic tract
Dr. Misbah-ul-Qamar

Pathway for temperature signals
• Thermal signals are transmitted in almost parallel but
not exactly the same pathways as pain signals
• On entering spinal cord, signals travel for few segments
upward & downward, then terminate in laminae I, II &
III of dorsal horns
• After some processing, signals enter ascending thermal
fibers that cross to opposite anterolateral sensory tract
• Then terminate in both the reticular areas of brain
stem & ventrobasal complex of thalamus
• Some thermal signals are also relayed to
somatosensory cortex from ventrobasal complex
Dr. Misbah-ul-Qamar

Temperature decreasing mechanisms
:
These mechanisms get activated when the
temperature of the body is too high and body has
to lose heat.
• Vasodilation of blood vessels by inhibition of
sympathetic centers in the posterior
hypothalamus.
• Sweating produces cooling by evaporation.
• Slight increase in RR
• Decreased heat production by decreased
shivering and chemical thermogenesis.
Dr. Misbah-ul-Qamar

Temperature increasing mechanisms:
• When the body is too cold the temperature
control mechanisms get activated like
• Vasoconstriction caused by stimulation of
posterior hypothalamic sympathetic center.
• Piloerection causes hair to stand upright and trap
an insulator layer of air next to the body to
conserve heat.
• Increase in thermogenesis (heat production) by
increasing shivering , sympathetic activation and
thyroxine secretion
Dr. Misbah-ul-Qamar

Thermogenesis:
• MECHANICAL THERMOGENESIS:
• Shivering
• CHEMICAL THERMOGENESIS:
• a) Sympathetic chemical excitation of heat
production(short term heat production)
• b) Increased thyroxine production (long term
heat production)
Dr. Misbah-ul-Qamar

Mechanism of shivering:
• Primary motor center for shivering is located in the
dorsomedial portion of posterior hypothalamus .
• This area is inhibited by signals from the heat centers in
the anterior hypothalamus .
• It is excited by cold signals from skin and spinal cord.
• Cold→ primary motor center for shivering→ bilateral
tracts down the brainstem→ lateral column of spinal
cord→ anterior motor neuron→ increased muscle tone
due to over activity of anterior motor neurons
• Shivering starts as a result of feedback oscillation of
muscle spindle stretch reflex mechanism.
Dr. Misbah-ul-Qamar

Chemical thermogenesis(high cellular
metabolism)
• SHORT TERM:
• Activation of sympathetic system and release of
epinephrine and nor epinephrine is responsible for
excessive metabolism.
• Epinephrine and nor epinephrine are responsible to
uncouple oxidative phosphorylation .
• This leads to heat production and no ATP generation.
• This phenomenon is more pronounced in animals having
brown fat .
• In adults 10-15% increase in heat production by chemical
thermogenesis.
• In children heat production can increase up to 100 %.
Dr. Misbah-ul-Qamar

• LONG TERM CHEMICAL THERMOGENESIS BY
THROXINE:
• Anterior hypothalamus is cooled down →TRH
release by hypothalamus →TSH release by
anterior pituitary→ Thyroxine release by thyroid
gland → increased cellular metabolism and heat
production.
• This mechanism requires months to develop and
prolonged exposure to cold.
• More pronounced in animals
Dr. Misbah-ul-Qamar

Role of anterior hypothalamic pre-
optic area:
(heat center)• Hypothalamic pre optic area serves as a thermostat for
the body.
• Anterior hypothalamus has large number of heat sensitive
neurons.
• It also has around 1/3 cold sensitive neurons.
• Heat sensitive neurons increase their firing rate 2-10 fold in
response to a 10oC rise in body temperature
• When hypothalamic pre optic area is heated ,3 changes
take place
• a) profuse sweating all over the body
• b) intense vasodilation
• c) decreased heat production
Dr. Misbah-ul-Qamar

Posterior hypothalamus (cold center)
• Posterior hypothalamus is important as it
integrates the central and peripheral temperature
sensory signals.
• This special area is located in the posterior
hypothalamus bilaterally near the mammillary
body.
• Signals from the anterior hypothalamic pre optic
area and elsewhere in the body are integrated in
the posterior hypothalamic area to activate heat
producing and heat conserving reactions of the
body.
Dr. Misbah-ul-Qamar

“SET POINT” FOR TEMPERATURE
CONTROL
• The body core temperature is maintained at
37.1C or 98.8F .
• This temperature is called set point of the
temperature control system.
• If the body temperature rises above this point ,
all the heat losing mechanisms come into play.
• If the body temperature falls below this point , all
he heat conserving and heat generating
mechanisms are activated.
Dr. Misbah-ul-Qamar

Behavioral control of body
temperature:
• Psychic sensations of being over heated or
being too cold are sent to the person .
• If over heated ,person moves to a cold room ,
takes cold drinks , light cotton clothing,
sprawling, seeking shade etc.
• If it is too cold, appropriate adjustments like,
moving to a warm room, hot drinks and
insulating clothes are made.
Dr. Misbah-ul-Qamar

Thermal events during exercise
• In a cool/ moderate environment, heat
production during exercise is directly
proportional to exercise intensity
• Venous blood draining exercising muscles
distributes the excess heat throughout the
body core
• Method of heat loss during continuous
exercise is modified according to ambient
conditions
Dr. Misbah-ul-Qamar

Heat storage in body during exercise
• Any heat produced by working muscles that is not
lost, must be stored in body tissues
• Body heat gain during exercise= heat produced-
heat loss
• Exercise using large muscle groups (i.e: legs) can
result in large amounts of heat production
• Increase in body temperature during exercise
depend on
– Bodyweight/mass
– Specific heat of body tissue
Dr. Misbah-ul-Qamar

Heat index
• It is the measure of body’s perception of how
hot it feels
• The index is calculated by combining the air
temperature & relative humidity to compute
an apparent temperature
• If air temperature is 82oF & humidity is 80%,
HI is 89oF.
• High humidity increases an individual’s
perception of how hot the environment feels
Dr. Misbah-ul-Qamar

Physiologic responses to exercise in
hot weather
• Competition b/w active muscles & skin for limited
blood supply
– Muscles– blood & oxygen for sustained activity
– Skin– blood to facilitate heat loss to keep the body cool
• Cardiovascular response: adjustment—dec. blood
volume returning to heart dec. end diastolic
volume dec. SV
• Compensation: cardiovascular drift gradual upward
drift in HR
• Energy production: exercise in hot environment inc.
O2 uptake use of more glycogen produce more
lactate earlier fatigue & exhaustion
Dr. Misbah-ul-Qamar

• Body fluid balance: sweat– filtration of plasma.
Reabsorption of Na & Cl in passing through the duct
• Increased sweat rates– quick movement, less time for
reabsorption, loss of sodium & chloride
• With training aldosterone stimulated for more
reabsorption of Na & Cl
• Sweat production in hot weather: 1L/hr/m2– 2-4% of
body weight dec. blood volume dehydration
triggering aldosterone, ADH dec. Na excretion & inc.
water reabsorption in kidneys fluid retention
Dr. Misbah-ul-Qamar

Exercise performance in hot
environment
It is impaired due to following factors
• Accelerated muscle fatigue
– Increased free radical production
– Decreased muscle pH
– Muscle glycogen depletion
• Cardiovascular dysfunction
– Reduced stroke volume
– Decreased cardiac output
– Decreased muscle blood flow
• CNS dysfunction
– Decreased motivation
– Reduced voluntary activation of motor units
– Muscle fatigue
Dr. Misbah-ul-Qamar

Exercise in the cold
• What is cold stress?
• It is an environmental condition which causes
loss of body heat & threaten homeostasis
• Major cold stressors are:
– Air
– Water
Dr. Misbah-ul-Qamar

Following mechanisms are observed in case of exercise in
cold
• Shivering which increases 4-5 fold increase in resting
heat production
• Nonshivering thermogenesis which increases
metabolism by activating sympathetic nervous
system increased internal heat production
• Peripheral vasoconstriction due to sympathetic
stimulation of smooth muscles in arterioles 2
advantages: decreased heat loss from surface &
decreased metabolism of skin cells (less O2
requirement)
Dr. Misbah-ul-Qamar

Physiological response to exercise in
cold
• When muscle is cooled, it is weakened
fatigue occurs more rapidly
• With prolonged exposure to cold
– Vasoconstriction decreased circulation to
subcutaneous fat decreased FFA for fuel
– Energy supplies diminish
– Susceptibility to hypothermia increases
Dr. Misbah-ul-Qamar

Heat Acclimatization
• These are several mechanisms by which a
person’s ability to tolerate heat is improved
who have been living in hot climate for long
time.
Dr. Misbah-ul-Qamar

Mechanisms of acclimatization to heat
• The mechanisms are:
• More effective sweating: when exposed to high teperature,
acclimatized person sweats more heavily upto 4L/hr as against
1.6L/hr in unacclimatized person
• Conservation of NaCl: excessive sweating in unacclimatized
person hyponatremia (due to loss of NaCl in sweat)greater
secretion of aldosterone NaCl content of sweat & urine decreases
remarkably in acclimatized person
• More vasopressin (ADH) is secreted renal blood flow is
decreased urinary volume is decreased to conserve water
• Dilation of cutaneous blood vessels
• Total blood volume may also decrease
Dr. Misbah-ul-Qamar

Acclimatization to cold
• Not as efficient as heat acclimatization
• Only seen in primitive (fishermen,
washermen) people who live at 0oC
• There is decreased shivering at low
temperatures also
• Less cold induced pain perception is also
observed in cold acclimatized person
Dr. Misbah-ul-Qamar

ABNORMALITIES OF
TEMPERATURE REGULATION
Dr. Misbah-ul-Qamar

FEVER/PYREXIA
• Fever refers to increased body temperature
above normal , caused by toxic substances that
can affect temperature regulating centers.
• Resetting of the set point to a higher level
• Causes of fever:
• Bacterial and viral infection
• Brain tumors
• Environmental conditions
Dr. Misbah-ul-Qamar

RESETTING THE HYPOTHALAMIC
TEMPERATURE REGULATION CENTER
• PYROGENS:
• Substances that can raise the hypothalamic set point
above normal
• They include:
• Proteins
• Breakdown products of proteins
• Lipopolysaccharide toxins released from bacterial cell
wall
When the hypothalamic set point is raised all the
mechanisms to raise body temperature become active as
well.
Dr. Misbah-ul-Qamar

Mechanism of action of pyrogens:
• Pyrogens either act directly on the hypothalamic
center
• Or they act indirectly via the cytokines especially IL-1
• Bacterial breakdown products → phagocytosed by
leukocytes and macrophages → cytokines especially IL1
is released by the phagocytic cells → IL1 induces the
formation of PGE 2 → PGE 2 acts on hypothalamus to
cause fever reaction.
• Antipyretics are the drugs that decrease the formation
of PGE2 and reduce fever e.g, aspirin
Dr. Misbah-ul-Qamar

Features of febrile conditions
• CHILLS: Shivering and vasoconstriction result
into chills in an attempt to raise the body
temperature up to the new hypothalamic set
point.
• CRISES OR FLUSH : When the pyrogen is
removed and set point is back to normal , all
the body mechanisms to lose heat like
sweating and vasodilation become active .
• This takes the body temperature back to
normal
Dr. Misbah-ul-Qamar

Hyperpyrexia:
• Fever of above 41.5˚C or 106.7˚F is called
hyperpyrexia
• Seen in
• Severe infections
• CNS hemorrhage
Dr. Misbah-ul-Qamar

Hyperthermia:
• Differs from hyperpyrexia in that
• The set point remains unchanged
• Doesn’t respond to antipyretics
Dr. Misbah-ul-Qamar

Types of hyperthermia:
• Heat stroke
• Drug induced
– Amphetamines
– Cocaine
• Malignant Hyperthermia
• Inherited genetic abnormality in Ca release in
skeletal muscle. Increased release of calcium
turns on muscle contraction
• Triggered by some anaesthetic agents
Dr. Misbah-ul-Qamar

Disorders due to increased heat:
• In order of increasing severity
• Heat syncope
• Heat cramps
• Heat exhaustion
• Heat stroke
Dr. Misbah-ul-Qamar

Heat syncope:
• Due to history of vigorous physical activity for
about 2 hours
• Results from cutaneous vasodilation
• Cerebral and systemic hypotension
• Leading to syncope
• TREATMENT:
• Rest in a cool place
• Fluids by mouth
Dr. Misbah-ul-Qamar

Heat cramps:
• Due to excessive Na loss in sweat , painful heat cramps occur.
• Relieved by NaCl replacement and cold environment.
Heat exhaustion:
• Excessive loss of salt and water in sweat leads to
hemoconcentration, hypovolemia ,hypotension, headache, vertigo,
nausea and collapse of patient(due to less blood supply to brain)
• The skin is cold and clammy with normal or subnormal temperature
• Treatment :recumbent position of the patient
• Removal of patient to a cold place
• Salt and water replacement
Dr. Misbah-ul-Qamar

Heat stroke: ( failed compensation)
• Life threatening emergency which damages
the hypothalamus
• Core temperature rises to point that
hypothalamus ceases to function
• Hyperthermia
• Set point remains unchanged
• Doesn’t respond to antipyretics
• Sign: absence of sweating
Dr. Misbah-ul-Qamar

HEAT STROKE:
• Body temperature rises up to 105-108 ˚F
• Failure of all the heat dissipating mechanisms.
• Occurs during heat wave when temperature and
humidity is very high
• Symptoms:
• Hot and dry skin.
• Dizziness ,abdominal distress and vomiting ,delirium
,loss of reflexes, loss of consciousness ,circulatory
shock ,hyperpyrexia ,death may occur due to neuronal
damage , renal failure and MI
Dr. Misbah-ul-Qamar

Loss of temperature regulation at low
temperature
• The hypothalamic temperature regulation is impaired
when the body temperature falls to around 94˚F
• Lost when the body temperature falls to 85˚F
• There is two folds decrease in the cellular metabolic
rate for each 10 degree fall in temperature.
• CNS depression ensues sleepiness and loss of shivering.
• At 77˚ F there is cardiac standstill
Dr. Misbah-ul-Qamar

Hypothermia:
Decrease in body temperature below 35C (95F) is
called hypothermia.
• it is a clinical state of subnormal body
temperature when the body fails to produce
enough heat to maintain the normal activities
• Elderly are more susceptible to hypothermia
Setback of hypothermia:
Impairment of metabolic activities
Becomes fatal when temperature drops below 31C
Dr. Misbah-ul-Qamar

Presentation of hypothermia
• Person exposed to cold for a long period of
time
• Also seen in patients of
• Myxedema , Addisons disease , hypoglycemia
• FEATURES:
• Shallow breathing , bradycardia ,hypotension
,loss of consciousness, arrythmias
Dr. Misbah-ul-Qamar

Frostbite:
• Surface area of the body can freeze upon
exposure to cold. This is called frostbite.
• Ice crystals develop in the blood stream and cells
causing permanent circulatory and tissue
damage.
• Upon thawing , gangrene develops and the area
has to be removed surgically.
• The vascular smooth muscles become paralyzed
due to extreme cold leading to improved blood
supply to the tissues .This protective mechanism
is very well developed in arctic animals.
Dr. Misbah-ul-Qamar

Pathophysiological changes in frostbite
Dr. Misbah-ul-Qamar

Artificial hypothermia:
The temperature of a person is decreased by
• Sedatives….which reduce the over activity of hypothalamic
center
• Use of ice or cooling blankets
USES:
Heart surgery can be done after hypothermia so that heart
can be stopped artificially for several minutes at a time.
Hypothermia decreases whole body metabolic rate by approx.
8%, oxygen demand diminishes & oxygen consumption in
tissues is reduced
Low metabolic rate allow aerobic metabolism to continue
during periods of compromised oxygen supply
Dr. Misbah-ul-Qamar

cryopreservation
Dr. Misbah-ul-Qamar

Temperature dpt

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Temperature dpt

Similar to Temperature dpt (20)

More from DrMisba

More from DrMisba (10)

Recently uploaded

Recently uploaded (20)

Temperature dpt