Thermoregulation is a process that allows your body to maintain its core internal temperature. All thermoregulation mechanisms are designed to return your body to homeostasis. This is a state of equilibrium. A healthy internal body temperature falls within a narrow window. The average person has a baseline temperature between 98°F (37°C) and 100°F (37.8°C). Your body has some flexibility with temperature. However, if you get to the extremes of body temperature, it can affect your body’s ability to function. For example, if your body temperature falls to 95°F (35°C) or lower, you have “hypothermia.” This condition can potentially lead to cardiac arrest, brain damage, or even death. If your body temperature rises as high as 107.6°F (42 °C), you can suffer brain damage or even death. Many factors can affect your body’s temperature, such as spending time in cold or hot weather conditions. Factors that can raise your internal temperature include: fever exercise digestion Factors that can lower your internal temperature include: drug use alcohol use metabolic conditions, such as an under-functioning thyroid gland Your hypothalamus is a section of your brain that controls thermoregulation. When it senses your internal temperature becoming too low or high, it sends signals to your muscles, organs, glands, and nervous system. They respond in a variety of ways to help return your temperature to normal.

1. Saad Salih Mahdi
‫ﻣﮭدي‬ ‫ﺻﺎﻟﺢ‬ ‫ﺳﻌد‬
Second stage
Group: A
saadiylep@ced.nahrainuniv.edu.iq
Dear Department of Physiology
Supervisors:

2. Talk about normal body
temperature
Hypothalamus
Talk about hemostasis
mechanism
Introduction
01Contents:
Figure 1.
Estimated normal range of body “core” temperature.
(Modified from DuBois EF: Fever. Springfield, IL: Charles C. Thomas,
1948.)
The skin, the subcutaneous tissues, and especially the fat
of the subcutaneous tissues act together as a heat insulator
for the body. The fat is important because it conducts
heat only one-third as readily as other tissues. When no
blood is flowing from the heated internal organs to the
skin, the insulating properties of the normal male body
are about equal to three-quarters the insulating properties
of a usual suit of clothes. In women, this insulation is
even better. The insulation beneath the skin is an effective
means of maintaining normal internal core temperature, even
though it allows the temperature of the skin to approach the
temperature of the surroundings.
conclusion
Discuses information
Fever
Talk about role of fever
Clinical correlations
Talk about some diseases
effect on thermoregulation
02
03
04
05
NORMAL BODY TEMPERATURES:
Body Core Temperature and Skin Temperature. The
temperature of the deep tissues of the body—the “core”
of the body—usually remains very constant, within ±1°F
(±0.6°C), except when a person has a febrile illness. Indeed,
a nude person can be exposed to temperatures as
low as 55°F or as high as 130°F in dry air and still maintain
an almost constant core temperature. The mechanisms
for regulating body temperature represent a beautifully
designed control system. In this chapter we discuss this
system as it operates in health and in disease. The skin
temperature, in contrast to the core temperature,
rises and falls with the temperature of the surroundings.
The skin temperature is important when we refer to
the skin’s ability to lose heat to the surroundings. Normal Core
Temperature. No single core temperature
can be considered normal because measurements in
many healthy people have shown a range of normal temperatures
measured orally, as shown in Figure 1,
from less than 97°F (36°C) to greater than 99.5°F (37.5°C). The
average normal core temperature is generally considered
to be between 98.0°F and 98.6°F when measured orally
and about 1°F higher when measured rectally.
BODY TEMPERATURE IS CONTROLLED
BY BALANCING HEAT PRODUCTION
AND HEAT LOSS
When the rate of heat production in
the body is greater
than the rate at which heat is being
lost, heat builds up
in the body, and the body temperature
rises. Conversely, when heat loss is
greater, both body heat and body
temperature decrease. Most of the
remainder of this chapter is concerned
with this balance between heat
production and heat loss and the
mechanisms by which the body
controls this production and loss.
Insulator System of the Body

3. Radiation:
NORMAL THERMOREGULATION
• Thermoregulation, like other physiologic control systems in the brain, uses negative
feedback to minimize perturbations
• Regulations occur with hypothalamic set point system
• The processing of thermoregulatory information occurs in three
phases:
03
02
01 Afferent thermal sensing
Central regulation
Efferent responses
01
1. Cold receptors : A-delta fibers
- Just beneath epidermis, 10x in number
- Maximal discharging rate b/w 25 – 30 °C
2. Warm receptors : unmyelinated C-fibers
- Deeper skin; proximity to great vessels/viscera/abdominal wall/ pons/
medulla/spinal cord
- Maximal discharging rate b/w 45-50 °C
3. Vagus – role unknown
Afferent thermal sensing

4. 02
• Site of processing: POAH
Efferent control: posterior hypothalamus
• POAH contains temperature sensitive neurons (cold and heat sensitive
neurons)
• Predominant input is from peripheral receptors, central receptors regulate
once peripheral inputs are disrupted (central neuraxial anesthesia, SC
transection)
• Functional in term neonate, may be impaired in premature, elderly, critically ill.
• The interthreshold range is 0.4°C in awake state & 3.5°C in GA
• It extends more into hypothermic range than hyperthermic in
awake as well as GA
• This range is bounded by the sweating threshold at its upper end
and by vasoconstriction at the lower end
• Exact mechanism of threshold determination is Unknown
• THERMONEUTRAL ZONE: ambient temp range at which O2
demand is minimal & temp regulation is achieved through
nonevaporative physical processes only (i.e. vasoconstriction/
dilation)
Central regulation
• Behavioral responses: mainly governed by skin temperature
Includes heating the room, putting jacket, seeking shelter etc.
• Autonomic responses: mainly by core temperature, 20% by skin
Includes:
01 02
Cold defense Heat defense
increase heat production by shivering &
nonshivering thermogenesis, voluntary
muscle activity; decrease heat loss by
vasoconstriction (first change)
increase heat loss by vasodilatation
(marked blood flow rise),
sweating
Efferent responses

5. Mechanisms of heat loss / heat gain
Surface of all objects emit heat in form of
Electromagnetic radiation.
Rate of emission α Temperature
Loss/ gain by transfer of thermal energy during collisions
between adjacent molecules
– Heat is conducted from Molecule to Molecule
Mechanisms of heat loss / heat gain
Conductive heat loss or gain is aided by
movement of air / water next to body.
-Cool air replacing warm air.
Water evaporates from skin & membrane lining the respiratory
tract MAJOR PROCESS for Loss of body heat.
• 600Kcal/L required to transfer water from fluid to gaseous state.
- Heat required to evaporate water from the surface is conducted
from the surface cooling it.
Radiation
Conduction
Convection
Evaporatio
• Skin is not a perfect insulator
• Temp of outer surface of skin is between external temp & core temp. (net conduction = 0)
• Skin acts as insulator by change in blood flow.
• The heat from within is brought out by the blood and lost to the outside.
• Vasoconstrictor sympathetic nerves firing rates:
- in response to cold
- in response to heat
SKIN & ITS ROLE

6. Thermoreceptors detect changes in the balance between heat loss &
production due to metabolic rate (exercise).
Tow types :
Output from hypothalamus is sent to effectors via:
Peripheral on Skin
Central in hypothalamus (integrating center),
spinal cord, abdominal organs.
sympathetic nerves to sweat glands
skin arterioles & adrenal medulla
Motor neuron to skeletal muscles
Core temp is maintained relatively constantly.
Peripheral thermoreceptors help identify heat & cold.
Temperature – Regulating reflexes
• All the mechanisms are Graded and not All or None
responses.
• 250C to 300 C or 750F to 860F is known as a
thermoneutral zone.
• At temps lower than this TNZ max vasoconstriction
cannot prevent heat loss from exceeding heat production
& this requires the body to increase heat production.
• At temps above this TNZ max vasodilation cannot
eliminate the heat as fast as it is produced & this requires
another heat loss mechanism ‘SWEATING’
Thermoneutral zone (TNZ)

7. Nervous Mechanisms
Thermoregulatory centers
Reflex Mechanisms
Efferent Nerves
Endocrine
Adrenal Medulla
Adrenal Cortex
Thyroid
Behavior & Voluntary
control
Control Mechanisms
Direct action
04030201
Reflex
Mechanisms
Sensitive
thermoreceptors
Efferent
Nerves
Autonomic
Efferent
Nerves
Somatic
Behavioral &
Voluntary Control
Nerves to skeletal
muscle (tone, activity,
shivering)
Nerves to respiratory
muscles
in the skin carry
information via
cutaneous nerves
and hypothalamus
Sympathetic adrenergic
vasomotor nerves
(cutaneous
vasoconstriction &
vasodilatation)
Sympathetic cholinergic
• Animals move from warm
to cold regions
• Curling up of body in cold
conditions
• Clothing in woolens in
winter and thin cotton
clothing in summer.
• Fans, air conditioners,
heaters & central heating

8. Desired Effect Mechanism
Decreased heat
lose
Vasoconstriction of skin vessels
Reduction of surface area (curling
up)
Behavioral responses (warm
clothes)
Increased Heat
Production
Increased muscle tone
Shivering & increased voluntary
activity
Epinephrine secretion (minimal)
Increased appetite
Desired Effect Mechanism
Increase heat
lose
Vasodilation of skin vessels
Sweating
Behavioral response
Decreased Heat
Production
Decreased muscle tone
Decreased secretion of epinephrine
(minimal)
Decreased Appetite
Effector mechanisms in Temperature Regulation
Stimulated by Cold Stimulated by Heat
01Hypothermia
01 • Reduction in temp < 350C
• At 270C the metabolism is greatly reduced
(<280C unable to correct by itself)
• HR, BP & RR are decreased
• Unconscious state
• Exposure to low temps
• Cardiac surgery where heart is stopped

9. 02Hyperthermia
A • Fever is an elevation of body temperature due to a
“resetting of the thermostat”
• > 990F
• Bacterial / Viral Infections, trauma, lesions of CNS,
exposure to high temperatures & drug induced.
• Increased heat production by shivering (rigor) &increased
metabolism
• Diminished heat loss by vasoconstriction
• Skin is warm & flushed
• Subsides by sweating
• Serious Condition, high environmental temp
• Overheating of body, impaired sweating
• Headache, restlessness & mental confusion
• Hyperpyrexia (410C or 1060F)
• Delirium, convulsions collapse & COMA
• Death results if untreated
• Temp to be brought down to 1020C with ice packs
Heat Stroke
B

10. Core body temperature >37°C
Core body Temperature <37°C
Conclusion

11. 01
02
03
04
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References
Essentials of Clinical Neurophysiology, Third
Edition; Karl E. Misulis, PhD and Thomas C.
Head, PhD Butterworth Heinemann, Burlington,
MA, 2003. ISBN: 0-7506-7441-5
Germann, W.J., Stanfield, C.L. (eds.)
(2002)_Principles of Human Physiology,
Pearson Education, Inc./ Benjamin
Cummings, San Francisco, CA
Guyton AC and Hall JE (eds.) (2000)
Textbook of Medical Physiology, 10th edition.
W.B. Saunders Co., Philadelphia, PA.
Bipin Kumar. 2001. Human
Physiology. Campus Book
International, New Delhi.
Martini, F.H. and Nath, J. L. 2009.
Fundamentals of Anatomy & Physiology.
Pearson Benjamin Cummings. USA.
Tortora, G.J. and Grabowski, S.R. (eds.)
(2000) Principles of Anatomy and Physiology,
9th edition. John Wiley & Sons, Inc., New
York, NY.