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1. ENERGY BALANCE AND
TEMPERATURE REGULATION

2. Energy balance terminology
• First law of thermodynamics: energy can neither
be created nor destroyed, it can only be transferred
from one form to another.
• Basal metabolic rate (BMR): a reflection of the
body’s “idling speed”, or the minimal waking rate of
internal energy expenditure. It is the metabolic
activity necessary to maintain the basic body
functions at rest.
• Metabolic rate: the rate at which energy is
expended by the body during both external and
internal work.

3. All energy used by cells is
ultimately provided by food intake
• Each cell in the body needs energy to perform its functions.
• Ingested food constitutes energy input to the body.
• Chemical energy in nutrient molecules are released through
digestion.
• Energy output or expenditure falls into two categories,
external work and internal work.
• External work is the expanded when skeletal muscles
contracted to move external objects or to move the body in
relation to the environment
• Internal work constitutes all other forms of biological energy
expenditure that do not accomplish mechanical work
outside the body.
• Encompass two types of energy-dependent activities:
skeletal muscle activity and all energy-expending activities.

4. Not all energy in nutrient molecules
can be harnessed to perform
biological work
• The energy in nutrient molecules not used to energize
work is transformed into thermal energy (heat).
• The heat is used to maintain body temperature.
• Metabolic rate = energy expenditure/unit of time
• The basic unit of heat energy is calorie (the amount of
heat required to raise the temperature of 1g of H2O by
1 degree Celsius).
• The rate of heat production vary depending on several
factors, such as exercise, anxiety, shivering, and food
intake.
• The BMR is the metabolic activity necessary to
maintain the basic body functions at rest.
• The thyroid hormone is the primary determinant of the
rate of basal metabolism.

5. Energy input must equal energy
output to maintain a neutral energy
balance
• Three possible states of energy
balance: neutral energy balance,
positive energy balance and
negative energy balance.
• Theoretically, total body energy
content could be maintained at a
constant level by regulating the
magnitude of food intake,
physical activity, or internal work
and heat production.
• The body tries to compensate for
undereating/overeating by
increasing/decreasing the body’s
efficiency of energy use.
• Regulation of food intake is the
most important factor in the
long-term maintenance of
energy balance and body weight.

6. Food intake is controlled primarily
by the hypothalamus
• Blood-borne chemical factors that signal the body’s
nutritional state are important in regulating food intake.
• They are the involuntary regulatory signals of appetite.
• Multiple molecular signals together ensure that feeding
behaviour is synchronized with the body’s immediate and
long-term energy needs.
• The arcuate nucleus of the hypothalamus plays a central
role in long-term control of energy balance and body weight
and the short term control of food intake from meal to meal
• Feeding or appetite signals give rise to the sensation of
hunger, driving us to eat.
• Satiety signals tell us when we have had enough and
suppress the desire to eat.
• Two subsets of the arcuate nucleus, one subset releases
neuropeptide Y and the other releases melanocortins
derived from opiomelanocortin (POMC).

7. • Neuropeptide Y leads to increased food intake, thus
promoting weight gain.
• Melanocortins suppress appetite, thus leading to
reduced food intake and weight loss.
• Long-term control
• Leptin and insulin are important blood-borne signals that play
roles in long-term control of the body weight.
• Leptin suppresses appetite by inhibiting hypothalamic out of
appetite-stimulating neuropeptide Y and stimulating output
of appetite-suppressing melanocortins.
• Insulin stimulates cellular uptake, use, and storage of
nutrients.
• Short-term control
• Two peptides important in short-term control of food intake
are ghrelin for hunger and peptide YY for fullness.
• A satiety centre in the brain stem processes signals important
in the feeling of being full and contribute to short-term
control of meals.

8. Cholecystokinin as a satiety signal
• CCK is one of the gastrointestinal hormones
released from the duodenal mucosa during
digestion of a meal.
• It is also an important satiety signal for regulating
the size of meals.
• It is secreted in response to the presence of
nutrients in the small intestine.
• It contributes to the sense of being filled after a
meal has been consumed but before it has been
digested and absorbed.

9. People’s eating habits are also
shaped by psychological, social, and
environmental factors
• Food often plays a prime role in entertainment,
leisure, and business activities.
• The amount of pleasure derived from eating can
reinforce feeding behaviour.
• Stress, anxiety, depression, and boredom have also
been shown to alter feeding behaviour in ways
unrelated to energy needs.
• Environmental influences , such as the amount of
food available, play an important role in
determining the extent of food intake.

10. Obesity occurs when more
kilocalories are consumed than are
burned up
• Obesity is excess fat content in the adipose tissue
stores.
• Possible causes:
• Disturbance in leptin-signaling pathway can result from leptin
resistance or faulty in leptin receptors in the brain, and can
cause high levels of leptin.
• Lack of exercise
• Differences in extracting energy from food
• Hereditary tendencies
• Development of an excessive number of fat cells as a result of
overfeeding
• Certain endocrine disorders such as hypothyroidism
• Too little sleep
• An abundance of convenient, highly palatable, energy-dense,
relatively inexpensive foods
• Emotional disturbances in which overeating replaces other
gratifications

11. Android and gynoid obesity
• Obese patients can be classified
into two categories: android, a
male-type of adipose tissue
distribution, and gynoid, a
female-type distribution.
• Android obesity is characterized
by abdominal fat distribution
(apple shaped) due to greater
proportion of visceral fat
• Gynoid obesity is characterized
by fat distribution in the hips and
thighs (pear shaped)
• Android obesity is associated
insulin resistance, type 2
diabetes, heart disease, etc.
• Gynoid obesity is not associated
with the high risk of these
diseases

12. The converse of obesity is
generalized nutritional deficiency
• The obvious causes for reduction of food intake
below energy needs are:
• Lack of food
• Interference with swallowing or digestion
• Impairment of appetite.
• Anorexia nervosa patients have a pathological fear
of gaining weight.
• Characteristics include altered hormone secretion,
absence of menstrual periods, and low body heat.

13. Temperature regulation

14. Humans are constantly producing
heat
• Heat production depends on the oxidation of metabolic fuel
derived from food.
• An increase in temperature speeds up cellular chemical
reactions.
• A decrease in temperature slows down these reactions.
• Humans homeostatically maintain body temperature at a
level optimal for stable cellular metabolism as cell function
is sensitive to fluctuations in internal temperature.
• Moderate elevations of body temperature begin to cause
nerve malfunction and irreversible protein denaturation.
• In contrast, the body’s tissues can transiently withstand
substantial cooling

15. Internal temperature is
homeostatically maintained at 37.8
degree Celsius
• Normal body temperature varies among individuals and
varies throughout the day.
• The variation is largely due to an innate biological rhythm or
‘biological clock’.
• Temperature varies from organ to organ. The temperature
within the central core, which consists of the abdominal and
thoracic organs, the CNS, and the skeletal muscles, remains
fairly constant.
• Core temperature is subject to precise regulation to
maintain its homeostatic constancy.
• The core tissues function best at a relatively constant
temperature of around 37.8 degrees Celsius.
• The skin and subcutaneous fat constitute the outer shell and
within the shell is generally cooler.

16. Several easily accessible sites are
used for monitoring body
temperature
• The oral and axillary temperatures are comparable,
whereas rectal temperature is higher.
• Temporal temperature is the best determinant of
core temperature because it is nearly identical to
the temperature of the blood exiting the heart

17. Heat input must equal heat output to
maintain a stable core temperature
• Heat input occurs by way of heat gain
from the external environment and
internal heat production.
• Heat created by the body’s energy
expenditure is important in maintaining
core temperature.
• Heat output occurs by way of heat loss
from exposed body surface to the
external environment. More heat is
generated than required to maintain
normal body temperature, so excess
heat must be eliminated.
• Temperature balance disturbed by:
• Changes in internal heat production for
purposes unrelated to regulation of body
temperature, e.g., exercise
• Changes in the external environment
temperature that influences the degree of
heat gain or heat loss that occurs between
body and environment.

18. Heat exchange takes place by
radiation, conduction, convection,
and evaporation
• The temperature of an object is a measure of the
concentration of heat within the object.
• Heat always moves down its concentration gradient – down
a thermal gradient from a warmer to a cooler region.
• Radiation is the emission of heat energy from the surface of
a warm body in the form of electromagnetic waves, or heat
waves, which travel through space. When radiant energy
strikes an object and is absorbed, the energy of the wave
motion is transformed into heat within the object.
• Conduction is the heat transfer between objects of differing
temperatures that are in direct contact with each other,
with heat moving down its thermal gradient from the
warmer to cooler object. The body loses or gains heat by
conduction to the layer of air in direct contact with the
body.

19. • Convection is the transfer of
heat energy by air (or water)
currents. Convection currents
are when the body loses heat
by conduction to the
surrounding cooler air, the air
in immediate contact with the
skin is warmed and the
warmed air rises while cooler
air moves in next to the skin to
replace the vacating warm air.
• Evaporation is the conversion
of a liquid such as sweat into a
gaseous vapor, a process that
heat, which is absorbed from
the skin

20. The hypothalamus is the body’s
thermostat
• The hypothalamus receives afferent information about the
temperature in various regions of the body and initiates
extremely complex, coordinated adjustments in the heat-gain
and heat-loss mechanisms as necessary to correct deviations.
• The hypothalamus is notified continuously of both the core
and the skin temperature by specialized temperature-sensitive
receptors called thermoreceptors.
• Central thermoreceptors monitor core temperature and
located in the hypothalamus and abdominal organs.
• Peripheral thermoreceptors monitor skin temperature
throughout the body.
• Two centres for temperature regulation are in the
hypothalamus:
• The posterior region, activated by cold, triggers reflexes that mediate
heat production and heat conservation.
• The anterior region, activated by warmth, initiates reflexes that
mediate heat loss.

21. Shivering is the primary involuntary
means of increasing heat production
• The body can gain heat as a result of internal heat
production generated by metabolic activity of from the
external environment if the latter is warmer than the
body temperature.
• Because body temperature is usually higher than
environmental temperature, metabolic heat production
is the primary source of body heat.
• The rate of metabolic heat production can be increased
primarily by changes in skeletal muscle activity.
• In response to a fall in core temperature caused by
exposure to cold, the hypothalamus increases muscle
tone and shivering begins which increases skeletal
muscle activity and heat is generated.
• Muscle tone is the constant level of tension within the
muscles.

22. • In the rise of core temperature by heat exposure,
two mechanisms reduce heat-producing skeletal
muscle activity:
• Muscle tone is reflexly decreased
• Voluntary movement stops
• Non-shivering (chemical) thermogenesis also plays
a role in thermoregulation.
• Non-shivering thermogenesis is mediated by the
hormones epinephrine and thyroid hormone which
increase heat production by stimulating fat
metabolism.

23. The magnitude of heat loss can be
adjusted by varying the flow of blood
through the skin
• The insulating capacity of the skin can be varied by controlling the
amount of blood flowing through.
• Skin blood flow serves two functions:
• It provides a nutritive blood supply to the skin
• Most skin blood flow is for temperature regulation
• The skin’s blood vessels diminish the effectiveness of the skin as an
insulator by carrying heat to the surface where it is can be lost from
the body by radiation and the conduction-convection process.
• Skin arteriolar vasodilation increases heat loss.
• Skin vasoconstriction decreases heat loss by keeping the warm
blood in the central core.
• The skin vasomotor responses are coordinated by the hypothalamus
by means of sympathetic nervous system output.
• Increased sympathetic activity produces heat-conserving
vasoconstriction in response to cold.
• Decreased sympathetic activity produces heat-losing vasodilation in
response to heat.

24. The hypothalamus simultaneously
coordinates heat-production and
heat-loss mechanisms
• In response to cold exposure, the posterior region of the
hypothalamus directs increased heat production (e.g.
shivering) and simultaneously decreasing heat loss by skin
vasoconstriction.
• Further heat loss can be prevented by behavioural adaptations
such as postural changes that reduces exposed surface area
from which heat can escape, as well as putting on warmer
clothing.
• In response to heat exposure, the anterior part of the
hypothalamus reduces heat production by decreasing skeletal
muscle activity and promotes increased heat loss by inducing
skin vasodilation.
• Sweating accomplishes further heat loss through evaporation.
• Voluntary measures such as using fans, drinking cold
beverages and wearing cooler clothes promotes heat loss.
• Light-coloured clothing reflect radiant energy.