Topic 2, L3 - Nutrition, Metabolism and Energy Balance II

Question 1

Energy Balance

Answer 1

Energy released from food must equal total energy output (calorie expenditure)

Question 2

What are resting calories ?

Answer 2

Calories needed to maintain basic body functions when you’re not doing activities

Question 3

What is energy intake ?

Answer 3

The calories we take in from eating

Energy derived from absorbable foods = Energy liberated during food oxidation

Question 4

What is energy output ?

Answer 4

Energy expenditure / release / loss through the performance of basic essential metabolic functions + purposeful activities (eg. exercise)

• Immediately lost as heat (~60%)
• Used to do work (driven by ATP)
• Stored as fat OR glycogen

Question 5

Nearly all energy from food is eventually converted to heat, which cannot be used to do work, but it …

Answer 5

• Warms tissues + blood
• Helps maintain homeostatic body temperature
• Allows metabolic reactions to occur efficiently (most enzymes have an optimal body temp range which must be upheld in order for them to work efficiently)

Question 6

Body Mass (BM)

Answer 6

Maintained when energy intake (consumed) = energy expenditure (used)

Question 7

Body Mass Index (BMI)

Answer 7

Formula used to determine obesity based on a person’s weight relative to height
- Not a direct measurement of how much fat person is carrying around → Formula does not take into account that high BMI can be result of large muscle mass

To calculate : BMI = wt (kg) /height in (m)2

eg. Person is 175 cm tall & has a weight of 70 kg
BMI = 22.86 (normal body weight)

Question 8

What is obesity ?

Answer 8

Greater intake / consumption than expenditure of energy → Most of which is then stored as fat instead of the body getting rid of it ( efficient storage system )

25 % or greater of total body fat (men), 35 % or greater of total body fat (women)

• Stored mainly in adipocytes within intraperitoneal cavity / subcutaneous tissue (increase in adipocyte storage = inc in # & size of adipocytes)

Result of stress, sedentary lifestyles, abnormal eating behaviours, childhood overnutrition, neurogenic abnormalities, genetic factors, gut microbiome

Question 9

Current Obesity Statistics (US)

Answer 9

• 2 out of 3 adults are overweight
• 1 out of 3 is obese
• 1 in 10 has diabetes
• 17% of children are obese (compared with only 5% 40 years ago)

Question 10

Obese people have higher incidence of …

Answer 10

• Atherosclerosis (hardening of arteries, may lead to heart disease / attack)
• Diabetes mellitus (Type 2) – biggest risk factor, adipose tissue may release hormones affecting insulting signalling, leading to issues with blood glucose regulation
• Hypertension (high BP as a result of increased vasculature length to accommodate tissues, more energy required to pump blood)
• Heart disease
• Osteoarthritis (extra tissue → P on lower limb joints)

Question 11

What is metabolic syndrome ?

Answer 11

Cluster of 5 risk factors
- ↑ Waist circumference
- ↑ Blood pressure
- ↑ Blood glucose ( hyperglycemia )
- ↑ Blood triglycerides
- ↓ Blood HDL cholesterol

Apple shaped body – Higher risk (mostt weight accumulates in abdominal cavity)

Presence of these factors can :
- 2x chance of heart disease
- 5x increased risk of diabetes

Consequence : Development of insulin resistance → have receptors for binding of insulin hormone, somehow pathway following that has become affected

Question 12

What areas of the hypothalamus release peptides that influence feeding behavior ?

Answer 12

• Arcuate nucleus (ARC) – Major hub, lesions can cause abnormal food behaviours
• Lateral hypothalamic area (LHA) – Controls food intake, excites motor drive for feeding, encourages food-seeking behaviour
• Ventromedial nucleus (VMN) – Satiety center, inhibits feeding center (feeling of fullness)

Multiple hormones in nuclei that release from Gi tract / adipose tissues to converge to regulate food intake / energy expenditure

Question 13

Regulation of Food Intake

Answer 13

Arcuate nucleus (ARC) : Some ARC neurons release neuropeptide Y (NPY) & agouti-related peptides (AgRP) that enhance appetite
- Interact with neurons in LHA to release orexins (orexigenic) substances that stimulate feeding / appetite
- Other ARC neurons release pro-opiomelanocortin (POMC) & cocaine-/amphetamine-regulated transcript (CART), NTs which suppress appetite

Lateral hypothalamic area (LHA) : _Promote hunger_ when stimulated by neuropeptides (e.g., NPY)

Ventromedial neurons (VMN) : Cause satiety through release of corticotropin-releasing hormone (CRH) when stimulated by appetite-suppressing peptides (e.g., POMC and CART)

• see diagram -

Question 14

Feeding behaviour & hunger is regulated by …

Answer 14

• Neural signals from GI tract (eg. distension)
• Bloodborne signals related to body energy stores
• Hormones
• To lesser extent, body temp & psychological factors

Operate through brain thermoreceptors, chemoreceptors, and others

Food intake is subject to both short- & long-term controls that go up to ARC

Question 15

Short-term regulation of food intake

Answer 15

Neural signals from digestive tract
- High protein content of meal increases and prolongs afferent vagal signals
- Distension sends signals along vagus nerve that suppress hunger center

Nutrient signals related to energy stores
- Increased nutrient levels in blood depress eating
- Rising blood glucose levels
- Elevated blood amino acid levels
- Blood levels of fatty acids

Hormones
- Gut hormones (e.g. insulin & CCK) depress hunger
- Glucagon & epinephrine stimulate hunger (high lvls of glucagon = low blood sugar, body needs to use reserves to meet metabolic needs)
(epinephrine tells u that u need to replenish after fight or flight stimulated response)
- Ghrelin (Ghr) from stomach stimulates appetite; levels peak prior to mealtime

Question 16

Long-term Regulation of Food Intake

Answer 16

Leptin – Peptide hormone secreted by fat cells / adipocytes in response to increased body fat mass
- Indicator of total energy stores in fat tissue
- Protects against weight loss in times of nutritional deprivation / deficiency
- Acts on ARC neurons in hypothalamus
- Suppresses secretion of NPY—potent appetite stimulant
- Stimulates expression of appetite suppressants
(eg. CART peptides)

Rising leptin level causes some weight loss but is no “magic bullet” for obese patients
- Obese people have high leptin levels but seem to be resistant to its action

Question 17

Additional Factors

Answer 17

• Temperature – Cold activates hunger to inc metabolic activity which inc amount of heat produced
• Stress – Depends on individual
• Psychological factors
• Adenovirus infections
• Sleep deprivation – inc in feeding behaviours
• Composition of gut bacteria

Question 18

What is metabolic rate ?

Answer 18

Total heat produced by chemical reactions + mechanical work of body
- Average caloric expenditure
- Only small percentage of energy from food used by functional system, rest will stimulate processes that will eventually generate heat

Can be measured :
- Directly – Calorimeter measures heat liberated off individual into water chamber
- Indirectly – Respirometer measures oxygen consumption (directly proportional to heat production)

Question 19

What is the Basal Metabolic Rate (BMR) ?

Answer 19

Minimum energy body needs to perform its most essential activities (EXISTING, breathing, keeping warm)

• Measured at REST, in postabsorptive state (12-hour fast) – starts 4h after end of meal consumption
• Reclining position
• Relaxed mentally & physically
• Room temperature 20 – 25°C

any small activity will generate heat & play into BMR

Recorded as kilocalories per square meter of body surface per hour (kcal/m2/h)
eg. 70 kg adult BMR = 66 kcal/h

Question 20

BMR is influenced by …

Answer 20

• Age and gender : BMR decreases with age & males have disproportionately higher BMR (higher amount of skeletal muscles)
• Body temperature : BMR increases with temperature (with every 10 degree rise in temp, BMR can inc by 120 %)
• Stress: BMR increases with stress (Sympa NS activated)
• Thyroxine : Increases oxygen consumption, cellular respiration, rate of chem rxns & BMR
• Testosterone : Increases BMR by 10 - 15 %, inc amount of skeletal muscle mass

Question 21

What is the Total Metabolic Rate (BMR) ?

Answer 21

Rate of energy consumption to fuel all ongoing activities [ daily energy expenditure ]

• Increases with skeletal muscle activity and food ingestion (food-induced thermogenesis)
• Greatest with protein ingestion (more energy to process)

Components are : (add them together)
- Basal energy expenditure (BMR)
- The thermic effect of food (TEF) – Energy required for ingestion, absorption, storage of food (up with proteins)
- Energy expended on physical activity (thermic effect of activity = TEA)

Total metabolic rate (TMR) = Total daily energy expenditure (TDEE)

Question 22

Regulation of Body Temperature

Answer 22

Only ~ 40% of energy released by catabolism can be captured by ATP; the rest is lost as heat
- Cannot be used to do work
- Warms the tissues and blood
- Helps maintain the homeostatic body temp

Body temperature reflects the balance between heat production and heat loss

• _At rest_, the liver, heart, brain, kidneys & endocrine organs generate most heat
• During exercise, heat production from skeletal muscles increases dramatically

Question 23

What is the normal body temperature range in humans ?

Answer 23

37°C ± 5°C (98.6°F)

• Optimal enzyme activity at this temperature

Increased temperature denatures proteins (begin to unravel - lose functional ability) & depresses neurons

• ~43°C (109°F) is the limit for life
• BUT LOWER in children under 5, temperature of 41°C (106°F) can lead to convulsions

Tissues can tolerate low body temperatures better (slows down metabolic rate, used to use ice baths for surgery)

Question 24

Core & Shell Temperature

Answer 24

Core (organs within skull & thoracic and abdominal cavities) has highest temperature
- Rectal temperature is best clinical indicator
- Core temperature is strictly regulated & is fairly constant to PROTECT

Blood is major agent of heat exchange between core and shell

Shell (skin) has lowest temperature
- Fluctuates between 20°C and 40°C

Question 25

What are the 4 mechanisms of heat transfer ?

Answer 25

1. Radiation : Loss of heat by infrared rays ; objects are not in contact
2. Conduction : Heat transfer between molecules of objects in direct contact
3. Convection : Heat transfer to surrounding air
4. Evaporation : Heat loss due to evaporation of water from body surfaces; heat absorbed by water during evaporation is known as heat of vaporization
   (sweating & water evaporates from skin of mouth)

Insensible heat loss – Accompanies insensible water loss from lungs, oral mucosa, and skin
- Loss ~ 10% of basal heat production )

Sensible heat loss – When body temperature rises and sweating increases water vaporization, body cooled

Question 26

Factors contributing to heat production

Answer 26

• Basal metabolism
• Muscular activity (shivering)
• Thyroxine & epinephrine (stimulating effects on metabolic rate)
• Digestion
• Temperature effect (warmer cells metabolize faster, producing more heat)

Question 27

Factors contributing to heat loss

Answer 27

• Radiation
• Conduction / convection
• Evaporation

Question 28

What is the thermaregulatory role of the hypothalamus ?

Answer 28

Thermoregulatory centers : Preoptic region of hypothalamus is main integrating center for thermoregulation

2 thermoregulatory centers
- Heat-loss center
- Heat-promoting center

Hypothalamus receives afferent input from :
- Peripheral thermoreceptors in shell (skin)
- Central thermoreceptors in core (some in hypothalamus)

Initiates appropriate heat-loss & heat-promoting activities

Question 29

Heat Promoting Mechanisms

Answer 29

–> Constriction of cutaneous blood vessels –
(Regulated by sympathetic NS, reduce blood flow to skin so chances of heat dissipating drops)
–> Shivering – Heat generated from skeletal muscle activity
–> Increases in metabolic rate – Chemical (non-shivering) thermogenesis : via epinephrine and norepinephrine stimulated by cold temperatures (mechanism seen in infants) &
brown adipose tissue in infants and adults (used mainly to gen heat instead of source of energy)
–> Enhanced release of thyroxine (speeding everything up, seen only infants)

Question 30

Heat Loss Mechanisms

Answer 30

–> Heat-promoting center is inhibited
–> Dilation of cutaneous blood vessels
–> Enhanced sweating

Question 31

Homeostatic imbalances involving mechanisms of body temperature regulation :

Answer 31

• Hypothermia
• Hyperthermia
• Heat exhaustion
• Fevers

Question 32

Hypothermia

Answer 32

• Low body temperature where vital signs decrease
• Shivering stops at core temp of 30 - 32°C
• Can progress to coma and death by cardiac arrest at ~ 21°C

Question 33

Hyperthermia

Answer 33

• Elevated body temp depresses the hypothalamus
• Positive-feedback mechanism, heat stroke begins at core temperature of 41°C
• Can be fatal if not corrected

Question 34

Heat Exhaustion

Answer 34

• Also referred to as exertion-induced heat exhaustion
• Heat-associated collapse after vigorous exercise
• Due to dehydration & low blood pressure
• Heat-loss mechanisms are still functional
• May progress to heat stroke if body is not cooled and rehydrated promptly

Question 35

Fever

Answer 35

Controlled hyperthermia mostly due to infection, but also cancer, allergies, or CNS injuries

–> Macrophages release cytokines called pyrogens that cause release of prostaglandins from hypothalamus, resetting thermostat higher

• Triggers heat-producing mechanisms, and temperature rises
• The set-point temperature of the body will remain elevated until prostaglandins (PGE) are no longer present & / OR natural body defenses or antibiotics reverse disease process

Cryogens (eg. vasopressin) reset thermostat to lower (normal) level, activating heat-loss mechanisms, so temperature falls

Aspirin and other NSAIDs inhibit fever by blocking prostaglandin production –> causing resetting of thermostat (just treats symptom)

Question 36

What problems can arise as a result of TH hyposecretion ?

Answer 36

In adults : Myxedema
- Symptoms include low metabolic rate, thick and/or dry skin, puffy eyes, feeling chilled, constipation, edema, mental sluggishness, lethargy
- If due to lack of iodine, a goiter may develop
( ↑ synthesize of unusable thyroglobulin causes thyroid to enlarge )

In infants : Cretinism
- Symptoms include intellectual disabilities, short and disproportionately sized body, thick tongue and neck

Question 37

What problems can arise as a result of TH hypersecretion ?

Answer 37

Most commonly, Grave’s disease can occur

Autoimmune disease in which body makes abnormal antibodies directed against thyroid follicular cells

• Antibodies mimic TSH, stimulating TH release
• Symptoms include elevated metabolic rate, sweating, rapid and irregular heartbeats, nervousness, and weight loss despite adequate food
• Exophthalmos may result – Eyes protrude as tissue behind eyes becomes edematous and fibrous
• Treatments include surgical removal of thyroid or radioactive iodine to destroy active thyroid cells