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OBJECTIVES
1-Understand the basis of energy balance.
2-Define BMR and its significance.
3-Respiratory Quotient.
4-Understand the basis of thermal balance.
5-Explain the thermoregulatory response
to cold and hot atmosphere.
Metabolism
Anabolism
Glucose + Energy---------Glycogen
Catabolism
Glycogen----------Glucose + ENERGY
Energy in the form of ATP
ATP : combustion of food stuffs
,carbohydrates, lipids, proteins.
Degradation of ATP → 24 kcal/molecule.
Synthesis of most intracellular components.
Synthesis of glucose.
Synthesis of fatty acids.
Synthesis cholesterol,phospholipids, hormones,
Synthesis of urea.
Source of muscle energy.
Energizes active transport across membranes.
Energizes glandular secretion.
Energizes nerve conduction.
60%---------BMR.
8%----------Thermic effect of food &
cold –induced thermogenesis.
7%----------Spontaneous purposeless
activity.
25%---------Purposeful physical activity.
Kilocalorie(Kcal): the amount of heat required to
raise the temperature of one Kg. of water from
15-16 °C.
( kcal= capital C)
Kilocalorie = 1000 calorie.
Physical heat value: the amount of energy
liberated when 1 gm. of substrate is completely
oxidized outside the body
Caloric value of food ( physical heat value)
CHO ------------4.1 C/gm
Fats--------------9.3 C/gm
Protein-----------5.6 C/gm
The amount of energy liberated by 1 gm. of food
substrate when they are completely oxidized
inside the body.
CHO--------------------4.0 C/gm.
Fats----------------------9.0 C/gm.
Protein------------------4.1 C/gm.
*** physiological heat value of protein (4.1) less
than physical heat value( 5.6) due to incomplete
oxidation of protein as complete oxidation lead
to formation of nitric acid which is fatal.
*** The difference between physical and
physiological values are due to variations in GIT
absorption, 98% CHO, 95% fats and 92% protein
Is the amount of heat generated when
1 liter of oxygen used to oxidize
different food stuffs.
CHO produces 5 C.(kcal)
Fat produces 4.7 C.(kcal)
protein produces 4.5 C.( kcal)
Mixed food produces 4.8 C. (kcal)
CO2 production
RQ = --------------------- as a ratio
O2 consumption.
At rest:
O2 consumption=250-300 ml/min(VO2).
CO2 production =200-250ml/min(VCO2).
1.
2.
3.
4.
5.
Importance
of
RQ:
Determines the nature of food substance oxidized in different
tissues and under
different conditions.
CHO ------------RQ=1.
Fat---------------RQ=0.7.
Protein-----------RQ=0.8.
Transformation of one food substance into another one.
CHO(O2 – rich) ----------------Fat (O2-poor)---------------------more CO2 production so higher RQ.
Determines the caloric value of O2 using special metabolic tables.
Denotes the type of food utilization after their absorption
If RQ=1 ----------CHO utilization.
If RQ=0.7---------Fat utilization.
Negative RQ:( arterial CO2 > venous CO2 ) as in
- HCL secretion in stomach.
- HCO3 secretion in pancreas
- Formation of intraocular formation.
- Utilization of CO2 by the kidney to get red of H+.
The absolute minimal energy expenditure
of the body to exist under basal
conditions.
Criteria of basal conditions:
* at the morning.
*12-14 after the last meal.
*Complete physical and mental rest.
*Resting and supine position.
*Comfortable temperature 20-25°C.
*Normal body temperature.
1.
2.
3.
4.
5.
Generating & maintaining ionic
gradients and other molecules
across membranes.
The mechanical work of respiration.
Circulation of blood.
Production of muscle tone, signals
conduction in nervous system.
Obligate heat loss via body surfaces
to the environment.
Factors affecting BMR
1. Physiological factors:
* Age:
Newborn= 25C/H/M2
Age2-5 years=60C/H/M2
Age 20 years=40C/H/M2
Above 20 years → Decreased 1C/10
years.
* Sex:
BMR is lower in female by about 7%
due to more fat store with little
metabolic activity.
Normal value of BMR:
In adult man 40 C/H/M2 ± 15% .
Clinical expression of BNR:
Expressed as a % of increase or decrease
from
the normal standard value for the subject.
e.g. If BMR = 60 C/H/M2( + 20 C/H/M2)
Exceeding the normal standard value
by 20
so, +50% ( higher than normal value
i.e.
15% for his age and sex)
* Race:
# pure race as Chinese have
lower BMR.
# Mixed race as Egyptians have
higher BMR.
# Dark races have higher BMR
than white races.
* Climate:
# BMR is higher 10% in cold zone
than in hot zone.
* Physical habits:
# Athletes have BMR about 10%
higher than in sedentary due to
more muscle bulk and lesser
amount of fat stores.
* Dietetic habit:
# prolonged ingestion of protein
increases BMR 10% more than
eating CHO. or mixed diet.
* Pregnancy:
# pregnant women have higher
BMR than non pregnant due to
additional metabolism of fetus.
* Anxiety & stress:
# Higher BMR due to increase
the level of stress hormone;
adrenaline, noradrenaline,
cortisone.
* Sleep:
# Lower BMR by 10-15% due to
- Decreased skeletal muscle
tone.
- Decreased activity of SNS.
2. Pathological factors:
# Higher BMR,
. Hyperthyroidism up to 100%
. Hyperpituitarism due to
- G.H.
- TSH
. Hyperadrenalism : due to more
secretion of catecholamines.
. Hyperpyrexia: Higher BMR by
10-14% for each 1°C rise in body
temperature.
. Heart failure: Higher BMR due to
increase activity of respiratory
muscles.
. Diabetes insipidus: Higher BMR
to maintain body temperature.
Lower BMR:
# Hypothyroidism
# Hypopituitrism
# Hypofunction of adrenal cortex.
# Hypothermia: Decreased BMR
10% for each 1°C lower.
# Prolonged starvation,
- Depression of SNS.
- Decreased catecholamines.
- Decreased thyroxine and
corticoids.
3. Chemical factors:
* Hormones,
# Thyroid h.: most stimulant.
# TSH
# Adrenaline
# ACTH & cortisone.
# G.H. : increase BMR 15-20%
due to direct stimulation of
cellular metabolism.
# Male sex h.: increase BMR
10-15%.
* Drugs:
# Caffeine:
- Central stimulant action.
- Increase CAMP.
# Antithyroid agents :
- block production of thyroid h.
# Alcohol:
- Increase heat loss due to
cutaneous V.D. so ↑ BMR to
maintain body
temperature.
The body temperature of human
body is maintained within 0.6° C of
its normal value 37.0 °C(98 °F) .
Constant body temperature is
essential for optimum enzymatic
activity.
Homeostasis depends upon the
balance between heat gain & heat
output.
1. Diurnal Rhythm
↓ in the morning→↑ in the early
afternoon→↑ in the midafternoon
( maximum activity).
2. Children have higher temperature .
3. Adult women show body
temperature changes related to
menstrual cycle.
4. Prolonged inactivity & exposure to
cold environment →↓body
temperature.
5. Emotional stress, muscular
exercise, activity, and exposure to
hot environment
→↑ body temperature.
6. Febrile illness & state of thyroid
gland affect body temperature.
1. Core temperature.
Site: Deep organs
----- almost keep constant.
----- Oral, Rectal,Axillary routes.
----- Oral < Rectal by o.5°C
----- Axillary < Rectal by 1°C
----- Rectal is the most accurate route.
----- Ranges between ( morning oral )
36.5 – 37.2°C at room
temperature 24 -25°C.
2. Skin temperature:
----- Surface temperature.
----- Fluctuates with ambient
temperature.
----- Highest in areas of head ,
chest ,and abdomen 34°C, big
muscles 30°C and small
muscles,28°C.
Thermal balance
Heat gain
Heat loss
1.
Heat production:
. BMR.
. Exercise.
. Specific dynamic action (SDA).
. Extra- metabolism by:
* Thyroxine.
* Growth hormone & testosterone.
* Sympathetic nervous system.
* Cell activity.
2. Heat uptake :
. Ambient temperature > Skin temperature.
1. Most of heat loss is produced by
deep organs especially liver, brain
,heart and skeletal muscles.
2. Conveyed to the surface through
the tissues to the skin only if the
skin temperature is < core
temperature.
Rate of heat Loss depends upon :
1. Rate of heat production by the
body tissues.
2. Rate of heat conduction from
deep organs to skin.
3. Rate of heat transfer from the
skin to the surroundings.
1. Skin blood supply( cutaneous
blood supply).
Source of heat production:
* In 70-kg normal person, Energy
requirements =
At rest ====== 75 – 80 Kcal / hour.
During exercise ==== 1400 Kcal/ hour.
1. Behavioral responses,
- in cold weather ---- increased food
intake.
- in hot weather ---- decreased food
intake.
2. Physiological responses,
a) Muscle tone:
- increased gradually by signals from hypothalamus,
↑ MR up to 50 – 100 %.
b) Shivering:
- It is involuntary response to a fall in core body
temperature.
- It can be stopped or reduced by voluntary
pathways.
- It is characterized by , not rhythmic , no actual
muscle shaking, gradually increase in MT above a
certain level leads to shivering begins( asynchronous
contraction and relaxation of small antagonistic
muscle groups a rate of about 10 – 20 / second.
- It is controlled via hypothalamic signals.
- Most of energy is transformed into heat, since no
external work is done.
- It can be abolished by ,alcohol,crure.
- It can be induced by ingestion of cold food.
3. Endocrinal responses( chemical
thermogenesis) :
a) Catecholamines & SNS excitation.
-↑MR by uncoupling phosphorylation
- ↑FFA release of fat stores
- VC of skin blood vessels→↓ heat loss
- Stimulate glycogenolysis in liver
b) Thyroid hormone.
- Long exposure to cold stimulate
thyroid hormone secretion →↑MR by
uncoupling phosphorylation.
c) Hypothalamic hormone.
- TSH.
- ACTH & Glucocorticoids.
- ADH.
d) Effect of clothing.
- Protect the body against heat
loss.
- Clothes act as air traps which is
a bad
conductor of heat.
2- Rate of heat conduction from
deep organs to the skin
Blood flow to the skin from the body
core provides heat transfer. Blood
vessels are distributed profusely in
SC tissues. The rate of cutaneous
blood flow into skin venous plexuses
vary 0 – 30% of cardiac output
according to the surrounding
temperature and the state of CVS
system.
* A high rate of cutaneous blood
flow (VD)
↓
↑ heat conduction from core to
skin
↓
↑ heat loss as during exposure to
hot environment
A low rate of cutaneous blood flow
(VC)
↓
↓ heat conduction from core to skin
↓
↓ heat loss as during exposure to
cold environment
* The degree of VC or VD of arterioles
and the anastomosis that supply
blood to venous plexuses of the skin
is controlled by :
* VC is controlled by SNS.
* VD is controlled by local factors
as
heat & metabolites( mainly )
3. Rate of heat transfer from the
skin to the surroundings
1. Radiation 60 - 70 % of heat loss.
2. Conduction 15% of heat loss.
3. Evaporative heat loss :
- Latent heat of vaporization
=580kcal/1Kg of water vaporized.
so, amount of heat loss by evaporation
=580kcal/h X amount of water
evaporated
- Each ml of evaporated water removes
with it 0.6 kcal.
- Under resting conditions , 500 ml /day is
evaporated , so , 500 X 0.6 = 300 kcal/
day.
- Heat loss by the skin is increased
dramatically by – sweating in hot dry
climate
and during muscular
exercise.
- Evaporative heat loss is the only mean
of heat loss when the body is exposed to
high ambient temperature.
4. Convection.
- It is the bulk of air movement surrounding the
skin surface and is used as a way of heat
loss
- Convection also increases evaporative heat
loss.
- Also, it increases the degree of conduction.
- Water has a higher heat conductivity than air.
- Effect of clothing: entraps air adjacent to the
skin---- increases thickness of the private zone
adjacent to the skin and decreases the flow of
convection of air currents.
Physiological Regulation of Heat
Exchange
HUMAN BODY
Environmental
Temperature
Rate of Heat Exchange with Environment
depends on :
* Skin temperature.
- Different from one portion to
another portion.
- Skin, subcutaneous fat act as
insulating blanket around the core of body
protecting against heat loss or heat gain
rapidly.
- Skin temperature is determined by
skin blood flow ( VC or VD ).
* Rate of Sweat production:
Heat loss by evaporation is regulated by controlling the
rate of sweat production by
-
Distributed all over the skin.
Innervated by sympathetic cholinergic fibers.
Stimulated by catecholamines (stress, anxiety)
Stimulated by aldosterone.
Blocked by atropine.
Controlled by hypothalamic center.
* Mechanism of sweat secretion:
- Active process.
- The deep subdermal coiled part
secretes a precursor or primary secretion.
- The duct portion of the gland modify
the primary secretion in response to
sympathetic cholinergic fibers.
- Na & Cl reabsorption in the ductal part
under the effect of aldosterone.
- Rate of sweat secretion 0-1.5 L/hour=
900Kcal/Hour.
- Protein- free filtrate.
* Composition of sweat secretion :
- Water
: 99.2%.
- Specific gravity
: 1001 – 1006.
- PH
: 3.8 -- 6.5.
- State of osmolarity : hypotonic.
- Na+ Concentration : 142mEq/L.
- Cl Concentration : 104mEq/L.
- Urea Concentration : 0.02%.
- Lactic acid Concentration : 0.3%
1.
2.
3.
Thermoreceptors
- peripheral & central receptors
↓
Temperature – regulating centers
- Heat – gain center
- Heat – loss center
- Set – point (36.5 – 37.2)
↓
Effector organ system
- Skin, skin blood vessels, sweat glands.
- Skeletal muscles.
- Endocrinal glands.
Neuronal Effector Mechanisms when the
body exposed to hot environment:
To balance Heat production = Heat loss.
1. ↓ Heat production.
* Inhibit shivering mechanism.
* Inhibit chemical thermogenesis.
* Decreased appetite (↓food intake).
2. ↑ Heat loss.
* VD of skin blood vessels → ↑heat
transfer to the skin as much as 8 fold.
* Sweating : ↑ body temperature
above critical body temperature 37.1ºC
→increased sweating →↑ rate of
evaporative heat loss.
Neuronal Effector Mechanisms when the
body exposed to cold environment:
1.↑ Heat production.
* Gradual increase in muscle tone.
* Hypothalamic stimulation of
shivering.
* Chemical thermogenesis.
* Sympathetic excitation of heat
production.
* Behavioral response:
- Moving into heated place.
- Wearing suitable clothes.
- Increased food intake.
2. ↓ Heat loss:
* VC of skin blood vessels through
stimulation of posterior hypothalamus
stimulation of SNS →↓heat transfer to
the skin.
* Piloerection: is caused by sympathetic
stimulation , not well developed in
humans.
2. Long period exposure to hot
environment
Adaptation to hot climate in 1-3 weeks.
- ↑ sweat production from 1.5 – 14 L/h.
- ↑ number of sweat ducts.
- ↑ NaCl reabsorption and K+depletion in
sweat &kidney under the effect of
aldosterone to avoid heat exhaustion.
* Exercise:
- Body temperature may rise 39.4 –
40.8ºC.
- Profuse sweating &marked skin VD.
- Loss of salt and water into sweat
and shunting of blood to the skin
lead to heat cramps.
- Extreme elevation of core
temperature may cause heat
exhaustion (shock and collapse due
to excessive sweating, dehydration
and hypovolaemia).
2. Long period of exposure to cold
environment:
* ↑ Heat production:
- ↑ Catecholamines secretion.
- ↑ Thyroxine.
- ↑ Appetite & fat storage
mechanisms.
* ↓ Heat loss:
- Cutaneous VC.
- Inhibit sweating mechanism.