Metabolism New

8/4/2019 Metabolism New

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Energy balance &

metabolic rate


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Metabolism means changes , it is used to refer to all chemical and

energy transformation processes that occur in the body.

It is divided into two processes :

1- anabolism which means formation of proteins, fats, complexCarbohydrates& high energy compounds from simple moleculeswith taking up energy that is stored in these compounds.2- catabolism which is a complex, slow oxidation of carbohydratesFats & proteins which produces CO2, H2O and energy that is liberated in

small usable amounts.Energy transfer :

When pure oxygen is used to burn carbohydrates, fats and proteinsoutside the body, large amounts of energy are released suddenly in theform of heat. Inside the body, the energy needed by physiologicalprocesses is not only heat but :

energy to cause muscle contraction or to do secretion by the glands,these processes take place through special enzymes& energy transfersystems which apply the energy liberated by catabolism to theformation of high energy compounds.


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High energy compounds :

1- high energy phosphate compounds :they include :Adenosine triphosphate (ATP)Creatine phosphate (CP)Guanosine triphosphate (GTPCytidine triphosphate (CTP)

Uridine triphosphate (UTP)Inosine triphosphate (ITP)

2-Acyl-Co A compounds :e.g. Acetyl-Co A which is also calledactive acetate .

The main functions of ATP are :to energize the synthesis ofcellular compounds, to energize muscle contraction& activetransport across membranes, absorption from intestine orkidneys, formation of glandular secretion and maintainance ofIonic concentration gradient in nerves .


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Units of heat energy:

1-The calorie :(cal, gram calorie, small calorie, or standardcalorie): it is the amount of heat energy necessary to raise the

temperature of one gram of water 1 degree from 15c to 16c.

2- The kilo- calorie (Kcal, the Calorie): it equals 1000 cal, and is

the unit which is commonly used in physiology& medicine.

Energy balance :

In the body there is an energy balance between caloric intake ,

provided by the absorbed food, and energy output. If thecaloric intake is less than the energy output, the balance is

negative and there is weigh loss by catabolism of glycogen fats& proteins.


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On the other hand, if the energy intake exceeds energy loss,

the balance is positive, and there is weight gain. to be in

energy equilibrium, the energy input must equal the energy

output

Physical caloric (heat) value of food:

It is the amount of energy in Kcal which is liberated bycomplete oxidation of a food substance outside the body.

Oxidation of 1 gram of carbohydrates produces 4.1

KCal/gramOxidation of 1 gram of fat produces 9.3 KCal/ gram

Oxidation of 1 gram of protein produces 5.3 KCal/ gram

Physiological caloric value of food:

Oxidation of food substances inside the body, it equals:4.1K Cal/gram of carbohydrate.

9.3 Kcal/ gram of fat.

4.1K Cal/ gram of protein.


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The physiologic caloric value of protein is less than its physical

caloric value because protein is incompletely oxidized in the body

To CO2, H2O and urea .

Measurement of physiological heat value is done by using special

Calorimeter.Caloric intake (in K Cal)=

Dry weight in grams of carbohydrates ingested X 4

Dry weight in grams of fats ingested X9

Dry weight in grams of proteins ingested X4


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Metabolic rate ( energy output )

The energy liberated by catabolism, appears as external work,

energy storage and heat .

Energy output= external work+ energy storage+ heat .

_ The metabolic rate is the amount of energy liberated per unit oftime.

When no external work is done as during isometric contraction

of skeletal muscles, all of the energy expended by the body is

converted into heat. (this energy was stored as ATP).

Metabolic rate is measured by either direct or indirect calorimetry.


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Direct calorimetry :

In this method the metabolic rate is determined by measuring the total

quantity of heat liberated from the body in a given time provided that

the person is not performing any external work. The subject is placed

In a large constructed calorimeter, which is an air chamber that is well

Insulated& no heat can leak through its walls. Heat liberated from the

subject's body warms the air of the chamber which is maintained

constant by a cool water bath. The rate of heat gain by H2O bath is

measured by a thermometer, it equals the rate at which heat is liberated

by the subject's body. Direct calorimetry is used only in research centers.


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Indirect calorimetrySince most of energy expended in the body is derived from reactions

Which utilizes oxygen, the metabolic rate can be calculated from the rate

Of oxygen consumption.

Energy equivalent of oxygen:It is the amount of energy liberated per liter of oxygen utilized in the body.

It differs according to the type of metabolized food ,it is greater for carbo-

Hydrates than for fats or proteins. For a mixed diet it equals 4.82 K Cal.

Metabolic rate =O2 consumption per unit of time x 4.82

(in K Cal/unit of time) (in liters)

O2 consumption is usually measured with a metabolator.(an apparatus),it is a

Spirometer filled with oxygen with a CO2 absorbing system.


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The respiratory qutient(RQ)

It is the ratio (in the steady state) of the volume of CO2 produced to the

Volume of oxygen consumed per unit of time

produced2volume of CORQ=

volume of O2 consumed per unit timeRQ could be measured for the whole body or for individual organ ortissue.

Importance of RQ:

1- it idicates the type of food being utilized.

-RQ for CHO= 6/6 = 1

RQ for fat = 102/ 145 = 0.7

RQ for protein = 0.82


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Contin. Imp. Of RQ

2- Determination of precise energy equivalent of O2:

After determination of RQ we can find out the oxygen heat value from the

metabolic table then we can calculate the metabolic rate .

Metabolic rate = O2 consumption/hour x O2 heat value

Energy equivalent of oxygen or the energy liberated when one liter of O2

Is used to oxidize food :

for oxidation of carbohydrate = 5 K Cal / L

for oxidation of fat = 4.7 K Cal / L

for oxidation of protein = 4.5 K Cal /L


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Continu. Imp. RQ3-RQ estimation is an evidence for transformation of one food

substance into another as in case of transformation of carbohydrateswhich is rich in O2 into fat which is poor in O2. : inside the body O2 is

thus released and forms CO2 without any increase in atmospheric O2

Consumption . The RQ is there fore is increased to above 1.

On the other hand, transformation of fat into carbohydrate (gluco neo-

Genesis) , here fats use O2 for transformation to carbohydrates andmore O2 to oxidize carbohydrate to CO2 & H2O so :

produced from oxidation2CORQ =

O2 consumed for transformation + oxidation

in this case the RQ is below 0.7


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Factors increasing RQ :

Hyperventilation , severe muscular exercise , metabolic acidosis andfevers .

Factors decreasing RQ :

Hypoventilation & apnea . Metabolic alkalosis (due to retention ofCO2) , recovery from exercise : due to use of CO2 in reformation ofbicarbonate which was used up in the beginning of exercise. RQ mayreach 0.5 .

- in diabetes Mellitus ( untreated ) RQ is 0.7

- during HCL secretion , Stomach has negative RQ it takes more CO2from arterial blood than out put to venous blood.

- RQ of brain & cornea equal 1(main fuel is glucose )


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Metabolic table:

RQ O2 heat value in cal. CHO % Fat %

o.7 4.68 0 100

o.85 4.86 50.7 49

0.87 4.88 57.5 42

0.95 4.98 84 16

1 5.04 7 100 0

Metabolic rate = O2 consumption/ hour x O2 heat value


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Energy RequirementsCategory Age K Cal./ day

Children 1-3 years 900-1300

4-6 years 1300-2300

7-10 years 1650-3300

Males 15-18 years 2100- 3900

above 67 years 1650- 2450

Females 15-18 years 1200- 3000above 67 years 1200- 2000

Pregnancy + 300

Lactation + 500


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Calculation of B.M.RA male aged 20 years, his height is 168cm. ,body weight is 70 kg. ,

Body surface area is 1.5 m2 :

Suppose O2 consumption in 10 minutes (using respirometer)

2500 ml O2 : 2500 ml / 10 min. 250 ml/ 1 min.

250 x 60 = 15000 ml/ hour = 15 L/ hour

As energy equivalent for 1 L of O2 =4.84 KCal

So energy produced = 15 x 4.84 = 72.6 K Cal/ hour

B.M.R in K Cal /m2/hour =72.6 1.5 = 48.4 K Cal /m/ h.

-The standard value for B.M.R. at age 20 years is 41.4 K Cal/m/h.

%16.9= +100x41.448.4so % excess =

41.4


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Energy expenditure per hour duringdifferent types of activity for a man 70 Kg

Type of activity Calories per hour.

Sleeping 65

Awaking & lying in bed 77

Sitting at rest 100

Dressing % undressing 118Typewriting rapidly 140

Walking slowly 200 (2.6 miles/h.)

Active exercise 290

Strenuous exercise 450

Swimming 500Running (5.3 miles/h.) 570

Walking upstairs 1100

Daily utilization for lying in bed all the day 1650 Calory.

Daily utilization with doing heavy work about 6000 Calory


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Factors affecting the metabolic rate:1-muscular exercise (most imp. Factor), maximal exercise can increase

The metabolic rate to 200 % of normal, there is increased O2 consumptionnot only during exertion but also for some time after the end of theexercise to repay what is called O2 debt.

2-Recent food ingestion (specific dynamic action of food-SDA): it is

defined as :it is the obligatory energy expenditure that occurs duringfood assimilation into the body .it is affected by :

a- type of food :an amount of proteins( provide 100 Kcal) can increasetotal metabolism by :

30 Kcal, a similar amount of carbohydrates increases it 6 Kcal& a similar

amount of fat increases it by 4 calories .b- amount of food :because proteins has the highest SDA, the greater theproteins ingested, the more increase in metabolic rate. heat liberatedafter protein intake is taken from energy stores of the body, soprolonged protein intake can lead to loss of body weight& could treatobesity. Causes of SDA:sympathetic activity after food intake, extra

energy is needed to glycogen from CHO, fatty acids stim. Metabolism.


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SDA of proteins may be due to de-amination of amino acids in the liveror from the stimulatory effect of some amino acids on cellular

chemical processes.

3-environmental temperature: when it is lower than body temp. the

metabolic rate increases due activation of heat conserving mechanisms

persons living in cold climate have increased thyroxin.

4-Fevers increase the metabolic rate because it increase the cellularchemical reactions. 1c increases metabolic rate 14% of basal level.

5-Sympathetic stimulation increases metabolic rate due to liberation ofcatecholamines which causes muscle& liver glycogenolysis. also

Oxidative phosphorylation with heat liberation from cells of brown fat.

6-Sleep:metabolic rate falls to 15% below normal due to: decreased

Skeletal muscle tone& decreased symp. activity.

7-Age: it is greater in young child due to high rate of cellular reactions

needed for growth. 8- sex: metabolic rate is higher in males than

Females due to stimulatory effect of testosterone& great muscle bulk.


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Cntin. Factors affecting metabolic rate

9-Hormones : sex hormones, thyroxine& growth

hormones, all

stimulate cellular metabolism.

10-malnutrition decreases metabolic rate due to decreasein circulating catecholamines& thyroid hormone

specially with prolonged starvation with decresednecessary food substances in the cells . of about 30%.

11- Emotional state: anxiety& tension elevate the

metabolic ratedue to increased epinephrine, but depression decreasesmetabolic rate.

12-Race: pure races as Chinese and Indians have a lower

BMR than mixed races as Americans & Egyptians.


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Regulation of food intake

Hunger: it means craving (strong desire) for

food+ hunger contraction of stomach.

Appetite :means desire for a specific typeof food.

Satiety: means feeling of fulfillment in theQuest for food.


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Neural centers for regulationof food intake

1- hypothalamic center:

a- feeding (hunger c.):in lateral hypothalam.

b- satiety center:in ventromedial nucleus of

hypothalamus.

2- other centers : a-the amygdala& prefrontal

cortex(they belong to limbic system). b-brain stem centers as

salivation& swallowing, they r excited by

signals from hypothalamus.


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Factors regulating food intake

1-long-term regulation: a-Nutritional regulation: glucostatic, lipostatic &

aminostatic theories.neurons r affected by :level

of blood glucose, fatty acids &amino acids andthen stimulation of either feeding or satiety

centers.

b-effect of body temperature: cold exposure

causes over-eating.

c-feed-back signals from adipose tissue: itreleases leptin to inform the hypothalamus about

energy storage.


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2- short-term regulation:-A- alimentary factors:

i-gastro-intestinal filling.

ii-gasro-intestinal hormones.

iii-oral factors.

B- psychological factors:

Sight, smell& taste of food, all affect foodintake..(further readings)


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The basal metabolic rate

In order to compare the metabolic rates of different persons, which result

from the inherent activity of the tissues without the effect of exercise and

external factors , the metabolic rate is measured the so called basalconditions. It is called basal metabolic rate. (BMR)

Definition : it is the rate of energy output measured under the following

basal condition:1- complete physical and mental rest .

2- in the post absorptive state or after 12-14 hours after last meal.

3- at a comfortable room temperature which from 20-25c for dressedperson ( no shivering , no sweating )

BMR is expressed in K Cal / m / h. It is usually expressed as apercentage of increase or decrease above or below the normalstandard value for age and sex. normally it is 15% of normal value

Factors affecting BMR are those affecting the metabolic rate except theeffect of exercise, food intake& environmental temperature


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Diseases that changes BMR

Diseases that increase BMR :

1- hyperthyroidism (100% )2-hype- pituitrism.

3- hyper-adrinalism.

4- fevers.

5- blood diseases as polycythemia& leukemia with over activity ofbone marrow.

6- heart failure with increasedrespiratory muscle activity.

7- diabetes insipidus with heat lossin urine.

Exogenous factors as:caffeine ,

Adrenaline, amphetamine&thyroxine.

Diseases that decrease BMR :

1-hypothyroidism.

2-hyopo-pituitrism.

3-hypo function of adrenal

crtex.4-under nutrition& starvation.

5-shock& nephrosis.

6-hypothermia as duringsurgical operations.

Exogenous factors as: propyl-

thiouracil, iodides.

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