Metabolism means changes , it is used to refer to all chemical andenergy transformation processes that occur in the body. It is divided into two processes : 1- anabolism which means formation of proteins, fats, complex Carbohydrates& high energy compounds from simple molecules with taking up energy that is stored in these compounds. 2- catabolism which is a complex, slow oxidation of carbohydrates Fats & 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 proteins outside the body, large amounts of energy are released suddenly in the form of heat. Inside the body, the energy needed by physiological processes 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 transfer systems which apply the energy liberated by catabolism to the formation of high energy compounds.
High energy compounds : 1- high energy phosphate compounds :they include : Adenosine triphosphate (ATP) Creatine phosphate (CP) Guanosine triphosphate (GTP Cytidine triphosphate (CTP) Uridine triphosphate (UTP) Inosine triphosphate (ITP) 2-Acyl-Co A compounds :e.g. Acetyl-Co A which is also called active acetate . The main functions of ATP are :to energize the synthesis of cellular compounds, to energize muscle contraction& active transport across membranes, absorption from intestine or kidneys, formation of glandular secretion and maintainance of Ionic concentration gradient in nerves .
Units of heat energy: • 1-The calorie :(cal, gram calorie, small calorie, or standard calorie): it is the amount of heat energy necessary to raise the • temperature of one gram of water 1 degree from 15°c to 16°c. • 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 the caloric intake is less than the energy output, the balance is negative and there is weigh loss by catabolism of glycogen fats & proteins.
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 by complete oxidation of a food substance outside the body. Oxidation of 1 gram of carbohydrates produces 4.1 KCal/gram Oxidation 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.
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
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.
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.
Indirect calorimetry Since 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.
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 RQ=volume of CO2 produced volume of O2 consumed per unit time RQ could be measured for the whole body or for individual organ or tissue. 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
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
Continu. Imp. RQ 3-RQ estimation is an evidence for transformation of one food substance into another as in case of transformation of carbohydrates which 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 and more O2 to oxidize carbohydrate to CO2 & H2O so : RQ = CO2 produced from oxidation O2 consumed for transformation + oxidation in this case the RQ is below 0.7
Factors increasing RQ : • Hyperventilation , severe muscular exercise , metabolic acidosis and fevers . • Factors decreasing RQ : • Hypoventilation & apnea . Metabolic alkalosis (due to retention of CO2) , recovery from exercise : due to use of CO2 in reformation of bicarbonate which was used up in the beginning of exercise. RQ may reach 0.5 . • - in diabetes Mellitus ( untreated ) RQ is 0.7 • - during HCL secretion , Stomach has negative RQ it takes more CO2 from arterial blood than out put to venous blood. • - RQ of brain & cornea equal 1(main fuel is glucose )
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
Energy Requirements Category 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- 3000 above 67 years 1200- 2000 Pregnancy + 300 Lactation+ 500
Calculation of B.M.R A 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 /m²/ h. -The standard value for B.M.R. at age 20 years is 41.4 K Cal/m²/h. so % excess = 48.4 – 41.4 x 100 = + 16.9 % 41.4
Energy expenditure per hour during different 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 118 Typewriting rapidly 140 Walking slowly 200 (2.6 miles/h.) Active exercise 290 Strenuous exercise 450 Swimming 500 Running (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
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 consumption not only during exertion but also for some time after the end of the exercise 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 during food assimilation into the body .it is affected by : a- type of food :an amount of proteins( provide 100 Kcal) can increase total 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 the proteins ingested, the more increase in metabolic rate. heat liberated after protein intake is taken from energy stores of the body, so prolonged protein intake can lead to loss of body weight& could treat obesity. Causes of SDA :↑sympathetic activity after food intake, extra energy is needed to glycogen from CHO, fatty acids stim. Metabolism.
SDA of proteins may be due to de-amination of amino acids in the liver or 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 cellular chemical reactions. 1°c increases metabolic rate 14% of basal level. 5-Sympathetic stimulation increases metabolic rate due to liberation of catecholamines 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.
Cntin. Factors affecting metabolic rate 9-Hormones : sex hormones, thyroxine& growth hormones, all stimulate cellular metabolism. 10-malnutrition decreases metabolic rate due to decrease in circulating catecholamines& thyroid hormone specially with prolonged starvation with decresed necessary food substances in the cells . ↓ of about 30 %. 11- Emotional state: anxiety& tension elevate the metabolic rate due to increased epinephrine, but depression decreases metabolic rate. 12-Race: pure races as Chinese and Indians have a lower BMR than mixed races as Americans & Egyptians.
Regulation of food intake Hunger: it means craving (strong desire) for food+ hunger contraction of stomach. Appetite :means desire for a specific type of food. Satiety: means feeling of fulfillment in the Quest for food.
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.
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 and then stimulation of either feeding or satiety centers. b-effect of body temperature: cold exposure causes over-eating. c-feed-back signals from adipose tissue: it releases leptin to inform the hypothalamus about energy storage.
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 food intake……..(further readings)
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 basal conditions. 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 20-25°c for dressed person ( no shivering , no sweating ) BMR is expressed in K Cal / m² / h. It is usually expressed as a percentage of increase or decrease above or below the normal standard value for age and sex. normally it is± 15% of normal value Factors affecting BMR are those affecting the metabolic rate except the effect of exercise, food intake& environmental temperature
Diseases that increase BMR : 1- hyperthyroidism (100% ↑ ) 2-hype- pituitrism. 3- hyper-adrinalism. 4- fevers. 5- blood diseases as polycythemia & leukemia with over activity of bone marrow. 6- heart failure with increased respiratory muscle activity. 7- diabetes insipidus with heat loss in 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 during surgical operations. Exogenous factors as: propyl- thiouracil, iodides. Diseases that changes BMR