The body metabolism and energy exchange. Physiological basis of rational nutrition. Thermoregulation. Lecture
Types of energy according to nature: 1. Electrical. 2. Mechanical. 3. Chemical (ATP). All of them (1 -3) are transformed into heat.
Unit of heat energy is calorie, kcal.
Direct calorimetry- measuring of the total amount of energy liberated in a given time.
Direct calorimetry
Q = gm (t 2 – t 1), Q – heat produced; g - quotient; m – amount of water, t 1 – initial temperature, t 2 - final temperature
Indirect calorimetry. More than 95% of the energy expended in the body is derived from oxidizing of various foodstuffs. The metabolic rate can also be calculated by studying the exchange of gases, from the quantities of oxygen absorbed and carbon dioxide released.
Indirect calorimetry
The calorific equivalent of oxygen Ø for carbohydrates 5. 05 kcal; Ø for fat it is about – 4. 70 kcal; Ø for protein it is about – 4. 50 kcal.
The calorific equivalent of oxygen is the amount of heat liberated by the utilization of one liter of oxygen in the organism
The respiratory quotient (RQ). RQ is the ratio between the volume of CO 2 released and the volume of O 2 consumed.
The respiratory quotient ØFor carbohydrates RQ is 1, 0; Øfor proteins - 0, 8; Øfor fats - 0, 7; Øfor a mixed diet: 0, 85.
Factors affecting the metabolic rate • Muscular activity during or before measurement • Recent ingestion of food • High or low environmental temperature • Height, weight and surface area • Sex, age, growth • Reproduction, lactation • Emotional state • Body temperature • Circulating levels of T 3, T 4, Ad, NA
Conditions of basal metabolic rate examination : 1. Mental and physical rest 2. A comfortable temperature (18 -20˚C) 3. 12 -14 hours after a meal.
Surface law by Rubner: the energy expenditure of warmblooded animals is proportional to their surface area.
BMR is about 1700 kcal (male); 1500 kcal (female) – 10% lower 1 kcal per kg per hour
Initial metabolic rate Basal metabolic rate + 20% basal metabolic rate.
Labor metabolic rate. 1 group (mental work): 3200 kcal (male); 3000 kcal (female) 2 group (operators of machines): 3500 kcal (male); 3000 kcal (female) 3 group (partially mechanized physical work): 4000 kcal (male); 3500 kcal (female) 4 group (heavy physical work): 5000 kcal (male).
The rules of rational nutrition 1. Energy well-balance. 2. The ratio between proteins, fats, carbohydrates must be 1: 1: 4. 3. Food must contain proteins, fats, carbohydrates, vitamins, microelements etc. 4. Food intake must be 3 -4 times per day. 5. Foodstuffs must be safe.
THERMOREGULATION
Homeothermic or warmblodded: the body temperature doesn’t depend on the environment.
Poikilothermic or cold-blooded: the body temperature depends on the environment.
Isothermia is a constancy of body temperature.
Heterothermic: hibernating mammals.
Normal body temperature is about 36, 6 -37˚C.
Measurement of body temperature Axillary < Oral < Rectal temperature 36, 7 – 37, 0˚C 0, 2˚C 0, 5˚C
Temperature is the highest in liver +38˚C and lowers on skin surface (24, 4 - 28, 5˚C).
Core temperature is the temperature of deep located organs.
Shell temperature is the temperature of the body surface – (the skin).
? Early in morning the temperature is the lowest (between 4. 00 to 6. 00 a. m. ). ? In the afternoon the temperature is highest (between 6. 00 to 8. 00 p. m). ? In women the rectal temperature rises at the time of ovulation (13 -14 days).
Heat production (chemical thermoregulation. )
These are exothermic chemical reactions.
Skeletal muscles give 60%, a liver - 30%, other organs -10% of heat.
Heat production: 1) Basic metabolic processes (oxidation of foodstuffs, break down of brown fat in infants). 2) Food intake (specific dynamic action of the food) 3) Muscular activity (voluntary contraction of skeletal muscles, involuntary contraction of skeletal muscles (shivering).
Heat loss (physical thermoregulation).
Skin (sweet glands) – 80%; respiratory system – 13%; gastrointestinal tract – 5%; excretion of urine and faeces – 2%.
Mechanisms of heat loss: üRadiation üConduction üConvection üEvaporation
Radiation (60% at 21˚C). It is the transfer of heat by infrared electromagnetic radiation from one object to another at a different temperature with which it is not in a contact.
Conduction (3%) is heat exchange that occurs between objects or substances at different temperatures that are in contact with one another.
Convection (15%) is the transfer of heat by the movement of molecules away from the area of contact
Evaporation (22% ) is the conversion of a liquid into a vapor.
Sweating consist of 2 processes: üproduction (secretion) of sweat; üits evaporation. Every day 0, 5 l of sweat is produce. In physical work - 10 l and more.
Classification of thermoreceptors: 1) Cold, warmth 2) Peripheral (skin, vessels), central (hypothalamus)
Mechanisms activated by heat üIncreased heat loss üCutaneous vasodilatation üSweating üIncreased respiration ü Decreased heat production üAnorexia, apathy, inertia
Mechanisms activated by cold ü Increased heat production ü Increased voluntary activity ü Increased secretion of Ad and NA ü Decreased heat loss ü Cutaneous vasoconstriction ü Pilomotoric reflex ü Curling up
Center of thermoregulation The center of heat production is located in the posterior hypothalamus. The center of heat loss is located in the anterior hypothalamus.
Comfortable temperature is 18 -20 C, for naked person is 28 C, in the water is 35 C.
Hypothermia when the temperature in the axilla falls below 35˚C.
Hyperthermia when the temperature in the axilla rises above 37˚C.
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