CYCLE 4 UNIT 5
BMR - basal metabolic rate - definition, value, factors affecting.
1. The amount of energy liberated per unit of time is defined as metabolic rate. 2. Basal metabolic rate (BMR) is the minimum energy of biochemical reactions in the body per time unit that sustains the very resting activity of metabolism. 3. It depends on activity of such essential organs as nervous system, cardiovascular system (mainly heart), kidney, etc. 4. Basal metabolic rate (BMR) is the minimum maintaining the lowest possible activity of the cardiac muscle, respiratory system, gastrointestinal system, urinary systems, resting muscular and neural tonus, constant temperature, mental activity, etc. 5. BMR is defined as the metabolic rate measured with the subject awake in the morning, fasting, at neutral ambient temperature and resting horizontally in the respiratory steady state. 6. BMR depends on personal factors (weight, age, height, sex). The best way of expressing BMR is calculation of energy output per unit of body surface area because such a parameter seems to correlate with oxidative processes the most. 7. Average adult human organism produces about: - 1700 - 2000 kcal/day (7.11 - 8.36 MJ/24 h). - approximately 1000 kcal/m2/24 h. - approximately 1 kcal (4.1868 kJ) per 1 kg of the body mass/hour. - approximately 35 - 40 kcal/m2/h. - BMR in kcal = 10 x (body mass - kg) + 6,25 x (height in cm) - male -161 female +5kcl Depends on: 1. Sex - higher in men than in women (depends on fat tissue). 2. Age - to 5 y. of age increases, then, after 21 declines (2%/10years). 3. Body surface 4. Fever - increases about 12-14 % for every 1°C over the norm. 5. Malnutrition - decreases. 6. Sleep - decreases. 7. Hormones - thyroid hormones and norepinephrine increases.
Calorimetry - direct and indirect.
Direct calorimetry is an accurate method used to quantify human energy expenditure during rest and physical activity. A known volume of water at a specified temperature is circulated through a series of coils at the top of the chamber. The water absorbs the heat produced by the subject, similarly to bomb calorimetry. The chamber is insulated and ventilated with exhaled air passing from the room through chemicals that removes moisture and absorbs CO2. Oxygen is added to the air recirculated through the chamber. Direct measurement of heat production in humans has limited applications. It is expensive and time-consuming Indirect Indirect calorimetry is the most common and clinically feasible method of measuring energy expenditure. It is called "indirect" because the caloric burn rate is calculated from a measurement of oxygen uptake. Direct calorimetry is a measurement of heat released by the body, which is technically difficult and clinically impractical. Because of this very direct relationship between caloric burn and oxygen consumed, measurements of oxygen uptake (VO2) and caloric burn rate are virtually interchangeable. Indirect calorimetry is based on the fact that burning of 1 „big" Calorie (Kilocalorie, kcal) in conditions of resting human organism requires 0.21 liters of oxygen. The caloric equivalent of oxygen is approximately 4.82 kcal/L of O2 (carbohydrates - 5.05 kcal/L, proteins 4.6 kcal/L, fat 4.82 kcal/L). It means that aerobic metabolism of the human body that burns 1 liter of oxygen in ambient temperature, at sea level releases 4.82kcal
Physiological and physical caloric values of carbohydrates, proteins, lipids.
Energy equivalent of oxygen (energy released per 1L of O2 used): Energy equivalent of oxygen expresses an amount of energy liberated per 1L of oxygen spent in conditions of human organism: Carbohydrates - 5.05 kcal Proteins - 4.60 kcal Fats - 4.70 kcal Average diet - 4.82 kcal 1 kcal = 1Cal
Obesity - types, reasons.
For obesity type description is necessary to depict the body mass components, e.i. adipose tissue mass (Body fat percentage) and lean body mass. Body fat percentage measurement techniques used: Antropometric measurments (skinfold test) Computed tomography (CT scan), Magnetic resonance imaging (MRI), Dual energy X-ray absorptiometry (DEXA) Hydrostatic weighing, one of the most accurate methods of body fat calculation, involves weighting a person underwater. Obesity is most commonly caused by a combination of: Excessive dietary calories, Lack of physical activity that reduces daily energetic expenses of the human body, Genetic susceptibility, Metabolic disturbances leading to decrease of basal metabolic rate or to ingest higher number of meals than recommended for each person. Primary obesity is mostly related and caused by genetic disorders of metabolic control of cellular activities. Secondary obesity develops due to the environmental conditions that influence human organism. Mutations and genetic polimorfisms of the: Hormones and their receptors (Polymorphisms in various genes controlling appetite and metabolism predispose to obesity when sufficient calories are present): (leptin, ghrelin, proopiomelanocortin, NPY, adrenergic receptors) Metabolically active substances: (insulin, IGF-1, IGF-2, GH, apoprotein CII/CIII, apoprotein E, lipase, lipoproteins (LDL, HDL, VLDL), adrenergic receptors, T3, T4) Thermogenesis factors: (phosphorylating enzymes, adrenergic receptors, T3, T4)
Proper body mass. Lean body mass (LBM).
Proper body mass corresponds to body mass that provides the longest possible survival of organism in the good health state. Epidemiological Surveillance pointed out, that overweight, and especially obesity, corresponds to higher mortality, similarly to people with lower body mass (underweight person or BMI > 18,5). Lean body mass (LBM) - the mass of all tissues of the organism without the body fat mass.
Respiratory quotient.
The respiratory quotient (RQ) is the ratio of the steady state of the volume of CO2 produced to the volume of O2 consumed per unit of time. RQ = CO2 produced / O2 consumed • It should be distinguished from respiratory exchange ratio (R) which is the ratio of CO2 to O2 at any given time whether or not equilibrium has been reached. R is affected by factors other than metabolism. Average value of RQ for human body metabolism at rest equals 0.82.
