64. Basal- and resting energy metabolism, factors affecting metabolic rate Flashcards
BMR = Basal metabolic rate
-Basal metabolic rate (BMR) is defined as the energy production in resting state.
BMR - RMR
- In the case of animals, it is difficult to meet all requirements. Therefore, we determine the resting metabolic rate (RMR) in animals.
Metabolic spectrum
-Heat turnover, which takes place above basal metabolic rate (BMR or RMR) and which depends on the activity of the animal or the state of production, is called “metabolic spectrum”.
The exact measurement of metabolic spectrum is complicated, since oxygen consumption does not always reflect energy release. E.g., during excessive muscle activity, the oxygen breathed in becomes insufficient for the energy production taking place in the body.
Energy produced in anaerobic processes is also released to maintain activity of the muscles. In this case, oxygen debt develops in the body, which is balanced only after finishing the activity. It is a practical experience, that after finishing excessive muscle work, frequency of breathing still remains enhanced.
Fullfillment for the estimation of BMR:
Estimation of basal metabolic rate:
- complete rest (no muscular activity)
- lying posture
- no psychic excitement
- neutral environmental temperature.
- 12 to 14-hour fasting
- no heavy physical activity before the measurement
-In this case, most of the energy released in the body is utilized for the maintenance of constant body temperature.
25% of it is necessary for the maintenance of basic vital functions, and activity of the cells.
RMR measurements
- Measurements are normally before morning feeding, in natural or experimental conditions, the animal is at a standing still, lying or resting.
- The difference between basal metabolic rate and resting metabolic rate involves specific dynamic action, the amount of energy necessary for production (milk, egg) and the amount of energy, which is used for real vital processes.
Body size
- Absolute values of metabolism mostly depend on the size of the examined body.
- Animals of larger mass produce more heat during the same time than animals of smaller weight.
-If the relationship between body weight and metabolic rate is plotted on a logarithmic scale, the result is a straight line, the steepness of which is 0.75.
Body surface
Body surface area = k × body weight2/3
k constant is between 0.09 and 0.12.
Since body temperature of some animals in not much different from environmental temperature, changes of body surface area relative to body weight cannot be considered as the cause of changes of basal metabolic rates relative to changes of body weight.
Neural and hormonal effects
Secretion of thyroid hormones increases biological oxidation, while, in the case of their decreased synthesis, lower values of metabolic rate can be observed.
Complete lack of thyroid hormones = BMR decreases to 40- 60 %.
Increases activity of sympathetic nervous system, release of epinephrine and norepinephrine increases metabolism of several organs. It has a direct action on hepatic glycogenolysis, thus, increasing activity of the cells.
- Male sexual hormones increase basal metabolic rate.
- A direct stimulation by growth hormone may increase metabolism by 15-20%.
- During sleeping, basal metabolic rate is decreased by 10-15%,
- Malnutrition decreases metabolism of the cells to the 1/5th of the normal values.
Specific dynamic action
Within an hour after food intake, there is an increase of basal metabolic rate, which lasts for 2-3 hours. This is called specific dynamic action of nutrients.
Specific dynamic action of a particular
nutrient is defined as the energy needed for the assimilation of that foodstuff in the body.
After consumption of proteins, this value is 30%, after carbohydrate intake: 5-7%, after consumption of fats: 5-10%.
Volatile fatty acids can increase the metabolic rate in ruminants by 20-25%.
Temperature
– Body temperature
Changes of the internal temperature alter metabolism mainly by changing velocity of chemical reactions (van’t Hoff ‘ law). The most common changes of internal temperature are due to excessive muscular work or fever.
– Environmental temperature
Changes of environmental temperature, both under the lower critical temperature and above the upper critical temperature, induces the increase of metabolism. Persistent changes of the environmental temperature have an impact of 10-20 % on metabolism, albeit its value is higher at cold zones than at tropic zones. This is developed mainly because of acclimatization mechanisms of thyroid hormones.
Muscle work (activity)
Increases of muscular activity are considered as the most common causes of elevation of metabolism. The most intensive rising of metabolism, in connection with muscular activity, can be detected in horses during sports. In these animals:
– Gallop: maximal metabolism = RMR x (5 -10)
– Full gallop: maximal metabolism = RMR x (35 - 40!!).
Small animals, have certain disadvantages: requires a higher increase of metabolism.
Production
Require high amounts of energy above the resting value, depending on the type of their product.
Efficiency:
The hen is most efficiently producing species, while the beef cattle is producing less efficiently.
Kleiber’s formula
BMR = k × bodyweight 0.75
This formula can be used between body weights of 20g and 600 kg (so called: mouse-elephant curve). The absolute quantity of metabolism (y axis on the left) increases if plotted on a log-log chart, while the metabolic rate related to the log of the body weight (y axis on the right) decreases linearly when plotted against the log body weight).
