Lab 21
Determination of the respiratory coefficient of germinating seeds
Principle of the method. Respiratory coefficient (RK)- indicator of gas exchange of living tissues. This is the ratio of the amount of carbon dioxide released during respiration to the amount of oxygen absorbed:
DC = CO2 / O2.
The value of the respiratory coefficient depends on a number of reasons. The first factor is the chemical nature of the substrate oxidized during respiration. If carbohydrates are used, then DC is close to unity:
C6H12O6 + 6O2 = 6 CO2 + 6 H2O.
If more reduced substances, fats and proteins, are oxidized, then more oxygen is consumed than carbon dioxide is released, and DC is less than one. For example, during the oxidation of stearic acid, the CO2:O2 ratio is 18:26, that is, 0.69.
When oxidizing substances containing more oxygen than carbohydrates, the respiratory coefficient is greater than one. Thus, when breathing due to oxalic acid according to the equation 2C2O2H2 + O2 = 4 CO2 + 2H2O, the respiratory coefficient is 4.
The second factor determining the DC value is aeration conditions. With a lack of oxygen in the air, that is, under anaerobic conditions, the DC increases and, in the case of carbohydrate oxidation, becomes above one.
The DC value indicates the completeness of substrate oxidation. If during the oxidation of carbohydrates the decomposition process does not proceed to completion, but intermediate products that are more oxidized than carbohydrates accumulate, then the DC value becomes less than one. A similar phenomenon is observed in intensively growing objects.
Goal of the work: determine the respiratory coefficient of germinating seeds.
Progress: In the experiment, they use a device consisting of a test tube, which is tightly closed with a rubber stopper, with a horizontal tube with divisions inserted into it. Place the test tube in a flask, which is both a stand and a thermal insulator.
Fill ½…2/3 of the volume of the test tube with germinating wheat or sunflower seeds and tightly close it with a stopper with a measuring tube. A prerequisite for correct observation is the constancy of the temperature of the device, since its operation is associated with changes in the volume of gases.
Therefore, the mounted device must reach room temperature, which is achieved within 5...7 minutes.
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Equipment and materials: 1) sprouted seeds of soft wheat ( Triticum aestivum L.), peas ( Pisum sativum L.) etc.; 2) 20% oxalic acid solution; 3) water tinted with methylene blue; 4) porcelain cup; 5) tweezers; 6) ruler; 7) pipette with a retracted end; 8) strips of filter paper measuring 2x6 cm.
Installation for determining the respiratory coefficient: A thin glass tube bent at a right angle is inserted into a test tube with a well-fitted rubber stopper. The horizontal elbow of the tube is graduated by attaching a strip of graph paper to it using rubber rings, and the test tube is placed in a tall (along the length of the test tube) glass with cotton wool.
Control questions
1. Classification of enzymatic respiratory systems. Mechanisms of action.
2. Pathways for the transformation of the respiratory substrate. Glycolysis. Pentose phosphate cycle.
3. Oxidative phosphorylation in plant mitochondria.
4. Krebs cycle.
5. The concept of respiratory coefficient. Methods for determining the respiratory coefficient.
6. Ecology of breathing. Dependence of respiration on endogenous and exogenous factors.
Methods for measuring energy expenditure (direct and indirect calorimetry).
Education and energy consumption.
The energy released during the breakdown of organic substances accumulates in the form of ATP, the amount of which in the tissues of the body is maintained at a high level. ATP is found in every cell of the body. The largest amount is found in skeletal muscles - 0.2-0.5%. Any cell activity always coincides exactly in time with the breakdown of ATP.
The destroyed ATP molecules must be restored. This occurs due to the energy that is released during the breakdown of carbohydrates and other substances.
The amount of energy expended by the body can be judged by the amount of heat it gives off to the external environment.
Direct calorimetry is based on the direct determination of heat released during the life of the body. A person is placed in a special calorimetric chamber, in which the entire amount of heat given off by the human body is taken into account. The heat generated by the body is absorbed by water flowing through a system of pipes laid between the walls of the chamber. The method is very cumbersome and can be used in special scientific institutions. As a result, they are widely used in practical medicine. method of indirect calorimetry. The essence of this method is that the volume of pulmonary ventilation is first determined, and then the amount of absorbed oxygen and released carbon dioxide. The ratio of the volume of carbon dioxide released to the volume of oxygen absorbed is called respiratory quotient . The value of the respiratory coefficient can be used to judge the nature of oxidized substances in the body.
During the oxidation of carbohydrates, the respiratory coefficient is equal to 1, since for the complete oxidation of 1 molecule of glucose to carbon dioxide and water, 6 molecules of oxygen are required, and 6 molecules of carbon dioxide are released:
С 6 Н12О 6 +60 2 =6С0 2 +6Н 2 0
The respiratory coefficient for protein oxidation is 0.8, for fat oxidation - 0.7.
Determination of energy consumption by gas exchange. The amount of heat released in the body when 1 liter of oxygen is consumed - caloric equivalent of oxygen - depends on the oxidation of which substances oxygen is used. The caloric equivalent of oxygen during the oxidation of carbohydrates is 21.13 kJ (5.05 kcal), proteins - 20.1 kJ (4.8 kcal), fats - 19.62 kJ (4.686 kcal).
Energy consumptionin humans is determined as follows. The person breathes for 5 minutes through a mouthpiece placed in the mouth. The mouthpiece, connected to a bag made of rubberized fabric, has valves. They are designed so that a person freely inhales atmospheric air and exhales air into the bag. Using a gas clock, the volume of exhaled air is measured. The gas analyzer indicators determine the percentage of oxygen and carbon dioxide in the air inhaled and exhaled by a person. The amount of oxygen absorbed and carbon dioxide released, as well as the respiratory quotient, are then calculated. Using the appropriate table, the caloric equivalent of oxygen is determined based on the respiratory coefficient and energy consumption is determined.
Work 3. Determination of respiratory quotient
An important indicator of the chemical nature of the respiratory substrate is the respiratory coefficient ( DK) – ratio of the volume of carbon dioxide released ( V(CO 2)) to the volume of absorbed oxygen ( V(O 2)). When carbohydrates are oxidized, the respiratory coefficient is 1; when fats (more reduced compounds) are oxidized, more oxygen is absorbed than carbon dioxide is released and DK < 1. При окислении органических кислот (менее восстановленных, чем углеводы соединений) DK > 1.
Magnitude DK depends on other reasons. In some tissues, due to difficult access of oxygen, along with aerobic respiration, anaerobic respiration occurs, which is not accompanied by the absorption of oxygen, which leads to an increase in the value of DK. The value of the respiratory coefficient is also determined by the completeness of oxidation of the respiratory substrate. If, in addition to the final products, less oxidized compounds accumulate in the tissues, then DK < 1.
The device for determining the respiratory coefficient (Fig. 8) consists of a test tube (Fig. 8, a) or another glass vessel (Fig. 8, b) with a tightly fitting stopper into which a measuring tube with a graph paper scale is inserted.
Materials and equipment. Germinating seeds of sunflower, barley, peas, beans, flax, wheat, 20% sodium hydroxide solution, 2 cm 3 syringe, colored liquid, Petri dish, chemical test tube, U-shaped tube, elastic tube, plug with hole, anatomical tweezers, strips of filter paper (1.5-5 cm), graph paper, hourglass for 3 minutes, test tube rack.
Progress. Add 2 g of germinating sunflower seeds to a test tube. Close the test tube tightly with a stopper connected by an elastic tube to a U-shaped glass tube, and use a pipette to introduce a small drop of liquid into the end of the tube, creating a closed atmosphere inside the device. Be sure to maintain a constant temperature during the experiment. To do this, place the device on a tripod, thereby avoiding heating it with your hands or breath. Determine how many scale divisions the drop will move inside the tube in 3 minutes. To get an accurate result, calculate the average of the three measurements. The resulting value expresses the difference between the volume of oxygen absorbed during respiration and the volume of carbon dioxide released.
Open the device with the seeds and place in it with tweezers a strip of filter paper rolled into a ring, pre-soaked in NaOH solution. Re-close the test tube, place a new drop of colored liquid into the measuring tube and continue measuring its speed at the same temperature. The new data, from which you again calculate the average value, expresses the volume of oxygen absorbed during respiration, since the released carbon dioxide is absorbed by alkali.
Calculate the respiratory coefficient using the formula: , where DK– respiratory coefficient; IN– volume of oxygen absorbed during respiration; A– the difference between the volume of oxygen absorbed during respiration and the volume of carbon dioxide released.
Compare the values of the respiratory coefficients of the proposed objects and draw a conclusion about the chemical nature of the respiratory substrates of each of the objects.
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1 Device for observing gas exchange during the respiration of plants and animals PGD (educational): instruction manual / ed. T.S. Chanova. – M.: Education, 1987. – 8 p.
respiratory coefficient (RK)
the ratio of the volume of carbon dioxide released through the lungs to the volume of oxygen absorbed during the same time; the value of D.c. when the subject is at rest depends on the type of food substances oxidized in the body.
Encyclopedic Dictionary, 1998
respiratory quotient
the ratio of the volume of carbon dioxide released during breathing during a certain time to the volume of oxygen absorbed during the same time. Characterizes the features of gas exchange and metabolism in animals and plants. In a healthy person it is approximately 0.85.
Respiratory coefficient
the ratio of the volume of carbon dioxide released from the body to the volume of oxygen absorbed during the same time. Indicated by:
Determination of DC is important for studying the characteristics of gas exchange and metabolism in animals and plant organisms. When carbohydrates are oxidized in the body and oxygen is fully available, DC is 1, fats ≈ 0.7, proteins ≈ 0.8. In a healthy person at rest, DC is 0.85 ╠ 0.1; during moderate work, as well as in animals that eat predominantly plant foods, it approaches 1. In humans, during very long work, fasting, in carnivores (predators), as well as during hibernation, when, due to the limited reserves of carbohydrates in the body, dissimilation increases fat, DC is about 0.7. DC exceeds 1 with intensive deposition in the body of fats formed from carbohydrates supplied with food (for example, in humans when restoring normal weight after fasting, after long-term illnesses, as well as in animals during fattening). The DC increases to 2 with intense work and hyperventilation of the lungs, when additional CO2, which was in a bound state, is released from the body. DC reaches even greater values in anaerobes, in which most of the released CO2 is formed by oxygen-free oxidation (fermentation). DK below 0.7 occurs in diseases associated with metabolic disorders, after heavy physical work.
In plants, DK depends on the chemical nature of the respiratory substrate, the content of CO2 and O2 in the atmosphere and other factors, thus characterizing the specifics and conditions of respiration. When the cell uses carbohydrates for respiration (grain seedlings), the DC is approximately 1, fats and proteins (germinating oilseeds and legumes) ≈ 0.4≈0.7. With a lack of O2 and difficult access (seeds with a hard shell), the DC is 2≈3 or more; high DC is also characteristic of growth point cells.
1. What process ensures the release of energy in the body? What is its essence?
Dissimilation (catabolism), i.e., the breakdown of cellular structures and compounds of the body with the release of energy and decay products.
2. What nutrients provide energy in the body?
Carbohydrates, fats and proteins.
3. Name the main methods for determining the amount of energy in a sample of a product.
Physical calorimetry; physicochemical methods for determining the amount of nutrients in a sample with subsequent calculation of the energy contained in it; according to tables.
4. Describe the essence of the method of physical calorimetry.
A sample of the product is burned in the calorimeter, and then the released energy is calculated based on the degree of heating of the water and the calorimeter material.
5. Write a formula for calculating the amount of heat released during combustion of a product in a calorimeter. Decipher its symbols.
Q = MvSv (t 2 - t 1) + MkSk (t 2 - t 1) - Qo,
where Q is the amount of heat, M is the mass (w - water, k - calorimeter), (t 2 - t 1) is the temperature difference between water and calorimeter after and before combustion of the sample, C is the specific heat capacity, Qo is the amount of heat generated by the oxidizer .
6. What are the physical and physiological caloric coefficients of a nutrient?
The amount of heat released during the combustion of 1 g of a substance in a calorimeter and in the body, respectively.
7. How much heat is released when 1 g of proteins, fats and carbohydrates are burned in a calorimeter?
1g protein – 5.85 kcal (24.6 kJ), 1g fat – 9.3 kcal (38.9 kJ), 1g carbohydrates – 4.1 kcal (17.2 kJ).
8. Formulate Hess’s law of thermodynamics, on the basis of which the energy entering the body is calculated based on the amount of digested proteins, fats and carbohydrates.
The thermodynamic effect depends only on the heat content of the initial and final reaction products and does not depend on the intermediate transformations of these substances.
9. How much heat is released during the oxidation of 1 g of proteins, 1 g of fats and 1 g of carbohydrates in the body?
1 g of proteins – 4.1 kcal (17.2 kJ), 1 g of fats – 9.3 kcal (38.9 kJ), 1 g of carbohydrates – 4.1 kcal (17.2 kJ).
10. Explain the reason for the difference between the physical and physiological caloric coefficients for proteins. In which case is it greater?
In the calorimeter (physical coefficient), the protein decomposes to the final products - CO 2, H 2 O and NH 3 with the release of all the energy contained in them. In the body (physiological coefficient), proteins break down into CO 2, H 2 O, urea and other substances of protein metabolism, which contain energy and are excreted in the urine.
The content of proteins, fats and carbohydrates in food products is determined, their amount is multiplied by the corresponding physiological caloric coefficients, summed up and 10% is subtracted from the sum, which is not absorbed in the digestive tract (losses in feces).
12. Calculate (in kcal and kJ) the energy intake when 10 g of proteins, fats and carbohydrates are taken into the body with food.
Q = 4.110 + 9.310 + 4.110 = 175 kcal. (175 kcal - 17.5 kcal) x 4.2 kJ, where 17.5 kcal is the energy of undigested nutrients (losses in feces - about 10%). Total: 157.5 kcal (661.5 kJ).
Calorimetry: direct (Atwater-Benedict method); indirect, or indirect (methods of Krogh, Shaternikov, Douglas - Holden).
14. What is the principle of direct calorimetry based on?
On direct measurement of the amount of heat generated by the body.
15. Briefly describe the design and operating principle of the Atwater-Benedict camera.
The chamber in which the test subject is placed is thermally isolated from the environment; its walls do not absorb heat; inside they are radiators through which water flows. Based on the degree of heating of a certain mass of water, the amount of heat consumed by the body is calculated.
16. What is the principle of indirect (indirect) calorimetry based on?
By calculating the amount of energy released according to gas exchange data (absorbed O 2 and released CO 2 per day).
17. Why can the amount of energy released by the body be calculated based on gas exchange rates?
Because the amount of O 2 consumed by the body and CO 2 released corresponds exactly to the amount of oxidized proteins, fats and carbohydrates, and therefore the energy consumed by the body.
18. What coefficients are used to calculate energy consumption by indirect calorimetry?
Respiratory coefficient and caloric equivalent of oxygen.
19. What is called the respiratory coefficient?
The ratio of the volume of carbon dioxide released by the body to the volume of oxygen consumed during the same time.
20. Calculate the respiratory coefficient (RC) if it is known that the inhaled air contains 17% oxygen and 4% carbon dioxide.
Since atmospheric air contains 21% O 2, the percentage of absorbed oxygen is 21% - 17%, i.e. 4%. CO 2 in exhaled air is also 4%. From here
21. What does the respiratory coefficient depend on?
22. What is the respiratory coefficient during the oxidation in the body to the final products of proteins, fats and carbohydrates?
During the oxidation of proteins – 0.8, fats – 0.7, carbohydrates – 1.0.
23. Why is the respiratory quotient lower for fats and proteins than for carbohydrates?
More O 2 is consumed for the oxidation of proteins and fats, since they contain less intramolecular oxygen than carbohydrates.
24. What value does a person’s respiratory quotient approach at the beginning of intense physical work? Why?
To one, because the source of energy in this case is mainly carbohydrates.
25. Why is a person’s respiratory coefficient greater than one in the first minutes after intense and prolonged physical work?
Because more CO 2 is released than O 2 is consumed, since lactic acid accumulated in the muscles enters the blood and displaces CO 2 from bicarbonates.
26. What is called the caloric equivalent of oxygen?
The amount of heat released by the body when consuming 1 liter of O 2.
27. What does the caloric equivalent of oxygen depend on?
From the ratio of proteins, fats and carbohydrates oxidized in the body.
28. What is the caloric equivalent of oxygen during the oxidation in the body (in the process of dissimilation) of proteins, fats and carbohydrates?
For proteins - 4.48 kcal (18.8 kJ), for fats - 4.69 kcal (19.6 kJ), for carbohydrates - 5.05 kcal (21.1 kJ).
29. Briefly describe the process of determining energy consumption using the Douglas-Holden method (full gas analysis).
Within a few minutes, the subject inhales atmospheric air, and the exhaled air is collected in a special bag, its quantity is measured and gas analysis is carried out to determine the volume of oxygen consumed and CO 2 released. The respiratory coefficient is calculated, with the help of which the corresponding caloric equivalent of O 2 is found from the table, which is then multiplied by the volume of O 2 consumed over a given period of time.
30. Briefly describe M. N. Shaternikov’s method for determining energy expenditure in animals in an experiment.
The animal is placed in a chamber into which oxygen is supplied as it is consumed. CO 2 released during respiration is absorbed by alkali. The energy released is calculated based on the amount of O2 consumed and the average caloric equivalent of O2: 4.9 kcal (20.6 kJ).
31. Calculate energy consumption in 1 minute if it is known that the subject consumed 300 ml of O 2. The respiratory coefficient is 1.0.
DK = 1.0, it corresponds to the caloric equivalent of oxygen equal to 5.05 kcal (21.12 kJ). Therefore, energy consumption per minute = 5.05 kcal x 0.3 = 1.5 kcal (6.3 kJ).
32. Briefly describe the process of determining energy consumption using the Krogh method in humans (incomplete gas analysis).
The subject inhales oxygen from the metabolimeter bag, the exhaled air returns to the same bag, having previously passed through a CO 2 absorber. Based on the readings of the metabolimeter, the O2 consumption is determined and multiplied by the caloric equivalent of oxygen 4.86 kcal (20.36 kJ).
33. Name the main differences in calculating energy consumption using the Douglas-Holden and Krogh methods.
The Douglas–Holden method involves calculating energy consumption based on data from a complete gas analysis; Krogh's method - only by the volume of oxygen consumed using the caloric equivalent of oxygen characteristic of basal metabolic conditions.
34. What is called the basal metabolism?
Minimum energy consumption that ensures homeostasis under standard conditions: while awake, with maximum muscular and emotional rest, on an empty stomach (12 - 16 hours without food), at a comfortable temperature (18 - 20C).
35. Why is basal metabolism determined under standard conditions: maximum muscular and emotional rest, on an empty stomach, at a comfortable temperature?
Because physical activity, emotional stress, food intake and changes in ambient temperature increase the intensity of metabolic processes in the body (energy consumption).
36. What processes consume basal metabolic energy in the body?
To ensure the vital functions of all organs and tissues of the body, cellular synthesis, and to maintain body temperature.
37. What factors determine the value of the proper (average) basal metabolic rate of a healthy person?
Gender, age, height and body mass (weight).
38. What factors, besides gender, weight, height and age, determine the value of the true (real) basal metabolic rate of a healthy person?
Living conditions to which the body is adapted: permanent residence in a cold climate zone increases basal metabolism; long-term vegetarian diet – reduces.
39. List the ways to determine the amount of proper basal metabolism in a person. What method is used to determine the value of a person’s true basal metabolic rate in practical medicine?
According to tables, according to formulas, according to nomograms. Krogh method (incomplete gas analysis).
40. What is the value of basal metabolism in men and women per day, as well as per 1 kg of body weight per day?
For men, 1500 – 1700 kcal (6300 – 7140 kJ), or 21 – 24 kcal (88 – 101 kJ)/kg/day. Women have approximately 10% less than this value.
41. Is the basal metabolic rate calculated per 1 m 2 of body surface and per 1 kg of body weight the same in warm-blooded animals and humans?
When calculated per 1 m 2 of body surface in warm-blooded animals of different species and humans, the indicators are approximately equal, when calculated per 1 kg of mass they are very different.
42. What is called a working exchange?
The combination of basal metabolism and additional energy expenditure that ensures the functioning of the body in various conditions.
43. List the factors that increase energy consumption by the body. What is called the specific dynamic effect of food?
Physical and mental stress, emotional stress, changes in temperature and other environmental conditions, specific dynamic effects of food (increased energy consumption after eating).
44. By what percentage does the body’s energy consumption increase after eating protein and mixed foods, fats and carbohydrates?
After eating protein foods - by 20 - 30%, mixed foods - by 10 - 12%.
45. How does ambient temperature affect the body’s energy expenditure?
Temperature changes in the range of 15 – 30C do not significantly affect the body’s energy consumption. At temperatures below 15C and above 30C, energy consumption increases.
46. How does metabolism change at ambient temperatures below 15? What does it matter?
Increasing. This prevents the body from cooling down.
47. What is called the body’s efficiency during muscular work?
Expressed as a percentage, the ratio of the energy equivalent to useful mechanical work to the total energy expended in performing that work.
48. Give a formula for calculating the coefficient of performance (efficiency) in a person during muscular work, indicate its average value, decipher the elements of the formula.
where A is energy equivalent to useful work, C is total energy consumption, e is energy consumption for the same period of time at rest. The efficiency is 20%.
49. What animals are called poikilothermic and homeothermic?Poikilothermic animals (cold-blooded) - with an unstable body temperature, depending on the ambient temperature; homeothermic (warm-blooded) - animals with a constant body temperature that does not depend on the ambient temperature.
50. What is the importance of constancy of body temperature for the body? In which organs does the process of heat formation occur most intensively?
Provides a high level of vital activity relatively regardless of ambient temperature. In muscles, lungs, liver, kidneys.
51. Name the types of thermoregulation. Formulate the essence of each of them.
Chemical thermoregulation - regulation of body temperature by changing the intensity of heat production; physical thermoregulation - by changing the intensity of heat transfer.
52. What processes provide heat transfer?
Heat radiation (radiation), heat evaporation, heat conduction, convection.
53. How does the lumen of skin blood vessels change when the ambient temperature decreases and increases? What is the biological significance of this phenomenon?
When the temperature drops, the blood vessels in the skin narrow. As the ambient temperature rises, the blood vessels in the skin dilate. The fact is that changing the width of the lumen of blood vessels, regulating heat transfer, helps maintain a constant body temperature.
54. How and why does heat production and heat transfer change with strong stimulation of the sympathoadrenal system?
Heat production will increase due to stimulation of oxidative processes, and heat transfer will decrease as a result of narrowing of skin vessels.
55. List the areas of localization of thermoreceptors.
Skin, cutaneous and subcutaneous vessels, internal organs, central nervous system.
56. In what parts and structures of the central nervous system are thermoreceptors located?
In the hypothalamus, reticular formation of the midbrain, in the spinal cord.
57. In which parts of the central nervous system are thermoregulation centers located? Which structure of the central nervous system is the highest center of thermoregulation?
In the hypothalamus and spinal cord. Hypothalamus.
58. What changes will occur in the body with a long-term absence of fats and carbohydrates in the diet, but with an optimal intake of protein from food (80 - 100 g per day)? Why?
There will be an excess of nitrogen consumption by the body over intake, and weight loss, since energy costs will be covered mainly by proteins and fat reserves that are not replenished.
59. In what quantity and in what ratio should proteins, fats and carbohydrates be contained in the diet of an adult (average version)?
Proteins – 90 g, fats – 110 g, carbohydrates – 410 g. Ratio 1: 1, 2: 4, 6.
60. How does the state of the body change with excess fat intake?
Obesity and atherosclerosis develop (prematurely). Obesity is a risk factor for the development of cardiovascular diseases and their complications (myocardial infarction, stroke, etc.), and reduced life expectancy.
1. What is the ratio of basal metabolic rates in children of the first 3–4 years of life, during puberty, at the age of 18–20 years and adults (kcal/kg/day)?
Up to 3–4 years of age, children have approximately 2 times more, during puberty – 1.5 times more than adults. At 18–20 years old it corresponds to the adult norm.
2. Draw a graph of changes in basal metabolic rate in boys with age (in girls, basal metabolic rate is 5% lower).
3. What explains the high intensity of oxidative processes in a child?
A higher level of metabolism of young tissues, a relatively large surface area of the body and, naturally, greater energy expenditure to maintain a constant body temperature, increased secretion of thyroid hormones and norepinephrine.
4. How do energy costs for growth change depending on the age of the child: up to 3 months of life, before the onset of puberty, during puberty?
They increase in the first 3 months after birth, then gradually decrease, and increase again during puberty.
5. What does the total energy expenditure of a 1-year-old child consist of and how is it distributed as a percentage compared to an adult?
In a child: 70% falls on the basal metabolism, 20% on movement and maintaining muscle tone, 10% on the specific dynamic effect of food. In an adult: 50 – 40 – 10%, respectively.
6. Do adults or children 3–5 years of age expend more energy when performing muscular work to achieve the same beneficial result, by how many times and why?
Children, 3 to 5 times, since they have less perfect coordination, which leads to excessive movements, resulting in significantly less useful work for children.
7. How does energy expenditure change when a child cries, by what percentage, and as a result of what?
Increases by 100–200% due to increased heat production as a result of emotional arousal and increased muscle activity.
8. What part (in percentage) of an infant’s energy expenditure is provided by proteins, fats, and carbohydrates? (compare with the adult norm).
Due to proteins - 10%, due to fats - 50%, due to carbohydrates - 40%. In adults – 20 – 30 – 50%, respectively.
9. Why do children, especially in infancy, quickly overheat when the ambient temperature rises? Do children tolerate increases or decreases in ambient temperature more easily?
Because children have increased heat production, insufficient sweating and, consequently, heat evaporation, an immature thermoregulation center. Demotion.
10. Name the immediate cause and explain the mechanism of rapid cooling of children (especially infants) when the ambient temperature drops.
Increased heat transfer in children due to a relatively large body surface, abundant blood supply to the skin, insufficient thermal insulation (thin skin, lack of subcutaneous fat) and immaturity of the thermoregulation center; insufficient vasoconstriction.
11. At what age does a child begin to experience daily temperature fluctuations, how do they differ from those in adults, and at what age do they reach adult norms?
At the end of 1 month of life; they are insignificant and reach the adult norm by five years.
12. What is a child’s temperature “comfort zone”, what temperature is it within, what is this indicator for adults?
The external temperature at which individual fluctuations in the temperature of a child’s skin are least pronounced is in the range of 21 – 22 o C, in an adult – 18 – 20 o C.
13. Which thermoregulation mechanisms are most ready to function at the time of birth? Under what conditions can the mechanisms of trembling thermogenesis be activated in newborns?
Increased heat generation, predominantly of non-shivering origin (high metabolism), sweating. Under conditions of extreme cold exposure.
14. In what ratio should proteins, fats and carbohydrates be contained in the diet of children aged three and six months, 1 year, over one year and adults?
Up to 3 months – 1: 3: 6; at 6 months – 1: 2: 4. At the age of 1 year and older – 1: 1, 2: 4, 6, i.e., the same as in adults.
15. Name the features of the metabolism of mineral salts in children. What is this connected with?
There is retention of salts in the body, especially increased need for calcium, phosphorus and iron, which is associated with the growth of the body.
11 Energy exchange
An indispensable condition for maintaining life is that organisms receive energy from the external environment, and although the primary source of energy for all living things is the Sun, only plants are capable of directly using its radiation. Through photosynthesis, they convert the energy of sunlight into the energy of chemical bonds. Animals and humans get the energy they need by eating plant foods. (For carnivores and partly for omnivores, other animals - herbivores - serve as a source of energy.)
Animals can also directly receive energy from the sun's rays; for example, poikilothermic animals maintain their body temperature in this way. However, heat (received from the external environment and generated in the body itself) cannot be converted into any other type of energy. Living organisms, unlike technical devices, are fundamentally incapable of this. A machine that uses the energy of chemical bonds (for example, an internal combustion engine) first converts it into heat and only then into work: the chemical energy of the fuel → warm → work (expansion of gas in the cylinder and movement of the piston). In living organisms, only this scheme is possible: chemical energy → Job.
So, the energy of chemical bonds in the molecules of food substances is practically the only source of energy for an animal organism, and thermal energy can only be used by it to maintain its body temperature. In addition, heat, due to rapid dissipation in the environment, cannot be stored in the body for a long period. If excess heat occurs in the body, then for homeothermic animals this becomes a serious problem and sometimes even threatens their life (see Section 11.3).
11.1. Sources of energy and ways of its transformation in the body
A living organism is an open energy system: it receives energy from the environment (almost exclusively in the form of chemical bonds), converts it into heat or work, and in this form returns it to the environment.
Components of nutrients that enter the blood from the gastrointestinal tract (for example, glucose, fatty acids or amino acids) are not themselves capable of directly transferring the energy of their chemical bonds to its consumers, for example, the potassium-sodium pump or muscle actin and myosin. There is a universal intermediary between food “energy carriers” and “consumers” of energy - adenosine triphosphate (ATP). He is the one direct source energy for any processes in living things
body. The ATP molecule is a combination of adenine, ribose and three phosphate groups (Fig. 11.1).
The bonds between acid residues (phosphates) contain a significant amount of energy. By splitting off the terminal phosphate under the action of the enzyme ATPase, ATP is converted into adenosine diphosphate (ADP). This releases 7.3 kcal/mol of energy. The energy of chemical bonds in food molecules is used for the resynthesis of ATP from ADP. Let's consider this process using glucose as an example (Fig. 11.2).
The first stage of glucose utilization is glycolysis During this process, a glucose molecule is first converted into pyruvic acid (pyruvat), while providing energy for ATP resynthesis. Pyruvate is then converted to acetyl coenzyme A - initial product for the next stage of recycling - Krebs cycle. The multiple transformations of substances that make up the essence of this cycle provide additional energy for the resynthesis of ATP and end with the release of hydrogen ions. The third stage begins with the transfer of these ions into the respiratory chain - oxidative phosphorylation, as a result of which ATP is also formed.
Taken together, all three stages of recycling (glycolysis, Krebs cycle and oxidative phosphorylation) constitute the process tissue respiration. It is fundamentally important that the first stage (glycolysis) takes place without the use of oxygen (anaerobic respiration) and leads to the formation of only two ATP molecules. The two subsequent stages (Krebs cycle and oxidative phosphorylation) can only occur in an oxygen environment (aerobic respiration). Complete utilization of one glucose molecule results in the appearance of 38 ATP molecules.
There are organisms that not only do not require oxygen, but also die in an oxygen (or air) environment - obligate anaerobes. These, for example, include bacteria that cause gas gangrene (Clostridium perfringes), tetanus (C. tetani), botulism (C. botulinum), etc.
In animals, anaerobic processes are an auxiliary type of respiration. For example, with intense and frequent muscle contractions (or with static contractions), the delivery of oxygen by the blood lags behind the needs of the muscle cells. At this time, ATP formation occurs anaerobically with the accumulation of pyruvate, which is converted into lactic acid (lactate). Growing oxygen debt. The cessation or weakening of muscle work eliminates the discrepancy between the tissue's need for oxygen and the possibilities of its delivery; lactate is converted into pyruvate, the latter either through the stage of acetyl coenzyme A is oxidized in the Krebs cycle to carbon dioxide, or through gluconeogenesis it turns into glucose.
According to the second law of thermodynamics, any transformation of energy from one type to another occurs with the obligatory formation of a significant amount of heat, which is then dissipated in the surrounding space. Therefore, the synthesis of ATP and the transfer of energy from ATP to the actual “energy consumers” occur with the loss of approximately half of it in the form of heat. Simplifying, we can represent these processes as follows (Fig. 11.3).
Approximately half of the chemical energy contained in food is immediately converted into heat and dissipated in space, the other half goes to the formation of ATP. With the subsequent breakdown of ATP, half of the released energy is again converted into heat. As a result, an animal and a person can spend no more than 1/4 of all energy consumed in the form of food to perform external work (for example, running or moving any objects in space). Thus, the efficiency of higher animals and humans (about 25%) is several times higher than, for example, the efficiency of a steam engine.
All internal work (except for the processes of growth and fat accumulation) quickly turns into heat. Examples: (a) the energy produced by the heart is converted into heat due to the resistance of blood vessels to the flow of blood; (b) the stomach does the work of secreting hydrochloric acid, the pancreas secretes bicarbonate ions, in the small intestine these substances interact, and the energy stored in them is converted into heat.
The results of external (useful) work performed by an animal or a person also ultimately turn into heat: the movement of bodies in space warms the air, erected structures collapse, giving up the energy embedded in them to the earth and air in the form of heat. The Egyptian pyramids are a rare example of how the energy of muscle contraction, expended almost 5,000 years ago, is still waiting for the inevitable transformation into heat.
Energy balance equation:
E = A + H + S,
Where E - the total amount of energy received by the body from food; A - external (useful) work; N - heat transfer; S- stored energy.
Energy losses through urine, sebum and other secretions are extremely small and can be neglected.