Hunger, appetite and satiation state. Substance and energy exchange, thermoregulation.

Purposeful behaviour as for food taking is in the state which has received the name hunger state. This is special motivation directed on dyscomfort liquidation, connected with nutrients insufficiency in organism. Hunger center is located in hypothalamus, its excitement is delt both with nervous and humoral factors. Important role in sensations forming connected with hunger plays afferent impulsation coming in central nervous system from alimentary tract receptors. Its different parts have their own electrical basal rhythms of food taking. Near-houred rhythms are evacuational activity regulators. Intestine main activity rhythm – is of 90-minutes. There is 20-minute period of stomach and small intestine activity, liver, pancreas and intestinal glands secretory activity in this rhythm and 70-minute period of relative rest. Activity occurs in stomach and gradually passes through small intestine. Periodic activity initial reason is physiological hunger state. Empty stomach and small intestine proximal part hungry activity increases hunger state. It causes unconscious motor anxiety in animals and, conscious, in people. Inhibitory influencings of this feeling are connected with autonomic nervous system sympathetic part. Hypoglycaemia acting on specialized hypothalamic glucoreceptors participates in hunger forming.

Appetite – is emotional sensation delt with striving for food taking. This sensation may be hunger part but also it can occur independently from physiological consumption. In this case it is the expression of congenital or aquired individual predisposition to definite food type. One should underline that food taking in human being is not always connected with hunger feeling and it is rather uncorrect. But, unfortunately, it is so. Why? The answer is very simple – habit to take food in definite time (by the way, it is not the worst variant) or because all surrounding people are eating at this time.

Satiation - appears as a result of food taking. It occurs because of oral cavity, pharynx, oesophagus, stomach, duodenum mechanoreceptors as well as olfactory and gustatory receptors stimulation. Such satiation is called sensor or primary. We have also secondary or metabolic satiation connected with hydrolysis products coming into blood. It appears usually after 1,5-2,0 hours after primary satiation. Peptide hormones decreasing alimentary behaviour (cholecystokinine, somatostatine, bombesine, calcitonine) or increasing it (gastrine, insuline, oxytocine) are essential for food taking regulation, hunger and satiation sense occurence.

Remember! The slower you will take food (to masticate longer, not to hurry up while transition from one dish to other) the faster and at less food amount (it is the most important!) satiation will come. Commonly, food must be taken till you won’t feel that you can eat the same amount. Than you must leave the table. You are feeling hunger but after some time you will fell the satiation. This is one of elements of feeding culture!

Substance and energy exchange – is an integrity of physical, chemical and physiological processes of substances and energy transition in human organism as well as substance and energy exchange between organism and environment. Substance and energy exchange provides organism plastic and energetic needs. One can differentiate 2 interconnected but directed oppositely processes. Anabolism – is the integrity of organic substances, cellular components and other tissular and organic structures biosynthetic processes. They are growth, development, biological structures renewal and continuous macroergs resynthesis as well as energetic substrates accumulation. Catabolism – is the integrity of complicated molecules, cellular components, tissues and organs destructive processes to simple substance. Nutrients rich in energy are assimilated and chemically transformed but ending metabolism products with lower energy content are released from cell. Organism must receive energy in suitable form for it from environment and return into environment corresponding energy amount in a form suitable for further usage. This process in organism is called energy exchange. All processes generating energy that require molecular oxygen participation are formed aerobic exchange system. Energy generation without oxygen participation is called anaerobic exchange.

Definite part of energy accumulated in fats, proteins and carbohydrates chemical bonds is used in course of biological oxidation process for ATP synthesis, other part is transformed in warmth. This warmth, released right after in nutrients biological oxidation process has received the name primary warmth. Energy accumulated in ATP and used further for chemical, transport, electrical processes performance, mechanical work producing transformed in warmth was named as secondary warmth. If to measure all warmth quantity having been formed in organism for 24 hours then this warmth will be the measure of nutrients chemical bonds sum energy taking into account that these nutrients underwent biological oxidation in course of measurement. According to warmth quantity having been formed in organism one can make the conclusion about energy expenditures to viability processes performance. Main energy source in organism for viability processes performance is nutrients biological oxidation. Oxidation is essential for this oxidation. Thus, having measured consumpted oxygen quantity for 1 min (1 h, 24 hours) one can say about organism energy expenditures size. There is a connection between oxygen quantity consumpted by organism for time unit and the quantity of warmth having formed in it for the same time. This connection is expressed through oxygen caloric equivalent – warmth quantity forming in organism at consumption 1 l of oxygen by it. For instance, it is equal to 5,05 ccal at carbohydrates burning.

Organism energy expenditures assessment may be performed by 2 ways:

· Direct biocalorymetry – is based on warmth quantity measurement directly disseminated by organism in warmth-isolated camera. It is a very exact method but it is used very seldom because it is cumbersome and expensive. This method principle is based on thermodynamics first law which means that all work transforms into warmth which we measure in calorymeters.

· Indirect biocalorymetry – is based on measurement oxygen quantity consumped by organism and further energy expenditures estimation with usage of data about respiratory coefficient (RC) and oxygen caloryc equivalent.

Respiratory coefficient – is released carbonic dioxide volume correlation to used oxygen volume. Given method essence can be described on the example of glucose oxidation: С₆Н₁₂О₆ + 6О₂ = 6СО₂+6Н₂О. This reaction is well known for you from biology, chemistry and biochemistry courses. Released carbonic dioxide volume is equal to one of used oxygen. Thus, at glucose oxidation RC= 6СО₂/О₂=1. In case of fats oxidation it is equal to 0,7, proteins – 0,8.

As all nutrients in organism are undergone to oxidation simultaneousely than after RC size determining one can approximately tell about dominant oxidation of one or other nutrient type. Every nutrient has its own energy valuation. That’s why on RC size one can estimate oxygen caloryc equivalent. If we know oxygen consumped amount we can estimate energy expenditure.

Organism energy metabolism consists of basal exchange and working addition.

Basal metabolism – is minimal level of expenditures necessary for organism viability support. It is defined under conditions of relatively complete physical and emotional rest. Under relative rest energy is expended to nervous system functions perfomance, constant substance synthesis, ion pumps work, body temperature support, respiratory musculature, smooth muscles, heart and kidney activity.

Basal metabolism determining is realized: in the morning, under rest state, on an empty stomach (the latest food taking must be 10-12 hours before investigation), at comfort temperature (22-24°C). Indicated standard conditions characterizes those factors which can influence on metabolism intensivity in human being. Metabolism intensivity is subjected to daily fluctuations. It is increased in the morning and is decreased in the night. It is changed at environment temperature changing (if it is below comfort zone than metabilism reactions intensivity is increased). In winter – is rised up, in summer – is reduced. Nutrients consumption, their further digestion (especially protheins) influence greatly on metabolism level. Metabolism intensivity and organism energetic expenditures increasing under food influence as for exchange and energy expenditures level taking place before eating is called specifically-dynamic food action. It is explained by energy expenditures to food digestion. Such food action may be up to 12-18 hours. It is mostly expressed at prothein food taking increasing metabolism intensivity up to 30 per cent and less significant at mixed food taking increasing metabolism intensivity up to 6-15 per cents. In babies specifically-dynamic food action is approximately on 30 per cents weaker than in adults. Prothein food causes basal metabolism increasing in children on 15-18% (in adults – on 30%); carbohydrate – on 10% (in adult – on 15%); fat – on 5% (in adult – on 15%).

In average basal metabolism size for person with mass 70 kg corresponds to 1600-1700 kcal /day (in women – less on 5-10%). Such factors as musculature development degree, liver, brain, heart, kidney, endocrine glands state influence on basal metabolism level. Basal metabolism is increased in small children with maximal velocity in the first year after birth (approximately from 120 to 600 kcal/day). After this basal metabolism growth is retarded again and accelerated again in puberty. But in children of any age basal metabolism level on 1 kg of mass is higher than in adults. It testifies to substance and energy metabolism more intensivity in children’s tissues comparatively to those in the adult. Basal metaboilsm in children depends on constitution. In thin and agile children basal metabolism is higher than in thick and dismoved. Basal metabolism is increased at fever (in average, on 5 per cent while body temperature increasing on 1°C).

Basal metabolism changes more than on 10 per cent may serves as diagnostic criterium of such organism states as thyroid dysfunctions, recovery after hard and durable diseases, intoxication and shock.

Basal energy metabolism plus working addition (something delt with working activity type) is equal to general (gross) metabolism. It is the characteristics of daily energy consumption. Its level depends on energy scale for different population groups.

Population groups and norm for them in kkal/day:

1-st – servant: men - 2500-2800, women – 2200-2400 (we belong to this group as people of mental activity.

2-nd – workers of light physical activity: men – 2750-3000, women – 2350-2550.

3-rd – of middle on gravity physical activity: men – 2950-3200, women – 2500-2700.

4-th – workers of hard physical activity: men - 3450-3700, women - 2900-3150.

5-th – of very hard work: men - 3900-4300. Women mustn’t be in this group.

Some scientists add one group – of non-working pensionners – their energy expenditures after their work stoppage must be significantly shortened and be not higher than in people of the 1-st group.

Mental activity doesn’t require too significant expenditures like physical activity. Expenditures are rised up at mental activity in average only on 2-3 per cent. But mental activity accompanied by light muscular activity, psycho-emotional tension, leads to expenditures increasing on 11-19 per cent and even more.

Substance and energy metabolism regulation. It includes regulatory systems of multiple organism functions – respiration, blood circulation, excretion, thermoregulation and others. Hypothalamus plays role of substance and energy metabolism regulator. It is explained by the fact that there are nervous nuclei and centers there influencing directly on hunger and satiation and thermoregulation. Autonomic nervous system parasympathetic and sympathetic parts serve as metabolism regulation efferent system. Mediators releasing on their endings influence directly or indirectly through secondary messengers on tissues function and metabolism. Endocrine system is managed by hypothalamus and serves as substance and energy metabolism efferent system. Hypophysis, hypothalamus and other endocrine glands hormones influence directly on cells growth and development, supporting in blood necessary level of different substances (glucose, free fat acids, mineral ions and others). Cell is essential effector in these reactions. The most freaquent effects of regulatory influencings to cell are the following changes: of catalytic enzymes activity and their concentration, modulators, adenylates, common predecessors and common intermediate products action. Glucose concentration in blood (under norma it is equal to 0,8-1,2 g/l) is one of environmental integral indexes reflecting metabolism in organism.

Thermal exchange and body temperature regulation. Temperature influences greatly on alive processes course in organism. Physico-chemical base of this influence is chemical reactions course velocity change. That’s why body temperature influences upon its cells activity. Organism tissues temperature is defined by cellular structures metabolic thermal production velocity correlation to forming warmth dissemination velocity into environment. Such processes velocity correlation disorder leads to body temperature change. Mechanisms fixed in course of evolution by means of which organism may express resistance to lower and higher environmental temperature are essential for this.

All organisms according to mechanisms of homeostasis supporting are divided into 3 main groups:

· poikylothermal – changeable, which have no the ability to support body temperature on constant level, cold-blooded – amphibias, reptiles, fishes, crustaceas;

· homoiothermal – similar, warm-blooded, which can support body temperature on relatively constant level with daily and season fluctuations in the limits of 2 degrees – mammals, human beings;

· poikylohomoiothermal – under favourable conditions they belong to homoiothermal organisms, under unfavourable – to poikylothermal. Some insects reproduced by partenogenesis (ants, thermites, beans), colibry, crocodiles, tortoises, rodents, Chiroptera (flying mice) belong to this group.

Body temperature constant level in humans may be served only under the condition of dynamic equllibrium between heat production and heat emission. Such equillibrium is supported by thermoregulation physiologic mechanisms. One can differentiate 2 ways of thermoregulation: chemical and physical.

I. Chemical thermoregulation is performed by means of enforcement or weakening of cellular and tissular metabolism intensivity and expressed in heat production amount change. Heat source in organism are many organs and tissues but portion of their participation in heat production is rather various. Maximal heat production in organism occurs in muscles, liver and kidneys. One can say about 2 thermogenesis types:

1) Contractive – is linked with muscular thermoregulative activity. In turn, one can differentiate 2 subtypes of it:

· Thermoregulative tone - is analogous to muscular pose tone. It is performed like low-freaquened incomplete tetanus (impulses freaquency is 16 per 1 minute). Muscles of neck, trunk and extremities flexors are involved in this reaction. That’s why human being changes his pose (curls up into ball).

· Trembling – in switched on when internal body temperature becomes its reducing.

2) Non-contractive – connected with activation of heat special sources is realized due to brown fat tissue existance which in comparison with white fat has more mitochondrias (brown colour is provided by iron-containing enzymes – cytochromes which are important part of mitochondrial oxidative enzymatic system. Fat acids oxidation velocity in it predominates that in white fat in 20 times.

II. Physical thermoregulation is realized by means of heat emission changes. One can differentiate several heat emission ways:

· Heat radiation – heat releasing (emission) by organism due to infrared radiation out off body surface. Under rest state heat emission by this mechanism is about 60 per cent.

· Heat conduction and convection – direct heat emission to subjects attached to skin, air. It is the more intensive the more is temperature difference of body surface, air, surrounding subjects. Organism losses up to 15 per cent of warmth by this method.

· Evaporation – the way of heat dissemination by organism into surrounding environment due to its expenditure to sweat or moisture perspiration from skin surface and moisture from mucosae. Organism looses up to 19-20 per cent of heat by evaporation.

Thermoregulation is body temperature constant level supporting. It is performed by principle of self-regulation. Receptor structures - are receptors of coldness, warmth and burning. They are located in skin and mucosae. Excitement threshold for receptors of coldness (their amount is bigger and they are located more superficial than receptors of warmth) is in limits of 20-33°C (average - 26°C); for receptors of warmth - 40-46°C (average - 43°C) and for receptors of burning – everything that higher than 45°C.

Thermoregulative center is located in hypothalamic nuclei. Physical thermoregulation is performed by hypothalamic nuclear group located between anterior comissure and optic chiasma (heat emission center). Shortly, heat emission center is located in posterior hypothalamus. Under comfort (thermoneutral) conditions thermal equillibrium providing body temperature support at normal level is not in need of correction by special thermoregulative mechanisms. Environment temperature below than comfort causes activity increasing in perypheral receptors of coldness. This “cold” information increases the posterior hypothalamus efferent structures tone and causes hypersympathycotony as the result of such increasing. It is accompanied by cutaneous and subcutaneous vessels tone increasing. Result of these reactions: organism isolation increasing and heat serving by means of heat emission reducing. This process also leads to pilomotor reflex occurence (activation of smooth muscles fibres function rising hair covering). Parallely to this due to posterior hypothalamus work activating pose muscular tone regulatory system (thermoregulative tone and trembling appearence) heat production increasing occurs in organism (contractive thermogenesis). Due to adrenaline and noradrenaline releasing in course of this reaction energetic exchange in all tissues becomes stimulated particularly in brown fat tissue (non-contractive thermogenesis). Such heat production adrenergetic stimulation is triggered by thyroid hormones action the releasing of which is increased at cooling. When organism is warmed up coldness receptors activity is reduced that leads to hypothalamic efferent structures tone decreasing. As a result sympathetic nervous system influencies on cutaneous and subcutaneous vessels are reduced and this reaction is accompanied by cutaneous blood supply increasing. Heat exchange adrenergic and thyroid activation is decreased in parallel to this. Thermoregulatory center influencings decreasing causes muscular tone and thermogenesis reducing connected with it. Under over heating conditions special sympathetic structures are activated managing perspiration through cholinergic nervous fibres. Heat emission through evaporating is increased as a result of this.

Human body temperature under norma is about 37°C. It is changeable in course of 24 hours: maximal - to 16-18 hours, minimal – to 4 hours. If temperature is decreased - it’s hypothermia, if it is increased – hyperthermia. At temperature reducing below 35°C behaviour disorders take place, up to 31°C - human being is unconscious, at 24-26°C - he is dead. At body temperature increasing up to 39-41°C delirium can begin; at 41-43°C – heat shock and above 43°C - death. Sweat glands activity is essential for heat regulation. Their general amount on human body is up to 2,5 mln. The biggest number – on face, palms, soles, axillas (arm-pits). One can see constant (invisible) evaporation during which sweat is released from skin surface right after its emission. When forming sweat amount is big, it is accumulated near skin surface in drops (visible evaporation). Sweat releasing is observed not only in course of physical activity but also during mental activity. In course of psychical excitement and some emotions (fear, wrath, pain) cold sweat appears in people. Coldness sensation occurs because of skin cooling as vessels are constricted and skin blood supply is decreased simultaneousely with sweat emission. Sympathetic nervous endings in sweat glands are considered to be cholinergic i.e. containing mediator acetylcholine releasing while excitement. Impulses causing sweat emission at temperature increasing come into sweat glands through cholinergic nervous endings while causing emotional sweating (sweat releasing) – through adrenergic. Under norma sweat amount per day reaches up to 500-900 ml, in summer – in 2-3 times more. At high temperature and hard physical activity – in 5-10 times and even more significant.

In a child who has just born rectal temperature is 37,7-38,2°C. In 1 hour it becomes its decresing up to 35 and even lower than 32°C; but then it is increased and in 12-24 hours it reaches 36-37°C. New-borns temperature depends greatly on external (environmental) temperature. Part of children have transitory fever in 2-3 days – temperature increasing up to 39-40°C. It is linked with protein excessive coming into organism and with water insufficiency. Fever may last from several hours to several days and goes away without any consequences. Temperature in children has some peculiarities. First, skin temperature is higher in children due to better vascularization. Second distinguishing feature: children have right-left asymmetry in cutaneous temperature. Third, thermoregulation in children is less perfect than in adult. It is expressed in unconstant body temperature. Fourth, thermoproduction increasing is expressed weakly, cold trembling is absent. Thermoregulation insufficient effectiveness is also delt with relatively large body surface as well as organism low thermoisolation. Fifth, conscious body temperature control develops weakly in children of the first years. Children may not complaint on temperature dyscomfort at coldness and overheating, that’s why the adult must take care of baby cloth’s temperature to air temperature and humidity. It’s beyond compare that this information is essential not only for future doctors but for all people as parents. Thermoregulation development and thermal exchange conditions reach adult indexes at 15-16 years.

 

 

Lecture 26.