Definition of physiology


Physiology studies the functions that maintain the life of living beings.

The characteristics of life :

  • Movement.
  • The growth.
  • The reproduction.
  • breathing.
  • The digestion.
  • absorption.
  • The circulation.
  • excitability.

All these manifestations of life depend on chemical reactions, all of these chemical reactions is called metabolism.

According to their specialties the body's cells are grouped into well individualized systems, ensuring system functions :
– Nutrition, respiration, excretion, circulation….
– nervous system v égétatif : ensures vegetative function

relationship function : individual's relationship with the outside world

– Senses Sensory function.
– muscle motor function system.
– Reproductive system reproductive function.

The multiplicity of cells and their specialization require coordination process to preserve the functioning :
– Integration.
– Regulation.

The regulatory function by chemical mediator :
– hormonal relationship.
– nervous relationship.

internal environment concept :
Importance of the stability of the internal environment :
The stimuli may be responsible for an imbalance of internal environment :
external :
Heat, cold, noise, lack oxygen, lack of water
Internal :
Pain, inflammation, sadness, depression

homeostasis : the body is able to maintain relatively constant conditions of the internal environment, thanks to the physiological regulatory processes (hormonal, nerve).

The body responds to bring the conditions of the internal environment of their low states.. Thermal : -T° – physical -chimique – biochemical


Goals :

  • Knowing the methods of calorimetry.
  • Explain the conditions and the interest of the measurement of basal metabolism.
  • Quote variations in factors of basal metabolism.
  • Knowing the nutritional needs and the principles of a balanced mixed diet.

Definition :

Bioenergetics is the study of energy exchanges in the body. The energy available to the body as chemical energy provided by food (carbohydrates, lipide protide). It can be stored in the form of phosphorylated compounds (ATP, ADP, CP creatine phosphate), or be used to produce mechanical work (muscle contraction, pulmonary ventilation, cardiac activity!…) or chemical process (development of new molecules).

  • energy : term for all forms of work and heat.
  • Metabolism.
  • Anabolism.
  • Catabolisme.
  • enthalpy : maximum energy released during oxidation, is the difference between the substrate of the energy content (initial state), and that of the oxidation product (final state).
  • entropy : disordered energy unable to provide work.
molecular renewal, Growth

Of study of energy exchange

Application of the principles of thermodynamics :

Law of thermodynamics applied to living matter (the body) : ç'est the principle of equivalence and conservation of energy.

In the body any transformation of energy shows a share of thermal energy :

Energy → Mechanical work (20%)
→Chaleur (80%)

In an energy transformation represent only the initial and final states.

The enthalpy is the maximum energy (W) released during the oxidation, is the difference between the energy content of the oxidized substrate (initial state), and the oxidation products (final state).

ΔH = W finale – In initiale,
.DELTA.h represents = Change in enthalpy.
C6 H1206 + 602 → 6C02 + 6H20 – 2813KJ mole.
ΔH =-2813KJmole

The body is not an isolated system, conservation of energy that expresses the energy received is equal to the energy dissipated in the outside world.

The energy supplied in the form of chemical energy from food that is metabolized or energy produced by the substrates.

energy dissipated as heat, mechanical work, osmotic work… is the energy expended.

Metabolized energy = energy expended. dissipated
Produced by Trayail Substrates + Heat

Measurement Methods.

  • Calorimetry direct measure energy expended (dissipated).
  • Indirect calorimetry measuring the energy produced by the substrates.

Equivalence of different forms of energy :

mechanical, electric, chemical, osmotic… where the same units of measurement is used kilocalorie.

The units

Definition :

• lkCal is the amount of energy which can raise the temperature of 1 kg of water of 15 ° C to 16 ° C. lkCal = 4,185kJ

direct calorimetry :

At rest the dissipated energy appears as heat, So measuring energy expenditure amounts to measuring the heat.

Technical : Lavoisier calorimeter or ATWATER and BENEDICT.

indirect calorimetry :

• Food Thermochemistry :

It is based on the energy substrates : G / L / P it requires a long-term observation with weighing, precise composition…

The amount of energy used by the body is estimated from the calculation of the & rsquo; energy provided by food intake (method ingesta), or measuring the C02 and the & rsquo; urea excreted by the body (méthode des Egesta).

– 1g carbohydrate → → 4kcal 17kJ.
– 1g lipide→ 9kcal → 38KJ.
– 1g protide → 4kcal → 17KJ.

Food, Sources & rsquo; energy

• Respiratory Thermochemistry :

This method is based on the calculation of the energy used by the body from the measurement of oxygen consumption (V02).

For an accurate calculation of the energy provided by food, must determine the energy value, oxygen which corresponds to the nature of the oxidized foods.

The caloric equivalent varies with the type of food :
Carbohydrates → 5.05kcal / LO2.
Fat → 4,70kcal / LO2.
Protides → 4,70kcal / LO2.

In the time of measurement of the V02, it is difficult to know the exact contribution of each 3 substrates : in practice one uses the average caloric equivalent.

The mean caloric equivalent of 02 is equal to :
4,8 kcal / L02 I E02 = 20 kJ / L02.

Value observed in subjects receiving a Standard Power.

EX : If an individual has a V02 of 0,250L / min, the amount of energy is used to brighten : 0,250 x 20 = 5kJ / mn.

Technique : spiromètre

The respiratory quotient (R) : is the ratio of the volume of carbon dioxide (VC02) product on the volume of oxygen (V02) consumed during the same time.


R carbohydrates = 1 R lipids = 0,7 R protide = 0,8

Change in energy trade :

global aspect of energy exchange and matter :

  • In adults

On a long interval, the organization's plan is stationary so the mass is constant.

On a short interval, non-stationary regime :
During fasting and exercise : use of reserves.
At meal : set aside.

  • At the & rsquo; child

During growth : the body accumulates chemical energy in the form of building new living matter

energy exchanges vary with physiological state.

The main causes of variation :

  • Muscle activity.
  • The outside temperature : thermorégulation.
  • ‘ The specific dynamic action of food (A D S) or

food thermogenesis.

1- muscle activity :

And,energy expenditure compared to a body at rest, and muscle activity, we observe that it is larger in the second case.

This expense compared to the rest represents the energy cost of mechanical work done

2- thermorégulation :

Exchanged of energies vary with the medium temperature.

homeothermic (man) maintain constant body temperature, over a wide range of outdoor temperatures.

If the man is exposed to changes in T °, it sets up thertabrégulation processes which allow it to maintain its ï”° closest to 37 ° C.

Thermogenesis result of cellular oxidation and muscle activity is influenced by thyroid and adrenal hormones.

Heat exchange between the organism and its environment are made by :

-Conduction : require contact with an object, low if the subject is standing, increase if the subject is lying on the ground.

– Convection : is effected by fluid displacement in which the subject is located, in air or in water.

– Radiation : are more important especially as the difference of T ° between the skin and the environment is great.

– Evaporation : are a major source of heat loss through the respiratory tract or the skin (sweating).

T ° of thermal neutrality

In humans , the curve Nf metabolism according LAT ° exterior is concave upward and passes through a minimum for a value called , by definition T ° de thermal neutrality (T°N T) for which expenses are harmed thermoregulations.

Energy expenditure increases when T ° outside deviates more or less than T N T °

The value of T is T ° N :
– at the naked man T ° N T = 26 °.
– ° in the lightly clad man T N T = 21 °

Cold Zone : T° ext. < T°N T.
Hot Zone : T° ext. > T°N T.

the additional observed when the room T ° energy expenditure deviates more or less in ° T N T represents the cost of operation of the thermoregulation which both in the direction of the protection against heat or against cold.

Fight against cold :

Man adapts to cold by reducing the thermolysis (heat loss) and increasing therrnogenèse (heat).

Heat generation can be increased by the thrill of thermogenesis, who, is an involuntary muscle activity, which all of the spent chemical energy is converted into heat.

The elevation of muscle tone, and voluntary muscle activity are 2 important mechanisms, that increase thermogenesis.

Thermogenesis postprandial contributes to heat production, useful in the fight against the cold (dietary adaptation according to the seasons and climates).

Fight against the hot :

The man fight against a rise in the ambient temperature, reducing thermogenesis by decreasing muscle activity, and increases thermolysis.

Thermolysis increases cutaneous vasodilation, which increases heat loss parnonejuction et.convection.

Changes in energy expenditure and body ° T
depending on the room T °

D E : energy expenditure

3- specific dynamic action of food (ADS) :

Energy expenditure is greater during the period following the food intake POST-MEAL.

This additional energy is called : A .D .S .

– Special features for ads :

  • postprandiale.
  • This energy is not used during muscle activity.
  • Energy not used by the endothermic reactions of syntheses.
  • Appears mandatory as heat.
  • ADS protein is high, but for low fat.
  • Not related to digestive functioning.

The operating expenses and background

The energy expenditure of the body is broken down into two parts :

  • The operating expense is the sum of all expenses related to muscle activity, thermoregulation and ADS.
  • background expense is energy expenditure remaining, when cancels the operating expenditure.

The bottom expense :

The physiological significance of the background expenditure corresponds to the energy cost of organ function, who constantly remains active under basal conditions (heart, respiratory muscles, rein …) this expense is related to the maintenance of the major functions required for 1 life.

basal metabolism : M.B.

BMR is defined as energy expenditure assessed kcql / H / m2 or W / m2, measured in basal conditions, that is to say :

  • Young : hypoproteic the last meal should be taken at least 12 hours before àl6h.
  • The muscular and mental rest from 30 min supine, under conditions of semi-darkness, and absence of sound stimuli.
  • thermal neutrality : absence of control against hot and cold, This corresponds to 26 ° if the subject is exposed to 21 ° if the subject is slightly Yetu.


Expenditure third base / body surface area at baseline
(with an empty stomach, strict rest, T ° thermoneutral)
• Normal :
45-50 watts/ m2

• physiological changes in basic metabolism :

  • Sex : < in women
  • Race, weather: < Asian or hot climates
  • Age :
  • Birth : 40w/m2
  • 60-65 w/m2 at 6 years
  • 50 w/m2 at 25 years
  • Stable and adulthood 40-50 w/m2 towards 70-80 years

• basic pathological changes in metabolism :

  • Fever
  • Hypothyroidism (myxoedème)
  • hyperthyroidism


It must provide daily :

  • Energy.
  • S & rsquo; water.
  • minerals.
  • Vitamins.

Sufficient, for the functioning of the body, the development of the individual (period of growth, pregnancy).

The power of a subject can vary quantitatively or qualitatively, a balance is essential, the weight of which the measurement is simple, is a food control conditions.

WEIGHT : ideal weight is the lowest mortality and morbidity.

It is calculated by the formula of QUETELET which calculates the body mass index (IMG).

IMC (kg/m2) = Mass / size2

Coverage of energy requirements :

The daily calorie intake offsets the energy costs of basal metabolism and those related to the activity of the subject.

The daily calorie intake includes ration maintains, more caloric supplement (C S) or work ration, whose value depends on the activity of the subject (professional, sports, period of growth).

The ration maintains :

  • Man = 2000 to 2200kcal / 24.
  • Women = 1600 in 1800kca / 24h.

Caloric supplement (S C) : depends on the professional activity or sport Topic.

EX :

  • Working with light physical activity S C 500kcal / 24h.
  • Working with strenuous activity O C. is 1500kcal / 24.
  • Working in extreme conditions (in mines or in cold weather conditions) S C can reach 4000kcal / 24h.

Law of isodynamie :

Carbohydrates, lipids and proteins are interchangeable for energy needs, it is the food isodynamie.

The isodynamie has limits :

The intake of essential amino acids and maintenance of nitrogen balance is a necessity.

Lipids can not be eliminated from the diet as they provide essential fatty acids.


protein :

These are food manufacturers, they provide the necessary amino acids., to the synthesis of endogenous proteins, and are energy substrates.

Contribution of essential amino acids :

Are not synthesized by the body, must be provided by food.

  • L’isoleucine.
  • lysine.
  • methionine.
  • phenylalanine.
  • the thréonine.
  • tryptophan.
  • the valine.

Lipids :

Lipids are energy foods, they provide the essential fatty acids linoleic acid, arachidonic acid, indispensable and allow the absorption of fat soluble vitamins A, D, E, and K.

Carbohydrates :

Provide energy.

represent 50% at 55% food ration.

Stored in the liver and muscle (glycogen).

The sugars slowly digested, and rapid digestion.

vitamins :

Essential for life are catalysts of biochemical reactions.

  • soluble lives : The vit, vit D, etc.
  • soluble Vit : white B1, white B6, lives B12 vit C etc..

mineral balance.

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