Integration of tissue metabolism


I- Introduction :

In living systems of many metabolic pathways operate simultaneously. Each of & rsquo; they must be able to detect & rsquo; state other to function optimally and meet the needs & rsquo; an organization. Quels sont les principes de buse d’intégration du métabolisme tissulaire ?

II- Interconnection of metabolic pathways :

The catabolism of basic strategy is to create the & rsquo; ATP, reducing power and basic modules for biosynthesis.

  • L & rsquo; ATP is & rsquo; universal energy unit. The potential binding ATP phosphoryl group transfer allows the latter island was used as a source of energy in muscle contraction, active transport, l & rsquo; signal amplification and biosynthesis.
  • ATP is produced by the oxidation of energy molecules such as glucose, fatty acids and aminoacidcs. L & rsquo; common intermediate in most of these oxidations is acetyl CoA which is completely oxidized to CO2 through the cycle of citric acid with concomitant formation of NADH and FADH2. These

last transfer their electrons to the respiratory chain to form ATP.

• The NADPH is the main donor of & rsquo; electrons in reducing biosynthesis.

The pentose phosphate supplies most of the required NADPH.

  • Biomolecules are constructed from a relatively small group of elementary modules.
  • The ways of biosynthesis and degradation are almost always separate. This separation allows the biosynthesis pathways and degradation to be thermodynamically favorable at all times. The separation of biosynthetic pathways and degradation pathways contributes greatly to the efficiency of metabolic control.

1- repeating units of metabolic regulation :

The anabolism and. catabolism must be coordinated precisely. The metabolism is controlled in different ways :

– Interactions allostériques : Enzymes which catalyze the metabolic pathway engaging steps are regulated allostériquemcnt (case of acetyl CoA carboxylase in the synthesis of fatty acids). These interactions enable them to adjust their actjvité based on detected signals.

– covalent modification : Some regulatory enzymes are controlled by covalent modification (exemple phosphorylation), in addition to their allosteric interactions.

– Rate of enzyme

– Compartment lion.

– metabolic specialization of organs.

Opposite paths such gluconeogenesis and glycolysis are subject to reciprocal regulation in such a way that & rsquo; usually a channel is quiescent when the & rsquo; another is very active.

2- essential metabolic pathways :

Glycolyse : cytosolic pathway, converts glucose molecule into two molecules of pyruvate with concomitant production of both ATP and two molecules of NADH.

Citric acid cycle and oxidative phosphorylation.

Pentose phosphate pathway.


Synthesis and breakdown of glycogen.

Synthesis and degradation of fatty acids.

3- metabolic crossroads :

There are three key intersections : le glucose 6-phosphate, pyruvate and acetylCoA.

For metabolic glucose 6-phosphate
Key for metabolic pyruvate and acetyl CoA

III- Metabolic profile of the various bodies :

Cellular energy requirements vary d & rsquo; s fabric it & rsquo; other.

A- The brain :

Glucose is virtually the only energy molecule of the human brain, it is glueo- dependent. It has no energy reserves .11 consumes about I20g / day . which corresponds to 60% of glucose consumption by the & rsquo; & rsquo whole; body to the idle state.

Glucose is brought to brain cells by the carrier non-insuliiio depetulant glucose GLUT3.

Los fasting, eétoniques the body partially replace glucose as an energy source.

B- The muscle :

The main energy molecules muscle are glucose, fatty acids and cétoiliques body. This is the link storage 3/4 glycogen body.

In postprandial, muscles use d & rsquo; first glucose d & rsquo; foodborne.

Resting, Ucides fats are the main source of energy that satisfies 85% energy needs.

During a high intensity exercise of short duration, they only use glucose. The

speed read glycolysis far exceeds that of the cycle of citric acid and most of the lactate pyruvate is reduced as it passes through the liver where it is converted to glucose (de Cori cycle).

When "read young, they use ketone bodies, or amino acids. sparing glucose for the "from" dependent luco (Red cells, white blood cells, the renal medulla, the retina….).

C- the myocardium :

Unlike the skeletal muscle, myocardium works almost exclusively aerobically. \”having no glycogen stores, fatty acids are the main source of & rsquo; energy more ketone bodies, lactate but lesser degree glucose.

D- Adipose tissue :

Triglycerides banked in adipose tissue is a huge reservoir of metabolic energy. These are essentially made to the fat cells by VLDL synthesized a liver.

In postprandial, adipose tissue uses first the foodborne glucose. If not, it consumes preferably fatty acids.

E- Liver :

The metabolic activities "read liver are essential for the supply of energy to the brain, muscle and other peripheral organs. It can quickly mobilize glycogen and gluconeogenesis perform to satisfy their "glucose needs.

It plays a central role in the regulation of lipid metabolism. When energy is abundant fatty acids are synthesized, esterified, then directed to adipose tissue. In the fasting state, however, fatty acids are converted into ketones by the liver.

In postprandial. liver first uses the dietary glucose, otherwise it consumes "the preference fatty acids but also -cétoacidcs derived from the degradation of amino acids.

IV- Energy reserves :

The quality and energy reserves vary from one fabric to another.

A- the glucose :

  • Glucose is stored as glycogen in the liver (I50g) and muscle (300g).
  • The carbohydrate energy reserves, as glycogen is very limited: energy independence liver glycogen is 24.

B- Fatty acids :

  • Fatty acids are stored as triglycerides in the liver and especially in adipose tissue (more than 10% body weight).
  • The lipid energy reserves are almost unlimited.

C- Amino arid :

  • Muscle proteins are not. d & rsquo; a point of energy sweats, an amino acid stock : they are assigned to contraction.
  • However, during prolonged fasting, muscle proteolysis produces amino acids that are used for energy purposes.

V- The metabolism depending on the power-fasting cycle and muscle activity :

There are three particular situations :

The postprandial : Those are the 4 hours after having a meal

  • The period of young
  • The muscle activity period.

All metabolic adaptations aim to maintain glucose homeostasis, that is to say a constant blood glucose. In the last two situations, Glucose is commonly used glucose-dependent tissues while other energy fuels (fatty acids and ketone bodies) are offered to- tissues less demanding as to the nature of the energy substrate.

In times post. prandial

Following In taking a meal, the glucose, amino acids and fatty acids are transported from the intestine to the blood. This leads through the & rsquo; increasing the insulin / glucagon ratio (l & rsquo; Insulin is secreted by the P cells of pancreatic islets l.angherans endocrine in response to the & rsquo; increased blood sugar, glucagon by Ct cells in response to the decrease in blood glucose) :

  • Using glucose as the energy substrate for most fabrics.
  • The start of anabolismes (reserve development of energy molecules) :
  • glycogen synthesis in the liver cl muscles (from glucose and gluconeogenic amino acids.
  • lipogenesis in the liver and adipose tissue (from glucose and amino acids).
  • protein synthesis.

In times of young :

blood glucose level begins to decrease several hours after a meal, which leads to decreased secretion of the island & rsquo; insulin and increased glucagon secretion (decrease in the insulin / glucagon ratio) that signals the & rsquo; fasting state.

The normal blood glucose level is with inniiilcnii :

  • in hepatic glycogenolysis.
  • in hepatic gluconeogenesis (in particular from glycerol).
  • to In adipose tissue lipolysis.

When fasting is prolonged (beyond one day) glycogenolysis runs out, lack of glycogen, lipolysis of the adipose tissue is amplified, as hepatic gluconeogenesis from glycerol and amino acids produced by muscle proteolysis triggered by cortisol.

Ketogenesis starts from lipolytic fatty acids. Ketone bodies covering a growing part of the brain's energy needs, especially muscle and myocardium.

In times of & rsquo; muscle activity :

Metabolic adaptation is triggered by adrenaline (secreted by the adrenal medulla) and noradrenaline (the nerve endings of the sympathetic system) secreted in response to the decrease in blood glucose.

– Muscle activity of high intensity and short duration (Sprinter)

  • Muscles do not consume glucose anaerobic glycogenolysis after their own and that of the liver.
  • Hepatic gluconeogenesis converts lactate from muscle glycolysis to glucose reassigned to the muscle (cycle of lactate-pyruvate Cori).

– Muscle activity of moderate intensity and long duration (marathoner)
Muscles consume aerobically :

  • Glucose derived from their own glycogenolysis.
  • The fatty acids of lipolytic origin.
  • Amino acids proteolysis triggered by cortisol. Alanine is released from muscle substrate hepatic gluconeogenesis (cycle alanine-pyruvate de Felig).

Course of Pr S.A. HAMMA – Faculty of Constantine