Metabolic Integration and the Metabolic Pathways

Metabolism, Catabolism and Anabolism

            Metabolism is the product of chemical reactions that occur in a cell, which enable it to keep living, growing and dividing. Metabolic processes usually involved catabolism and anabolism. Catabolism means the process of obtaining energy and reducing power from nutrients. Anabolism is the synthesis in living organism of more complex substances from simple ones together with the storage of energy.

Homeostasis and Metabolic Integration

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Human bodies are made up of integrated and complex system of organs, each with its own requirements for nourishment and energy utilization.  Our tissues moreover share a common circulation system.  Controlling and limiting of the blood levels of ions, lipids and sugars must be sustain for a healthy situation and maintenance.  The restrictions are valid at rest, while we work and after meals.  We need to organize our bodies and survive under differing situations.  Physical activity and meals greatly affect the processes in the circulation.

Integration of metabolism has important short-term and long-term functions.  Perhaps the most crucial short-term element is the maintenance of a stable blood glucose level.  Maintenance of blood glucose levels over 2.5-3 mmol/l is essential for brain function.  One might expect, therefore, that nature had equipped us with an enough glucose reserve.    Surprisingly, the total amount of glucose in the blood and liver is limited that they can be exhausted in minutes.  The same result, a quick reduction of blood glucose levels will result to loss of consciousness which will be followed by administration of large doses of insulin (insulin-shock therapy).  The body’s metabolic balance can quickly be disturbed through excessive activity or hormonal derangement. And yet, this does not normally occur.  Physiological processes adjust carbohydrate and fat metabolism such that blood glucose values do not fall markedly.  If we have a shortage of sugar, fat metabolism takes over.  Integration of metabolism protects us against metabolic tragedies and other health problems.

Integration of Fuel Metabolism

Carbohydrates are essential component and source of energy for living cells. Glucose coming from carbohydrates provides the main source of energy. “Carbohydrate Stress” occurs when the blood glucose level fall below the normal homeostatic level that commonly occurs during fasting state. The fed state can last for about three hours after the ingestion of the meal. The post absorptive or early fasting state occurred during a time span of from 3 to 16 hours following the meal. The fasting state usually lasted up to two days without additional food intake. The starvation state on the other hand is marked by prolonged deprivation for several weeks duration. In the post absorptive state tissues no longer derive energy from ingested glucose. A metabolic shift occurs in an effort to save body protein. The fat stores become the major supplier of energy. The blood level of fatty acids increase sharply and these replace glucose as the preferred fuel of heart, liver, skeletal muscles tissue that oxidize them for energy. Survival time in starvation depends on the quantity of stored fat before starvation. When the fat reserves are gone, the degradation of essential proteins begins, leading to loss of liver and muscle function which will lead eventually to death.

Metabolic Pathways

 Metabolic pathways for carbohydrates include glycolysis (glucose oxidation in order to obtain ATP),Citric acid cycle (Krebs’ cycle) – (acetyl-CoA oxidation in order to obtain GTP and valuable intermediates) and Gluconeogenesis (glucose synthesis from smaller precursors, to be used by the brain). Metabolic pathway for lipids includes Fatty Acid b-oxidation (fatty acids breakdown into acetyl-CoA, to be used by the Krebs’ cycle). And lastly, Urea cycle (disposal of NH4+ in less toxic forms) as metabolic pathway in proteins.


“Integration and Regulation of Fuel Metabolism” (2000) Integration and Regulation of Fuel Metabolism . . Retrieved September 13, 2008, from

“Integration of Metabolism” (2008). Integration of Metabolism. Retrieved

September 13, 2008, from



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