PHASES OF METABOLISM

 

INTRODUCTION: The degradation of foodstuffs occurs in three stages. 

 (1) In the first stage, digestion in the gastrointestinal tract converts the macromolecules into small units. For example, proteins are digested to amino acids. This is called primary metabolism. 

Physiologyof the gastrointestinal tract  

(2) Then these products are absorbed, catabolized to smaller components, and ultimately oxidized to CO₂. 

Carbondioxide  

(3) The reducing equivalents are mainly generated in the mitochondria by the final common oxidative pathway, citric acid cycle. Thecitric acid cycle  In this process, NADH or FADH₂ are generated. This is called secondary or intermediary metabolism. Then these reduced equivalents enter into the electron transport chain (ETC, or Respiratory chain), where energy is released. This is the tertiary metabolism or Internal respiration or cellular respiration.  

Carbohydrates enter the glycolysis pathway, converted to acetyl CoA and are oxidized in the citric acid cycle. Carbohydrate metabolism is centered on glucose, and is mainly used for provision of energy to the body. Lipid metabolism is centered on fatty acids, which are also used for provision of energy. Amino acids are mainly meant for body building purpose. However, most of the amino acids are eventually transaminated, the carbon skeletons are oxidized. This will provide some energy. But energy production is not the main purpose of amino acid metabolism.

RELATED;

1. GLYCOLYSIS  

2. THE CITRIC ACID CYCLE  

3. PROTEIN ENERGY MULNUTRITION

4.  DIGESTION OF LIPIDS

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