METABOLIC PROFILE OF ORGANS

 

INTRODUCTION: The metabolic pattern or metabolic profile of different organs is different depending on its function. Moreover, the organs are able to adapt to metabolic alterations in fed state and starvation. Calories are stored in the body as fat and glycogen. The approximate percentage of storage form of energy otherwise known as total fuel reserve present in a normal human body is, fat 85%, glycogen 1%, and proteins 14%. 

[glycogen] [proteins] [fats]

Fat stores are mobilized actively only on prolonged fasting, even though adipose tissue fat is undergoing turnover on a daily basis. Caloric homeostasis is maintained regardless of whether a person is well fed, fasting, or in a state of starvation. Similarly metabolic profile of various organs and tissues change to adapt to physiological and pathological states, so that caloric homeostasis is maintained unless extreme conditions set in. The reciprocal regulation of glycolysis and gluconeogenesis is the major deciding factor in the flux of metabolic intermediates through these pathways. 

[glycolysis]

Brain: First, although brain represents only 2% of adult body weight, it needs 10–20% cardiac output. About 750 ml of blood circulates through the brain per minute. Neurons can survive only a few minutes without blood supply. Occlusion of blood supply to brain causes unconsciousness within 10 seconds. Secondly, there is no stored fuel in the brain. Glucose, the preferred fuel for the brain, should be in continuous supply. Glucose can freely enter the brain cells. 

[the blood brain barrier] 

To add on, the total consumption of glucose by brain is about 120 g/day (480 kcal). Thus, about 60% of the total carbohydrate intake by the body is metabolized by the brain. Moreover, about 25% of the oxygen consumed by the adult body is due to glucose oxidation in brain. In children, this may be as high as 50% however.

Brain under conditions of anoxia: In anoxia the rate of lactate production by glycolysis rises to 5 or 8 times within one minute. 

[lactate]

Brain and acetoacetate: The brain is unable to utilize fatty acids as a source of fuel since the fatty acids complexed to albumin are unable to traverse the blood brain barrier. [blood brain barrier] 

But, brain can effectively utilize acetoacetate. This is again a survival technique in diabetic and starvation ketosis.

Brain and starvation: During starvation, a significant part (60-70%) of the energy requirement of the brain is then met by ketone bodies.

Skeletal Muscle: The skeletal muscle forms about 45% of the total weight of the body. About 0.5% muscle weight is due to glycogen content. Following a meal, the muscle glycogen content increases by about 1% of the total weight.

Muscle metabolism after a meal: The uptake and storage of glucose by the skeletal muscle is under the influence of insulin.

RELATED;

1.  Metabolism and metabolic disorders

2.  Biochemistry 

3.  Metabolism during starvation

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