Malnutrition: Fasting and Starvation PDF

III. MALNUTRITION Fasting and Starvation Hepatic gluconeogenesis occurs at expense of protein degradation in muscle and triglyceride degradation in adipose tissue. The synthesis of glucose from alanine in liver is closely li...

III. MALNUTRITION Fasting and Starvation Hepatic gluconeogenesis occurs at expense of protein degradation in muscle and triglyceride degradation in adipose tissue. The synthesis of glucose from alanine in liver is closely linked to the urea cycle. Hepatic ketogenesis occurs at expense of the fatty acids released from triglyceride degradation in adipose tissue. protein aa glutamine glutamate pyruvate glucose a-ketoglutarate gluconeogenesis alanine alanine glutaminolysis glutaminolysis urea glucose ketone CO2, H2O glycerol-P glycerol-P bodies lipolysis fatty acids acetyl-CoA ketone fatty acids ketogenesis bodies 27  III. MALNUTRITION Starvation The breakdown of fatty acids via -oxidation to acetyl-CoA is followed by the entrance of the latter into the tricarboxylic acid cycle, where it is oxidized to CO2. This is dependent upon the presence of oxaloacetate, the acceptor of acetyl-CoA, which condenses with acetyl-CoA to form citrate. During starvation, metabolism shifts to provide fuel for the brain, i.e, hepatic glucose metabolism glucose is shifted towards gluconeogenesis making oxaloacetate unavailable to condense with acetyl-CoA. The concentration of acetyl CoA increases and its fate is diverted to the formation of ketone bodies. BALANCED DIET STARVATION / DIABETES glucose gluconeogenesis fatty acyl-CoA fatty acyl-CoA acetyl-CoA acetyl-CoA ketone bodies oxaloacetate citrate || citrate oxaloace tate malate isocitrate malate isocitrate fumarate fumarate succinate succinyl-CoA succinate succinyl-CoA 28  III. MALNUTRITION Starvation Starvation leads to a syndrome known as marasmus, which is not restricted to a particular age group but is common in children under 1 year of age in developing countries. In marasmus, fat is mobilized as an energy source to the liver for ketogenesis. Muscle temporarily provides amino acids (glutaminolysis) to the liver for the synthesis of glucose (gluconeogenesis). Glucose and ketone bodies are metabolized by brain. Ultimately, energy and protein reserves are exhausted, and the child starves to death. Adults can suffer marasmus as a result of diseases that prevent swallowing (cancer of the throat or esophagus) or interfere with access to food (dementia or stroke). ketogenesis TG fatty acids fatty acids ketone bodies ketone bodies glucose CO2 + H2O glutaminolysis gluconeogenesis Proteins amino amino glucose acids acids urea 29