NFS311-Starvation - An Overview of Starvation During...

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An Overview of Starvation: During starvation or prolonged fasting state, the glycogen storage is used up and the level of insulin in the circulation is low and the level of glucagon is very high. The main means of energy production is lipolysis. Glycerol goes to gluconeogenesis and fatty acids enter TCA cycle via acetyl CoA to produce energy. Proteolysis provides alanine which also enters gluconeogenesis. Lactate produced from pyruvate enters gluconeogenesis pathway too. Too much Acetyl CoA produces ketone bodies which you can detect in the urine exam. Brain starts to use ketone bodies as source of energy. Starvation In-Depth: (excellent reference) I. The well-fed, or postabsorptive, state. After we consume and digest an evening meal, glucose and amino acids are transported from the intestine to the blood. The dietary lipids are packaged into chylomicrons and transported to the blood by the lymphatic system. This fed condition leads to the secretion of insulin, which is one of the two most important regulators of fuel metabolism, the other regulator being glucagon . The secretion of the hormone insulin by the β cells of the pancreas is stimulated by glucose and the parasympathetic nervous system. In essence, i nsulin signals the fed state—it stimulates the storage of fuels and the synthesis of proteins in a variety of ways . For instance, insulin initiates protein kinase cascades—it stimulates glycogen synthesis in both muscle and the liver and suppresses gluconeogenesis by the liver. Insulin also accelerates glycolysis in the liver, which in turn increases the synthesis of fatty acids. The liver helps to limit the amount of glucose in the blood during times of plenty by storing it as glycogen so as to be able to release glucose in times of scarcity . How is the excess blood glucose present after a meal removed?
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Insulin accelerates the uptake of blood glucose into the liver by GLUT2. The level of glucose 6-phosphate in the liver rises because only then do the catalytic sites of glucokinase become filled with glucose. Recall that glucokinase is active only when blood-glucose levels are high. Consequently, the liver forms glucose 6-phosphate more rapidly as the blood-glucose level rises. The increase in glucose 6-phosphate coupled with insulin action leads to a buildup of glycogen stores. The hormonal effects on glycogen synthesis and storage are reinforced by a direct action of glucose itself. Phosphorylase a is a glucose sensor in addition to being the enzyme that cleaves glycogen. When the glucose level is high, the binding of glucose to phosphorylase a renders the enzyme susceptible to the action of a phosphatase that converts it into phosphorylase b, which does not readily degrade glycogen. Thus, glucose allosterically shifts the glycogen system from a degradative to a synthetic mode.
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NFS311-Starvation - An Overview of Starvation During...

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