Metabolism
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A hypoglycaemic adolescent with an enlarged liver and gout
Key points from this exercise:
In the fasting state muscle glycogen can be an indirect source of blood glucose as a result of anaerobic glycolysis in muscle, with the release of lactate into the bloodstream, and gluconeogenesis from this lactate in the liver.
In healthy people, injection of glucagon results in mobilisation of glucose from liver glycogen and elevation of blood glucose concentration.
Failure of glucagon injection to raise blood glucose may be due to a number of possible defects:
defective glucagon receptors
lack of glycogen phosphorylase
lack of phosphorylase kinase
lack of glucose 6-phosphatase
In healthy people, injection of adrenaline results in mobilisation of glucose from liver glycogen and elevation of blood glucose concentration, as well as increased lipase activity in adipose tissue, leading to release of non-esterified fatty acids into the bloodstream.
Failure of adrenaline injection to raise blood glucose may be due to a number of possible defects:
defective adrenaline receptors
lack of glycogen phosphorylase
lack of phosphorylase kinase
lack of glucose 6-phosphatase
Both galactose and fructose are phosphorylated by hexokinase, and galactose 6-phosphate and fructose 6-phosphate are isomerised to glucose 6-phosphate, which can normally be hydrolysed to release free glucose into the bloodstream.
Lack of glucose 6-phosphatase in liver leads to accumulation of glycogen that cannot be utilised, and hence to profound fasting hypoglycaemia, as well as persistent lactic acidosis.
Persistent lactic acidosis can lead to the development of gout, because lactate inhibits the renal clearance of uric acid.
Type I glycogen storage disease, due to lack of glucose 6-phosphatase, can be treated by feeding small frequent meals, so as to maintain a more or less constant blood concentration of glucose, without it rising so high that glycogen synthesis is activated.
See also the exercise on gout and hyperuricaemia