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NBME 23 Answers

nbme23/Block 3/Question#3

An 18-hour-old male newborn is 61 cm (24 in) long ...

Decreased gluconeogenesis

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submitted by sajaqua1(229),

Because the baby's mother has Type 1 Diabetes mellitus, it is plausible that they had elevated blood glucose levels during or shortly before birth. Insulin does not cross the placenta, but glucose does, so during birth the neonate would have been hyperglycemic. This would lead to the neonatal pancreas releasing insulin, driving glucose into cells and turning down gluconeogenesis; this is why the baby is hypoglycemic right now.

B) Decreased glycogen concentration- I don't know the glycogen concentration compared to an adult patient, but a decrease in glycogen concentration would indicate glycogen/glucose release, which would not be a hypoglycemic state. C) Decreased glycogen synthase activity- decreased glycogen synthase activity indicates energy catabolism, and would lead to higher serum glucose levels. D) Decreased serum insulin concentration- decreased serum insulin would lead to higher levels of glucose in serum. E) Increased serum insulin-like growth factor- IGF does not bind nearly as well to insulin receptors as insulin does, and so would have to be in extremely high concentrations to have this effect. IGF is associated with somatic growth and muscle development.

yotsubato  His glycogen concentration is high, since he's been hyperglycemic with lots of insulin until birth. +3  
alexb  Also explains why he's 12 pounds. +1  
krewfoo99  Also, think of it like this: Insulin causes hypoglycemia, thus this baby must have increased insulin. It is also an anaobolic hormone which is clear by the babys weight. Insulin increases glycogen synthase activity, and causes an increase in concentrations of glycogen. Decrease in insulin would do exactly the opposite +  

my understanding of the question is that he is asking about the cause of neonatal hypoglycemia.

as you know insulin will be high prenatally due to hyperglycemia and high levels will persists.

so if you think about hypoglycemia...the normal response for the glycogen concentration is to decrease (as well as glycogen synthase) and the gluconeogenesis to increase. so a person with impaired gluconeogenesis (which is abnormal) is more likely to develop hypoglycemia