Pathophysiology Normal blood glucose is regulated very narrowly, usually from 80-90 mg/dL (4.4-5 mmol/L). Glucose levels increase transiently after meals to 120-140 mg/dL (6.6-7.7 mmol/L). Feedback systems return the glucose concentration rapidly back to the preprandial level, usually within 2 hours after the last absorption of carbohydrates. Insulin and glucagon are the important hormones in the immediate feedback control system of glucose. When blood glucose increases after a meal, the rate of insulin secretion increases and stimulates the liver to store glucose as glycogen. When cells (primarily liver and muscle) are saturated with glycogen, additional glucose is stored as fat. When blood glucose levels fall, glucagon secretion functions to increase blood glucose levels by stimulating the liver to undergo glycogenolysis and release glucose back into the blood. In starvation, the liver maintains the glucose level via gluconeogenesis. Gluconeogenesis is the formation of glucose from amino acids and the glycerol portion of fat. Muscle provides a store of glycogen and muscle protein breaks down to amino acids, which are substrates utilized in gluconeogenesis in the liver. Circulating fatty acids are catabolized to ketones, acetoacetate, and B-hydroxybutyrate and can be used as auxiliary fuel by most tissues, including the brain. The hypothalamus stimulates the sympathetic nervous system, and epinephrine is secreted by the adrenals causing the further release of glucose from the liver. Over a period of hours to days of prolonged hypoglycemia, growth hormone and cortisol are secreted and decrease the rate of glucose utilization by most cells of the body. In the newborn, serum glucose levels decline after birth until age 1-3 hours, then they spontaneously increase. Liver glycogen stores become rapidly depleted within hours of birth, and gluconeogenesis, primarily from alanine, can account for 10% of glucose turnover in the newborn infant by several hours of...