What is Glycaemia?

Example 32.3 (A day of glycaemia)

Breakfast at 8: glycaemia rises from $0.9$ to $1.3\,\mathrm{g}/\mathrm{L}$ by 9 and is back at $1.0$ by 10, the excess having gone into liver and muscle glycogen. From 10 to 13 the liver releases glycogen and the level holds near $0.9$. A run at 17 draws $60\,\mathrm{g}$ into the muscles in an hour; the liver empties half its store to keep pace, and the level dips to $0.8$. Overnight, the liver makes new glucose from amino acids, and at 7 the level is $0.9\,\mathrm{g}/\mathrm{L}$. Three hundred grams have passed through a pool of five.

Example 32.5 (The loop in action)

After a meal the glycaemia climbs; within minutes the $\beta$ cells release insulin, the muscles and fat cells open their glucose transporters, the liver switches to making glycogen, and the level falls back — at which point insulin secretion falls too. Between meals the drift downward is met by glucagon, glycogen is broken down, and the level holds. Neither hormone is ever absent; their ratio moves, and the glycaemia follows it within a narrow band.

Example 32.8 (Managing a day with type 1)

A teenager with type 1 measures her glycaemia before each meal with a drop of blood, counts the carbohydrate on her plate, and injects a dose of fast insulin proportional to it — about one unit per $10\,\mathrm{g}$ — plus a slow insulin once a day for the background. Too much insulin, or a missed meal, and the level falls below $0.6\,\mathrm{g}/\mathrm{L}$: sweating, trembling, confusion, corrected by sugar in minutes. Too little, and the level stays above $2\,\mathrm{g}/\mathrm{L}$ with thirst and fatigue, and the vessels take the damage silently. She is doing, by hand, what her $\beta$ cells did by feedback.