Integration of metabolism: fed, fasting and diabetes
Introducido| English | Significado |
|---|---|
| fed state | fed state |
| fasting state | fasting state |
| glycated haemoglobin | glycated haemoglobin |
| diabetic ketoacidosis | diabetic ketoacidosis |
| insulin resistance | insulin resistance |
One system, one switch
- Metabolism is one system with a switch. Insulin and glucagon are the lever, the organs are the gears.
- Diabetes is the switch jammed, and the most useful single case in all of medicine for seeing how the parts fit.
Fed and fasting
- In the fed state 进食状态, insulin is high: glucose enters cells, glycogen fills, and extra carbon becomes fat.
- In the fasting state 空腹状态, glucagon is high: the liver breaks down glycogen (hours), then makes glucose (days), then makes ketones as the brain adapts.
Match each state to what the liver does.
Dificultad 2/5 · 140 monedas + un pequeño bono en el primer intento de hoy
The liver is the arbiter; the hormone ratio and the time since eating decide which way it runs.
Worked example: the timeline of a fast
- 0–4 h: absorbed food is used and insulin falls. 4–12 h: liver glycogen drains. 12–24 h: the bank is nearly empty and gluconeogenesis ramps up from muscle amino acids, glycerol and lactate.
- Days 1–3: ketones rise and muscle protein is spared. By day 3 ketones give about a third of brain energy; after weeks, up to two-thirds.
Put the main glucose sources of a fast in the order they take over.
Dificultad 3/5 · 200 monedas + un pequeño bono en el primer intento de hoy
Each source covers a time window, and each handover uses a mechanism from an earlier lesson.
How one signal sets every organ
- Glucagon raises cAMP, so PKA phosphorylates key enzymes (PFK-2, glycogen synthase, phosphorylase, fat lipase). Insulin lowers cAMP and switches on phosphatases, so the same enzymes lose their phosphates.
- One signal, read by four organs, keeps them from working against each other.
How does glucagon turn on glycogen breakdown in the liver?
Dificultad 1/5 · 100 monedas + un pequeño bono en el primer intento de hoy
Glucagon → cAMP → PKA → phosphorylase on, glycogen synthase off. Insulin does the opposite, by removing those phosphates.
A three-month record
- Glucose sticks slowly to haemoglobin. Glycated haemoglobin 糖化血红蛋白 (HbA1c) builds up over the red cell's ~120-day life, so it records about three months of glucose.
- HbA1c ≥ 6.5% indicates diabetes. A glucose reading tells you about now; HbA1c tells you about the last three months.
Why does HbA1c reflect about three months of glucose?
Dificultad 1/5 · 100 monedas + un pequeño bono en el primer intento de hoy
Glucose attaches slowly and permanently to Hb, so the fraction glycated records the average glucose over the cell's life.
The brain normally uses 120 g of glucose a day. On day 3 of a fast, ketones supply a third of its energy. How many grams of glucose a day does it still need?
Dificultad 2/5 · 140 monedas + un pequeño bono en el primer intento de hoy
Two-thirds of 120 = 80 g, still supplied by gluconeogenesis, largely from muscle protein: which is why ketones that spare protein matter.
Worked example: the switch jammed off
- (Fictional patient, type 1 picture) With no insulin, cells read "fasting" even though blood glucose is high. Fat pours out, the liver floods the blood with ketones, and muscle breaks down.
- Ketones make the blood acidic, so breathing becomes deep and fast to blow off CO₂. Glucose spills into urine and drags water with it: thirst and dehydration. This is diabetic ketoacidosis 糖尿病酮症酸中毒.
In diabetic ketoacidosis, why does breathing become deep and fast?
Dificultad 1/5 · 100 monedas + un pequeño bono en el primer intento de hoy
Ketone acids lower blood pH; breathing out more CO₂ partly corrects it. Every sign follows from one switch read as "fasting".
Type 2: the switch that sticks
- In type 2 diabetes insulin is present but tissues respond poorly: insulin resistance 胰岛素抵抗.
- The same ledger moves in the same direction, but more gently, over years instead of hours, and ketoacidosis is rare.
Three common slips
- "Insulin just lowers glucose." It sets the direction of every fuel: glucose, fat and protein.
- "The brain can skip glucose." Ketones replace only part of it, and only after days.
- Mixing HbA1c with glucose. HbA1c is a three-month average; a glucose reading is minutes.
Insulin's only job is to move glucose into cells.
Dificultad 1/5 · 100 monedas + un pequeño bono en el primer intento de hoy
Insulin sets the direction of all fuels; without it fat breakdown and ketone production run unchecked, as in ketoacidosis.
Recap
- Insulin and glucagon are one lever on all organs: fed → store; fasting → glycogen, then new glucose, then ketones.
- Glucagon phosphorylates key enzymes through cAMP; insulin removes the phosphates.
- HbA1c ≥ 6.5% means diabetes; ketoacidosis is fasting metabolism running with high glucose.