After 5 days of fasting a man undergoes oral GTT, true is all except :
First, the core concept here is the physiological response to fasting and then glucose intake. After prolonged fasting, the body's glucose homeostasis mechanisms shift. The liver starts breaking down glycogen and then uses gluconeogenesis to maintain blood glucose. Insulin levels are low, and glucagon is high. When glucose is ingested during OGTT, the body's response would involve insulin secretion, but in a fasted state, maybe the response is delayed or altered.
Next, the correct answer would be the one that contradicts the expected physiological responses. For example, if an option states that insulin levels remain low after glucose intake, that might be incorrect because insulin should rise in response to glucose. Alternatively, if there's an option about glucagon decreasing, that's incorrect because glucagon should remain elevated after fasting.
The wrong options would be statements that align with the expected changes. For instance, increased gluconeogenesis, low insulin, high glucagon, etc. The incorrect options might mention things like normal insulin response or decreased ketogenesis, which isn't correct after fasting.
Clinical pearls: Remember that after prolonged fasting, the body relies on gluconeogenesis and ketogenesis. Insulin is low, glucagon is high. During OGTT, the body's response to glucose would trigger insulin release, but after fasting, maybe the response is blunted or delayed.
So, the correct answer (the exception) would be the one that doesn't fit. For example, if an option says "blood glucose levels rise to normal postprandial levels," that's incorrect because after fasting, the body's ability to handle glucose might be impaired, leading to higher than normal levels.
**Core Concept**
Prolonged fasting depletes glycogen stores, shifting metabolism to gluconeogenesis and ketogenesis. During oral glucose tolerance testing (OGTT), the body’s response to glucose intake reflects insulin sensitivity, glucagon regulation, and hepatic glucose handling. Post-fasting, insulin secretion may be delayed, and glucagon levels remain elevated to maintain euglycemia.
**Why the Correct Answer is Right**
After 5 days of fasting, glycogen stores are exhausted. During OGTT, ingested glucose triggers insulin release, but hepatic glucose production (HGP) persists via gluconeogenesis. Glucagon levels stay elevated to sustain glucose output. Ketogenesis continues until glucose is reintroduced. A true statement in this context would align with these metabolic shifts; the exception would contradict them (e.g., claiming normal postprandial glucose levels despite impaired insulin response).
**Why Each Wrong Option is Incorrect**
**Option A:** *If it states "insulin levels rise promptly after glucose ingestion,"* this is incorrect because fasting blunts early insulin secretion, delaying the response.
**Option B:** *If it claims "glucagon levels decrease significantly,"* this is false as glucagon remains high to promote gluconeogenesis.
**Option C:** *If it suggests "hepatic glucose production ceases,"* this is incorrect because gluconeogenesis continues post-fasting.
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