Which metabolic pathway is activated in the liver during prolonged fasting to create glucose from non-carbohydrate sources like amino acids?

Appeared in: RML 2023

Explanation

Gluconeogenesis is the metabolic process of synthesizing glucose from non-carbohydrate precursors.
This pathway is crucial for maintaining blood glucose levels during periods of prolonged fasting, starvation, or intense exercise, after glycogen stores are depleted.
The primary substrates for gluconeogenesis are lactate, glycerol (from fats), and glucogenic amino acids (from proteins), as mentioned in the question.
It occurs mainly in the liver, which then releases the newly synthesized glucose into the bloodstream for use by the brain, red blood cells, and other tissues.

Option A: Glycogenesis is the process of storing excess glucose by converting it into glycogen. This is an anabolic pathway that is active in the fed state when blood glucose levels are high.
Option B: Glycolysis is the catabolic pathway that breaks down glucose to produce ATP (energy) and pyruvate. It consumes glucose rather than creating it.
Option D: Glycogenolysis is the breakdown of stored glycogen to release glucose. While it does produce glucose during fasting, it is the primary source in the early stages. The question specifies prolonged fasting and the use of non-carbohydrate sources, which is the specific role of gluconeogenesis after glycogen is depleted.

Clinical Relevance

Nursing practice connection: Knowing Carbohydrate metabolism pathways in the liver helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Understanding gluconeogenesis is vital for nurses managing patients with diabetes, as excessive gluconeogenesis, stimulated by low insulin and high glucagon, contributes to hyperglycemia.
In patients who are NPO (nothing by mouth) for extended periods before surgery, the body relies first on glycogenolysis and then on gluconeogenesis to maintain essential blood glucose levels for brain function.
What if? If the patient had just eaten a large meal, the dominant pathway would be Glycogenesis, stimulated by insulin to store excess glucose as glycogen, not Gluconeogenesis.

How to Approach the Question

First, identify the key terms in the question: 'prolonged fasting,' 'create glucose,' and 'non-carbohydrate sources.'
Break down the prefixes and suffixes of the options. 'Gluco' or 'Glyco' refers to glucose/glycogen. 'Neo' means new. 'Genesis' means creation. 'Lysis' means breakdown.
Analyze the options based on these meanings:
Glyco-genesis = Glycogen creation.
Glyco-lysis = Glucose breakdown.
Gluco-neo-genesis = New glucose creation.

Concept Tested & Keywords

Concept Tested: Carbohydrate metabolism pathways in the liver
Stem keywords: metabolic pathway, liver, prolonged fasting, create glucose, non-carbohydrate sources, amino acids
Lead-in keywords: Which
Clinical cues: The phrase 'prolonged fasting' is a key clinical cue, as it distinguishes the required pathway from those active in the fed state or early fasting.
Clinical cues: The mention of 'non-carbohydrate sources' specifically points away from pathways that use glucose or glycogen directly.

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E6 Harper's Illustrated Biochemistry2023 (pp 26-793 of 813) p. 165-167

E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 1 (pp 26-370 of 370) p. 155-157

E6 Biochemistry U Satyanarayana— Part 1 (pp 26-420 of 840) p. 251-253

Practise the full RML 2023

Attempt every question from this paper in a timed mock, then review the full solution for each one.