Gluconeogenesis Overview

Some tissues, such as the brain, red blood cells (RBC), kidney medulla, lens and cornea of the eye, testes, and exercising muscle, require a continuous supply of glucose as a metabolic fuel. Liver glycogen, an essential postprandial source of glucose, can meet these needs for <24 hours in the absence of dietary intake of carbohydrate .

During a prolonged fast, however, hepatic glycogen stores are depleted, and glucose is made from noncarbohydrate precursors. The formation of glucose does not occur by a simple reversal of glycolysis, because the overall equilibrium of glycolysis strongly favors pyruvate formation (that is, the change in standard free energy [ΔG⁰] is negative). Instead, glucose is synthesized de novo by a special pathway, gluconeogenesis, which requires both mitochondrial and cytosolic enzymes. [Note: Deficiencies of gluconeogenic enzymes cause hypoglycemia.] During an overnight fast, ~90% of gluconeogenesis occurs in the liver, with the remaining ~10% occurring in the kidneys. However, during prolonged fasting, the kidneys become major glucoseproducing organs, contributing ~40% of the total glucose production. [Note: The small intestine can also make glucose.] Figure 1 shows the relationship of gluconeogenesis to other essential pathways of energy metabolism.

Figure 1: Gluconeogenesis shown as one of the essential pathways of energy metabolism. The numbered reactions are unique to gluconeogenesis. P = phosphate; CO2 = carbon dioxide.

مواضيع ذات صلة

آلية عمل المجموعة الأولى من الهرمونات

الهرمونات وآليات الاستتباب

تدرك (تقويض) الهرمونات وتعطيلها

نقل الهرمونات في البلازما

تغاير خزن الهرمونات وإفرازها

تخليق POMC ومعالجته

The Amino Acids

Absorption & Transport of Transition Metals

Physiologic Roles of The Essential Transition Metals

تخليق الأنجيوتنسين

تخلیق PTH

تخليق الأنسولين