Carbohydrate Digestion

Forms of Carbohydrate Simple sugars Starch Glycogen Fiber

CHO Digestion Amylase Sucrase Lactase Maltase

Carbohydrate (CHO) Digestion

Digestion of carbohydrate in the Small Intestine Pancreatic amylase is released Intestinal cells release maltase, sucrase, and lactase Maltose + maltase glucose + glucose Sucrose + sucrase glucose + fructose Lactose + lactase glucose + galactose Monosaccharides are absorbed

Disaccharides digestion

► Glucose is the most important carbohydrate ► Glucose is the major metabolic fuel of mammals. ► Monosaccharide from diet : - Glucose - Glucose - Fructose - Fructose - Galactose - Galactose ► Fructose and Galactose glucose at the liver

Glucose transporters (GLUT) ► GLUT1~5 GLUT1: RBC GLUT1: RBC GLUT4: adipose tissue, muscle GLUT4: adipose tissue, muscle

The metabolism of glucose ► glycolysis ► aerobic oxidation ► pentose phosphate pathway ► glycogen synthesis and catabolism ► gluconeogenesis

glycogen Glycogenesis Glycogenolysis Pentose phosphate pathway Ribose, NADPH Glycolysis lactate H 2 O+CO 2 aerobic oxidation Digestion absorption starch Lactate, amino acids, glycerol glucose Gluconeo- genesis

Galactose Metabolism

Fructose Metabolism

 Blood glucose carbohydrate metabolism : 1. Glycolysis 1. Glycolysis 2. Glycogenesis 2. Glycogenesis 3. HMP Shunt 3. HMP Shunt 4. Oxidation of Pyruvate 4. Oxidation of Pyruvate 5. Kreb’s Cycle 5. Kreb’s Cycle 6. Change to lipids 6. Change to lipids  Fasting blood glucose carbohydrate metabolism : 1. Glycogenolysis 1. Glycogenolysis 2. Gluconeogenesis 2. Gluconeogenesis

Glycogen is a polymer of glucose residues linked by   (1→4) glycosidic bonds, mainly   (1→6) glycosidic bonds, at branch points.

GLYCOGENESIS Synthesis of Glycogen from glucose Synthesis of Glycogen from glucose Occurs mainly in muscle and liver cell Occurs mainly in muscle and liver cell The reaction : The reaction : Glucose Glucose-6-P Glucose Glucose-6-P (Hexokinase / Glucokinase) (Hexokinase / Glucokinase) Glucose-6-P Glucose-1-P Glucose-6-P Glucose-1-P (Phosphoglucomutase) (Phosphoglucomutase) Glucose-1-P + UTP UDPG + Pyrophosphate Glucose-1-P + UTP UDPG + Pyrophosphate (UDPG Pyrophosphorylase) (UDPG Pyrophosphorylase)

GLYCOGENESIS Glycogen synthase catalyzes the formation of α- 1,4-glucosidic linkage in glycogen Glycogen synthase catalyzes the formation of α- 1,4-glucosidic linkage in glycogen Branching enzyme catalyzes the formation of α- 1,6-glucosidic linkage in glycogen Branching enzyme catalyzes the formation of α- 1,6-glucosidic linkage in glycogen Finally the branches grow by further additions of 1 → 4-gucosyl units and further branching (like tree!) Finally the branches grow by further additions of 1 → 4-gucosyl units and further branching (like tree!)

SYNTHESIS OF GLYCOGEN

GLYCOGENESIS AND GLYCOGENOLYSIS PATHWAY

GLYCOGENOLYSIS The breakdown of glycogen The breakdown of glycogen Glycogen phosphorylase catalyzes cleavage of the 1 →4 linkages of glycogen to yield glucose-1- phosphate Glycogen phosphorylase catalyzes cleavage of the 1 →4 linkages of glycogen to yield glucose-1- phosphate Debranching enzyme hydrolysis of the 1→6 linkages Debranching enzyme hydrolysis of the 1→6 linkages The combined action of these enzymes leads to the complete breakdown of glycogen. The combined action of these enzymes leads to the complete breakdown of glycogen.

GLYCOGENOLYSIS Phosphoglucomutase Phosphoglucomutase Glucose-1-P Glucose-6-P Glucose-1-P Glucose-6-P Glucose-6-phosphatase Glucose-6-phosphatase Glucose-6-P Glucose Glucose-6-P Glucose Glucose-6-phosphatase enzyme a specific enzyme in liver and kidney, but not in muscle Glucose-6-phosphatase enzyme a specific enzyme in liver and kidney, but not in muscle Glycogenolysis in liver yields glucose export to blood to increase the blood glucose concentration Glycogenolysis in liver yields glucose export to blood to increase the blood glucose concentration In muscle glucose-6-P glycolysis In muscle glucose-6-P glycolysis

Carbohydrate Metabolism Glycogenolysis Activation  Physiologic -- in response to increased blood glucose utilization during prolonged exercise.  Pathologic -- as a result of blood loss.  Acute stress (regardless of source): activates glycogenolysis through the action of catecholamine hormone, epinephrine (released by the adrenal medulla).  During prolonged exercise: both glucagon and epinephrine contribute to stimulation of glycogenolysis.  Physiologic -- in response to increased blood glucose utilization during prolonged exercise.  Pathologic -- as a result of blood loss.  Acute stress (regardless of source): activates glycogenolysis through the action of catecholamine hormone, epinephrine (released by the adrenal medulla).  During prolonged exercise: both glucagon and epinephrine contribute to stimulation of glycogenolysis. Glycogenolysis is activated in response to stress

Insulin Carbohydrate Metabolism Hormonal regulation Inhibition of Glycogenolysis  Insulin secreted by pancreas -cells when blood [glucose] is high.  Synthesized as single peptide chain zymogen: proinsulin.  In secretory granules, selective proteolysis releases an internal peptide and a 2-chained insulin hormone.  Insulin elicits uptake and intracellular use or storage of glucose.  Hyperglycemia results in elevated blood [insulin] associated with fed state.  Hyperinsulinemia associated with “insulin resistance” and if chronic can lead to diabetes type-2 and related pathologies.  Insulin secreted by pancreas -cells when blood [glucose] is high.  Synthesized as single peptide chain zymogen: proinsulin.  In secretory granules, selective proteolysis releases an internal peptide and a 2-chained insulin hormone.  Insulin elicits uptake and intracellular use or storage of glucose.  Hyperglycemia results in elevated blood [insulin] associated with fed state.  Hyperinsulinemia associated with “insulin resistance” and if chronic can lead to diabetes type-2 and related pathologies. Antagonist of glucagon, epinephrine (adrenalin), cortisol

BLOOD GLUCOSE Blood glucose is derived from: 1. Diet 2. Gluconeogenesis 3. Glycogenolysis in liver Insulin play a central role in regulating blood glucose Glucagon increase blood glucose Growth hormone inhibit insulin activity

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