Carbohydrate DigestionCarbohydrate Digestion

Forms of CarbohydrateForms of Carbohydrate

• Simple sugars• Starch• Glycogen• Fiber

CHO DigestionCHO Digestion

AmylaseSucraseLactaseMaltase

Carbohydrate (CHO) DigestionCarbohydrate (CHO) Digestion

Digestion of carbohydrate in the Digestion of carbohydrate in the Small IntestineSmall 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 carbohydrateGlucose is the most important carbohydrate► Glucose is the major metabolic fuel of Glucose is the major metabolic fuel of

mammals. mammals. ► Monosaccharide from diet :Monosaccharide from diet :

- Glucose- Glucose

- Fructose- Fructose

- Galactose- Galactose► Fructose and Galactose glucose at the Fructose and Galactose glucose at the

liverliver

Glucose transporters (GLUT)Glucose transporters (GLUT)

►GLUT1~5GLUT1~5

GLUT1: RBCGLUT1: RBC

GLUT4: adipose tissue, muscleGLUT4: adipose tissue, muscle

The metabolism of glucoseThe metabolism of glucose

►glycolysisglycolysis►aerobic oxidationaerobic oxidation►pentose phosphate pathwaypentose phosphate pathway►glycogen synthesis and glycogen synthesis and

catabolismcatabolism►gluconeogenesisgluconeogenesis

glycogen

Glycogenesis Glycogenolysis

Pentose phosphate pathway

Ribose, NADPH

Glycolysis lactate

H2O+CO2

aerobic oxidation

Digestion absorption

starch

Lactate, amino acids, glycerol

glucose

Gluconeo-

genesis

Galactose Metabolism

Fructose Metabolism

Blood glucose carbohydrate metabolism :Blood glucose carbohydrate metabolism :

1. Glycolysis1. Glycolysis

2. Glycogenesis2. Glycogenesis

3. HMP Shunt3. HMP Shunt

4. Oxidation of Pyruvate4. Oxidation of Pyruvate

5. Kreb’s Cycle5. Kreb’s Cycle

6. Change to lipids 6. Change to lipids Fasting blood glucose carbohydrate Fasting blood glucose carbohydrate

metabolism :metabolism :

1. Glycogenolysis1. Glycogenolysis

2. Gluconeogenesis 2. Gluconeogenesis

GlycogenGlycogen is a polymer of is a polymer of glucoseglucose residues linked byresidues linked by (1→4) glycosidic bonds, mainly(1→4) glycosidic bonds, mainly (1→6) glycosidic bonds, at (1→6) glycosidic bonds, at

branch points.branch points.

GLYCOGENESISGLYCOGENESIS

• Synthesis of Glycogen from glucoseSynthesis of Glycogen from glucose

• Occurs mainly in muscle and liver cellOccurs mainly in muscle and liver cell

• The reaction :The reaction :

• Glucose Glucose-6-PGlucose Glucose-6-P (Hexokinase / Glucokinase)(Hexokinase / Glucokinase)

• Glucose-6-P Glucose-1-PGlucose-6-P Glucose-1-P (Phosphoglucomutase)(Phosphoglucomutase)

• Glucose-1-P + UTP UDPG + Glucose-1-P + UTP UDPG + PyrophosphatePyrophosphate

(UDPG Pyrophosphorylase)(UDPG Pyrophosphorylase)

GLYCOGENESISGLYCOGENESIS

• Glycogen synthase catalyzes the formation Glycogen synthase catalyzes the formation of of αα-1,4-glucosidic linkage in glycogen -1,4-glucosidic linkage in glycogen

• Branching enzyme catalyzes the formation Branching enzyme catalyzes the formation of of αα-1,6-glucosidic linkage in glycogen-1,6-glucosidic linkage in glycogen

• Finally the branches grow by further Finally the branches grow by further additions of 1 additions of 1 →→ 4-gucosyl units and 4-gucosyl units and further branching (like tree!)further branching (like tree!)

SYNTHESIS OF GLYCOGENSYNTHESIS OF GLYCOGEN

GLYCOGENESIS AND GLYCOGENOLYSIS GLYCOGENESIS AND GLYCOGENOLYSIS PATHWAYPATHWAY

GLYCOGENOLYSIGLYCOGENOLYSISS

• The breakdown of glycogenThe breakdown of glycogen

• Glycogen phosphorylase catalyzes Glycogen phosphorylase catalyzes cleavage of the 1cleavage of the 1→4 linkages of glycogen to →4 linkages of glycogen to yield glucose-1-phosphateyield glucose-1-phosphate

• Debranching enzyme hydrolysis of the 1→6 Debranching enzyme hydrolysis of the 1→6 linkageslinkages

• The combined action of these enzymes leads to The combined action of these enzymes leads to the complete breakdown of glycogen.the complete breakdown of glycogen.

GLYCOGENOLYSISGLYCOGENOLYSIS

PhosphoglucomutasePhosphoglucomutase

• Glucose-1-P Glucose-6-PGlucose-1-P Glucose-6-P

Glucose-6-phosphataseGlucose-6-phosphatase

• Glucose-6-P GlucoseGlucose-6-P Glucose

• Glucose-6-phosphatase enzyme a Glucose-6-phosphatase enzyme a specific enzyme in liver and kidney, but specific enzyme in liver and kidney, but not in muscle not in muscle

• Glycogenolysis in liver yields glucose Glycogenolysis in liver yields glucose export to blood to increase the blood export to blood to increase the blood glucose concentrationglucose concentration

• In muscle glucose-6-P glycolysisIn muscle glucose-6-P glycolysis

Carbohydrate MetabolismCarbohydrate Metabolism GlycogenolysisGlycogenolysis ActivationActivationCarbohydrate MetabolismCarbohydrate Metabolism GlycogenolysisGlycogenolysis ActivationActivation

Physiologic -- in response to increased blood glucose Physiologic -- in response to increased blood glucose utilization during prolonged exercise.utilization during prolonged exercise.

Pathologic -- as a result of blood loss.Pathologic -- as a result of blood loss.

Acute stress (regardless of source): activates Acute stress (regardless of source): activates glycogenolysis through the action of catecholamine glycogenolysis through the action of catecholamine hormone, epinephrine (released by the adrenal medulla).hormone, epinephrine (released by the adrenal medulla).

During prolonged exercise: both glucagon and epinephrine During prolonged exercise: both glucagon and epinephrine contribute to stimulation of glycogenolysis.contribute to stimulation of glycogenolysis.

Physiologic -- in response to increased blood glucose Physiologic -- in response to increased blood glucose utilization during prolonged exercise.utilization during prolonged exercise.

Pathologic -- as a result of blood loss.Pathologic -- as a result of blood loss.

Acute stress (regardless of source): activates Acute stress (regardless of source): activates glycogenolysis through the action of catecholamine glycogenolysis through the action of catecholamine hormone, epinephrine (released by the adrenal medulla).hormone, epinephrine (released by the adrenal medulla).

During prolonged exercise: both glucagon and epinephrine During prolonged exercise: both glucagon and epinephrine contribute to stimulation of glycogenolysis.contribute to stimulation of glycogenolysis.

Glycogenolysis is activated in response to stress Glycogenolysis is activated in response to stress Glycogenolysis is activated in response to stress Glycogenolysis is activated in response to stress

InsulinInsulin Carbohydrate Carbohydrate MetabolismMetabolismHormonal regulationHormonal regulation Inhibition of Inhibition of GlycogenolysisGlycogenolysis

InsulinInsulin Carbohydrate Carbohydrate MetabolismMetabolismHormonal regulationHormonal regulation Inhibition of Inhibition of GlycogenolysisGlycogenolysis

Insulin secreted by pancreas Insulin secreted by pancreas -cells when blood [glucose] is high. -cells when blood [glucose] is high.

Synthesized as single peptide chain zymogen: proinsulin. Synthesized as single peptide chain zymogen: proinsulin.

In secretory granules, selective proteolysis releases an internal In secretory granules, selective proteolysis releases an internal peptide and a 2-chained insulin hormone. peptide and a 2-chained insulin hormone.

Insulin elicits uptake and intracellular use or storage of glucose.Insulin elicits uptake and intracellular use or storage of glucose.

Hyperglycemia results in elevated blood [insulin] associated with Hyperglycemia results in elevated blood [insulin] associated with fed state.fed state.

Hyperinsulinemia associated with “insulin resistance” and if Hyperinsulinemia associated with “insulin resistance” and if chronic can lead to diabetes type-2 and related pathologies. chronic can lead to diabetes type-2 and related pathologies.

Insulin secreted by pancreas Insulin secreted by pancreas -cells when blood [glucose] is high. -cells when blood [glucose] is high.

Synthesized as single peptide chain zymogen: proinsulin. Synthesized as single peptide chain zymogen: proinsulin.

In secretory granules, selective proteolysis releases an internal In secretory granules, selective proteolysis releases an internal peptide and a 2-chained insulin hormone. peptide and a 2-chained insulin hormone.

Insulin elicits uptake and intracellular use or storage of glucose.Insulin elicits uptake and intracellular use or storage of glucose.

Hyperglycemia results in elevated blood [insulin] associated with Hyperglycemia results in elevated blood [insulin] associated with fed state.fed state.

Hyperinsulinemia associated with “insulin resistance” and if Hyperinsulinemia associated with “insulin resistance” and if chronic can lead to diabetes type-2 and related pathologies. chronic can lead to diabetes type-2 and related pathologies.

Antagonist of glucagon, epinephrine (adrenalin), cortisol Antagonist of glucagon, epinephrine (adrenalin), cortisol Antagonist of glucagon, epinephrine (adrenalin), cortisol Antagonist of glucagon, epinephrine (adrenalin), cortisol

BLOOD GLUCOSEBLOOD 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

Good luck!! Thank youGood luck!! Thank you