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Carbohydrate Digestion

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Carbohydrate Digestion * * * * * * * * * * * * * * * * * Forms of Carbohydrate Simple sugars Starch Glycogen Fiber CHO Digestion Amylase Sucrase Lactase Maltase ... – PowerPoint PPT presentation

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Title: Carbohydrate Digestion


1
Carbohydrate Digestion
2
Forms of Carbohydrate
  • Simple sugars
  • Starch
  • Glycogen
  • Fiber

3
CHO Digestion
Amylase
Sucrase
Lactase
Maltase
4
Carbohydrate (CHO) Digestion
5
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

6
Disaccharides digestion
7
  • Glucose is the most important carbohydrate
  • Glucose is the major metabolic fuel of mammals.
  • Monosaccharide from diet
  • - Glucose
  • - Fructose
  • - Galactose
  • Fructose and Galactose glucose at the
    liver

8
Glucose transporters (GLUT)
  • GLUT15
  • GLUT1 RBC
  • GLUT4 adipose tissue, muscle

9
The metabolism of glucose
  • glycolysis
  • aerobic oxidation
  • pentose phosphate pathway
  • glycogen synthesis and catabolism
  • gluconeogenesis

10
glycogen
Glycogenolysis
Glycogenesis
starch
lactate
Glycolysis
Digestion absorption
glucose
aerobic oxidation
Lactate, amino acids, glycerol
H2OCO2
Gluconeo-genesis
Pentose phosphate pathway
Ribose, NADPH
11
Galactose Metabolism
12
Fructose Metabolism
13
  • Blood glucose carbohydrate metabolism
  • 1. Glycolysis
  • 2. Glycogenesis
  • 3. HMP Shunt
  • 4. Oxidation of Pyruvate
  • 5. Krebs Cycle
  • 6. Change to lipids
  • Fasting blood glucose carbohydrate
    metabolism
  • 1. Glycogenolysis
  • 2. Gluconeogenesis

14
  • Glycogen is a polymer of glucose residues linked
    by
  • ? (1?4) glycosidic bonds, mainly
  • ? (1?6) glycosidic bonds, at branch points.

15
GLYCOGENESIS
  • Synthesis of Glycogen from glucose
  • Occurs mainly in muscle and liver cell
  • The reaction
  • Glucose Glucose-6-P
  • (Hexokinase / Glucokinase)
  • Glucose-6-P Glucose-1-P
  • (Phosphoglucomutase)
  • Glucose-1-P UTP UDPG Pyrophosphate
  • (UDPG Pyrophosphorylase)

16
GLYCOGENESIS
  • Glycogen synthase catalyzes the formation of
    a-1,4-glucosidic linkage in glycogen
  • Branching enzyme catalyzes the formation of
    a-1,6-glucosidic linkage in glycogen
  • Finally the branches grow by further
    additions of 1 ? 4-gucosyl units and further
    branching (like tree!)

17
SYNTHESIS OF GLYCOGEN
18
GLYCOGENESIS AND GLYCOGENOLYSIS PATHWAY
19
GLYCOGENOLYSIS
  • The breakdown of glycogen
  • Glycogen phosphorylase catalyzes cleavage of the
    1?4 linkages of glycogen to yield
    glucose-1-phosphate
  • Debranching enzyme hydrolysis of the 1?6 linkages
  • The combined action of these enzymes leads to the
    complete breakdown of glycogen.

20
GLYCOGENOLYSIS
  • Phosphoglucomutase
  • Glucose-1-P Glucose-6-P
  • Glucose-6-phosphatase
  • Glucose-6-P Glucose
  • 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
  • In muscle glucose-6-P glycolysis

21
Carbohydrate Metabolism Glycogenolysis Activation
Glycogenolysis is activated in response to stress
  • 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.

22
Insulin
Carbohydrate Metabolism Hormonal regulation
Inhibition of Glycogenolysis
Antagonist of glucagon, epinephrine (adrenalin),
cortisol
  • Insulin secreted by pancreas b-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.

23
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

24
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