Carbohydrates

• Carbohydrates


  Hydrates of aldehyde or ketone derivatives based on the location of the CO functional group
• The presence of a double bond and a negative charge in the enol anion makes glucose an active reducing substance
• Functions of carbohydrates


  • Energy
  • Sparing body protein
  • Preventing ketosis
• Types of carbohydrates


  • Simple carbohydrates (monosaccharides, disaccharides)
  • Complex carbohydrates (polysaccharides)
• Monosaccharides

  • Glucose
  • Fructose
  • Galactose
• Disaccharides


  • Maltose
  • Lactose
  • Sucrose
• Three fates of glucose at the liver

  1. Energy

  2. Storage as glycogen

  3. Released to blood

  
• Pancreas


  • Functions as both an endocrine and exocrine organ in the control of carbohydrates metabolism
  • Produces and secretes amylase (exocrine)
  • Secretes insulin, glucagon and somatostatin (endocrine)
• Glycolysis


  Breakdown of carbohydrates (glucose-phosphate derivatives produces pyruvic or lactic acid and the energy stored of phosphate bond of the ATP)
• Gluconeogenesis


  Formation of glucose from other than carbohydrates

  
• Lipolysis


  Formation of glucose from fats

  
• Lipogenesis


  Conversion of carbohydrates to fats
• Glycogenolysis


  Stimulating the breakdown of glycogen
• Glycogenesis


  Conversion of glucose to glycogen

  
• Hormones


  • Insulin
  • Glucagon
  • Somatostatin
  • Cortisol and corticosteroids
  • Catecholamines
  • Growth hormone
  • Thyroid hormones
  • Adrenocorticotropic hormone
• Insulin


  Synthesized by the B-cells of the islets of Langerhans in the pancreas, only hormone that decreases glucose levels

  
• Glucagon


  Synthesized by the A-cells of the islets of Langerhans in the pancreas, primary hormone responsible for increasing glucose

  
• Somatostatin


  Produced by the delta cells of the islets of Langerhans in the pancreas
• Cortisol and corticosteroids


  Secreted by the cells of the zona fasciculata and zona reticularis of the adrenal cortex, decreases intestinal entry of glucose into the cell

  
• Catecholamines


  Released from the chromaffin cells of the adrenal medulla, inhibits insulin secretion
• Growth hormone


  Secreted by the anterior pituitary gland, decreases entry of glucose into the cell

  
• Thyroid hormones


  Secreted by the thyroid gland
• Adrenocorticotropic hormone (ACTH)


  Stimulates release of cortisol from the adrenal cortex
• Clinical conditions of carbohydrate metabolism

  • Hyperglycemia
  • Hypoglycemia
  • Diabetes mellitus
• Hyperglycemia


  Increase in blood glucose levels, caused by severe infection, dehydration, pregnancy, pancreatectomy, hemochromatosis, insulin deficiency, abnormal insulin receptor
• Hypoglycemia


  Decreased glucose levels, with symptoms like tremors, palpitations, anxiety, diaphoresis, dizziness, tingling, blurred vision, confusion, behavioral changes
• Diabetes mellitus


  Group of metabolic disorders characterized by hyperglycemia resulting from defects in insulin secretion, insulin or both, leading to ketosis
• Classification of diabetes

  • Laboratory findings (increased glucose in plasma and urine, increased urine SG, ketones in serum and urine, decreased blood and urine pH, electrolyte imbalance)
• Diagnostic criteria for diabetes mellitus

  • Normal
  • Impaired
  • Diagnostic
• Gestational diabetes mellitus (GDM)


  Disorder characterized by impaired ability to metabolize carbohydrates usually caused by insulin deficiency, metabolic or hormonal changes, with onset or first recognition during pregnancy
• Diabetes insipidus


  Deficiency of ADH (vasopressin) released by the posterior pituitary gland, causing polyuria with low SG, polydipsia, polyphagia
• Samples for glucose measurement

  • RBS (Random Blood Sugar)
  • FBS (Fasting Blood Sugar)
  • 2-Hour PPBS
  • Glycated HGB/HbA1c
  • Fructosamine
  • OGTT (Oral Glucose Tolerance Test)

  
• Chemical methods for glucose measurement

  • Oxidation reduction methods (Folin Wu, Nelson-Somogyi, Neocuproine, Benedict's, Fehling's)
  • Condensation method (Ortho-toluidine)

  
• Enzymatic methods for glucose measurement

  • Glucose oxidase method (Colorimetric, Polarographic)
  • Hexokinase method

  
• Genetic defects in carbohydrate metabolism

  • Galactosemia
  • Essential fructosuria
  • Hereditary fructose intolerance
  • Fructose-1,6-biphosphate deficiency
  • Glycogen storage diseases
• Galactosemia


  Congenital deficiency of one of three enzymes involved in galactose metabolism (galactose-1-phosphate uridyl transferase, galactokinase, uridine diphosphate galactose-4-epimerase)
• Essential fructosuria


  Autosomal recessive disorder characterized by fructokinase deficiency, clinically benign condition
• Hereditary fructose intolerance


  Clinical features include irritability, lethargy, seizures and hepatomegaly
• Fructose-1,6-biphosphate deficiency


  Clinical features include hypoglycemia, lactic acidosis, convulsions and coma
• Glycogen storage diseases


  • Type 1 Von Gierke Disease
  • Type 2 Pompe's Disease
  • Type 3 Forbes cori disease
  • Type 4 Anderson's Disease
  • Type 5 Mcardle's Disease
  • Type 6 Hers' disease
  • Type 7 Taurus disease