1. MLAB 2401: Clinical Chemistry Keri Brophy-Martinez
Carbohydrate Overview

2. Introduction
Organisms rely on the oxidation of complex organic compounds to obtain energy
Three general types of compounds provide chemical energy to our cells
Lipids=Fats
Amino acids = Proteins
Carbohydrates= Sugars, starches

3. Carbohydrates Major food source & energy supply of body
Primary source of energy for brain, erythrocytes, retinal cells
Depending on individual diet, 50-90% of the body's carbohydrate intake is in the form of
Grains - cereals, bread
Starchy vegetables - potatoes
Legumes - beans, peanuts
other sources = sugar, molasses, lactose from milk, fructose from fruit
Stored primarily as liver and muscle glycogen

4. Description and Classification of Carbohydrates
Contain C, H and O molecules
Contain a C=O (ketone) and an –OH(aldehyde) functional group
Classification
Based on certain properties
The size of the base carbon chain
Location of the CO functional group
Number of sugar units
Stereochemistry of compound

5. Chemical Properties
Some ( not all ) carbs are reducing substances (donate electrons)
Chemical reduction of other substances
These sugars must contain an aldehyde or ketone group
Reducing sugars
Glucose
Maltose
Lactose
Fructose
Galactose
Sucrose is not a reducing substance

6. Carbohydrate Metabolism
Glucose is primary energy source
Nervous tissue can not concentrate or store carbohydrates, so a steady supply of glucose is needed
Once the level of glucose falls below a certain range, normal function is impaired

7. Carbohydrate Breakdown
Dietary Carbohydrates
Mouth
Salivary amylase
Dextrins/ Maltose
Stomach/Intestines
Pancreatic amylase
Monosaccharide
Absorption into intestinal mucosa
Delivered to liver

8. Carbohydrate Breakdown
Ultimate Goal
Convert glucose to CO2 and water with ATP as a by-product
Possible channels
Converted to liver glycogen and stored
Metabolized to CO2 and H2O
Converted to keto-acids, amino acids, and proteins
Converted to fats and stored in adipose tissue

9. Biochemical Pathways in Carbohydrate Breakdown
Embden-Meyerhoff pathway
Converts glucose to pyruvate/lactate
Primary energy source for humans
Hexose monophosphate shunt
Oxidizes glucose to ribose and CO2
Produces NADPH as an energy source
Glycogenesis
Converts glucose to glycogen

10. Carbohydrate Metabolism
Glycolysis – the conversion of glucose and other hexoses into lactate or pyruvate
Breakdown of glucose for energy production
Glycogenesis – the conversion of glucose to glycogen
usually in liver & muscle
Excess glucose is converted and stored as glycogen
High concentrations of glycogen in liver and skeletal muscle
Glycogen is a quickly accessible storage form of glucose

11. Carbohydrate Metabolism
Glycogenolysis – the breakdown of glycogen to form glucose
Glycogenolysis occurs when plasma glucose is decreased
Occurs quickly if additional glucose is needed
Controlled by hormones & enzymes
Gluconeogenesis – the formation of glucose from non-carbohydrate sources, such as amino acids, glycerol & fatty acids into glucose
Occurs mainly in the liver

12. Glycolysis
Glycogenolysis
Gluconeogenesis
Glucose
Glycogenesis

13. Carbohydrate Metabolism
Also related:
Lipogenesis – the conversion of carbohydrates to fatty acids
Fat is another energy storage form, but not as quickly accessible as glycogen
Lipolysis – the decomposition of fat
The sum or net of all of these processes determines the level of blood glucose.

14. Regulation of Plasma Glucose
Organs / systems involved in glucose regulation
Liver : Glucose Glycogen Glucose
Muscle
Skeletal & heart
Pancreas
Synthesizes hormones Insulin and Glucagon, somatostatin
Other Endocrine glands
Anterior pituitary gland ( growth hormone)
Adrenal gland (epinephrine and cortisol)
Thyroid gland (thyroxine)

15. Regulation of Plasma Glucose
If plasma glucose is decreased :
Glycogenolysis
The liver releases glucose into the plasma (quick response)
Gluconeogenesis and lipolysis
If plasma glucose is increased :
Glycogenesis
Liver stores glucose as glycogen
Lipogenesis
Formation of lipids

16. Hormones that Regulate Glucose
Insulin
Most important & only one to decrease glucose level
Synthesized in the Beta cells of the Islets of Langerhans (in the pancreas)
Released when plasma glucose is increased

17. Action / Effects of insulin
Facilitates glucose entry into cells
cell membranes need insulin to be present for glucose to enter
Promotes liver glycogenesis
glucose to glycogen
Promotes glycolysis
speeds up utilization of glucose in cells
Promotes synthesis of lipids from glucose
Such as the formation of Triglycerides
Promotes amino acid synthesis from glucose intermediates
Decreases / inhibits glycogenolysis and gluconeogenesis

18. Insulin Control Insulin secretion controlled by: Blood glucose level
Certain Amino Acids ie. leucine, & arginine

19. Counterregulatory Hormones
Glucagon
2nd most important glucose regulatory hormone
Referred to as a hyperglycemic agent
Synthesized in alpha cells of the islets of Langerhans

20. Action/Effect of Glucagon
Stimuli – decreased plasma glucose
Action
Increases glycogenolysis & gluconeogenesis
Promotes breakdown of fatty acids
Promotes breakdown of proteins to form amino acids
Increases plasma glucose concentration

21. Other Regulatory Hormones
Epinephrine
One of two glucose regulating hormones from the adrenal gland
Origin – adrenal medulla
Action/effect
Inhibits insulin secretion & release
Promotes lipolysis
Stimulates glycogenolysis
Immediate release of glucose
Stimuli
Neurogenic - based on physical / emotional stress.
Adrenal tumors

22. Other Regulatory Hormones
Glucocorticoids - such as cortisol
Origin – adrenal cortex
Effect – antagonistic to insulin
increases blood glucose
promotes gluconeogenesis from breakdown of proteins
inhibits the entry of glucose into muscle cells
Stimuli – anterior pituitary’s ACTH

23. Other Regulatory Hormones
Growth Hormone (GH) and Adrenocorticotropic Hormone (ACTH)
Origin – anterior pituitary gland
Effect – antagonistic to insulin
Increases plasma glucose levels
inhibits insulin secretion
inhibits entry of glucose into muscle cells
inhibits glycolysis
inhibits formation of triglycerides from glucose
Stimuli
decreased glucose stimulates its release
increased glucose inhibits its release

24. Other Regulatory Hormones
Thyroid hormones (such as thyroxine)
Origin – thyroid gland
Effect
increases absorption of glucose from intestines
Promotes comversion of liver glycogen to glucose
Stimuli – pituitary gland’s TSH

25. Other Regulatory Hormones
Somatostatin
Origin-Delta cells of the islets of Langerhans in the pancreas
Effect - increase plasma glucose
Actions
antagonistic to insulin,
inhibits endocrine hormones including glucagon & growth hormone

26. References
Bishop, M., Fody, E., & Schoeff, l. (2010). Clinical Chemistry: Techniques, principles, Correlations. Baltimore: Wolters Kluwer Lippincott Williams & Wilkins.
Sunheimer, R., & Graves, L. (2010). Clinical Laboratory Chemistry. Upper Saddle River: Pearson .