CARBOHYDRATE OVERVIEW MLAB 2401: Clinical Chemistry Keri Brophy-Martinez.
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Transcript of CARBOHYDRATE OVERVIEW MLAB 2401: Clinical Chemistry Keri Brophy-Martinez.
Introduction2
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
Carbohydrates3
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
Description and Classification of Carbohydrates
Contain C, H and O moleculesContain 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
Chemical Properties5
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
Carbohydrate Metabolism
Glucose is primary energy sourceNervous 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
Carbohydrate Breakdown
Dietary
Carbohydra
tes
•Mouth•Salivar
y amylase
Dextrins/
Maltose
•Stomach/Intestines
•Pancreatic amylase
Monosaccharide
•Absorption into intestinal mucosa
•Delivered to liver
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
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
Carbohydrate Metabolism10
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
Carbohydrate Metabolism11
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
Carbohydrate Metabolism13
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.
Regulation of Plasma Glucose14
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)
Regulation of Plasma Glucose15
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
Hormones that Regulate Glucose
16
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
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
Insulin Control18
Insulin secretion controlled by: Blood glucose level Certain Amino Acids ie. leucine, & arginine
Counterregulatory Hormones 19
Glucagon 2nd most important glucose regulatory hormone
Referred to as a hyperglycemic agent
Synthesized in alpha cells of the islets of Langerhans
Action/Effect of Glucagon20
Stimuli – decreased plasma glucoseAction
Increases glycogenolysis & gluconeogenesis Promotes breakdown of fatty acids Promotes breakdown of proteins to form amino
acids Increases plasma glucose concentration
Other Regulatory Hormones 21
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
Other Regulatory Hormones 22
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
Other Regulatory Hormones 23
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
Other Regulatory Hormones 24
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
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