Carbohydrates Flashcards
For the glucose oxidase method what substances can falsely decrease glucose deduced (inferred measurement) if their levels are high (increased)?
Uric acid, bilirubin and ascorbic acid.
What is the greek word for “sugar”?
Saccharides
What is our main source of energy in our diet? What % is it?
Carbs, 80% of our body’s energy comes from carbohydrates.
What particular organs in particular need carbs?
Carbs are the primary energy source for the brain, erythrocytes and retinal cells.
Nervous system totally depends on it as it cannot store carbs and so needs a steady supply to function properly.
Where are carbohydrates stored in the body?
Liver and muscle.
What other sources of energy that are in the body that can be used by our cells for energy?
Amino acids and lipids.
What elements are carbohydrates composed of?
C, H, and O.
What molecular functional groups are contained within carbohydrates?
Contains C = O (carbonyl) and -OH (hydroxyl) functional groups.
What are two carbohydrate utilization diseases?
Hypoglycemia and
Hyperglycemia.
What are carbohydrates classification based on?
- Size of base carbon chain - 3C, 4C, etc.
- Location of the CO (i.e. C=O) functional group.
- Number of sugar units - number of monosaccharides.
- Stereochemistry of the compound.
What are 3, 4, 5 and 6 carbon chains called?
Triose (3 C atoms)
Tetrose (4 C atoms)
Pentose (5 C atoms)
Hexose (6 C atoms)
How many sugar units does a disaccharide, a oligosaccharide, and a polysaccharide have?
Disaccharide - Two monosaccharides.
Oligosaccharide - 2 - 10 sugar units
Polysaccharide - > 10 monosaccharides.
What is the definition of a monosaccharide and name some examples?
- Monosaccharides are simple sugars that cannot be hydrolyzed to a simpler form.
- E.g. Glucose, fructose, and galactose.
What is a disaccharide? Name some examples.
- Two monosaccharides joined by a glyosidic bond.
2. E.g. Sucrose, lactose, maltose.
What does the hydrolysis of a disaccharide make? What is the purpose?
- Hydrolysis of a disaccharide makes 2 monosaccharides.
2. Allows for absorption.
How many sugar units does an oligosaccharide have?
Oligosaccharide has 2 - 10 sugar units.
What are some examples of Polysaccharides?
Glycogen and starch.
What does hydrolysis and condensation reactions (aka dehydration synthesis) mean?
Hydrolysis - means a more complex sugar comes a part, water is broken down and consumed in the reaction.
Condensation (dehydration synthesis) - means two more simpler sugars come together, i.e. two monosaccharides come together and form a disaccaride + H2O.
What are two forms of carbohydrates?
Aldose and Ketose.
What is the difference between aldose and ketose?
Aldose - has the carbonyl group, O=C, at the end of its molecular structure.
Ketose - has the carbonyl group in the middle.
What are stereoisomers? Name some examples.
Stereoisomers are molecules with the same order and types of bond (same molecular formula) but different spatial arrangement and different properties.
Examples: Glucose and galactose, both C6H12O6 but are arranged differently in space.
What is an enantiomer?
Stereoisomers that are non-superimposable mirror images of each other such as D and L glucose.
C=O at the end of the chain such as galactose
Aldose sugar
A sugar in which the anomeric C is not involved in a glycosidic bond and can therefore undergo oxidation such as glucose
Reducing sugar
A simple sugar with a backbone containing 6 carbon atoms such as glucose
Hexose
The major form of stored carbohydrate in animals
Glycogen
A simple sugar with a backbone containing 3 carbon atoms such as glyceraldehyde
Triose
A method for representing molecules to show the configuration of groups around chiral centres
Fischer Projection
C=O usually positioned at the C2 (second carbon) and not at the end of the chain such as fructose
Ketose sugar
Electrons are lost
Oxidation
What type of sugar is it if the hydroxyl projection is to the right? left?
Hydroxyl group to the right: D
Hydroxyl group to the left: L
These are referred to as enantiomers as they cannot be overlapped and are non-superimposable. Mirror images.
What does our body need to do to carbohydrates?
Our body needs to break down carbohydrates into monosaccharides.
Describe the digestion process at the start of carbohydrates? middle/end?
- Starts in mouth with amylase, which starts to break down starch and glycogen.
- In duodenum disaccharides are further broken down by enzymes into monosaccharides.
- From gut to bloodstream to liver –> monosaccharides are absorbed, used, and/or stored in the liver as glycogen.
What pancreatic juices (or enzymes) break down disaccharides: maltose, lactose, and sucrose?
- Maltose is broken down by maltase to be 2 glucoses.
- Lactose is broken down by lactase to be glucose and galactose.
- Sucrose is broken down by sucrase to glucose and fructose.
What happens if you have deficiencies in pancreatic juices (enzymes) for breaking down disaccharides? Name an condition given as an example.
Results in malabsorption, nausea, vomiting, and abdominal cramping.
Example: Lactose intolerance.
What is the first step in the metabolism of glucose?
The first step of all pathways requires glucose to be catalyzed by hexokinase into glucose-6-phosphate using ATP.
What is the result of glycolysis?
Glycolysis (Embden-Meyerof Pathway) in the cytoplasm of the cell.
- 10 steps that result in the production of 2 ATP and 2 NADH = ENERGY!!
- Can occur aerobically or anaerobically
What happens in aerobic glycolysis?
Aerobic = Glucose to Pyruvate to Acetyl-CoA.
What happens in anaerobic glycolysis? Why is this important?
Anaerobic = Glucose to Pyruvate to Lactic Acid
- Energy via lactic acid fermentation
- Important for muscles (energy without oxygen)
- Lactate converted back to glucose
What happen in the tricarboxylic acid (TCA) cycle?
2 Pyruvate molecules from glycolysis will undergo pyruvate oxidation to yield Acetyl-CoA and 2 NADH
Acetyl-CoA enters the Tricarboxylic Acid (TCA) Cycle
Occurs in the inner space of mitochondria
What is the result of the tricarboxylic acid cycle (TCA) (aka Krebs)?
Results in 2 ATP, 6 NADH, 2 FADH2
NADH and FADH2 products continue into Electron Transport Chain,
What is the electron transport chain?
It is an electrochemical gradient along the mitochondrial cell membrane.
(Remember this membrane is folded into cristae that increase its surface area).
What are the inputs in terms of NADH and FADH into the electron transport chain?
2 NADH from glycolysis + 2 NADH from pyruvate oxidation + 6 NADH from TCA = 10 NADH into the ETC
2 FADH2 from TCA into the ETC
10 NADH and 2 FADH2 are oxidized
What are the energy outputs from the electron transport chain?
10 NADH → 30 ATP
2 FADH2 → 4 ATP
= 34 ATP from the ETC
How much ATP can be produced using glycolysis, TCA and the electron transport chain (ETC)?
Glycolysis + TCA + ETC = 38 ATPs!!!
How do cells that don’t have mitochondria metabolize glucose?
Hexose monophosphate shunt (HMP).
No mitochondria, no TCA, no ATP used or produced.
What is another name for the Hexose Monophosphate Shunt (HMP)? Why?
Pentose Phosphate Pathway
Products are:
- Pentose (5C sugar) called ribose-5-phosphate, which is used in DNA and RNA synthesis.
- Phosphate called NADPH.
What does NADPH do from the HMP (or pentose phosphate pathway)?
NADPH donates electrons providing reducing power and protects the cells from oxidative and free radical damage.
What cells secrete insulin?
Beta cells of the Islets of Langerhans in the pancreas secrete insulin.
What cells secrete glucagon?
Alpha cells of the Islets of Langerhans in the pancreas secrete glucagon.
What does insulin do that no other hormone does?
Insulin is the only hormone that decreases glucose levels.
It stimulates uptake of glucose into cells and increases glucose metabolism.
What is glycogenesis?
Storage of glucose as glycogen.
What is glycolysis?
Glycolysis is the breakdown of glucose.
Aerobic = glucose to pyruvate
Anaerobic = glucose to lactate
Insulin is referred to as a ____________ agent.
Hypoglycemic agent.
What does glucagon do?
Promotes glycogenolysis (glycogen broken down to glucose) and increase in gluconeogenesis (formation of glucose-6-phosphate from non-carb sources) when blood glucose is too low.
Glucagon is referred to as a __________ agent.
Hyperglycemic agent.
What is gluconeogenesis? Where does it take place.
Formation of new sugar from non-carbohydrate substances
Takes place in the liver and kidneys
What are sources in the body for gluconeogenesis?
Lactate, pyruvate, amino acids, and glycerol can be used to create glucose-6-phosphate
What is glycogenolysis? What’s the importance of it?
Breakdown of glycogen to glucose in liver for release into the bloodstream for use as energy
Keeps glucose levels constant between meals
What is glycogenesis?
Glucose to glycogen for storage
Bonding of glucose units to form glycogen chain
Stored primarily in liver and muscle
What is lipogenesis?
Excess glucose to fat
Stored in adipose tissue
What is lipolysis?
Breakdown of fat
Describe the balancing act in out bodies between times of eating and fasting?
Normal process:
Eat
Blood glucose rises > insulin released > glucose utilized by cells for energy (glycolysis) > converted to glycogen in the liver (glycogenesis) > converted to fat (lipogenesis) and stored > blood glucose returns to normal
Fasting
Blood glucose drops > glucagon released > glycogen broken down to glucose (glycogenolysis) > body uses other non-carb sources for energy (gluconeogenesis) > blood glucose returns to normal
(Draw the diagram on slide 21).
Are there other hormones that affect blood glucose?
Yes, they all increase plasma blood glucose.
FYI Examples are: Epinephrine, Cortisol, ACTH, GH (growth hormone), Thyroxine (T4), Somatostatin.
Insulin is the only hormone that decreases glucose levels though.
What do red blood cells lack for creating energy?
Red Blood Cells lack mitochondria, no TCA, no ATP used or produced. Therefore RBCs need to use the hexose monophosphate shunt (HMP).
What is the ideal blood sugar level?
~3.6 to 6.0 mmol/L
What is hypoglycemia?
Decrease in plasma glucose below normal fasting level.
What are the symptoms of hypoglycemia?
Hypoglycemia Symptoms: increased hunger, sweating, nausea and vomiting, dizziness, nervousness and shaking, blurred speech and mental confusion
What are some causes of hypoglycemia?
Can be caused by: fasting, organ failure resulting in diminished metabolic capacity, hormones levels such as low ACTH, tumors (insulinoma), congenital/enzyme deficiencies (G6PD deficiency)
What is hyperglycemia?
Hyperglycemia
Increase in plasma glucose above normal fasting level
What is galactosemia?
Genetic metabolic disorder (failure to thrive).
Unable to metabolize galactose, so it builds up to toxic levels
Galactose-1-phosphate uridylyltransferase (GALT) deficiency
Detect excess galactose in blood and urine
Part of Newborn Screening
Milk products are removed from baby’s diet
Undetected can lead to liver disease and brain damage
What is glucose-6-phosphate deficiency?
Glycogen storage disease resulting in hypoglycemia
Glycogen cannot be converted back to glucose
Glycogen builds-up in liver
What is diabetes insipidus?
Deficiency of pituitary ADH or antidiuretic hormone
Unable to control fluid levels
Excessive urination and thirst
What is diabetes mellitus (DM)?
Defects/deficiencies in insulin secretion or insulin action is referred to as Diabetes Mellitus (DM)
Type 1 Diabetes
Type 2 Diabetes
Gestational Diabetes Mellitus (GDM)
Diabetes due to other causes (Cystic Fibrosis, Drugs, neonatal diabetes, etc.)
What happens in type I diabetes? (cause/result)
Autoimmune destruction of β- cells of the Islets of Langerhans in the pancreas
Insulin deficiency
Increased levels of blood glucose that can’t enter cells
Body is starved of energy
Proteins and fats end up getting used for energy leading to a buildup of ketones
What happens in type II diabetes? (cause/result)
- Insulin resistance with insulin secretory defect. Relative, not an absolute, insulin deficiency. Ketosis is not common.
- Symptoms develop gradually: fatigue, urination, thirst, weight loss, blurred vision, frequent infections, slow healing of sores
What is the prevalence of Type II diabetes? What are risk factors.
90-95% of all cases of diabetes. Usually adult onset (over 40). Goes undiagnosed for several years until complications manifest.
Prevalence increases with age, obesity, inactivity, genetics, hypertension, smoking, etc.
How do you control Type II diabetes?
Control with diet, exercise, and anti-diabetic drugs (metformin and sulfonylureas)
What are some of the major complications with type II diabetes?
- Eye - retinopathy, high blood pressure to eye blood vessels cause damage, etc.
- Kidney disease - high blood pressure damages blood vessels and excess glucose overworks the kidneys –> nephropathy.
- Hyperglycemia damages nerves in peripheral nervous system –> pain/numbness.
- Increase risk of stroke, TIA, congnitive impairment.
- Increase risk of coronary heart disease.
- Narrowing of blood vessels in extremities, peripheral vascular disease –> feet wounds slow to heal/risk of gangrene, etc.
Why is glucose in blood unstable after being collected?
It is still being metabolized by RBCs, WBCs, or bacteria (if present).
Therefore it needs to be separated in the form of serum or plasma ASAP and run within 1 hour.
What are the guidelines from processing serum, plasma, and whole blood (glucometer) for glucose?
- Serum: Centrifuge after clot has formed.
Takes at least 30 minutes following collection, but if left for longer than 1 hour 7% of glucose will be lost. - Plasma: Can centrifuge immediately.
a) Heparin (green top).
b) Potassium oxalate and sodium fluoride (gray top) – if can’t process within two hours as sodium fluoride inhibits enzyme activity preventing glycolysis (acts as preservative) - Whole blood (Glucometer): Whole blood values are ~10-15% lower than plasma/serum.
What are the guidelines for handling urine for glucose measurement?
- Keep refrigerated at 4C.
2. Preservative added if applicable for test request.
What are the guidelines for handling cerebrospinal fluid for glucose measurement? Reference interval and % of plasma glucose?
- Analyze immediately.
- Reference interval 2.3 - 4.7 mmol/L.
- Approximately 60 to 70% of plasma glucose.
- Value lower if bacterial or fungal glycolysis is occurring. If it is normal then instead the patient may have viral meningitis (rule out).
What is “Fasting Plasma Glucose” (FPG)? Reference range and diagnostic criteria?
Fasting Plasma Glucose:
- Measures an individuals blood sugar level after fasting. No caloric intake for 8-16 hours. Can drink water.
- Reference range 3.6-6.0 mmol/L
- a) Diabetes Mellitus diagnosis > 7.0 mmol/L.
b) Impaired fasting glucose or Prediabetes 6.1-6.9 mmol/L
What is “Random Plasma Glucose”? Reference range and diagnostic criteria?
Random Plasma Glucose:
- Measures an individuals blood sugar level at random. Fasting or recently had food intake does not affect results.
- Reference range < 11.1 mmol/L
- Diabetes Mellitus > = 11.1 mmol/L
What are the critical values of glucose concentration in plasma that must be called in immediately?
Critical glucose values that must be called immediately:
< 2.5 mmol/L
>25.0 mmol/L
What is the screening program for Type II diabetes?
Screen every 3 years in individuals >= to 40 years of age or in individuals at high risk.
Age is related to risk of Type II diabetes and more screening should be done. Also the higher the glucose concentration is in your blood the more screening should be done.
What is the basis for hemoglobin A1C tests? Reference ranges?
Hemoglobin A1C tests (also called Glycosylated Hemoglobin):
- Normal adult hemoglobin has glucose attached. Rate of glycation directly proportional to plasma glucose concentration. Red cells live 120 days
- Level reflects average blood glucose level over previous 2-3 months. Less fluctuation from day-to-day and greater specimen stability.
Reference Range is 4.0–6.0% of total hemoglobin
Diagnostic of diabetes in adult is > 6.5%
Prediabetes range is 6.0-6.4%
What do doctors use A1C test results?
- Used to monitor patient’s long term glucose control. Will be high if glucose has been high.
- Fasting glucose does not give picture over time.
- Twice/year for patients under proper glycemic control
What type of specimen tube is used to collect samples for A1C tests?
EDTA whole blood. (Lavender).
What is gestational diabetes mellitus (GDM)?
Gestational diabetes mellitus (GDM):
1. Glucose intolerance during pregnancy
Metabolic and hormonal changes result in increased tissue cell resistance.
2. Body cannot produce enough insulin to deal with changes.
3. Identified through the oral glucose tolerance test, 1-14% of all pregnant women.
4. Following delivery diabetes could go away for turn into Type 2
Describe the parameters for when, how and the diagnostic criteria for the 50g Oral Glucose Tolerance Test (Gestational Diabetes Screen).
- 24 to 28 weeks of gestation
- No fasting required
- Drink 50 gram glucose solution within 5 minutes > 1 hour post drink plasma glucose collection
- Absence of GDM: 1 hour post challenge < 7.8 mmol/L
- GDM: 1 hour post challenge > 11.1 mmol/L
- Follow-up with 75g OGTT if 1 hour post challenge 7.8-11.0 mmol/L
Describe the parameters for when, how and the diagnostic criteria for the 2 hour 75 g OGTT?
2 hr 75 g OGTT (Gestational Diabetes Diagnosis):
- Done in the morning due to diurnal variation of glucose. Fasting plasma glucose collected > drink 75 gram glucose solution within 5 minutes > 1 hour post drink plasma glucose collection > 2 hour post drink plasma glucose collection.
- GDM (values from Shared Health Services and Diabetes Canada):
a) Fasting plasma glucose≥ 5.3 mmol/L
b) Plasma glucose 1 hr post challenge≥ 10.6 mmol/L
c) Plasma glucose 2 hr post challenge≥ 9.0 mmol/L - Absence of GDM: Results lower than above stated values
Describe the 2hr Oral Glucose Tolerance test (OGTT) for Pre-Diabetes (adult screening). How is it different/same from the similar test for gestational diabetes?
- Slightly different practice and interpretation of results for pre-diabetes compared to investigation of gestational diabetes. Still measures the body’s ability to utilize a high glucose load.
- Done in the morning following 8 hours of fasting. Fasting plasma glucose collected > drink glucose solution within 5 minutes > 2 hour post drink plasma glucose collection
- a) Normal < 7.8 mmol/L
b) Impaired Glucose Tolerance or Prediabetes 7.8 to 11.0 mmol/L
c) Diabetes Mellitus > 11.1 mmol/L
What factors affect the OGTT for adult screening?
Factors affecting OGTT include: medications, inactivity, obesity, stress, fever, endocrine dysfunctions and malabsorption or GI problems.
Summarize the main diagnostic criteria for diabetes. (This you really need to know).
- FPG >= 7.0 mmol/L (no caloric intake for 8 hrs)
- A1C >= 6.5% (in adults), std, validated assay in absence of factors that affect accuracy of A1C and not a suspected type 1.
- 2hrPG in a 75 g OGTT >= 11.1mmol/L
- Random PG >= 11.1 mmol/L (random, any time of day, w/o regard to when last meal was).
One needs 2 positive tests or post tests plus symptoms.
T/F. Type I diabetics are prone to Ketoacidosis.
True.
What is diabetic ketoacidosis (DKA) and the symptoms? Reference range of ketones.
Diabetic ketoacidosis (DKA): body reverts to metabolizing lipids. Excess Acetyl-CoA produced results in formation of ketone bodies. Reference range 0 - 0.3 mmol/L.
Symptoms:
- Fruity breath, dehydration and nausea, and possible eventually coma.
- Increased glucoe & ketones in blood and urine. Lowered blood pH.
What are three different types of ketone bodies?
Acetoacetate
Acetone
β-hydroxybutyrate
What other tests can be done to help tell us what is going on in the body with someone with diabetes?
- Ketones, reference range 0 - 0.3 mmol/L.
- Electrolytes, potassium will increase as it moves from the cell in DKA.
- Urine microalbumin, check for small amounts of albumin in urine. If kidneys are breaking down then you can get albumin in urine when there shouldn’t be any —> tests for nephron damage in kidney. Early detection of microvascular disease.
Note: Microalbuminuria = persistent albuminuria.
Describe what Lactose Tolerance Test is and how it is performed.
- Testing is performed the same way as OGTT, except the drink contains milk sugar.
a) Patient fasts for minimum of 8 hours.
b) Performed in the morning
c) Avoid strenuous exercise
d) Can drink water - Rise in peak glucose of at least 1.1 mmol/L is normal; a rise of less than 1.1 mmol/L is abnormal
What is the procedure for Lactose Tolerance Test?
Procedure:
- Collect fasting specimen and perform glucose analysis
- Do NOT proceed if fasting glucose is > 7.8 mmol/L
- Patient drinks lactose beverage (50g lactose in 300mL of water) and time is started
- Samples are collected at 0.5, 1, 1.5, and 2 hours
Note: If a non-gel separator tube is used (not the preferred sample type): Separate plasma right away from cells. Serum clots for 30 minutes but must be removed within 40 minutes from cells.
What is ‘renal threshold’, ‘glucosuria’, and how is glucose tested in urine?
- Renal Threshold: Level above 10.0 mmol/L will result in glucose in the urine. (We should not see glucose in urine).
- Glucosuria: Glucose in the urine as a result of ↑ plasma glucose and renal threshold being exceeded.
- Urine dipstick test:
a) Tightly cap urine to prevent evaporation.
b) Not used for diagnosis but informs primary care giver of renal function
c) Glucose, ketones, specific gravity, and proteins in urine –> Increased values in patients with Diabetes.
d) Clinitest reaction (Benedict’s modification) Cu2+ → Cu1+O
Reducing substance carries out reaction.
How can you use urine glucose measurements to review blood glucose measurements?
Ensure both measurements make sense, if plasma glucose is low and within the reference range then it wouldn’t make sense to have glucose in urine. If you have a miss-match case then investigate mixed up samples, and/or other possible errors.
What is the reference range for venous and capillary range of POCT?
3.9 to 5.8 mmol/L
What are some benefits of point of care testing (POCT)?
Point of care testing (POCT) Benefits:
- Good for Rural sites and in primary care centers
- Analysis on iSTAT 2 minutes
- Turn around time for result < 60 minutes
How is the glucose Oxidase (aka Trinder’s Reaction) used to measure glucose concentration? What falsely increases or decreases results?
- Colour produced is directly proportional to glucose concentration
- Colourimetric reaction read spectrophotometrically at appropriate wavelength for colour chromogen used
a) Brown colour produced = 425-475nm - Falsely decreased with increased levels of uric acid, bilirubin, and ascorbic acid
- Falsely increased with bleach contamination
How is the hexokinase method used to measure glucose concentration? What falsely increases or decreases results?
- NADPH is directly proportional to amount of glucose present. NADPH absorbance is read at 340 nm.
- Falsely decreased with gross hemolysis and extremely high bilirubin. Nothing noted for falsely increased.
What method is typically considered the reference method?
Hexokinase Method is considered more accurate than the glucose oxidase method.
Generally accepted as the reference method.
