CHOs Flashcards
General structures of CHOs, including formula
Composed of carbon, hydrogen, and oxygen in ratio of 1:2:1
- (CH2O)n
What contains 3,4,5,6 or more carbon atoms
Monosaccharides
Two monosaccharides linked together w/ the loss of a molecule of water
Disaccharides
Composition of lactose
Glucose + galactose
Composition of maltose
Glucose + glucose
Composition of sucrose
Glucose + fructose
Composition of glycogen
Multiple branches of glucose chains
Reagent used to detect “reducing sugars”
Benedict’s reagent
Composition of starch
Amylose and amylopectins (grains and starchy vegetables)
Significance of a positive test for reducing sugars
Galactose isn’t detected by a dipstick
- Therefore, if urine is negative for glucose w/ a dipstick but is positive w/ a Clinitest, they have galactose in urine (galactosemia)
Two analogically important reducing sugars
Glucose and galactose
Carb digestion
- Where does starch digestion begin and the enzyme responsible?
In the mouth by salivary amylase
Digestion of starch due to ____ ____ in the intestine
Pancreatic amylase
Four enzymes responsible for intestinal digestion
Lactase, maltase, sucrase, and galactase
What organ do these metabolic pathways occur in and specific starting and ending products
- Glycolysis (anaerobic and aerobic)
Breakdown of glucose (glucose → lactate ↔ pyruvate)
- Anaerobic: glucose → lactate/RBCs and skeletal muscle
- Aerobic: pyruvate → acetyl CoA/mitochondria
What organ do these metabolic pathways occur in and specific starting and ending products:
- Glycogenesis
Making glycogen (glucose-1-phosphate → glycogen)
- Occurs when there’s a decrease in blood glucose concentration
What organ do these metabolic pathways occur in and specific starting and ending products
- Kreb’s cycle (oxidative phosphorylation)
??
- Pyruvate → acetyl CoA → ATP, CO2, water
- Occurs in the mitochondria
What organ do these metabolic pathways occur in and specific starting and ending products:
- Glycogenolysis
Breaking down glycogen
- Glycogen → glucose-1-phosphate → glucose
- Occurs in muscle and liver tissues during a time of fasting
What organ do these metabolic pathways occur in and specific starting and ending products:
- Gluconeogenesis
Making new glucose from non-CHO sources
non-CHO sources → glucose
(non-CHO sources are amino acids, lactate, glycerol, and fatty acids)
- Occurs in the liver
What organ do these metabolic pathways occur in and specific starting and ending products:
- Hexose monophosphate pathway
??
- Glucose-6-phosphate → ribose + CO2
- Occurs in the liver
Specific site of production of insulin
Beta cells of islets of Langerhans of pancreas
Function of C-peptide
To ensure correct structure of insulin
Function of proinsulin
Storage form of insulin
General effect of insulin on blood glucose concentration
Decrease
Four specific anabolic effects of insulin
↑ glycogenesis
↑ lipid synthesis (esp. triglycerides and cholesterol)
↑ glycolysis
↑ amino acid synthesis
Action of insulin on cell membranes and resultant effect on blood sugar levels
↑ in cell membrane permeabilty to glucose
↓ in blood levels of glucose
Specific effects of insulin on cells in the liver
Liver: INHIBITS glycogenolysis and gluconeogenesis and STIMULATES glycogenesis and fatty acid synthesis
Two specific catabolic effects of insulin
↓ hepatic glycogenolysis and gluconeogenesis
Major factor that regulates the release of insulin
Blood glucose concentration
- Insulin is released from pancreas when circulating blood glucose is increased
Specific site of glucagon production
Secreted by alpha cells of pancreatic islets of Langerhans
General effect of glucagon on blood glucose concentration
↑ blood glucose
Two specific glucose metabolism effects of glucagon
- Stimulates glycogenolysis and gluconeogenesis to increase glucose
- Inhibits glucose-consuming pathways in the liver
Major factor that regulates teh release of glucagon
Secreted when glucose is decreased
General effect on blood glucose concentration (increase or decrease) of:
- Growth hormone
Increased
General effect on blood glucose concentration (increase or decrease) of:
- Epinephrine
Increased
General effect on blood glucose concentration (increase or decrease) of:
- Adrenocorticotrophic hormone (ACTH)
Increased
General effect on blood glucose concentration (increase or decrease) of:
- Cortisol
Increased
General effect on blood glucose concentration (increase or decrease) of:
- Thyroxine (T4)
Increased
General effect on blood glucose concentration (increase or decrease) of:
- Somatostatin
↑ glucose
- Secreted by delta cells of pancreatic islets of Langerhans; inhibit both glucagon and insulin from pancreas (which ↓ glucose)
- Can also inhibit growth hormone release (which ↑ glucose)
General effect on blood glucose concentration (increase or decrease) of:
- Somatomedins
↓ glucose
- produced in liver in response to stimulation by growth hormone
Hyperglycemia blood sugar value
Glucose > 100 mg/dL
Hypoglycemia blood sugar value in adults
Glucose < 50 mg/dL
Three specific diagnostic criteria for diabetes mellitus and specific laboratory values associated w/ the diagnostic criteria
- Fasting blood glucose > 126 mg/dL
- 2 hour post-parandial (2 HPP) glucose > 200 mg/dL during OGTT
- Clinical symptoms and random glucose > 200 mg/dL
Nine complications of diabetes
- Nephrophy (renal failure)
- Neuropathy (impaired sensation of feet)
- Heart disease and stroke
- Hypertension
- Blindness and retinopathy
- Amputations
- Dental disease
- Complications of pregnancy (birth defects, spontaneous abortion, excessively large baby)
- Life-threatening events
Four clinical symptoms used in the diagnosis of diabetes mellitus
- Polyuria
- Polyphagia
- Polydipsia
- Unexplained weight loss
One specific cause of Type 1 diabetes mellitus
Beta cell destruction
Five causes of beta cell injury in diabetes mellitus
- Genetic factors (HLA Ags on chromosome 6)
- Environmental factors
- Viral causes (measles, mumps, EBV, etc.)
- Chemical causes
- Autoimmune disease (85-90% of cases have detectable Abs)
Relative insulin concentration in Type 1 diabetes mellitus
Decreased to absent insulin (absolute insulinopenia)
Three general metabolic changes in Type 1 diabetes mellitus
- Inhibition of glycolysis
- Increased glycogenolysis, lipolysis, and gluconeogenesis
- Increased levels of acetyl CoA, converted to ketone bodies
Treatment of Type 1 diabetes mellitus
Administration of exogenous insulin injections
Type 2 diabetes mellitus
- 8 factors that predispose patients for the disease
- Older age (> 40 years old)
- Obesity (BMI > 30)
- Family history
- Sex (females more prevalent than males)
- History of gestational diabetes
- Impaired glucose metabolism
- Physical inactivity
- Race/ethnicity
Type 2 diabetes mellitus
- Two specific causes of the disease
Insuline resistance and beta cell failure
Type 2 diabetes mellitus
- Two factors that may predispose a patient to develop the disease
Genetic factors (stronger tendency than in Type 1) and environmental factors (obesity or increased caloric intake)
Type 2 diabetes mellitus
- Relative insulin concentrations
Variable (depends on cause and severity of disease)
Type 2 diabetes mellitus
- Treatment
- Weight loss
- Dietary changes
- Oral hypoglycemia agents (Glucophage)
A form of glucose intolerance diagnosed in some women during pregnancy
Gestational diabetes mellitus (GDM)
Possible long term effect of GDM
Women who had gestational diabetes have 35-60% chance of developing diabetes in the next 10-20 years
Screening test for gestational diabetes
O’Sullivan test
Caused by a single gene defect that causes faulty insulin secretion
Maturity-onset diabetes of youth (MODY)
Affected age group of MODY
Manifests before age 25
Four conditions that may cause secondary diabetes
- Pancreatic disease
- Cystic fibrosis
- Corticosteroid administration
- Hormonal disorders (Cushing’s disease, acromegaly, etc.)
Two hour post-parandial blood sugar levels associated w/ impaired glucose levels
140-199 mg/dL
Fasting blood sugar levels in impaired glucose tolerance
Fasting plasma glucose > 100 < 125 mg/dL
Hemoglobin A1c level in prediabetes diagnosis
5.7-6.4%
Symptoms unique to adolescent diabetes mellitus
They’re the same as adults, but also:
- Blurred vision
- Slow wound healing
- Acanthosis nigricans (skin around neck or armpits appears dark, thick, and velvety)
- Frequent infections
- Hypertension
Definition of double (hybrid) diabetes
Child has elements of both Type 1 and Type 2 diabetes mellitus
How do patients develop double diabetes?
- Type 1 becomes overweight then becomes insulin dependent
- Type 2 develops Abs to beta cells
What is the most important factor in the development of diabetes mellitus?
Important factor is weight gain in diabetic adolescents
Typical blood glucose levels and clinical findings in hypoglycemia
Symptoms: weakness, shakiness, sweating, nausea, rapid pulse, lightheadness, epigastric discomfort
Fasting blood sugar < 50 mg/dL
Severe hypoglycemia
- Cause
- Typical blood glucose concentration
- Caused by severe CNS dysfunction
- Blood sugar < 20-30 mg/dL
Hypoglycemia in neonates and infants
- Cause
- Typical blood glucose concentration
- Due to low glycogen stores at birth
- Blood glucose at approximately 35 mg/dL
Fasting hypoglycemia in adults
- Cause
- Typical blood glucose concentration
- Caused by certain drugs (most common), toxins, advanced liver disease, hormone deficiencies, isulinomas, septicemia, and end-stage renal failure
- Blood glucose < 45 mg/dL
Reactive hypoglycemia
- Cause
- Typical blood glucose concentration
- Occurs in everyday life after eating
- Postprandial symptoms if glucose is < 45-50 mg/dL
- Must rule out fasting hypoglycemia first
Specific enzyme defect in galactosemia
Galactase deficiency
Clinical symptoms and long-term effects of galactosemia
- Infants who fail to thrive on cow’s milk; vomiting and diarrhea
- Later, can cause liver disease, cataracts, and mental retardation
3 laboratory means of galactosemia diagnosis
- Screening urine for reducing substances via Benedict’s test (Clinitest)
- ID of the sugar by paper
- Direct assay of enzyme activity
Specific enzyme deficiency of lactose intolerance
Lactase deficiency
Clinical symptoms of lactose intolerance
- Abdominal pain
- Diarrhea
- Lactose in urine
Specific cause of glycogen storage diseases
Caused by deficiencies of a specific enzyme in glycogen metabolism
What are the 3 liver forms of glycogen storage diseases?
What are their 4 general clinical biochemical features?
- Types I, IV, and VI
- Are characterized by hepatomegaly, hypoglycemia, decreased insulin, and increased glucagon
What are the 4 muscle forms of glycogen storage disease?
What is 1 general clinical feature of the muscle forms of glycogen storage disease?
- Types II, III, V, and VII
- Appear in young adulthood during strenuous exercise
Specific enzyme deficiency in von Gierke’s disease
Deficiency of glucose-6-phosphatase
Is von Gierke’s disease a liver or muscle form of a glycogen storage disease?
Liver form (most common and most severe form)
Specific enzyme deficiency in Pompe’s disease?
Deficiency of alpha-1,4-glucosidase
Is Pompe’s disease a liver or muscle form of a glycogen storage disease?
Muscle form
Why should separation from the cells or testing must be performed w/in a half hour of venipuncture in glucose testing?
Glucose decreases up to 7% per hour or more when serum is left in contact w/ cells
- But if collected in a gold top w/ serum separator, we’re good
Why is oxalate-sodium fluoride the preferred anticoagulant in glucose testing?
Oxalate-sodium fluoride (gray top) inhibits enolase, a critical enzyme in the glycolytic pathway
Whole blood glucose value
60-90 mg/dL
- Values are 12-15% less than plasma b/c plasma is more concentrated in the same amount of specimen volume compared to whole blood
Plasma glucose value
70-100 mg/dL
Oxygenated, deoxygenated, and capillary blood glucose value
Oxygenated and capillary values are 2-5 mg/dL higher than deoxygenated samples
- This makes a huge difference in pediatric heel stick samples
What is the reason for the prompt analysis of CSF glucose?
Due to possible cellular utilization and resultant false picture
What is the relationship normally observed b/w plasma glucose and CSF glucose?
CSF is lower than plasma glucose (60-70%) at the same time
Clinical significance for urine glucose
- Specific renal threshold range for urine glucose
Glucose appears in urine after blood glucose exceeds renal threshold
- Renal threshold: 160-180 mg/dL
What are the 3 copper reductase methods for glucose?
- Benedicts test (Clinitest)
- Somogyi-Nelson
- Neocuproine Copper Reduction
Benedict’s Copper Reduction Test (Clinitest)
- Principle of measurement
Based on the reduction of cupric iron in supric sulfate; change in absorbance is measured
Benedict’s Copper Reduction Test (Clinitest)
- Clinical significance of a positive test
Used as a screen for diseases of inborn errors of CHO metabolism in newborns
Benedict’s Copper Reduction Test (Clinitest)
- Specific CHOs detected
Galactose and glucose
Benedict’s copper reduction test (Clinitest)
- Interferences
Includes false positives from other sugars, ascorbic acid, salicylates, penicillin, and uric acid
A two step reaction that is proposed to be the reference method when a protein-free filtrate is used
Hexokinase
Hexokinase reagents and products
Reagent: Hexokinase and glucose-6-phosphate dehydrogenase
Products: Glucose6-phosphate and 6-phosphoglyconate +NADPH + H+
The first step of hexokinase is ____ while the second is ____
Specific; non-specific
Absorbance in hexokinase is measured at ____
340 nm
A two-step reaction with the first step being specific and the second, non-specific
- Good method for serum, plasma, urine, and csf
- O-dianisidine is the chromogen
Glucose oxidase; “Trinder”
Glucose oxidase “Trinder” reagents
Glucose oxidase; peroxidase
Plasma glucose reference interval
- Adult
70-100 mg/dL
Plasma glucose reference interval
- Children
70-100 mg/dL
Plasma glucose reference interval
- Preemies
25-80 mg/dL
Plasma glucose reference interval
- Term babies
60-95 mg/dL
CSF glucose reference interval
60-70% of concommitant plasma levels
Whole blood glucose reference interval
- Adults
60-90 mg/dL
Urine glucose reference interval
- Random
- 24 hours
- 30 mg/dL for random urine glucose
- < 500 mg/24 hours
Patient preparation instructions for an oral glucose tolerance test (OGTT)
- Minimum of 150 g CHO for 3 days prior to the test
- Fasting for 10-16 hours (water only)
- Discontinue medications that alter glucose levels
- Normal amount of activity before and during test
3 indications for performing an intravenous glucose tolerance test
- Malabsorption
- Sprue (celiac disease)
- GI surgery
Can be used for preliminary diagnosis of diabetes mellitus; give 75 g oral glucose load or have patient a meal; 2 hours later if glucose is ____, may be diabetic
Postprandial testing; > 126 mg/dL
Used to diagnose gestational diabetes, performed at ____ to ____ weeks gestation; give ___ g glucose load to fasting patient and draw sample at 1 hour; if ____ mg/dL performe OGTT
O’Sullivan test; 24-28 weeks; 50g; > 140 mg/dL
Metabolic pathway that leads to ketone body formation
Formed from beta-oxidation of free fatty acids
Name 3 ketone bodies and their specific relative proportions in the blood
- Beta-hydroxybutyric acid (78%)
- Acetoacetic acid (20%)
- Acetone (2%)
Specific starting points of ketone bodies
Pyruvate, amino acids, and fatty acids
3 processes that lead to ketosis due to patient’s deficiency of glucose
Decreased sodium, decreased bicarbonate, and decreased blood pH
Why does the patient develop acidosis and hyperlipidemia?
The body is using fatty acids as energy in hyperlipidemia
Increased in free ketone bodies produces exess H+ ions in acidosis
5 conditions of decreased CHO availability that can lead to ketosis
- Starvation
- Frequent vomiting
- Glycogen storage diseases
- Alkalosis
- Alcoholism
Specific reagent used in colorimetric method (Acetest or Ketostix)
Sodium nitroprusside
Specific realtive activity w/ each of the three ketone bodies in the colorimetric method
Reacts ONLY w/ acetone and acetoacetate; 5x more sensitive to acetactate; does NOT react w/ beta-hydroxybutyrate
Specimen storage requirements for the colorimetric method (Acetest/Ketostix)
- Keep container closed (volatile analyte)
- Keep refrigerated (any microbes present will use up ketone bodies causing a false negative result)
Describe the pathogenies of hyperosmolar hyperglycemic nonketonic come (HHNC)
- Occurs in older patients
- Increased blood glucose (no ketosis)
- Increased osmolality
- Intracellular dehydration
- Cellular edema in the brain
Three causes of Type A lactic acidosis
Decreased tissue oxygenation from:
- Shock
- Hypovolemia
- Cardiac failure
Five causes of Type B lactic acidosis
Metabolic causes associated w/ disease (diabetes mellitus, neoplasia, liver diseases) or drugs/toxins (alcohol, salicylates)
Five causes of increased CSF lactate
- Levels should parallel blood values
- CVA
- Intracranial hemorrhage
- Bacterial meningitis (nromal in viral)
- Epilepsy
- Other CNS disorders
Patient preparation, specimen collection, and sample analysis requirements for lactate
- No tourniquet
- No exercising of arm
- Must be placed on ice IMMEDIATELY
- Separate from cells w/in 15 minutes of draw
Discuss the process of glycation
Glycation is the non-enzymatic addition of a sugar residue to amino groups of protein
- Glucose binds reversibly to accessible amino groups on hemoglobin to form a labile aldimine; aldomine intermediates form a stable ketoamine (irreversible “Amadori” rearrangement); conformation change of glucose to cyclic structures occurs
Why can the measurement for glycated hemoglobin be used to assess diabetic blood sugar control over a 3-4 month at a time span?
Since glycated hemoglobin formation is irreversible AND the normal RBC lifespan is 120 days, these tests assess diabetic compliance with therapy for the preceding 120 days! Levels are unaffected by day-to-day fluctuation, exercise, etc
Two general categories of glycated hemoglobin measurement methods
- Methods based on charge differences (ion exchange chromatography, HPLC, ELP)
- Methods based on structural differences (immunoassay and affinity chromatography)
Specific clinical application of measuring
- Insulin
Evaluates fasting hypoglycemia; not necessary to measure to diagnose diabetes mellitus
Specific clinical application of measuring:
- Proinsulin
Evaluates patients with benign or malignant beta-cell tumors of pancreas
Specific clinical application of measuring:
- C-Peptide (3)
Evaluates fasting hypoglycemia, insulin-producing beta-cell tumors, response to pancreatic surgery
Specific clinical application of measuring:
- Urine glucose (via dipstick)
Uses glucose oxidase to produce color change; specific for glucose only
Specific importance of urinary albumin and miroalbumin measurements in predicting diabetic nephropathy
Persistent proteinuria is the best indicator for renal disease and can be used to screen diabetics for nephropathy development
Importance of urinary micro albumin excretion
It precedes nephropathy and is a marker for mirovascular disease!
Excess of glucose in the bloodstream outside of reference range; often associated w/ diabetes mellitus
Hyperglycemia
Abnormally low blood glucose level
Hypoglycemia
Be able to draw and label 3-hour OGTT curves associated w/ a normal patient, a patient w/ diabetes mellitus, and an impaired glucose tolerance patient
- DM: FBS ≥ 126 mg/dL; glucose > 200 mg/dL
- IGT: FBS 101-125 mg/dL; at 2 hours back to FBS; never exceed 200 mg/dL
- Normal: FBS 70-100 mg/dL; at 2 hours back to FBS; never exceed 200 mg/dL
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Specific effects of insulin on cells in the muscle
Muscle: STIMULATES glycogenesis, glucose uptake and metabolism, amino acid uptake, and protein synthesis and INHIBITS protein catabolism and amino acid release
Specific effects of insulin on cells in the adipose tissue
Adipose tissue: STIMULATES glycerol and fatty acid synthesis and INHIBITS lipolysis