Exam #2 – Chemistry Test Answers – Flashcards

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How is urea synthesized?
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Proteins are catabolized into amino acids via enzymatic proteolysis. The amino acids undergo transamination and oxidative deamination to be converted into ammonia, which enters the "urea cycle". Urea is synthesized from the "urea cycle"
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What are some of the modes of urea excretion?
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90% of urea is excreted through its kidneys

 

There are some losses through the gastrointestinal tract and skin

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Disease states and disorders associated with urea (BUN) measurement
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Kidney disease shows accumulation of urea in blood

 

Uremic (azotemic) state: increase in [blood urea] 

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Discuss the methodologies used for urea nitrogen (BUN) measurement (pages 369 - 370)
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Fearon Reaction (chemical method): molecules of diacetyl condense with those of urea to form the chromogen diazine, which absorbs strongly at 540 nm.

 

Enzymatic Methods: based on preliminary hydrolysis of urea with urease to generate ammonia; use spectrophotometry (Berthelot reaction and enzymatic assays)

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Chemical structure of creatinine
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cyclic anhydride of creatine
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Synthesis of Creatinine (see p. 365)
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final product of decomposition of phosphocreatine as well as the spontaneous dehydration of creatine
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Mode of creatinine excretion
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Excreted in the urine

 

(note: although it is present in all body fluids and secretions and is freely filtered by the glomerulus)

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Clinical significance of creatinine
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marker of glomerular filtration rate

 

implicated in diabetes, hypertension, and congestive heart failure

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principle of Jaffe reaction
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creatinine reacts with picrate ion in an alkaline medium to yield an orange-red complex
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Analytical problem of Jaffe raction
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lack of specificity for creatinine

 

many compounds have been reported to produce a Jaffe-like chromagen 

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The greatest success in common usage and specificity for the Jaffe reaction (chemical method)
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use of a kinetic measurement approach in combination with careful choice of reactant concentrations
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Advantages of kinetic assays for Jaffe Reaction
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more specific, faster, and the analysis is automated
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Maximum concentration of picrate that can be used in a Jaffe reaction. Also name the concentration range employed in most methods.
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30 mmol/L maximum

 

3 - 16 mmol/L

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What can high concentrations of hydroxide cause in the Jaffe reaction?
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interference
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Absorbance maximum of the Jaffe reaction
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490 - 500 nm
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chemical sructure of uric acid
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nitrogenous compound (2,6,8-trihydroxypurine)
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Synthesis of uric acid (p. 370 - 371)
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major product of catabolism of the purine nucleosides adenosine and guanine.

 

Both endogenous and exogenous nucleic acids are degraded/catabolized into uric acid.

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Mode of excretion of uric acid
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Highly present in the urine and can be found in serum

 

 

Did you know that it can be crystallized in the serum and deposited in the joints?

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Clinical significance of uric acid
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there are more than 20 disorders of purine metabolism that cause hyperuricemia and hypouricemia

 

suspicious symptoms: kidney failure/stones in children or young adult, unexplained neurological problems in infant - adolescent, gout in man/woman <30 years old

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Cause of gout
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monosodium urate precipitates from supersaturated body fluids
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What are the three methods to measure uric acid?
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Phosphotungstic Acid Method, Uricase Method, and HPLC Method
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Drawback of the Phosphotungstic Acid (PTA) Method
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sunject to many interferences
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Advantage of the Uricase Methods
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more specific than the PTA methods
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Carbohydrate
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aldehyde or ketone derivatives of polyhydroxy alcohols composed of carbon, hydrogen, and oxygen in a ratio of 1:2:1
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Monosaccharide
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a simple sugar that consists of a single polyhydroxy aldehyde or ketone unit and is unable to hydrolyzed to a simple form
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Disaccharide
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two monosaccharides joined covalently by an O-glycosidic bond, with the loss of a water molecule.
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Polysaccharide
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the linkage of multiple monosaccharide units
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glycosidic linkage
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chemical bond between monosaccharides?
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Aldose
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 monosaccharide (a simple sugar) that contains only one aldehyde (-CH=O) group per molecule
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Ketose
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a monosaccharide containing one ketone group per molecule.
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Hexose
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any of the class of simple sugars whose molecules contain six carbon atoms, such as glucose and fructose.
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Isomer
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each of two or more compounds with the same formula but a different arrangement of atoms in the molecule and different properties
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Stereoisomer
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compounds that are identical in composition and differ only in spatial configuration
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Glycogenesis
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formation of glycogen from glucose
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Glycogenolysis
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the breakdown of glycogen to glucose
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Gluconeogenesis
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production of glucose from noncarbohydrate sources
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Glycolysis
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the breakdown of glucose by enzymes, releasing energy and pyruvic acid
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Anaerobic Glycolysis
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transformation of glucose to pyruvate when limited amounts of oxygen
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Acetyl-coenzyme A
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acetyl ester of coenzyme A, involved as an acetylating agent in many biochemical processes
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Glycogen
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an extensively branched polysaccharide containing many glucose residues and found particularly in muscle and liver cells for glucose storage
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Lipogenesis
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the metabolic formation of fat/lipids
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Lipolysis
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the breakdown of fats and other lipids by hydrolysis to release fatty acids
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Components of Maltose
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Glucose + Glucose
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Components of Lactose
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Glucose + Galactose
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Components of Sucrose
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Glucose + Fructose
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Starch Composition
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a mixture of amyloses and amylopectins
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Glycogen Composition
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similar to amylopectins, but branching is more extensive and is evident every 8 to 12 glucose residues
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Clinical Significance of Glycogen
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Glycogen Storage Disease (p. 382)
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Glycoprotein composition
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proteins that have carbohydrate groups attached to the polypeptide chain
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proteoglycan composition
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protein bonded to glycosaminoglycan groups
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Ingestion and Absorption of Carbohydrate
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Once eaten, amylase (salivary) breaks down starch into glucose and disaccharides into monosaccharides

 

Carbohydrates are absorbed in the intestines and liver

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main physiological functions of glucose
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structureal components in RNA and DNA

 

source of energy

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pentose phosphate pathway
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a biochemical pathway parallel to glycolysis that generates NADPH and pentoses (5-carbon sugars)
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Embden-Meyerhof pathway
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metabolic pathway that converts glucose to pyruvate
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Insulin effect in regulating blood glucose level
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It decreases blood glucose level via glycogenesis, glucose uptake (entering the cell), and lipogenesis
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Effects of glucagon in reguling blood glucose levels
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increases blood glucose via glycogenolysis and gluconeogenesis
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Maintenance of blood glucose levels in "fasting state"
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1) Decrease in blood [glucose] stimulate ?-cells of pancreas to secrete glucagon

 

2) Glucagon causes lipolysis, glycogenolysis, and gluconeogenesis to occur, yielding normal blood [glucose]

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The maintenance of glucose levels in the "fed state"
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1) An increase in blood [glucose] cause the ?-cells of the pancreas to release insulin

 

2) Insulin causes lipogenesis, glucose uptake, and glycogenesis to occur

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Growth hormone effect on blood glucose levels
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The growth hormone stimulates gluconeogenesis, enhances lipolysis, and antagonizes insulin-stimulated glucose uptake
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Type 1 Diabetes Mellitus
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Abrupt onset of symptoms: polyuria, polydipsia, and rapid weight loss

 

Insulinopenia (deficiency of insulin) due to loss of pancreatic ? cells; autoantibody may be involved

 

Peak incidence occurs in childhood and adolescence

 

 

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Type 2 Diabetes Mellitus
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Minimal symptoms, not prone to ketosis, and not dependent on insulin

 

[Insulin] may be normal, decreased, or increased; insulin action may be impaired

 

Obesity is commonly associated

 

 

 

 

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Gestational Diabetes Mellitus
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Carbohydrate intolerance of variable severity with onset or first recognition during pregnancy.
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Risks for Gestational Diabetes Mellitus
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1) women who have marked hyperglycemia during or soon after pregnancy

 

2) women who are obese

 

3) women whose GDM was diagnosed before 24 weeks' gestation

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Principle of glucose oxidase method
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Glucose + H2O + O2 >(glucose oxidase)> Glucaronic Acid + H2O2

 

H2O2 + Reducing Dye (color #1) >(peroxidase)> Oxidized Dye + H2O

 

The more oxidied dye there is, the more H2O2 produced, thus, the more glucose initially present

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Interferences of the Glucose Oxidase method
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uric acid, ascorbic acid, and bilirubin
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Principle of Hexokinase Method
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Glucose is phosphorylated in presence of hexokinase and forms Glucose-6-phosphate. Glucose-6-phosphate is oxidized by G6PD to another product in the presence of NADP+ or NAD+

 

The amount of reduced NADP or NADH produced is directly proportional to the amount of glucose in sample (340 nm ABS)

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Required Sample Types for Hexokinase Method
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plasma or serum.

 

NaF, with an anticoagulant may be used

 

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Sources of Interferences for Hexokinase Methods
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Hemolyzed specimens containing more than 0.5g of Hgb/dL 

 

drugs, bilirubin, and lipemia

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Specimens for Glucose Oxidase Method
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CSF
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Method used in lab to measure Glycohemoglobin A1C
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Helena GLYCO-Tek Affinity Column Method
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Principle of the Helena GLYCO-Tek Affinity Column Method
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The dihydroxyboryl group in the cellulose reesin has an affinity to cis-diol groups on simple sugars, thus allowing separation of glycated hemoglobins from non-glycated.

 

Elution with a basic developer removes non-glycated Hb. The glycated forms are eluted using sorbitol buffer. Then spectrophotometry

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Specimen for Glycohemoglobin methods
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Fresh, whole blood containing EDTA, heparin, or citrate. Packed cells are the specimen of choice.
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Interfering substances for the Glycohemoglobin method
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hemolyzed, lipemic, and icteric specimens
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Patient Preparation for Glucose Tolerance Test
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1) Patient has 3 days of unrestricted diet

2) Collect blood after patient has fasted for at least 8 hrs

 

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Procedure for Glucose Tolerance Test
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1) Collect patient sample from 8-hour fast

2) Give 75g of glucose

3) Collect blood every half hour (up to 2 hours)

4) Patient is considered diabetic if the 2-hour test tube (and another test tube) is ;200 mg/dL

 

Normally, 7% of blood glucose is lost every hour (cellular glycolysis)

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GTT normal glucose level
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70 - 90 mg/dL
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Criteria for diagnosing Diabetes Mellitus in fasting plasma glucose
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?126 mg/dL (7.0 mmol/L)
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Criteria for diagnosing Diabetes Mellitus in 2-hour plasma glucose
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?200 mg/dL (11.1 mmol/L)
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The two families of protein that modulate glucose transport into the cells
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1) sodium-dependent glucose transporter (promote the uptake of glucose and galactose from the lumen of the small bowel and their reabsorption from urine in the kidney)

 

2) facilitative glucose transporter (located on the surface of all cells)

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Methods used to measure ketones in body fluids
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1) Acetest

 

2) Ketostix

 

3) Determination of ?-hydroxybutyrate

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Most common analytical method of ketones
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sodium nitroferricyanide + ketones yield a purple complex
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Qualitative Method to measure Glucose in Urine
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Benedict's Test

 

Aldose + Cu(citrate)22- (blue) > carboxylate anion and Cu2O (brick red ppt)

 

If the color of the solution changes, glucose is present (spectrophotometry?)

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Quantitative Methods to measure Glucose in Urine
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Hexokinase and glucose dehydrogenase procedures are recommended for greatest accuracy
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Quantitative Method to measure Glucose in CSF
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Glucose oxidase
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Three Methods for Determination of Glycated Hemoglobins
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1) High-Performance Liquid Chromatography

2) Immunoassay

3) Affinity Chromatography (*done in lab)

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Lipids
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a class of compounds that are soluble in organic solvents but are nearly insoluble in water and that contain nonpolar carbon-hydrogen bonds
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Simple lipid
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compound that contains fatty acids and no prosthetic groups; simple fatty acids; monomers of complex lipids
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Complex lipid
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Lipid containing esters, fatty acids, alcohol groups, and other prosthetic groups; a macromolecule composed of simple lipids (e.g. triglycerides)
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triglyceride
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an organic compound made up of glycerol and three fatty acid chains. Fat is stored as triglycerides
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phospholipid
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a polar amphipathic lipid located on the surface of a lipoprotein; they are also found at the aqueous interface of biological membranes
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Lecithin
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any group of yellow-brownish fatty substances occurring in animal and plant tissues composed of phosphoric acid, choline, fatty acids, glycerol, glycolipids, triglycerides, and phospholipids.


major surfactant found in the lung; used along with sphingomyelin to assess fetal lung maturity

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Sphingomyelin
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a lipid compound that coats lung cells

 

substance that occurs widely in brain and nervous tissue, consisting of complex phosphoryl derivatives of sphingosine and choline

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Glycolipid
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a lipid with a carbohydrate component
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apoprotein
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protein that together with a prosthetic group forms a particular biochemical molecule such as a hormone or enzyme


apolipoproteins are the major components of lipoproteins

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Lipoprotein
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spherical particles involved in the transport of lipids with nonpolar neutral lipids (triglycerides and cholesterol esters) in their core and more polar amphipathic lipids (phospholipids and free cholesterol) at their surface
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lipase
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  1. a pancreatic enzyme that catalyzes the breakdown of fats to fatty acids and glycerol or other alcohols
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lipemia
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the presence in the blood of an abnormally high concentration of emulsified fat
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Saturated fatty acids vs. unsaturated types
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Saturated fatty acids have no double bond between their carbons

 

Monounsaturated fatty acids contain one double bond

Polyunsaturated fatty acids contain multiple double bonds

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Chylomicron
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A microscopically visible particle appearing in the plasma after a fatty meal.

 

Over 90% of TGL make up chylomicrons

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VLDL - Very Low Density Lipoprotein
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Composition: 50-65% TGL, 15% cholesterol, +proteins

 

Function: carries endogenous cholesterol and other TGL from liver to tissues

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LDL = Low Density Lipoprotein
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Composition: primarily cholesterol about 50%

 

Function: primary chosterol transport from liver to tissues; transports most of the TGLs?

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HDL = High Density Lipoprotein
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Composition: AI & AII apolipoprotein and contains cholesterol ester

 

Function: "cholesterol scavenger"; esterification of cholesterol and transports cholesterol from tissues to liver, where it is converted to bile acids and excreted.

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Emusification and absorption of dietary lipids
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The digestive enzyme, lipase, is water soluble and can only work at the surface of fat globules.  Digestion is greatly aided by emulsification, the breaking up of fat globules into much smaller emulsion dropletsBile salts and phospholipids areamphipathic molecules that are present in the bile. Motility in the small intestine breaks fat globules apart into small droplets that are coated with bile salts and phospholipids, preventing the emulsion droplets from re-associating
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Physiological Function of Lipids
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hormones, energy source, assisting digestion, structural component of cellular membrane
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