Carbohydrate Metabolism Flashcards
What is an oral glucose tolerance test (OGTT), and what is it used for?
A patient will take in a large volume of sugar water. Blood glucose levels will increase then decrease as the body releases insulin. It can be used to determine if the body is producing the correct amount of insulin to regulate blood glucose.
Describe a normal OGTT and compare it to an OGTT in a diabetic?
A diabetic produces ineffective insulin or no insulin at all so they would not see the decrease in blood glucose after the ingestion of sugar
What range of blood glucose levels would indicate hypoglycemia?
Anything below 70 mg/dL. Can be caused by impared hepatic glycogenolysis/gluconeogenesis/ high cellular uptake/ too much insulin
**Excessive Boozing = (+++) NADH in liver which will inhibit gluconeogenesis
What range of blood glucose would indicate hyperglycemia?
anything above 100 mg/dL
What glucose range would indicate normoglycemia?
70-100 mg/dL
What are the symptoms of hypoglycemia, and the long term consequences of hypoglycemia?
Stimulates the release of glycogen
List the processes, pathways, or reactions that increase blood glucose. (4)
- Digestion of dietary carbs
- Conversion of other dietary sugars to glucose
- Glycogenolysis- lysis of glycogen
- Gluconeogenesis- Synthesis of glucose
List the major pathways and reactions that contribute to the utilization of blood glucose. (5)
- Glucose Transporters or phosphorylation
- Glycolysis
- Glucogenesis
- Phosphogluconate pathway
- Sorbitol Pathway
List the major hormones important for regulating blood glucose,
INSULIN- Stimulates insulin uptake and storage
Describe the major metabolic role of insulin.
Liver- Stimulates storage of glucose as glycogen and citrate for the syn of Fatty Acids VLDL for storage in the adipocyte
Skeletal Muscle- stimulates utilization of glucose and citrate
Adipocyte- store triacylglycerol.
What are the counter-regulatory hormones? Why are they important?
Glucagone (+) blood glucose by stim glycogenolysis and gluconeogenesis
Epinepherine- stim glycogenolysis/ inhibits insulin secretion.
Cortisol- stim glucagone release
Growth Hormone- (+) hepatic glucose production/ (-) utilization in tissue
How do you measure blood or urine glucose concentrations?
Blood Glucose Assay- (hexokinase assay) Glucose Oxidase Assay. Enzyme reacts with glucose in the blood
Urine Glucose Assay- high glucose will spill from the blood to the urine
Describe three methods that can be used to measure sugars, and describe their specificity.
Glucose Oxidase assay and Hexose oxidase assay are the most specific.
Why is it essential to regulate blood glucose concentration?
The Brain Runs of Glucose and Oxygen, hypoglycemia = decreased uptake by the brain (less in girls of course) and impared cognition/ headache /confusion /shaking /
(?:305) In terms of carbohydrates, what is the major source in the diet?
Starch
What is a form of glucose storage in mammals?
Glycogen
What carbohydrate vitamin is required for hydroxylation of proline/lysine in collagen?
Vitamin C
What is a non-digestable carbohydrate that has important roles in digestion?
Fiber
List some functions of carbohydrates
Cofactors, DNA/RNA nucleotide sugar phosphate backbone, glycoproteins, glycolipids, proteoglycans, bacterial walls (NAG/NAM), cellulose, receptors, adhesion molecules, etc.
What two major hormones play a large role in glucose regulation in vivo?
Glucagone, insulin
What is an OGTT?
Oral glucose tolerance test, glucose levels measured after a meal to diagnose diabetes
T or F: after a meal insulin levels go down
F: they go up in response to increased blood glucose levels
T or F: after a meal insulin levels go down
Digestion, glycogenolysis, gluconeogenesis
What are some pathways that increase blood glucose?
Glycolysis, glycogenesis, pentose phosphate pathway
Where is insulin synthesized?
Beta cells of pancreas
What is insulin initially synthesized as? What is cleaved off of this and use as a glucose indicator in blood?
Preproinsulin, C peptide
What are the effects of epineprhine on blood glucose? Cortisol? Growth hormone?
Stimulates glycogenolysis/lipolysisincreases blood glucose; increases blood glucose long term; increases hepatic glucose production and reduces glucose use
What is the normal range of glucose in the blood?
70-100 mg/dL
Describe conditions of hypoglycemia
Shaky, nervous, hungry, sweaty, headache, mood change, confusion, tachycardia, loss of consciousness (in order from least severe to most)
Does hyperglycemia or hypoglycemia cause an increase in HbA1c?
Hyperglycemia
How is impaired glucose tolerance diagnosed?
Basis of OGTT, blood glucose values between normal and diabetic
What are 3 ways to measure glucose from blood?
Reduction methods, glucose oxidase assay, hexokinase assay
What are 2 ways to measure glucose from urine?
Reduction methods, glucose oxidase dipstick
What is the most used test? Which is the most specific test?
Glucose oxidase assay; Glucose oxidase assay
How do you actually measure glucose in the urine?
Catalyzes conversion of glucose to gluconic acid via oxygen and forms peroxide which reacts with a chromogen to form a colored product
What is the “Gold standard” test?
Hexokinase assay, specific and accurate test that uses G6P DH to catalyze oxidation of G6P and reduce NADP+ to NADH which can be measured at 340 nm on a spectrophotometer
What are some causes of glycosuria?
Decreased renal tubular reabsorption, pregnancy, etc. dipsticks can be used to measure glucose in urine (some use glucose oxidase test)
What is starch composed of? Which starch is most similar glucose?
linked glucose residues; glycogen
Describe the hydrolyzing starches of amylose and amylopectin
amylose=> unbranched chains of glucose residues linked alpha-1,4
amylopectin=> alpha-1,4- linked chains alpha-1,6 linked branches
T/F all dietary CHO must be first digested (hydrolyzed) to monosaccharides
True
What are the major dietary CHO?
starch, sucrose and lactose
What begins the process of digestion of polysaccarides?
Salivary and pancreatic amylases by hydrolyzing starch (amylose and amylopectin) and glycogen
Amylase hydrolyzes alpha-1,4-glycosidic linkages form what?
maltose, maltotriose, glucose, and limit dextrins
Where do pancreatic amylases work? What must be present for amylase to work there?
lumen of the intestine
HCO3 to change the pH so amylase can work in the intestine
What is the result of amylase?
initial digestion of starch into smaller chunks
What begins the process of digestion?
alpha dextrins
Describe the GI track from ingestion to feces
- Starch, lactose, sucrose
- salivary alpha-amylase
- sucrose, lactose combine with alpha Dextrins
- alpha dextrins receive alpha amylase (from pancreas) along with HCO3
- Tri and oligosaccharides maltose, isomaltase digested to monosaccharides for absorption by Disaccharidases found in the intestinal villa
6.
What are examples of disaccharidases and what do they help absorb?
Maltase, isomaltase
Sucrase
lactase
Where is CHO digestion completed?
4 enzymes associated with the intestinal brush border membrane
Describe the glucoamylase complex
cleaves glucose from nonreducing end of oligosaccharides, cleaves maltose and isomaltase
increases in complexity down small intestine
Describe the sucrase-isomaltase complex
highest activity in the jujenum
sucrase hydrolyzes sucrose
isomaltase cleaves alpha 1,4 and alpha 1,6 linkages
What does glucoamylase do?
Cleaves the bands joining molecules which is ALWAYS AT THE 1ST NONREDUCING END
Where is the N terminus of the sucrase-isomaltase?
cytoplasm
Why hydrolyzes the alpha 1,1 linkage found in trehalose? where is this found?
trehalase and trehalose is found in mushrooms and insect blood
Where does CHO digestion take place?
luminal surface
Define malabsorption of lactose
failure to digest and absorb sugars and show signs of clinical intolerance
Define lactose intolerance
abdominal symptoms that result from sugar malabsorption
clinical Sx=> diarrhea, steatorrhea, abdominal discomfort, distention, flatulence
age dependent common in blacks and asians
Tx=> add lactase to diet
What metobolizes lactose? What treatments may affect this?
intestinal bacteria so cancer Tx can affect
What are 3 disorders associated with CHO deficiency?
lactase, sucrase-isomaltase, trehalase deficiency
Describe the difference in serum amylase and urine amylase biochem tests
serum amylase=> amylase may be found in blood and decreased activity in acute and chronic hepatitis, and in pancreatic insuffiency
Urine amylase will occur when renal fxn is inadequate and amylase in the blood will be excreted from the urine
Describe how the lactose tolerance test works
drink 50 grams of lactose in water then measure glucose levels
How will lactase deficient patients show when taking the test?
increase of blood glucose is less than in healthy patients
How does the hydrogen breath test detected?
inability to metabolize various sugars including the inability to hydrolyze normal “sugars” and indigestible CHO
