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Carbohydrates
Chemistry of Carbohydrates
Question | Answer |
---|---|
What are the three groups of carbohydrates? | Monosaccharides,Oligosaccharides, polysaccharides |
What is the most common monosaccharides found in living organisms? | glucose |
Name three reducing sugars. | glucose, maltose and lactose |
What is the fundamental unit of starch? | D-glucose |
Name the three most common oligosaccharides and what they are composed of | Maltose (2 glucoses), Lactose (glucose and galactose), and Sucrose (glucose and fructose) |
Name the two components that make up starch. | amylose and amylopectin |
Name the nutrient polysaccharide of animal tissue. | glycogen |
How are carbohydrates metabolized? | monosacc. transported to liver; fructose and galactose converted to glucose; some glucose released into blood and some stored as glycogen |
How is glycogen formed? (glycogenesis) | glucose converted to glucose-6-phosphate, which is converted to glucose-1-phosphate, then converted touridine diphosphate glucose and finally glycogen |
What is different when glycogen is broken down (glycogenolysis) in the liver as opposed to other tissues of the body? | when glycogen is broken down in the liver, free glucose is released into the blood circulation, in other tissues G6P cannot be dephosphorylated so glucose stays in tissues to be used for energy and none is released into blood |
What is glycolysis? | breakdown of glucose to pyruvic acid or lactic acid for ATP production |
What is gluconeogenesis? | synthesis of glucose from non carbohydrate sources |
What is glycogenolysis? | breakdown of glycogen to glucose |
What is glycogenesis? | process of glycogen formation; glucose converted to glycogen |
What hormone lowers blood glucose levels? | insulin |
How does insulin work? | increases the uptake of glucose by muscle and fat cells by increasing the cell membrane’s permeability to glucose, increases the uptake of glucose by liver, and promotes glycogenesis and lipogenesis. |
Where is insulin produced? | beta cell of Islets of Langerhans |
What is C-peptide? | insulin is produced from proinsulin; when it is broken in beta cells, resultant parts are insulin and C-peptide; C-peptide is only found with endogenous insulin production |
Name the 5 glucose elevating hormones. | glucagon, epinephrine, growth hormone/ACTH, glucocorticoids, and thyroid hormones. |
How does glucagon work and where is it produced? | breaks down liver glycogen, stimulates liver gluconeogenesis, and hepatic lipolysis; alpha cells of pancreas |
What is the renal threshold for glucose and what does this mean? | 160-180 mg/dL; when blood glucose levels reach 160-180 glucose will spill over into the urine |
What is the most common cause of diabetes mellitus in the US? | idiopathic (this does not mean people with low IQ are more likely to get it!) |
What are the two types of diabetes mellitus? | IDDM and NIDDM |
Which is more severe disease? | IDDM (improperly named “juvenile” in the past); must be treated with insulin |
What are kussmaul respirations? | rapid, deep breathing; in diabetic ketoacidosis, bicarb has been depleted, pH is decreased, so body tries to blow off pCO2 to bring pH back to normal |
How does a person become hypoglycemic? | fasting12-14 hours or response to stimulus |
What types of stimuli can cause hypoglycemia? | tumors (pancreatic or non-pancreatic), deficiency of hormones (thyroid), drugs (insulin, ethanol) |
Name three inborn errors of carbohydrate metabolism that lead to hypoglycemia. | galactosemia, fructose intolerance and glycogen storage diseases |
What is CSF glucose used for? | neurologic disorders, bacterial meningitis |
How can glycolysis be slowed in collected specimens? | adding sodium fluoride, cooling specimen, separating cells from plasma/serum within 30 minutes |
How does the glucose oxidase method work? | glucose oxidized by glucose oxidase in presence of oxygen to form glucuronic acid and hydrogen peroxide; then peroxidase catalyzes the oxidation of chromogenic oxygen acceptor by hydrogen peroxide forming a colored product |
When testing for glucose in urine, how does the Benedict’s copper reduction test work? | semi-quantitative measurement that measures for reducing substances; reducing substances will react with copper sulfate to form reduced cuprous oxide and results in a color change |
What other sugars will give a positive test? | galactose, maltose and lactose |
What does glycated hemoglobin test for? | fraction of hemoglobin molecule that contains glucose, continuous for lifespan of RBC, used for determining compliance with therapy and control of diabetic patient for previous 8-10 weeks |
When is the OGTT used? | when fasting blood glucose is not clearly increased (old guidelines) |
In a normal person, when should the glucose level peak during an OGTT? | 30-60 minutes |
In a mildly diabetic patient, when should glucose levels peak? | 30-60 minutes |
In a severely diabetic patient, when should glucose levels peak? | may take longer than 60 minutes to peak |
If normal persons and mildly diabetic persons glucose levels both peak at 30-60 min, how do you determine diabetes in the mild cases? | mild diabetics do not return to normal |
What is a two-hour postprandial glucose test? | perform a fasting glucose and then test 2 hours after a mealor glucose dose of 100g (note: it has been replaced by fasting / 2 hr. specimens of OGTT per new guidelines) |
What is gestational diabetes? | diabetes first occurring while pregnant |
When should gestational diabetes screening be done? | (old guidelines) at 24-28 weeks; (new guideline) only on high risk patients |
List the tolerance tests: | Glucose (OGTT, 2 hr PP); Insulin (to detect dwarfism: low GH); Tolbutamide (pancreas tumors); Epinephrine (decreased in von Gierke’s) |