(14) Carbohydrates (C) Flashcards
Define carbohydrates.
The major food source and energy supply of the body. Stored as liver and muscle glycogen.
The two forms of carbohydrates are:
aldose and ketose
The chaining of sugars relies on what type of bond?
Glycoside bonds.
What traits must a carbohydrate have in order to be considered a reducing substance?
The carbohydrate must contain a ketone or an aldehyde group.
What enzyme is used in the digestion of carbohydrates?
Salivary amylase and pancreatic amylase.
________ is the only carbohydrate to be directly used for energy or stored as glycogen.
Glucose.
The first step for all three metabolic pathways requires glucose to be converted to what?
Glucose-6-phosphate.
Conversion of glucose to glucose-6-phosphate is catalyzed by what enzyme?
Hexokinase.
What metabolic pathway is used to convert glucose-6-phosphate to glycogen?
Embden-Meyerhof pathway or the hexose monophosphate pathway (HMP).
Define gluconeogenesis.
The conversion of amino acids to glucose.
Define glycogenesis.
The conversion of glucose to glycogen.
Define glycogenolysis.
The conversion of glycogen to glucose-6-phosphate.
Define glycolysis.
Metabolism of glucose. Produces pyruvate or lactate.
Define lipogenesis
The conversion of carbohydrates to fatty acids.
Control of blood glucose is under what two major hormones?
Insulin and glucagon.
Insulin and glucagon are produced by:
the pancreas.
Describe the function of insulin.
The primary hormone responsible for the entry of glucose into the cell.
Where is insulin synthesized?
By the beta-cells of islets of Langerhans within the pancreas.
Insulin decreases plasma glucose by:
increasing the transport entry of glucose in muscle and adipose tissue by way of nonspecific receptors.
Define hypoglycemic agent.
A hormone that decreases glucose levels (e.g., insulin).
Describe the action of insulin.
Increases glycogenesis and glycolysis; increases lipogenesis; decreases glycogenolysis.
Describe the action of glucagon.
Increases glycogenolysis; increases gluconeogenesis.
Where is glucagon synthesized?
Alpha-cells of islets of Langerhans in the pancreas.
Glucagon acts by:
Increasing plasma glucose by glycogenolysis and gluconeogenesis.
What two hormones produced by the adrenal gland affect carbohydrate metabolism?
Epinephrine and Glucocorticoids (cortisol).
Where is epinephrine synthesized?
Adrenal medulla.
Where is glucocorticoids (cortisol) synthesized?
Adrenal cortex.
Describe the action of epinephrine.
Increases plasma glucose by inhibiting insulin secretion; increase glycogenolysis; promotes lipolysis.
Glucocorticoids are produced by the stimulation of:
Adrenocorticotropic Hormone (ACTH).
Describe the action of cortisol.
Increases plasma glucose by decreasing intestinal entry into the cell; increases gluconeogenesis, liver glycogen, and lipolysis.
What two anterior pituitary hormones promote increased plasma glucose?
Growth hormone and ACTH.
Describe the action of growth hormone in glucose production:
Decreases the entry of glucose into the cells; increases glycolysis.
Describe the action of ACTH in glucose production.
Decreased cortisol stimulate the release of ACTH. ACTH releases cortisol which increases glucose by converting glycogen to glucose and promoting gluconeogenesis.
The thyroid gland is stimulated by the production of ________ to release ________ that increases plasma glucose.
TSH; thyroxine
Thyroxine increases plasma glucose by increasing:
glycogenolysis, gluconeogenesis, and intestinal absorption of glucose.
Where is somatostatin synthesized?
Delta-cells of the islets of Langerhans of the pancreas.
How does somatostatin increase glucose?
Inhibits insulin, glucagon, growth hormone, and other endocrine hormones.
Hyperglycemia is caused by an imbalance of:
hormones.
Define type 1 diabetes.
Characterized by inappropriate hyperglycemia primarily a result of pancreatic islet beta-cell destruction and a tendency to ketoacidosis.
Define type 2 diabetes.
Includes hyperglycemia that result from insulin resistance with an insulin secretory defect.
Define impaired fasting glucose.
Fasting glucose is increased above normal limits but not to the level of diabetes.
Define impaired glucose tolerance.
Glucose tolerance values above normal but below diabetes levels was retained.
Define type 1 diabetes mellitus.
A result of cellular-mediated autoimmune destruction of the beta-cells of the pancreas, causing an absolute deficiency of insulin secretion.
What age groups does type 1 diabetes commonly occur?
Childhood and adolescence.
List the laboratory findings in hyperglycemia.
Increased glucose (plasma & urine)
Increased urine S.G.
Increased osmolality (serum & urine)
Ketones in serum and urine
Decreased pH (blood & urine) (acidosis)
Electrolyte imbalance
Causes of gestational diabetes mellitus include:
metabolic and hormonal changes.
List the diagnostic criteria for diabetes mellitus.
(1) HbA1c >= 6.5%
(2) Fasting plasma glucose >= 126 mg/dL
(3) 2h plasma glucose >= 200 mg/dL during OGTT
(4) Random plasma glucose >= 200 mg/dL
Glucosuria can occur when the glucose concentration of plasma exceeds:
180 mg/dL
What ketone bodies contribute to acidosis?
Acetoacetate & beta-hydroxybutyrate
How is hyperglycemia affect serum osmolality?
Increased osmolality.
What is the glucose values for someone with nonketoic hyperosmolar state?
300 to 500 mg/dL
In nonketoic hyperosmolar state, severe dehydration contributes to what?
The inability to excrete glucose in the urine.
The laboratory findings of nonketotic hyperosmolar coma include:
Plasma glucose >1000 mg/dL
Normal or Elevated Na and K
Slight decreased bicarbonate
Elevated BUN and CREAT
Elevated osmolality
All adults beginning at the age of 45 years should be tested for diabetes every 3 years using what test(s)?
(1) Hemoglobin A1c
(2) Fasting plasma glucose
(3) 2-hour 75 g OGTT
Four methods of DM diagnosis are:
(1) HbA1c >6.5%
(2) Fasting plasma glucose >126 mg/dL
(3) 2-hour 75 g OGTT >200 mg/dL
(4) Symptoms plus fasting glucose >200 mg/dL
Reference range for fasting glucose.
70 - 99 mg/dL
Reference range for glucose tolerance.
2-h PG <140 mg/dL
Pregnant women should be screened for GDM between:
24 to 28 weeks of gestation.
The one-step approach for GDM diagnosis is:
2-hour OGTT with 75 g glucose load. Measurements at fasting, 1 hour, and 2 hours.
Fasting = >92 mg/dL
1-hour = 180 mg/dL
2-hour = >153 mg/dL
Any one of three of the criteria are met are positive for GDM.
Hypoglycemia is the result of:
an imbalance in the rate of glucose appearance and disappearance from the circulation.
Describe the Whipple triad.
Hypoglycemia should be made only in those who demonstrate:
(1) Hypoglycemic symptoms
(2) Plasma glucose concentration low (<50 mg/dL)
(3) Symptoms are relieved by correction (administered glucose or glucagon)
What are the laboratory findings in someone with beta-cell tumors (insulinoma)?
Decreased plasma glucose; extremely elevated insulin.
What is diagnostic criteria for insulinoma?
Change in glucose levels >= 25 mg/dL,
insulin level >= 6 uU/mL
C-Peptide >=0.2 nmol/L
proinsulin >= 5 pmol/L
beta-hydroxybutyrate <= 2.7 mmol/L.
Describe von Gierke disease (glucose-6-phosphate deficiency type 1).
Severe hypoglycemia that coincides with metabolic acidosis, ketonemia, and elevated lactate and alanine.
Describe galactosemia.
Congenital deficiency of one of three enzymes involved in galactose metabolism. Increased levels of galactose in plasma.
Describe fructose-1-phosphate aldolase deficiency.
Causes nausea and hypoglycemia after fructose ingestion.
Glucose concentration in whole blood is approximately ________ than the glucose concentration in plasma.
11% lower
What is the best anticoagulant for glucose testing?
Sodium fluoride.
(T/F) Fasting plasma glucose values have a diurnal variation.
True
The most common methods of glucose analysis use the enzyme:
Glucose oxidase or hexokinase.
________ is the most specific enzyme reacting with only beta-D-glucose.
Glucose oxidase
Why is hexokinase method considered more accurate over the glucose oxidase method?
Because the coupling reaction using glucose-6-phosphate dehydrogenase is highly specific; therefore less interference.
The testing methodology for the hexokinase reaction is.
Spectrophotometry.
For the hexokinase reaction, what may cause a false decrease in the glucose result?
Gross hemolysis and extremely elevated bilirubin.
For OGTT testing, the patient should be ambulatory and on a normal-to-high carbohydrate intake for ________ days before the test.
3
Define glycosylated hemoglobin.
The term used to describe the formation of a hemoglobin compound produced when glucose reacts with the amino group of hemoglobin.
For A1c testing, the rate of formation is:
directly proportional to the plasma glucose concentrations.
Glycosylated hemoglobin level at any one time reflects the average blood glucose level over the previous:
2 to 3 months.
Reference range for HbA1c testing.
4 to 6%
What two factors determine the glycosylated hemoglobin levels?
Average glucose concentration and the red blood cell life span.
What is the specimen requirement for HbA1c testing?
EDTA whole blood.
What is the preferred method for HbA1c testing?
Affinity chromatography.
Ketone bodies are produced by the liver through:
metabolism of fatty acids.
What is the specimen requirement for ketone testing?
Fresh serum or urine; tightly capped and analyzed immediately.
What is the most common testing method for ketone testin?
Sodium nitroprusside reacts with acetoacetic acid in alkaline pH to forms a purple color.
Diabetes mellitus causes progressive changes to the kidneys and ultimately results in:
diabetic renal nephropathy (diabetic kidney disease).
What is an early sign that diabetic kidney disease is occuring?
Increased urine albumin.
Persistent albuminuria is defined as:
Albumin-Creat ratio of 30 to 299 mg/g creatinine in two out of three urine collections over 3- to 6-month period.
