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MBOD Week 7 > Carb Metabolism and Blood Glucose > Flashcards

Carb Metabolism and Blood Glucose Flashcards

1
Q

What are some carbohydrates that form the major component of many diets?

A

Starch (major component) and disaccharides

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2
Q

How do mammals store glucose?

A

Glycogen. Glycogen is a branched chain homopolymer of glucose containing both alpha-1,4- and alpha-1,6- bonds

Some tissues, such as the brain and red blood cells, require glucose. Other tissues can use either glucose or fatty acids, but preferentially use glucose under certain conditions, ex. anoxia.

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3
Q

What are the 7 functions of carbohydrates in the cell?

A
  • nutrition (starch, dissacharides)
  • energy source (glucose)
  • energy storage (glycogen)
  • vitamins (Vit C)
  • non-nutritive dietary roles (fiber)
  • Structural
  • molecular recognition
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4
Q

What are some of the structural functions of carbohydrates?

A
  • Cofactors like NAD+ and nucleotides for DNA and RNA
  • Glycoproteins/proteoglycans (in CT)
  • Glycolipids, cerebrosides, gangliosides
  • Cellulose
  • Bacterial Cell wall
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5
Q

What cells consume exclusively glucose for energy?

A

Red Blood Cells and Brain

Note: Other tissues can use either glucose or fatty acids, but preferentially use glucose under certain conditions, ex. anoxia.

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6
Q

T or F: over a 24 hour period large fluctuations in blood glucose are expected

A

False - fluctuations in Blood Glucose should be small even during fasting periods

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7
Q

What hormones are key to controlling blood glucose?

A

Insulin- works to decrease BG

Glucagon- works to increase BG

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8
Q

What happens to blood glucose, insulin, and glucagon after a meal?

A
  • glucose Spikes a bit ~30 minutes after eating then back to normal after ~1.5 hrs
  • insulin levels increase
  • glucagon levels decrease
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9
Q

What happens to the insulin to glucagon ratio after a meal?

A

it increases

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10
Q

What is a normal glucose concentration?

A

70-100 mg/dL or slightly less

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11
Q

What types of signals help balance the need of fuels with tissue needs in order to maintain homeostasis?

A
  • Blood level of nutrient
  • Hormone Level
  • nerve impulse
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12
Q

What are 4 pathways that increase blood glucose?

A
  1. Digestion of dietary carbohydrates
  2. conversion of other dietary sugars to glucose
  3. Glycogenolysis - breakdown of glycogen
  4. Gluconeogenesis - sythesis of new glucose (largly completed by the liver)
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13
Q

What are 5 pathways that use blood glucose?

A
  • Glucose transporters and phosphorylation (keeps glucose in cell)
  • glycolysis
  • glycogenesis - synthesis of glycogen (liver, muscle)
  • The phosphogluconate pathways
  • Sorbitol pathway (converts glucose to fructose and sorbitol)
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14
Q

What is the phosphogluconate pathway often used for?

A

To synthesize other carbohydrate precursors like ribose and to make NADPH

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15
Q

T or F: insulin is a catabolic hormone

A

False - insulin stimulates glucose uptake and storage = anabolic hormone

Increases glucose uptake by muscle and adipose tissue, increases hepatic glycogenesis and lipogenesis

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16
Q

Where is insulin synthesized and what are the stages of insulin maturation?

A
  • In the pancreas by the ß-cells of the islets of Langerhans
  • Synthesized as pre-proinsulin (single chain polypetide) –> proinsulin —> insulin + C-peptide (which are stored in granules, and are eventually secreted)

A number of hormones are secreted which oppose the actions of insulin and are referred to as counter-regulatory hormones

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17
Q

What processes are upregulated by insulin in adipocytes?

A
  • insulin increases glucose uptake

- increases conversion of fatty acids to triacylglycerols

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18
Q

What processes are upregulated by insulin in the liver?

A
  1. Conversion of glucose to glycogen
  2. protein synthesis
  3. conversion of glucose to fatty acids that are exported as very low density lipoproteins (VLDL)
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19
Q

What processes are upregulated by insulin in skeletal muscle?

A
  1. conversion of amino acids to proteins

2. Conversion of glucose to CO2 and glycogen

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20
Q

What are 4 counter-regulator hormones for insulin?

A
  1. glucagon
  2. epinephrine
  3. cortisol
  4. growth hormone
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21
Q

How does glucagon counter insulin’s effects?

A
  1. stimulates glycogenolysis
  2. stimulates gluconeogenesis

aka increases blood glucose

22
Q

What cells secrete glucagon?

A

alpha cells of the pancreas

23
Q

What stimulates glucagon secretion?

A

hypoglycemia

24
Q

How does epinephrine work to counter the effect insulin?

A
  1. stimulates glycogenolysis
  2. stimuates adipose tissue lipolysis
  3. inhibits insulin secretion
25
Q

What stimulates epinephrine secretion?

A

stress (fight or flight response)

Secretion is markedly enhanced by hypoglycemia

26
Q

How does cortisol counter the effects insulin?

A

stimulates glucagon release and gluconeogenesis

long term need for fuel

27
Q

How does growth hormone counter the effects of insulin?

A

increases hepatic glucose production and reduces glucose use by some tissues

28
Q

What stimulates growth hormone production?

A

hypoglycemia

29
Q

What effects does glucagon have on skeletal muscle?

A

no effect

30
Q

Where does glucagon have the strongest effect?

A

In the liver

31
Q

What effects does glucagon have on the liver?

A
  1. amino acids are used to make glucose
  2. glycogen is degraded for glucose
  3. Prevents glucose conversion into fatty acids
32
Q

What effect does glucagon have on adipose tissue?

A
  1. promotes degradation of triacylglycerols to fatty acids (lipolysis)
33
Q

What are some causes of hypoglycemia?

A

caused by the inability of the liver to maintain normal blood glucose concentrations

  1. impaired hepatic glycogenolysis or gluconeogenesis
  2. excessive cellular uptake of glucose
  3. excessive doses of insulin (via tumor or injection)
  4. excessive alcohol consumption
34
Q

How can excessive alcohol consumption cause hypoglycemia?

A
  • increases NADH (an inhibitor of gluconeogenesis) in liver

- Disruption of NADH/NAD+ ratio affects a number of reactions

35
Q

What classifies mild hypoglycemia and what are it’s symptoms?

A

Blood glucose less than 68 mg results in decreased glc uptake by brain*

Blood glucose less than 54 mg% results in symptoms of hypoglycemia*

Signs and symptoms include feeling shaky, nervous, very hungry and sweaty.

The treatment includes quickly eating something with sugar such as 3 teaspoons of sugar, or orange juice.

36
Q

What classifies mild to moderate hypoglycemia and what are it’s symptoms?

A

Blood glucose less than 49 mg% results in cognitive dysfunction*

Signs and symptoms may include headache, mood change, confusion, and a rapid heat beat. The treatment is to quickly eat double the recommendations for a mild hypoglycemia. A tube of Insta-glucose provides the right dose according to the ADA (about 30 grams of glucose)

37
Q

What classifies severe hypoglycemia and what are it’s symptoms?

A
  • no values given
  • loss of consciousness
  • injection of glucagon or dextrose required
38
Q

What are common causes of hyperglycemia?

A
  • insulin deficiency (type 1 diabetes)
  • Decreased secretion of insulin
  • reduced ability to respond to insulin (type 2 diabetes)

If diabetes is untreated the body responds as if it were starving by increasing the mobilization of fuels from storage. This can increase the hyperglycemia and result in ketoacidosis (especially in Type 1 diabetes).

39
Q

What is hemoglobin A1c?

A

hemoglobin that is glycosylated non-enzymaticaly as a result of high blood sugar

Exposure of red blood cells to hyperglycemia results in nonenzymatic glycosylation of hemoglobin (HbA). An increase of hemoglobin A1c above 6% of the total hemoglobin indicates an elevated blood glucose concentration over the last 6-8 weeks. Hb A1c levels are now an invaluable tool to help diabetics monitor their blood glucose levels.

40
Q

What is an OGTT?

A

oral glucose tolerance test

41
Q

T or F: impaired glucose tolerance is often asymptomatic?

A

True

42
Q

If someone has impaired glucose tolerance what would you expect to see on their OGTT?

A

blood glucose values that were intermediate between that of a normal person and a diabetic

43
Q

What is the most common type of blood insulin test and how does it work?

A

GLUCOSE OXIDASE ASSAY

An enzyme of the oxidoreductase class that catalyzes the reaction: beta-D-glucose + O2 D-glucono-gamma-lactone + H2O2

The enzyme is a flavoprotein, and highly specific for beta -D-glucose. It is used in the clinical laboratory in the determination of “true” glucose. The enzyme catalyzes the conversion of glucose to gluconic acid by molecular oxygen, with the formation of hydrogen peroxide. In most versions of this assay, peroxidase transfers oxygen from hydrogen peroxide to an organic chromogen to form a colored product, which is measured spectrophotometrically. Glucose oxidase is used for home glucose testing.

44
Q

What is the gold standard of BG assays?

A

Hexokinase assay

45
Q

how much glucose does a normal person have in their urine?

A
  • very little
46
Q

When does glycosuria typically occur?

A
  • BG > 160-180 mg/dL

Usually glucose is not present in urine until the blood concentration in the blood is 160-180 mg/dL, the normal renal threshold for glucose

47
Q

What are some situations besides diabetes when glycosuria occurs?

A
  • decreased renal tubular absorption (could be a benign congenital issue)
  • Pregnancy (believed to be due to a lowered renal threshold.)
48
Q

What is glycosuria?

A

Glycosuria is the presence of significant quantities of glucose in the urine (Usually little if any glucose is excreted in the urine)

49
Q

What are the two basic tests used to screen or monitor glycosuria?

A

the glucose oxidase method which is specific for glucose and the copper reduction tests which detect reducing substances

50
Q

What are dipsticks?

A

Dipsticks, used for urinalysis, are sticks with several small pads attached. Each pad contains specific chemicals that react with substances found in urine. When a reaction occurs there is a color change that can be read by eye or with an automatic reader. Dipsticks allow multiple tests to be run on a urine sample. Common tests include urine glucose, ketones, pH, protein, specific gravity, and bilirubin. They are useful, but very qualitative.

MBOD Week 7 (6 decks)

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