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MBOD Week 7 > Digestion of Carbohydrates > Flashcards

Digestion of Carbohydrates Flashcards

1
Q

T or F: to be metabolized, all dietary CHO must be hydrolyzed to monosaccharides

A

True

The major dietary carbohydrates are starch, sucrose and lactose.

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2
Q

What is amylose?

A

unbranched chains composed of glucose residues linked alpha-1,4

starch is composed of amylose and amylopectin

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3
Q

How does amylopectin differ from amylose?

A

it contains alpha-1,4- linked chains with alpha-1,6-linked branches

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4
Q

How does glycogen compare to amylopectin?

A

similar but has even more branches

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5
Q

What is the function of salivary and pancreatic amylases and where are they located?

A

They initiate digestion of polysaccarides by hydrolyzing starch (amylose and amylopectin) and glycogen

Both straight chain and branched polysaccharides are hydrolyzed at the alpha-1, 4-glycosidic linkages

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6
Q

What types of bonds are broken by amylase are the biproducts of hydrolyses by amylase?

A
  • Breaks alpha-1,4-glycosidic linkages
  1. Maltose
  2. maltotriose
  3. glucose
  4. limit dextrins (alpha - dextrins)
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7
Q

Where does pancreatic amylase act?

A

In the lumen of the intestine

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8
Q

What releases bicarbonate into the GI tract?

A

pancreas

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9
Q

What are the products of the action of pancreatic alpha amylase on alpha dextrins?

A
  1. Trisaccharides
  2. Oligosaccharides
  3. Maltose
  4. Isomaltose
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10
Q

Can tri and disaccharides be transported into the bloodstream?

A

No, sugars must be broken down into their monomer components to be absorbed

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11
Q

What is the job of disaccharidases (oligosaharidases)?

A

They digest oligosaccharides into monosaccharides so that they can be absorbed. This occurs in the small intestine

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12
Q

What are some examples of oligosaccharide substrates for different disaccharidases?

A

Dextrins
Maltose -> glucose
isomaltose -> glucose
sucrose (sucrase -> glucose and fructose)
lactose (lactase -> glucose and galactose)
oligosaccharides

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13
Q

T or F: CHO digestion is completed by 5 enzymes that are specific for particular CHO’s?

A

False, there are FOUR enzymes and these enzymes have overlapping activity

These enzymes have overlapping specificity, and therefore we often refer to the activity they catalyze rather than the specific enzyme. For example, both the sucrose-isomaltase complex and the glucoamylase complex can hydrolyze maltose. Therefore when we refer to “maltase” activity, we are actually talking about two different enzymes, both of which can hydrolyze maltose

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14
Q

Where are the dissacharidases located?

A

In the intestinal brush border (aka intestinal villa) at the top of cells

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15
Q

What is the the function of the glucoamylase complex (an alpha-glucosidase) and where is it located?

A

Cleavage/hydrolysis of:

  1. Glucose from the nonreducing end of oligosaccharides
  2. maltose (a- 1,4 bonds)
  3. Isomaltose

located in the brush border

glucoamylase complex concentration increases progressively down the length of the small intestine from jejunum to ileum.

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16
Q

How much of total intestinal maltase and isomaltase activity is accounted for by glucoamylase?

A

20% maltase

10% isomaltase

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17
Q

What is the sucrase-isomaltase complex and where is it located?

A

Cleavage/Hydrolysis of:

  • sucrose (to glucose and fructose)
  • isomaltose (alpha- 1,6 bonds)

located in the brush border

Sucrase isomaltase complex and lactase are highest in the jejunum. (duodenum-jejunum-ileum)

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18
Q

What accounts for most of the maltase and isomaltase activity in the brush border?

A

Sucrase-isomaltase complex

  • 80% of total intestinal maltase actvity
  • > 90% isomaltase (intestinal alpha-1,6-oligosaccharidase) activity
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19
Q

How does glucoamylase work on trisaccharides?

A
  1. works on the linkage at non-reducing end releasing one glucose and leaving maltose
  2. the remaining Maltose is acted on by glucoamylase to release two glucose monomers
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20
Q

How are brush border enzymes (dissacharidases) such as sucrase-isomaltase oriented in the intestinal wall?

A
  • N-terminal end is found in the cell cytoplasm of intestinal cell
  • two domains that act on the different sugars sit across the membrane in the lumen of the intestine at brush boarder surface
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21
Q

What is lactase and what is it needed for?

A
  • brush border enzyme
  • hydrolyzes the ß-1,4-linkages found in lactose and some complex lipids
  • Needed to digest milk sugars
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22
Q

T or F: lactase activity declines with age in certain ethnic groups

A

True

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23
Q

What is trehalase?

A
  • brush border enzyme
  • hydrolyzes alpha-1,1-linkage in trehalose (Trehalose consists of 2 resides of glucose, linked alpha 1,1-. It is NOT a reducing sugar)
  • this is typically only found in insects and mushrooms
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24
Q

What does the presence of trehalase suggest about human diet?

A

The our ancestors likely consumed lots of insects and mushrooms

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25
Q

What is the activity of the sucrase domain in the sucrase-isomaltase complex?

A

sucrose –> glc + fru

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26
Q

What is the activity of the isomaltase domain of the sucrase-isomaltase complex?

A

hydrolyzes alpha-1,6-glycosidic linkages of isomaltose

27
Q

What is the activity of the maltase domain of the sucrase-isomaltase complex?

A

hydrolyzes alpha-1,4-glycosidic linkages of maltose

28
Q

What type of CHO digestion reactions happen in the oral cavity?

A

Starch is digested by salivary amylase to become linear and branched oligosaccharides

29
Q

What type of CHO digestion reactions happen in the intestinal lumen?

A

starch and dextrins are broken down by pancreatic amylase to maltos, maltotriose, and alpha-limit dextrins

30
Q

What type of CHO digestion reaction happen in the intestinal lumen?

A

Disaccharides are broken down by the 4 brush border enzyme complexes to their monomer components:

maltose → (alpha-glucoamylase complex + sucrase-isomaltase complex) → glucose

maltotriose -> (glucoamylase complex) → glucose

alpha-limit dextrin → (isomaltase) → maltose + maltotriose + glucose

lactose → (lactase) -> galactose + glucose

sucrose → (sucrase) → fructose + glucose

trehalose → (trehalase) → glucose

31
Q

What is malabsorption?

A

the failure to digest and absorb sugars

sometimes called maldigestion

32
Q

What is intolerance?

A

abdominal symptoms that result from malabsorptions

33
Q

What are the symptoms of intolerance and what are the causes of these symptoms?

A
  • diarrhea, steatorrea, abdominal discomfort, distention, flatulence
  • retention of non-absorbed nutrients within the lumen of the gut
34
Q

When are symptoms of malabsorption relieved?

A

following elimination of the foods containing the disaccharide

35
Q

How does non-absorbed lactose in the intestines ever get metabolized and where does this happen?

A

Lactose gets metabolized by intestinal bacteria to form:
1. organic acids that increase peristalsis resulting in diarrhea

  1. CO2 that results in distension, pain, and flatulence
    * happens in colon
36
Q

What is serum amylase?

A

the small amount of pancreatic amylase or salivary amylase that makes it to the blood

37
Q

When would you expect to see rises in serum amylase, how would you detect these rises?

A
  1. obstruction of the ducts
  2. inflammatory diseases
    (e. g. acute pancreatitis or obstruction of pancreatic ducts)
  3. mumps

** this results in regurgitation of amylase into the blood which leads to increased excretion in the kidney

38
Q

When would levels of serum amylase fall off?

A
  1. acute hepatitis

2. pancreatic insufficiency

39
Q

How is a lactose tolerance test performed?

Note: similar methods are used to test tolerance of other sugars

A
  1. Patient drinks 50 grams of lactose
  2. test blood glucose (BG) at regular intervals up to 2 hours after ingestion
  3. Normal individuals would have a BG increase of >1.7 mmoles/L (>31 mg/dL) over fasting BG levels
40
Q

What does isomaltase do?

A

hydrolyzes α-1,6-glycosidic linkages; cleaves isomaltose

41
Q

What does Sucrase do?

A

hydrolyzes sucrose to glc and fru.

42
Q

What does Lactase do?

A

hydrolyzes β-1,4-glycosidic linkages; hydrolyzes lactose to glc and gal.

43
Q

What does Trehalase do?

A

hydrolyzes trehalose to glc

44
Q

Summary of CHO digestion “membrane digestion”

A

maltose → (alpha-glucoamylase complex + sucrase-isomaltase complex) → glucose

maltotriose -> (glucoamylase complex) → glucose
alpha-limit dextrin → (isomaltase) → maltose + maltotriose + glucose

lactose → (lactase) -> galactose + glucose

sucrose → (sucrase) → fructose + glucose

trehalose → (trehalase) → glucose

45
Q

What is Malabsorption?

A

The failure to digest and absorb sugars ± signs of clinical intolerance (sometimes called maldigestion)

Symptoms of malabsorption should be relieved following elimination of the foods containing the disaccharide.

46
Q

What is intolerance?

A

Refers to abdominal symptoms that result from sugar malabsorption. The clinical features of malabsorption are due to the retention of non-absorbed nutrients within the lumen of the gut. Sometimes the term malabsorption is used instead of intolerance leading to confusion. Signs and symptoms are diarrhea, steatorrhea, abdominal discomfort, distention, and flatulence.

47
Q

What is lactose intolerance?

A

an age-dependent intolerance to dietary lactose. Very common in blacks and asians. Symptoms include cramps, bloating, moderate to severe pain, and moderate to severe diarrhea. Treatment involves avoiding milk or lactose containing materials, and/or adding lactase to the diet.
In lactase intolerance or deficiency, lactose is metabolized by intestinal bacteria. The sugar is metabolized to organic acids and CO2. Organic acids can increase peristalsis leading to diarrhea, and CO2 production can result in abdominal distension, pain, flatulence.

48
Q

Notes on serum amylase

A

Normally a small amount of amylase, which originates from the pancreas or salivary glands, is found in blood. Obstruction of the ducts or inflammatory diseases of these glands results in regurgitation of amylase into the blood and increased excretion via the kidney. Serum amylase is elevated in acute pancreatitis, obstruction of pancreatic ducts, and mumps. Activity is decreased in acute and chronic hepatitis, and in pancreatic insufficiency.

49
Q

Notes on URINE AMYLASE

A

If renal function is adequate, amylase in the blood is rapidly excreted in the urine. Elevation of the urinary amylase concentration occurs in the same situations in which serum amylase concentration is elevated.

50
Q

Notes on SERUM LIPASE

A

In pancreatitis, pancreatic lipase is released into the circulation along with amylase, and serum lipase activity can be used in conjunction with amylase to evaluate pancreatic function.

51
Q

Notes on Lactose Tolerance Test

A

For people suspected of having lactase deficiency, a lactose tolerance test can be used to confirm the diagnosis

One version of the test consists of drinking 50 grams of lactose in water and then measuring blood glucose 5, 10, 30, 60, 90 and 120 minutes later. In normal healthy patients the blood glucose should increase by >1.7 mmoles/L (>31 mg/dL) over fasting glucose levels. In lactase deficient patients, the increase in blood glucose is less. Similar tolerance tests can be carried out for other deficiencies, referred to as “SUGAR” TOLERANCE TESTS

52
Q

notes on hydrogen breath test

A

Sugars that are not digested pass into the large intestine, where they are metabolized by intestinal bacteria. This results in the production of several products including short chain fatty acids, hydrogen and other gases. These gases collectively are responsible for much of the pain, noise, and aroma associated with intestinal gases and flatulence. Some of the hydrogen diffuses through the intestinal wall and enters the blood stream, where it eventually reaches the lungs and is expired. Hydrogen is normally found in the expired air, but when “extra” food reaches the gut, the bacteria produce additional hydrogen. This test can be used to detect the inability to metabolize various sugars. This includes the inability to hydrolyze normal “sugars”, and indigestible carbohydrates such as the one found in beans.

53
Q

what are some indigestible carbs?

A

cellulose and raffinose

54
Q

What is BEANO?

A

Drug Sold OTC to minimize the gas from beans and other vegetables. BEANO contains an enzyme that hydrolyzes carbohydrate found in beans, which is not normally hydrolyzed by intestinal enzymes

55
Q

What is PRECOSE?

A

(ACARBOSE TABLETS) - Used in the treatment of diabetes. Inhibits alpha-glucosidase activity of the small intestine, which breaks down starches into monosaccharides. It must be taken with the first bite of a meal, and slows down carbohydrate digestion in the small intestine. Carbohydrates that are not digested move to the large intestine for digestion by bacterial fermentation. Also delays breakdown of sucrose. Initial doses of Precose lead to GI side-effects such as abdominal pain, diarrhea, and flatulence.

56
Q

What is lactase tablets used for?

A

can be added to milk to digest lactose, or they can be taken orally to mix with milk and other dairy products. Yoghurt contains lactase activity, and can be eaten along with dairy products to digest lactose.

57
Q

How is a lactose tolerance test performed?

Note: similar methods are used to test tolerance of other sugars

A
  1. Patient drink 50 grams of lactose
  2. test blood glucose at regular intervals up to 2 hours after ingestion
  3. Normal individuals would have a BG increase of >1.7 mmoles/L (>31 mg/dL) over fasting BG levels
58
Q

How does a hydrogen breath test work and what does it test for?

A
  • Tests for additional H2 in the blood

- H2 levels become elevated when bacteria in the gut become overactive from metabolizing undigested disaccacharides

59
Q

what are Cellulose and Raffinose (found in beans) example of?

A

indigestible carbs

60
Q

How does Beano work?

A

contains and enzyme that hydrolzyes raffinose in beans which is not normally hydrolyzed by intestinal enzymes.

61
Q

What does Precose do and how does it work?

A
  • used to treat diabetes and is ingested with the first bite of food
  • inhibits alpha-glucosidase activity in the small intestine
62
Q

Why are abdominal pain, diarrhea, and flatulence a result of taking Precose?

A

It leaves starches undigested which provides food for bacterial metabolism in the colon

63
Q

How can eating yogurt along with dairy products help to digest lactose?

A

it contains lactase activity

MBOD Week 7 (6 decks)

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