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603 Physiology > GI 8 > Flashcards

GI 8 Flashcards

1
Q

digestion

A

physical and chemical breakdown of ingested foods into absorbable molecules

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2
Q

Primary Site of Digestion?

A

Small intestine

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3
Q

Where do most enzymes in the small intestine come from?

A

the pancreas

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4
Q

absorption

A

movement of neutrients, water, and electrolytes from the lumen of the intestine into the bloodstream

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5
Q

3 Components of the Intestine that increase Surface Area

A
  1. Villi
  2. Microvilli
  3. Glycocalyx
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6
Q

glycocalyx

A

intestinal brush border on surface of microvilli, holds enzymes secreted from intestinal epithelial cells

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7
Q

2 Major Forms of Starch

A
  1. Amylose
  2. Amylopectin
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8
Q

Major Action of digestive enzymes?

A

hydrolysis

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9
Q

2 Phases of Digestion

A
  1. Luminal phase
  2. Membrane phase
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10
Q

Explain starch digestion by hydrolysis.

A

enzymes break bonds of the starches during the luminal phase into smaller molecules, but complete hydrolysis occurs during the digestive phase into singular monomers to be absorbed by the intestinal epithelium

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11
Q

Luminal phase of digestion

A

incomplete hydrolysis of nutrients

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12
Q

Membrane (brush border) phase of digestion

A

generates absorptive molecules or very short oligomers

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13
Q

What is a possible third step in digestion?

A

cytosolic proteolysis

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14
Q

Cytosolic proteolysis

A

short peptides undergo further digestion within the intestinal epithelial cell (cytosol) by intracellular hydrolases

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15
Q

2 Paths for Absorption

A
  1. Transcellular Path
  2. Paracellular Path
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16
Q

transcellular path for absorption

A

nutrient moves through intestinal cell into the interstitial fluid

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17
Q

paracellular path for absorption

A

nutrients move across tight junctions between the intestinal epithelial cells

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18
Q

Most common path for nutrient absorption?

A

transcellular path

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19
Q

4 Transcellular Transport Mechanisms

A
  1. Passive transport (facilitated diffusion)
  2. Primary active transport
  3. Secondary active transport
  4. Tertiary active transport
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20
Q

How are the active transport mechanisms named?

A

based on where the energy comes from

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21
Q

Primary Active Transport

A

direct consumption of metabolic energy, move across a membrane d/t presence of electrical or chemical gradient

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22
Q

2 Examples of Primary Active Transport Pumps

A
  1. Sodium-Potassium-ATPase pump
  2. Proton pump on parietal cells of gastric acid secretion
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23
Q

On which aspect of the cell will you find your primary active transport pumps?

A

basolateral side

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24
Q

Sodium Potassium ATPase Pump

A

pumps 3 Na+ in and 2 K+ out to create a gradient within the cell and generate energy for use by other transporters

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25
Q

Two Types of Secondary Active Transporters

A
  1. Sodium co-transporters
  2. Exchangers (countertransport, antiport)
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26
Q

Sodium CoTransport Protein

A

has binding sites for Na+ and other specific molecules (glucose, galactose, AAs, vitamins, bile acids)

27
Q

Secondary Active Transport

A

transport using the potential energy of a sodium gradient (rather than a direct use of metabolic energy)

28
Q

Exchangers

A

binding sites for two different ligands on opposite sides of the plasma membrane

29
Q

Tertiary Active Transport

A

driven by electrochemical gradients that were established by secondary active transport

30
Q

Of these pumps, label what type of transport each is.

A

Red = Primary
Purple = Secondary (exchanger)
Green = Secondary (sodium cotransporter)
Yellow = Tertiary

31
Q

What is a starch?

A

glucose polymer

32
Q

Three Forms of Plant Carbohydrates

A
  1. Starches
  2. Sugars
  3. Fibers
33
Q

How does the body digest fiber?

A

it is dependent on bacteria

34
Q

End product of carbohydrate digestion? (3)

A

Monosaccharides!
1. Glucose
2. Fructose
3. Galactose

35
Q

Fructose absoprtion is by what transport mechanism?

A

facilitated diffusion

36
Q

Glucose and galactose are absorbed through the apical surface by what transport mechanism?

A

Secondary active transport by cotransporters (specifically SGLT-1, sodium ______ linked tranporters)

37
Q

How are monosaccharides absorbed on the basolateral side?

A

facilitated diffusion (all three)

38
Q

oligomer

A

short peptide

39
Q

monomer of protein

A

amino acid

40
Q

Can carbs be digested with cytosolic proteolysis?

A

no

41
Q

5 Pancreatic Proteases

A
  1. Trypsinogen
  2. Chymotrypsinogen
  3. Proelastase
  4. Procarboxypeptidase A
  5. Procarboxypeptidase B
42
Q

Are any of the proteases secreted in active form?

A

no, all as zymogens from the pancreas

43
Q

Which protease is secreted the most?

A

trypsinogen (40% of all proteases)

44
Q

Where do you find pepsinogen and when is it activated?

A

in the stomach; activated as long as pH in the small intestine remains below 4.5

45
Q

What enzyme in the small intestine converts trypsinogen to its active form? Where is this found?

A

enterokinase, in the brush border (glycocalyx)

46
Q

What activates the remaining proteases in the small intestine?

A

trypsin

47
Q

Can trypsin act on trypsinogen?

A

yes

48
Q

Is protein digestion by pepsin in the stomach essential?

A

no, it is non-essential

49
Q

Peptidases

A

additonal enzymes present in the membrane phase of digestion to continue to break down proteins into monomers and oligomers

50
Q

Mechanism of amino acid transport across the apical membrane?

A

Secondary active (sodium cotransporter)

51
Q

Mechanism of dipeptide and tripeptide absorption across the apical membrane?

A

PEPT-1 (peptide transporter 1), cotransporter with H+ ion

52
Q

Mechanism by which amino acids cross the basolateral membrane?

A

facilitated diffusion

53
Q

Are lipids water soluble?

A

no

54
Q

3 Dietary Lipids

A
  1. Triglycerides
  2. Cholesterol
  3. Phospholipids
55
Q

amphipathic

A

hydrophilic and hydrophobic components

56
Q

Emulsification

A

bile salts surround lipids (preventing them from joining as one large glob, increasing surface area) and form micelles

57
Q

Micelle

A

lipid droplet surrounded by bile salts carried to the intestinal epithelial cells before the hydrophillic side dissolves inthe aqueous part

58
Q

Are all enzymes for lipid digestion secreted as zymogens?

A

No, some are secreted in active form (such as those for cholesterol esters or triglycerides (lipases))

59
Q

5 Steps of Lipid Absorption

A
  1. Form micelles in the lumen
  2. Diffuse across apical membrane
  3. Re-esterification
  4. Packaged into chylomicrons (vesicles)
  5. Excytosed across basolateral membrane into lymph (thoracic duct), and eventually to blood
60
Q

Where are bile salts absorbed?

A

ileum

61
Q

What % of lipid digestion products are re-esterified inside the cell?

A

70

62
Q

Are fat soluble vitamins absorbed the same way as lipids?

A

yes

63
Q

Mechanism of water soluble vitamin transport?

A

Soium-dependent cotransporters (secondary active transport)
(just like glucose, galactose, and AAs)

64
Q

Vitamin B12 absorption?

A

dependent on the intrinsic factor released by parietal cells, happens in the ileum

603 Physiology (22 decks)

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