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Physiology II > GI: Digestion and Absorption > Flashcards

GI: Digestion and Absorption Flashcards

1
Q

Enzymes for digestion are excreted from… (3)

A

salivary glands
gastric chief cells
exocrine pancreas

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2
Q

final breakdown of all substances occurs wehre?

A

small intestine

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3
Q

What are the two major steps of CHO digestion?

A

complex sugar to oligosaccharide (1:6 link)

oligosaccharaide to monosaccharide (1:4 link)

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4
Q

What percent of ingested CHOs are complex?

A

60% (glycogen, amylose, amylopectins)

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5
Q

both salivary and pancreatic alpha-amylase break what bond on CHOs?

A

1:4 alpha bonds

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6
Q

Luminal digestion of partially converted starch by pancreatic amylase results in what 5 products?

A

lactose, alpha-dextrin, maltotriose, maltose, sucrose

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7
Q

Membrane digestion of CHO results in what three products?

A

glucose, galactose, fructose

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8
Q

Lactose is broken down to _____ via…

A

glucose + galactose via lactase

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9
Q

alpha-dextrins are broken down to ______ via…

A

glucose via maltase + alpha-dextrinase

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10
Q

What 3 enzymes convert maltotriose and maltose to glucose?

A

maltase, sucrase, alpha-dextrinase

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11
Q

Sucrose is converted to ________ via…

A

glucose + fructose via sucrase

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12
Q

Disaccharidases/oligosaccharidases are what type of proteins?

A

intrinsic membrane proteins

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13
Q

Where are disaccharidases/oligosaccharidases synthesized?

A

epithelial cells

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14
Q

What are the two types of disaccharidases/oligosaccharidases

A

galactosidases (lactase)

alpha-glucosidases (sucrase, maltase, alpha dextrinase)

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15
Q

What brings fructose in from the lumen to the small intestinal epithelial cell?

A

GLUT5

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16
Q

What percent of ingested CHO are digested to glucose?

A

80%

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17
Q

Glucose transport occurs via…

A

secondary active transport due to high plasma glucose

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18
Q

This is a sodium dependent channel on the apical membrane responsible for glucose/galactose uptake.

A

SGLT1

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19
Q

SGLT-1 uses the sodium gradient to transport what two substances from the lumen to the epithelial ICF?

A

glucose and galactose

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20
Q

This channel on the basolateral surfaces transports glucose and galactose via facilitated diffusion…

A

GLUT2

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21
Q

Does the intestinal epithelial cell have a sodium-potassium ATPase?

A

yes

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22
Q

Most disorders of CHO absorption/digestion have what pathophysiology?

A

enzyme deficiency prevent breakdown to absorbable form

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23
Q

disorders of CHO digestion result in what?

A

osmotic diarrhea

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24
Q

This is a congenital enzyme deficiency that may not be evident until later in life. It is present in about 50% of the population.

A

lactase deficiency

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25
Q

Lactase deficiency prevents lactose digestion leading to…

A

osmotic diarrhea, abdominal distension

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26
Q

Proteins are ____% of caloric intake.

A

20-35%

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27
Q

A significant amount of protein comes from…

A

desquamated cells and gastric secretion

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28
Q

What catalyzes the conversion of trypsinogen to trypsin?

A

enteropeptidases

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29
Q

Gastric proteases (pepsins) are secreted from…

A

chief cells

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30
Q

Pancreatic enzymes from the _____ cells are activated in the ______

A

acinar cells

small intestine

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31
Q

What are the products of protein digestion?

A

amino acids and oligopeptides

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32
Q

Trypsin catalyzes the conversion of…

A

proenzymes to active enzymes

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33
Q

Protein digestion begins in the stomach where protein is converted to ______ and _____ via…

A

AAs and oligopeptides via pepsin

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34
Q

In the small intestine, what 5 enzymes break proteins down to oligopeptides, amino acids, dipeptides and tripeptides?

A

trypsin, chymotrypsin, elastase, carboxypeptidase A and B

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35
Q

oligopeptides/large peptides that remain in the lumen after enzyme digestion can be further digested by peptidases at the ______ to be transported into the cell.

A

brush border

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36
Q

Protein transport is similar to glucose in that it is ______ transport coupled to…

A

secondary active

coupled to sodium

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37
Q

Amino acids are transported from the lumen to the epithelial cell via…

A

sodium/AA cotransport

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38
Q

dipeptides and tripeptides are transported to the epithelial cell via…

A

H+ cotransport

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39
Q

What are the four protein cotransporters?

A

neutral AAs
dibasic AAs
dicarboxylic AAs
imino/proline

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40
Q

Within the epithelial cell in the small intestine, what breaks dipeptides and tripeptides to amino acids for passage to blood?

A

intra cellular peptidases

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41
Q

T/F: Amino acid transporters specific for the class of amino acid…

A

True

42
Q

What 3 diseases of protein digestion have the following characteristics?

  • insufficient trypsin in intestin
  • decreased protein absorption leading to malnutrition
A

pancreatic insufficiency/chronic pancreatitis/CF

43
Q

What disease of protein digestion has the following characteristics?

  • congenital defect in neutral AA transport
  • di and tripeptide absorption remains normal
A

hartnup disease

44
Q

What disease of protein digestion has the following characteristics?

  • absent dibasic AA transporter (for cystine, lysine, arginine) absent from guy and kidney
  • dibasic AAs lost in urine and feces
A

Cystinuria

45
Q

What three factors make fat digestion difficult?

A

hydrophobic
non water soluble enzymes
require churning/bile emulsification

46
Q

What are 4 key events in fat digestion?

A

secretion
emulsification
hydrolysis
solubilizing

47
Q

What must be secreted to digest fat?

A

bile and lipases

48
Q

What bonds must be hydrolyzed in fat digestion?

A

ester linkages

49
Q

lipid digestion products must be solubilized within____ to be delivered to enterocytes

A

micelles

50
Q

Which lipid digestion enzyme?

convert TGs to monoglyceride + 2 FFAs

breaks FFAs off the 1,3 positions

A

pancreatic lipase

51
Q

What prevents bile salt inhibition of pancreatic lipase?

A

colipase

52
Q

What catalyzes the conversion of 2 monoglyceride to glycerol + 1 FFA?

A

cholesterolester hydrolase

53
Q

cholesterol ester hydrolase can remove all three ester linkages, and removes fatty acids from what substances? (3)

A

cholesterol esters
vitamins A/D/E
glycerides

54
Q

What can hydrolyze phospholipids at the 2 position?

A

phospholipase A2

55
Q

products of fat digestion are quickly moved where with what substances?

A

bile acid micelles with lysophospholipid and cholesterol

56
Q

The micelle breaks down and products diffuse where?

A

apical surface of enterocyte

57
Q

Long-chain FFAs, 2-MG, phospholipids and cholesterol are absorbed into the enterocyte via…

A

simple diffusion

58
Q

Micelles diffuse through what layer to the mucosal surface?

A

unstirred layer

59
Q

what percent of ingested fat is removed by the small intestine?

A

95%

60
Q

Once inside the enterocyte, what is the fate of micelle components?

A

lipid reassembly

61
Q

What pathway of lipid reassembly?

2 monoglycerides + Fatty Acyl CoA → TGs

A

Monoglyceride acylation pathway

62
Q

What pathway of lipid reassembly?

glycolysis → P-Glycerol or diOH-AcetoneP → Alpha-GlycerolP → TGs

A

Phosphatidic Acid Pathway

63
Q

What large molecule has a core of TGs and cholesterol surrounded by phospholipids and apoproteins?

A

chylomicrons

64
Q

By what transport mechanism do chylomicrons leave enterocytes, and what do they enter?

A

exocytosis, enter lymph lacteals

65
Q

What is the composition of chylomicrons?

A

84% TGs, 8% phospholipids, 6% cholesterol, 2% apoproteins

66
Q

What abnormality of lipid digestion/absorption has the following characteristics?

  • gastrin secreting tumor
  • acidic small intestine
  • dysfunctional pancreatic lipase
A

abnormal digestion: Zollinger-Ellison Syndrome

67
Q

What abnormality of lipid digestion/absorption has the following characteristics?

  • generalized lymphatic dystrophy
  • steatorrhea
  • rare, macrophages in jejunal lamina
A

Abnormal absorption: Whipple’s Disease

68
Q

What are the fat-soluble vitamins?

A

A, D, E, K

69
Q

Fat soluble vitamins are processed in the same manner as dietary lipids, meaning they are transported in the lumen via _____ and enter circulation via…

A

transport micelles

circulation via chylomicrons

70
Q

Water soluble vitamins are most often absorbed via…

A

sodium dependent co-transport

71
Q

B12 binds to _______ which protects it from digestion, allowing it to be absorbed where?

A

intrinsic factor, absorbed in ileum

72
Q

Calcium absorption occurs where via…?

A

brush border via facilitated diffusion

73
Q

What causes expression of the calcium binding protein (intracellular calcium shuttle)?

A

Vit. D3

74
Q

What transporters are present on the basolateral membrane to allow calcium to enter circulation?

A

Calcium-ATPase

Sodium-Calcium Exchanger

75
Q

the amount of iron ingested is greater or less than the amount absorbed?

A

much greater (low absorption)

76
Q

Gastric acid promotes intestinal absorption and solubilization of iron via what process?

A

reduce from Fe3+ (ferric) to Fe2+ (ferrous)

77
Q

What is the plasma transporter for iron?

A

transferrin

78
Q

What is the intracellular storage depot for iron?

A

ferritin

79
Q

1.5-2.5 L of water is ingested per day. How much is secreted into the gut lumen by the GI tract?

A

7L

80
Q

What percent of water is lost in feces?

A

2%

81
Q

Is the stomach permeable to water?

A

no

82
Q

reabsorption of water has what osmolarity

A

isosmotic

83
Q

Water follows solute out of the basolateral membrane. So what transporters increase water absorption?

A

sodium cotransport of amino acids and sugars

84
Q

What is the primary site for sodium absorption in the small intestine?

A

jejunum

85
Q

What channels are present on the apical membrane of jejunal epithelial cells?

A

NHE, Sodium-Glucose/AA channels

86
Q

What channels are present on the basolateral membrane of jejunal epithelial cells?

A

Bicarb Channel, AA/Glucose Channles, Sodium-Potassium ATPase

87
Q

In the jejunum, is there a net secretion or net absorption of sodium bicarb?

A

absorption

88
Q

Describe the mechanism of Cl- absorption in the jejunum?

A

voltage driven paracellular absorption

89
Q

What transporters are present on the ilieal apical membrane?

A

NHE, Sodium-Glucose/AA channels

Cl-/HCO3 exchanger

90
Q

What transporters are present on the ilieal basolateral membrane?

A

Sodium-Potassium ATPase

Sugar/AA channels

Cl- channel

91
Q

In the jejunum, there is a net reabsorption of NaHCO3. What is reabsorbed in the ileum?

A

NaCl

92
Q

What is secreted into the lumen of ileal epithelial cells? What effect does this have on acid/base status?

A

H+ and HCO3- secretion, no change to acid/base

93
Q

What channels are present on the apical membrane of colon epithelial cells?

A

ENaC (in) and K (out)

94
Q

What stimulates ENaC channels on the apical membrane of colon epithelial cells?

A

Aldosterone

95
Q

What regulates the rate of potassium secretion in the colon?

A

flow

96
Q

What are three clinical effects of diarrhea?

A

Loss of fluid, bicarb, potassium

97
Q

What are three major causes of diarrhea?

A

decreases surface area for absorption

osmotic diarrhea

excessive secretion (cholera)

98
Q

Crypt cells have what channel on the basolateral surface that brings in chloride?

A

NKCC1

99
Q

Cholera toxin stimulates secretion of Cl- out of what channel, via increased production of _______ via…

A

CFTR channel

increases cAMP production via irreversible adenylyl cyclase activation

100
Q

How does water and sodium follow chloride in cholera?

A

paracellular

101
Q

What is an example of secretory diarrhea?

A

cholera

102
Q

how do you treat cholera?

A

oral rehydration therapy

Physiology II (28 decks)

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