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Gastrointestinal > Lecture 8: Digestion and Absorption > Flashcards

Lecture 8: Digestion and Absorption Flashcards

1
Q

What is the difference between cellular and paracellular transportation?

A

CELLULAR: through the cell
PARACELLULAR: substances travel between cells via tight junctions

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2
Q

Carbohydrates must be digested to ____________ to be absorbed through the intestine

A

monosaccharides

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3
Q

Starch is a mixture of both ____ and _________ polymers of glucose

A

straight; branched

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4
Q

What are the straight chain polymers?

A

Amylose

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5
Q

What are the branched polymers?

A

Amylopectin

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6
Q

What are the 3 disarccharides?

A

1) Trehalose (2 glucose)
2) Sucrose (glucose and fructose)
3) Lactose (glucose and galactose)

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7
Q

What are the 3 monosaccharides?

A

1) Glucose
2) Fructose
3) Galactose

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8
Q

Which crucial linkage in cellulose cannot be broken down by the body?

A

beta 1,4 linkage

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9
Q

What enzyme digests polysaccharides in the saliva and pancreas?

A

alpha amylase

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10
Q

Digestion of starch begins with which enzyme?

A

a amylase

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11
Q

Which bonds do pancreatic amylase digest?

A

alpha 1,4 bonds

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12
Q

What 3 disaccharides does amylase digestion produce?

A

1) a limit dextrins
2) maltose
3) maltotriose

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13
Q

The 3 dissarchide products from starch digestion (a limit dextrins, maltose, and maltotriose) are broken down into monosaccharides by which 3 intestinal BRUSH BORDER ENZYMES?

A

1) a dextrinase
2) maltase
3) sucrase

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14
Q

What carbohydrates do NOT require amylase digestion?

A

Disaccharides (trehalose, sucrose, lactose)

they have their own enzymes named after them but with ‘ase’ ending

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15
Q

What transporter carries GLUCOSE and GALACTOSE into the cell and what is special about it?

A

SGLT1

It is sodium dependent and ACTIVE (both sugars and sodium are traveling up their concentration gradient)

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16
Q

Where is SGLT1 located?

A

apical membrane of small intestine

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17
Q

Which transporter carries fructose into the cell?

A

GLUT5

ffffffructose fffffive

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18
Q

What transporter allows all 3 monosaccharides to pass via facilitated diffusion across the basolateral membrane?

A

GLUT2

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19
Q

In lactose intolerant patients, what is missing?

A

Lactase enzyme from the brush border

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20
Q

In lactase deficient patients, lactose remains undigested and unabsorbed in the intestinal lumen. This retains water and leads to ________ _________

A

osmotic diarrhea

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21
Q

Where is lactase missing in congenital lactose intolerance?

A

jejunum

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22
Q

What are the consequences of a mutation in SGLT1?

A

glucose-galactose mal absorption; severe diarrhea (fructose diet only)

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23
Q

What is the meaning of “essential” amino acids?

A

cannot be synthesized by body, need to be obtained by diet

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24
Q

Where does protein digestion start?

A

stomach (pepsin)

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25
Q

Where does protein digestion end?

A

small intestine (pancreatic and brush-border proteases)

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26
Q

What are the 2 classes of proteases?

A

1) endopeptidase (hydrolyze interior peptide bonds of proteins)
2) exopeptidase (hydrolyze one AA at a time from the C-terminal end)

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27
Q

What enzyme cleaves trypsinogen into its active form, trypsin?

A

enterokinase

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28
Q

What inactivates pepsin?

A

pancreatic HCO3

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29
Q

True or false: the partial protein digestion by pepsin is essential

A

FALSE (patients without a stomach do just fine)

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30
Q

What are the 5 major pancreatic proteases secreted as inactive precursors?

A

1) Typsinogen
2) Chymotrypsinogen
3) proelastase
4) Procarboxypeptidase A
5) Procarboxypeptidase B

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31
Q

Where is enterokinase located?

A

brush border epithelium

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32
Q

Which pancreatic enzyme is capable of autocatalysis?

A

Trypsin

33
Q

What is the digestable/absorbable products of protein digestion?

A

amino acids, di and tri peptides

34
Q

True or false: oligo peptides are absorbable

A

FALSE; they need to by further hydrolyzed by brush-border proteases

35
Q

What do amino acids transporters commonly symport with?

A

Sodium

36
Q

What do peptide transporters symport with?

A

H+

37
Q

Which transporters are responsible for the uptake of drugs?

A

peptide transporters

38
Q

How do amino acids exit the cell?

A

facilitated diffusion

39
Q

What are 3 disorders of protein digestion and absorption?

A

1) Single AA absorption (solution: absorb di or tri peptides that have AA hydrolyzed by enzymes in cytoplasm)
2) Trypsinogen deficiency (solution: eat diet of partially hydrolyzed proteins)
3) Cystinuria - transporter for dibasic AAs absent in small intestine/kidney

40
Q

What are the 4 categories of lipid in the diet?

A

1) Triglycerides (MAJOR SOURCE)
2) Phospholipids
3) Cholesterol
4) Vitamins A, D, E, and K (fat soluble)

41
Q

What is the functional benefit of emulsification in terms of digestion?

A

mixing of the stomach churns the dietary lipids into a suspension of fine droplets increasing surface area for digestive enzymes

42
Q

What does the emulsifying in the stomach?

A

dietary proteins

43
Q

What does the emulsifying in the small intestine?

A

bile acids

44
Q

Where does lipid digestion begin?

A

Stomach (gastric lipase secreted by gastric chief cells hydrolyzes 10% of dietary triglycerides to glycerol and free fatty acids)

45
Q

What is the biggest contribution of the stomach to lipid digestion?

A

Timing the emptying to allow enough time for pancreatic enzymatic action

46
Q

Where does the majority of lipid digestion occur?

A

small intestine

47
Q

What are the 3 important lipolytic enzymes in pancreatic juice that work at neutral pH?

A

1) pancreatic lipase
2) phospholipase A2
3) cholesterol ester hydrolase

48
Q

What lipid substrate does pancreatic lipase work on? And what critical cofactor does it rely on for efficacy?

A

Triglycerides (hydrolyzes them to monoglycerides and fatty acids)

needs COFACTOR COLIPASE to anchor lipase to fat droplet so that bile acids won’t inactive lipase

49
Q

What lipid substrate does phospholipase A2 work on?

A

Phospholipids (secreted as proenzyme and activated by trypsin)

50
Q

What lipid substrate does cholesterol ester hydrolase work on?

A

cholesterol - frees cholesterol and fatty acids

51
Q

What are the products of lipid digestion? How are the solubilized?

A

1) monoglycerides
2) fatty acids
3) cholesterol
4) lysolecithin

micelles

52
Q

What is the only lipid digestion byproduct that is water soluble?

A

Glycerol

53
Q

True or false: the lipid-containing micelles do not enter the cells

A

TRUE; the micelles drop off their contents at the apical membrane at the brush border where the lipids diffuse down their concentration gradient

54
Q

Where are bile salts reabsorbed?

A

ILEUM

55
Q

What happens to the lipid digestion products inside the cell?

A

they are re-esterified with FFA on the smooth ER to make triglycerides, cholesterol, and phospholipids again

56
Q

How are lipids exported from the cell after digestion?

A

Chylomicrons (triglycerides and cholesterol at the core and phospholipids and apoproteins on the outside)

57
Q

Where do chylomicrons travel?

A

lymphatic capillaries to the thoracic duct where they empty into the bloodstream

58
Q

What leads to disorders of lipid digestion?

A

1) Pancreatic insufficiency: defective enzyme secretion
2) Acidity of duodenal contents (ex: Zollinger-Ellison): pancreatic enzymes don’t function at optimal pH
3) deficiency of bile salts: no micelle formation
4) Abetalipoproteinemia: inability to form chylomicrons

59
Q

Where is a majority of the water absorbed in the GI tract?

A

Small intestine (remainder absorbed in colon)

60
Q

The tight junctions of the small intestine are _______ permitting a lot of paracellular movement while the tight junctions of the colon are _______ and do NOT permit paracellular movement

A

leaky; tight

61
Q

Where is the major site of Na+ absorption?

A

small intestine

62
Q

sodium enters the jejunal epithelial cells on the apical side via which 3 transporters?

A

1) Na-monosaccharide cotransporters
2) Na amino acid cotransporter
3) Na H exchanger

63
Q

In the Na/H exchanger, which ion enters the cell and which leaves it?

A

H leaves; Na enters

64
Q

What additional transporter is found in the ileum?

A

Cl/HCO3 exchanger in the apical and a Cl transporter in the basolateral

65
Q

In the ILEUM there is net absorption of ______ and in the JEJUNUM there is net absorption of ________

A

NaCl; NaHCO3

66
Q

Cl diffuses into the lumen through _________ while Na diffuses passively through ______ ______

A

channels; tight junctions

67
Q

Cl channels on apical membrane are usually ________ (open/closed)

A

closed

68
Q

What activates the Cl channels on apical membrane?

A

neurotransmitters (Ach, VIP)

69
Q

What is the secondary messenger which opens the Cl- channels?

A

cAMP

70
Q

What is osmotic diarrhea?

A

caused by the presence of non-absorbable solutes in the intestinal lumen (ex: lactase deficiency so lactose hangs out in the lumen and pulls water with it)

71
Q

What is secretory diarrhea?

A

caused by excessive secretion of fluid by crypt cells (ex: overgrowth of enterohepatic bacteria)

72
Q

What is necessary for calcium absorption in the small intestine?

A

vitamin D

73
Q

What is the path of calcium absorption in the small intestine?

A

Ca diffuses down electrochemical gradient –> bound to calbindin –> pumped across basolateral membrane by Ca-ATPase

74
Q

What does calcium malabsorption lead to?

A

rickets and osetomalacia

75
Q

Where does vitamin B12 bind when it is released from food by pepsin?

A

R proteins

76
Q

When does Vitamin B12 associate with Intrinsic Factor?

A

when it travels to duodenum and pancreatic proteases degrade R proteins

77
Q

What secretes IF?

A

gastric parietal cells (NEED THESE or get pernicious anemia)

78
Q

Where is B12 absorbed?

A

ileum

Gastrointestinal (8 decks)

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