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GI- Week 4 > Prunuske: Intestinal Absorption > Flashcards

Prunuske: Intestinal Absorption Flashcards

1
Q

What are the duodenal/jejunum features that facilitate digestion and absorption?

A
  1. Plicae circularis (SI slows transit of food)
  2. Villi increase SA
  3. Segmenting contractions facilitate mixing
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2
Q

Where does enzymatic hydrolysis of carbohydrates and proteins occurs?

A

in the lumen through pancreatic enzymes

at the microvillous membrane

in the enterocytes for peptides

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3
Q

Intraluminal hydrolysis of polymers (starch/glycogen) by a-amylase (salivary and pancreatic) leads to…

A

small di and tri-saccharides

branched dextrins

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4
Q

Are amylase blocker supplements (Phaseolus vulgaris- white bean protein extract) an effective way to promote weight loss?

A

NO

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5
Q

What drug has been used to treat type II diabetes?

A

Acarbose

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6
Q

Can amylase products be immediately absorbed?

A

NO

They require further cleavage into the 3 absorbable monosaccharaides at the brush border

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7
Q

What is end product inhibition?

A

glucose can inhibit lactase activity

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8
Q

How is the expression of brush border hydrolases regulated?

A

In the intestinal villi

Higher in the proximal than distal intestine

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9
Q

What protects brush border hydrolases from proteases?

A

Heavily glycosylated

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10
Q

What is sucrase isomaltase?

A

single polypeptide

contains 2 active sites that are cleaved into two pieces by trypsin

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11
Q

What is hypolactasia?

A

lactose intolerance

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12
Q

What causes hypolactasia?

A

Injury to absorptive cells:
Chron’s disease
Celiac disease
alcohol

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13
Q

A person w/ lactose intolerance often presents w/ diarrhea. Why?

A 
W/out lactase>
Bacteria in the gut ferment lactose>
GAS ACCUMULATION/PAIN>
increase in lactic acid>
increases osmotic load>
pulls water into lumen>
increased peristalsis/diarrhea
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14
Q

How to you tx hypolactasia?

A

avoid lactose

lactase (lactaid)

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15
Q

What may sequester monosaccharides form bacteria?

A

Uptake in the duodenum and jejunum through:

SGLT1
GLUT5

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16
Q

SGLT1

A

Na monosaccharide symporter

Actively takes up Glucose and galactose

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17
Q

What type of transport process does SGLT1 use?

A

Secondary active transport process (2Na/1sugar)

Depends on low Na generated by the Na/K pump

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18
Q

What facilitates fructose uptake?

A

Glut 5

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19
Q

How do monsaccharides leave the basolateral membrane and go to the liver?

A

Glut 2

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20
Q

What limits digestion of proteins in the stomach?

A

pepsin

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21
Q

When is pepsin inactive?

A

pH > 4.5

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22
Q

Once proteins reach the duodenum, what enzymes are secreted?

A

Pancreatic proteases

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23
Q

Pancreatic proteases, like endopeptidases and carboxypeptidases require what brush border enzymes for activation?

A

enteropeptidase

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24
Q

What type of proteins are resistant to digestion?

A

glycoslyated and PROLINE rich

25
Q

Where are AA absorbed?

A

villi of duodenum and jejunum

26
Q

How are AA transported across the apical membrane?

A

by Na dependent symporters that are dependent on the basolateral Na/K pump (secondary active transport

27
Q

What is PEPT1?

A

The peptide cotransporter!

Located on the lumenal side, it cotransports peptides w/ protons

28
Q

What supplies the luminal H for PEPT1?

A

Apical Na/H exchanger (NHE) that supplies H nad is suppored by hte basolateral Na/K/ATPase

29
Q

Peptides that are absorbed by PEPT1 are then…

A

digested by cytosolic proteases

30
Q

What happens to surplus AA?

A

transported into the blood

31
Q

In summary, how are peptides and AA transported out of the lumen?

A

Peptides cotransported w/ H

AA cotransported w/ Na

32
Q

What is the mechanism for passive immunity in infants?

A

for the first 6 mos, intact proteins are absorbed by endocytosis

M cells take up proteins which are transferred to lymphocytes as antigens

33
Q

Why do genetic disorders of apical AA transporters not result in AA def?

A

?

34
Q

What peptide transporter facilitates the uptake of many drugs?

A

PEPT1

35
Q

The majority of dietary lipids are…

A

TGs

36
Q

What is emulsification?

A

chewing breaks down particles and increases surface area for particles to be coated w/ bile salts and phospholipids

37
Q

Where does gastric lipase come from? What does it do? Optimal pH?

A

Chief cells

not required but facilitaes 10-30% of lipolysis

5.4

38
Q

Why does gastric lipase play a prominent role in neonates?

A

developmental delay of pancreatic enzyme expression in ppl w/ pancreatic insufficiency

39
Q

What triggers the release of CCK?

A

Free FA in the duodenum

40
Q

What does CCK do?

A

activates pancreatic acinar secretion of LIPASE and PROCOLIPASE

41
Q

What inhibits pancreatic lipase activity?

A

low pH and bile acids prevents lipase from binding to fat droplets

42
Q

What activates colipase and what does it do?

A

activated by Trypsin

binds bile acids and recruits lipase to cleave FA

43
Q

What enzymes from pancreas acinar cells that become active in the duodenum (higher levels of Ca) may contirbute to lipid digestion?

A

Cholesterol esterase

Phospholipase A2

44
Q

What is cholesterol esterase?

A

Hydrolyze hte 2 position of FA left untouched by lipase

45
Q

What does phospholipase A2 do?

A

converts phospholipids into FA and lysophospholipids

46
Q

Are inhibitors of fat assimilation effective for weight loss?

A

?

47
Q

What is olestra?

A

undigestable fat, too big to be absorbed

48
Q

What is a pancreatic lipase inhibitor used to tx obesity?

A

orlistat/xenical

49
Q

What effect does orlistat have?

A

Effect is modest and many patients regain weight if taken off drug

Reduces risk of type II diabetes and lowers blood pressure

50
Q

What are SE of orlistat?

A

Fatty stool
Causes abdominal cramping and diarrhea
Inhibit absorption of vitamins A, D, E, K

51
Q

What is critical micelle concentration?

A

the minimum level of bile salts that must be present before micelles will form and fat soluble vitamins can be packaged for uptake

52
Q

How do lipids enter enterycytes?

A
  1. nonionic diffusion
  2. collision w/ hte membrane
  3. carrier mediated transport
53
Q

What happens to most absorbed FA?

A

reassembed into triglycerides and coated with apoproteins to form chylomicrons

54
Q

What supports the absorption of vitamin B12?

A

IF

55
Q

Removal of the ILEUM or METFORMIN can interfere w/ the absorption of what vitamin?

A

B12

56
Q

Pts should be screened for B12 def especially if htey’re…

A

anemic

57
Q

Colipase/lipase def

A

chronic pancreatitis or congenital mutations (triglycerides only need 10-15% of normal enzyme levels).

Treat with pancreatic enzyme supplements

58
Q

Zolinger Ellision

A

excess H+ overwhelms the buffering capacity of bicarbonate in the duodenum. Leading to inactivation of pancreatic lipase (more sensitive to pH than proteases)

59
Q

What can cause poor lipid absorption?

A

Inadequate bile salt concentrations due to liver dysfunction or outflow of bile leads to emulsification problems.

Bile uptake defects in the terminal ileum (Crohn’s disease) leads to inadequate bile concentrations.

Abnormal chylomicron formation
(abetalipoproteinemia)

Abnormal lymphatic transport processes

Abnormal intestinal motility, short bowel syndrome, or rapid gastric emptying may lead to inadequate time for fat digestion and/or absorption.

GI- Week 4 (12 decks)

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