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M&R > Wk 3 TBL 5 Nutrient Malabsorption > Flashcards

Wk 3 TBL 5 Nutrient Malabsorption Flashcards

(52 cards)

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1
Q

Where is iron absorbed?

A

Predominantly duodenum/proximal jejunum

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2
Q

Where are bile salts primarily absorbed?

A

distal ileum only

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3
Q

Where is cobalamin (B12) absorbed?

A

only distal ileum

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4
Q

What 4 factors determine the efficiency of nutrient uptake?

A
  1. # villus absorptive cells
  2. presence of fxnal hydrolases to digest polymers to monomers
  3. nutrient specific transport proteins on brush border
  4. transit time (rapid -> less absorbed)
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5
Q

Manifestation of malabsorbed proteins?

A
  1. wasting
  2. edema
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6
Q

Manifestation of malabsorbed CHO/fat?

A
  1. steatorrhea (fat)
  2. abdominal cramping
  3. weight loss
  4. growth delay
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7
Q

Manifestation of malabsorbed fluid/electrolytes?

A
  1. diarrhea
  2. dehydration
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8
Q

Manifestation of malabsorbed calcium

A
  1. bone pain
  2. fractures
  3. tetany
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9
Q

Manifestation of malabsorbed iron

A
  1. anemia
  2. poor growth & dev in kids
  3. cheilosis (inflam condition -> cracking, crusting corners of mouth)
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10
Q

Manifestation of malabsorbed B12/folate

A
  1. macrocytic anemia
  2. glossitis
  3. cheilosis
  4. paresthesias (B12 only)
  5. ataxia (B12 only) - w/o coordination
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11
Q

Manifestation of malabsorbed vit E

A
  1. paresthesias, muscle weakness
  2. loss of reflexes, ataxia
  3. retinopathy
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12
Q

Manifestation of malabsorbed vit A

A
  1. night blindness
  2. xerophthalmia - abnormal drying of cornea and conjunctiva
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13
Q

7 Mechanistic classes for malabsorption

A
  1. Inadequate grastric mixing, rapid emptying, or both
  2. insufficient digestive agents
  3. abnormal milieu
  4. acutely abnormal epithelium
  5. chronically abnormal epithelium
  6. short bowel
  7. impaired transport
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14
Q

Causes of inadequate gastric mixing and/or rapid emptying

A
  1. gastroenterostomy (surgical anastomosis of stomach & sm intestine - ex. Roux-en-Y gastric bypass)
  2. Gastrocolic fistula (passage b/w stomach & colon)
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15
Q

Causes of insufficient digestive agents

A
  1. biliary obstruction and cholestasis
  2. cirrhosis (reduced bile production)
  3. chronic pancreatitis
  4. bile acid loss
  5. crystic fibrosis
  6. lactose intolerance
  7. pancreatic cancer
  8. pancreatic resection
  9. sucrase-isomaltase deficiency
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16
Q

Causes of abnormal digestive milieu

A
  1. abnorm motility secondary to diabetes, scleroderma, hypothyroidism, or hyperthyroidism
  2. bacterial overgrowth due to blind loops, diverticula in sm intestine
  3. Zollinger-Ellison syndrome (low duodenal pH)
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17
Q

Causes of acutely abnormal epithelium

A
  1. acute intestinal infections
  2. alcohol
  3. neomycin
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18
Q

Causes of chronically abnormal epithelium

A
  1. amyloidosis
  2. celiac disease
  3. Crohn disease
  4. ischemia
  5. radiation enteritis
  6. tropical sprue
  7. Whipple disease
  8. fructose malabsorption
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19
Q

Causes of short bowel

A
  1. intestinal resection (eg for Crohn’s, volvulus, intussusception, or infarction)
  2. jejunoileal bypass for obesity
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20
Q

Causes of impaired transport

A
  1. Hartnup disease - mutation in aa transporting affecting intestine and kidney -> pellagra-like symptoms - 3 D’s b/c tryptophan synthesizes niacin)
  2. abetalipoproteinemia
  3. intrinsic factor def (pernicious anemia)
  4. Lymphangiectasia = obstruction or malformation of intramucosal lymphatics of sm bowel or blocked lacteals

HAIL (a cab)

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21
Q

What are 7 diagnostic tests for malabsorption?

Study These Flashcards
A
  1. stool fat test (but steatorrhea is obvious so not often necessary)
  2. Stool elastase (or chymotrypsin or trypsin) measurement
  3. D-xylose test
  4. hydrogen breath test
  5. Schilling test
  6. Lipoprotein electrophoresis
  7. Celiac disease diagnostic tests - duodenal biopsy and anti-tissue transglutaminase antibody (tTG-IgA) serotologic test
22
Q

Why measure stool for elastase, trypsin or chymotrypsin?

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A

They are decreased w/ pancreatic insufficiency (cystic fibrosis) but not in intestinal mucosal disease

23
Q

What is the D-xylose test?

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A

Checks xylose in blood and urine.
D-xylose is a monosaccharide that should be absorbed by intestinal mucosa (no digestive enzymes reqd). It’s poorly catabolized in body, so used to determine if sm intestinal mucosa is absorbing normally.
If low, indicates prob w/ absorption

24
Q

What is the hydrogen breath test?

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A

Measures exhaled hydrogen gas produced by bacterial degradation of undigested/unabsorbed CHO
-if sugars not predigested, anaerobic bacteria in colon digest them -> gas, which gets absorbed in colon and carried to lungs, then expelled
-can be used for lactose intolerance, SIBO - both need to be ruled out when considering IBD

25
What is the Schilling test?
To eval B12 (cobalamin) if deficiency caused by insufficient intrinsic factor, pancreatic exocrine insufficiency, bacterial overgrowth or ileal disease. -oral radiolabeled B12 then IM dose of unlabled 1 hr later so radiolabeled doesn't bind to B12 deficient tissues -rarely done
26
What is lipoprotein electrophoresis?
Separates proteins based on size and charge Detects abetalipoproteinemia (AR, gene-encoded PRO reqd for chylomicron and VLDL synthesis) -> severe fat malabsorption, steatorrhea, and failure to thrive Dx made by absent ApoB from serum
27
Celiac disease diagnostic tests
1. duodenal biopsy 2. anti-tissue transglutaminase antibody (tTG-IgA) serotologic test
28
What enzymes begin digestion of proteins? Where?
1. HCl and pepsin 2. stomach
29
What are the roles of HCl and pepsin?
HCl (parietal cells) denatures/unfolds proteins, activates pepsinogen (chief cells) -> pepsin, and makes calcium and iron more soluble for absorption, aids B12 liberation from food proteins Pepsin clips long polypeptides into smaller chains to prevent refolding once pH neutralized in sm intestine
30
What is lecithin
group of common phospholipids
31
What molecules are insoluble in water
Dietary lipids, TGs, cholesterol, lecithin, fat-soluble vitamins.
32
What secretes pancreatic lipase?
Pancreatic acinar cells
33
What is a cofactor for pancreatic lipase?
Colipase
34
What is the role of pancreatic lipase?
1. hydrolyze TGs to FAs and monoacylglycerols
35
What happens after lipolysis?
1. The products (FAs and monoglycerides) mix with bile salts and phospholipids 2. Form micelles 3. Incorporate cholesterol and fat-soluble into micelles vitamines in hydrophobic centers
36
What step in lipid digestion can lead to fat-soluble vitamin deficiencies?
Failure to form micelles
37
What digests starch?
Pancreatic amylase, secreted by exocrine pancreatic acinar cells) -> oligosaccharides
38
What digests oligosaccharides?
Specific hydrolyases: sucrase, lactase, and maltase
39
What are the pancreatic proteases?
trypsin chymotrypsin elastase carboxypeptidase
40
What digests large oligopeptides that aren't broken down more by pancreatic proteases?
brush border hydrolases
41
What is CCK?
=cholecystokinin -release stimulated by aa and FAs from duodenal mucosa into bloodstream -stimulates amylase, lipase, colipase, and protease release from pancreatic acinar cells -stimulates contraction of gallbladder and relaxes the sphincter of Oddi -> release of bile into intestinal lumen
42
What cleaves trypsinogen?
Enteropeptidase cleaves it to trypsin at duodenal brush border
43
What is the role of trypsin?
cleave and activate more trypsinogen and other proteases and colipase
44
What causes the release of secretin?
Gastric acid stimulates release of secretin from upper small intestinal mucosa into blood
45
Role of secretin
1. stimulates HCO3- from pancreatic ductal cells -enhanced by acetylcholine and CCK
46
What is the role of bicarbonate?
1. neutralize acid in small intestinal lumen 2. optimize pH 6-8 for pancreatic enzyme activity and bile salt micelle formation
47
What is the role of epithelial cells that make up the brush border in lipid absorption?
1. LCFAs are transported or diffuse across microvillus membrane 2. resynthesize LCFAs into TGs forming chylomicrons 3. chylomicrons are exocytosed to mesenteric lymphatics, transported to thoracic duct
48
What happens to bile salts from micelles?
stay in intestinal lumen w/ some being absorbed across mucosa -most uptake occurs in distal ileum by Na+-dependent cotransport
49
What is a lacteal?
lymphatic capillary in villi of sm intestine
50
How are the sugar monomers transported into the enterocytes?
glucose and galactose: active transport via SGLT1 (sodium glucose cotransporter) and Na+ gradient across the apical membrane fructose: facilitated diffusion (GLUT 5) with gradient
51
How are sugar monomers transported across the basolateral membrane?
GLUT 2 facilitated diffusion -> portal vein
52
How are peptides and aas transported across the brush border?
Na+-dependent aa carriers or by H-coupled oligopeptide carrier PepT1

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