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Medical Biochemistry > Ch. 11: GI Digestion & Absorption > Flashcards

Ch. 11: GI Digestion & Absorption Flashcards

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USMLE® Step 1 flashcards
1
Q

What regulates secretory & absorptive activities of GI tract?

A

Hormones

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2
Q

Layers of GI tract (IN ➡️ OUT)?

A

Mucosa
Submucosa
Muscularis
Serosa

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3
Q

Saliva: pH?

principle ions?

A

pH 7.0 (hypotonic)

Na+, K+, Cl-, HCO3-

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4
Q

Catalytic fxn of amylase?

A

Hydrolysis of alpha (1➡️4) glycosidic linkages of starch & glycogen

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5
Q

What cell form & secrete bile? Shape of cells?

A

Hepatocytes

Polygon

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6
Q

What does bile contain?

A 
Bile acids
Bile pigments
Cholesterol
Phosphatidylcholine
Electrolytes
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7
Q

⬆️ conjugated bilirubin = problem with?

A

Gallbladder ➡️ duodenum pathway

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8
Q

⬆️ unconjugated bilirubin = problem with?

A

Liver

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9
Q

Endocrine hormones of pancreas?

A

Insulin
Glucagon
Somatostatin

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10
Q

Exocrine fxn of pancreas?

A

Synthesize & secrete digestive enzymes & HCO3- rich fluid

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11
Q

Proenzymes in pancreatic juice?

A

Trypsinogen
Chymotrypsinogen
Procarboxypeptidase
Proelastase

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12
Q

What converts trypsinogen ➡️ trypsin?

Where?

A

Enteropeptidase

Brush border of jejunal mucosa

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13
Q

Fxn of trypsin inhibitor in pancreatic juice?

A

Protects against indiscriminate autodigestion from intraductal activation of trypsinogen

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14
Q

Major fxn of large intestine?

A

Absorb water, Na+ & other electrolytes

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15
Q

What type of bacteria is in large intestine?

Fxn?

A

Anaerobic

Metabolize CHO ➡️ lactate, short chain FAs, & gases

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16
Q

Gastrin: Sources?

A

G cells (gastric antrum, duodenum)

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17
Q

Gastrin: Released due to chem, mech, neuronal stimulation of G cells

Ex?

A

Hypoglycemia

⬆️ Ca2+

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18
Q

What suppresses gastrin?

A

Acidification of antral mucosa

All members of secretin family

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19
Q

Gastrin: fxn?

A 
HCl secretion (parietal cells)
Pepsin secretion (chief cells)
Histamine secretion (enterochromaffin-like cells)
⬆️ gastric mucosal blood flow
Gastric motility
Proliferation of gastric mucosa
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20
Q

What is Zollinger-Ellison syndrome?

A

Tumors in stomach (keep secreting acid)

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21
Q

Ghrelin: Sources?

Fxn?

A

A cells of gastric fundus, other GI tract segments, hypothalamus

Promote food intake
Promote gastric motility
Stimulate growth hormone secretion

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22
Q

Cholecystokinin: Sources?

Fxn?

A

I cells of duodenum & jejunum, CNS

stimulate gall bladder & pancreatic secretions
Decrease appetite

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23
Q

Gastric Inhibitory Peptide (GIP) / Glucose-dependent insulinotropic polypeptide: Sources?

Fxn?

A

K cells (duodenum & jejunum)

Insulin secretion (beta-cells of pancreas)
Inhibits gastric secretion & motility
Stimulate FA synthesis in adipose tissue

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24
Q

Secretin: Sources?

Fxn?

A

S cells (upper portions of small intestine)

Secretion of bicarb-rich fluid (duct cells & biliary tract)
Augments action of CCK
⬇️ gastric acid secretion

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25
Q

Polypeptide YY: Sources?

Fxn?

A

L-cells (distal small & large intestines)

Inhibits food intake

26
Q

Somatostatin: Sources?

Fxn?

A

D-cells (pancreas & GI tract), hypothalamus

Inhibits secretion of GI tract hormones, growth hormone, & thyrotropin

27
Q

Glucagon-like peptide-1 (GLP-1): Sources?

Fxn?

A

L-cells (small & large intestines)

Promotes insulin secretion from beta-cells (pancreas)
Promotes beta-cell growth
Suppresses glucagon secretion from alpha-cells (pancreas)
Delays gastric emptying

28
Q

Glucagon-like peptide-2 (GLP-2): Sources?

Fxn?

A

L-cells (distal small & large intestines)

Promotes intestinal mucosal growth & repair
Inhibits gastric secretion

29
Q

Oxyntomodulin: Sources?

Fxn?

A

L-cells (distal small & large intestines)

Inhibits food intake
Inhibits gastric motility & acid production

30
Q

Endopeptidases: Digest ? ➡️ Into ?

A

Interior peptide bonds ➡️ peptides

31
Q

Exopeptidase: Digest ? ➡️ Into ?

A

Terminal peptide bonds ➡️ a.a.

32
Q

What things stimulates acid secretion?

A

Ach
Gastrin
Histamine (H2 receptor)
Bombesin

33
Q

What things suppress acid secretion?

A

Anticholinergic agents (atropine)
H2 receptor antagonists (cimetidine, ranitidine)
Prostaglandin E derivatives
Substituted benzimidazoles (omeprazole, pantoprazole)

34
Q

Digestion & absorption: CHO

Step 1?

A

Intraluminal hydrolysis via alpha-amylase:

starch & glycogen ➡️ oligosaccharides

35
Q

Digestion & absorption: CHO

Step 2?

A

Brush-border surface hydrolysis via oligosaccharidases:

Oligosaccharides & disaccharides ➡️ monomers

36
Q

Digestion & absorption: CHO

Step 3?

A

Transport of monosaccharides ➡️ enterocytes (Na/K-ATPase, semi-active transport)

37
Q

3 examples of CHO intolerance?

A

Lactose
Sucrose
Alpha-limit dextrin

38
Q

3 types of endogenous proteins? Grams per day digested?

A

1) secreted from GI tract organs & glands (20-30 g/d)
2) turnover of GI epithelium (30 g/d)
3) plasma proteins diffusing ➡️ intestinal tract (1-2 g/d)

39
Q

Major products of intraluminal digestion of protein?

A 
a.a. (30-40%)
small peptides (60-70%)
40
Q

4 active, carrier-mediated, Na+ dependent transport systems for free a.a.? Disorders associated with defects in each?

A

1) neutral a.a. ➡️ Hartnup disease
2) basic a.a. & cystine ➡️ cystinuria
3) asp & glu ➡️ dicarboxylic aminoaciduria
4) gly & imino acids ➡️ aminoglycinuria

41
Q

How are dipeptides & tripeptides transported into enterocytes?

A

Actively transported by Na-dependent mechanism

42
Q

Neonates have ability to absorb intact proteins after birth ➡️ allows them to do what?

A

Acquire passive immunity (absorbs Igs in colostrum)

43
Q

3 phases of lipid digestion?

A

1) luminal
2) intracellular
3) secretary

44
Q

4 diff phospholipases?

A

A1, A2, C, D

45
Q

What is celiac disease (gluten-sensitive enteropathy)?

A

Gliadins ➡️ production of Ab to endomysium of smooth muscle

46
Q

What is cystic fibrosis?

A

Multiple exocrinopathy & malabsorption due to lack of pancreatic enzymes ➡️ SI

47
Q

What is chronic alcoholism?

A

Malabsorption of foods & vitamins (due to liver and pancreas involvement, mucosal dysfunction)

48
Q

Lipid digestion abnormalities: rapid gastric emptying

Biochem disturbance & ex of disease?

A

⬇️ efficiency of lipid interaction w/bile & pancreatic secretions

Gastrectomy (Tx ulcers or neoplasms in stomach)

49
Q

Lipid digestion abnormalities: acidic duodenal pH

Biochem disturbance & ex of disease?

A

Inactivate pancreatic lipase
⬇️ ionization of bile acids

Zollinger-Ellison syndrome

50
Q

Lipid digestion abnormalities: ⬇️ CCK

Biochem disturbance & ex of disease?

A

Deficiency of bile & pancreatic secretions

Mucosal destruction disorders
regional enteritis
gluten enteropathy

51
Q

Lipid digestion abnormalities: congenital lipase/colipase deficiency

Biochem disturbance?

A

Defective lipolysis

52
Q

Lipid digestion abnormalities: pancreatic insufficiency

Biochem disturbance & ex of disease?

A

Defective lipolysis

Chronic pancreatitis
pancreatic duct obstruction (CF)

53
Q

Lipid digestion abnormalities: absent/⬇️ bile salts

Biochem disturbance & ex diseases?

A

⬇️ lipolysis (due to impaired micelle formation)

See table 11.3

54
Q

Define diarrhea? (Volume)

A

Amt of water excreted in feces > 500 mL

55
Q

Describe process of water absorption

A

Passive process

Coupled to transport of organic solutes & electrolytes (glucose & a.a.)

56
Q

What regulates absorption of Na+?

A

Aldosterone

57
Q

How is K+ absorbed?

A

Passive diffusion

58
Q

Impact of cholera & pertussis toxins on cell regulation pathways? (disorders of fluid/electrolyte absorption)

A

Cholera: ADP-ribosylation of Gs-alpha

Pertussis: ADP-ribosylation of Gi-alpha

59
Q

Impact of diphtheria toxin on cell regulation pathways? (disorders of fluid/electrolyte absorption)

A

ADP-ribosylation of EF2 ➡️ inhibits euk pro synthesis

60
Q

Disorders of fluid/electrolyte absorption: impact of E. coli?

A

Non-bloody diarrhea
Hemorrhagic colitis
Hemolytic uremic syndrome
Death

61
Q

Disorders of fluid/electrolyte absorption: pancreatic islet-cell tumor

Impact?

A

severe watery diarrhea

Medical Biochemistry (23 decks)

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