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Physiology > GI 4 - Accessory GI Organs- Pancreas, Liver and Gall Bladder > Flashcards

GI 4 - Accessory GI Organs- Pancreas, Liver and Gall Bladder Flashcards

1
Q

more than ____% of the pancreas is exocrine

A

90

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2
Q

what cells make up the exocrine pancreas

A

-acinar cells
- duct cells

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3
Q

what do acinar cells do

A

-synthesize and secrete hydrolases for digestion
-necessary for luminal digestion of carbohydrate, protein and fat

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4
Q

what do duct cells do

A

-secrete bicarbonate and water
-neutralizes gastric H+ by secreting HCO3- into the duodenum up to 145 mEq/L so acinar cells can function

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5
Q

what does impaired function of acinar cells result in

A

maldigestion and malabsorption

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6
Q

why doesnt the pancreas digest itself

A

proteolytic enzymes synthesized, stored and secreted as inactive precursors

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7
Q

what are proteolytic enzymes activated in the intestinal lumen by

A

enterokinase and trypsin

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8
Q

when is trypsin inhibitor secreted and what does it do

A

synthesized, stored and secreted with precursors
- prevents activation of trypsin while still in pancreas

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9
Q

what are the two stimuli for acini cell enzyme secretion

A

-CCK
- AcH/GRP (vagovagal reflex)

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10
Q

what are the effects of CCK

A
  • gallbladder -> contraction
  • pancreas -> acinar secretion
  • stomach -> stimulates receptive relaxation, reduces emptying, reduce HCl secretion
  • sphincter of Oddi -> relaxation
  • all of these result in protein, carbohydrate, lipid absorption and digestion. And matching of nutrient delivery to digestive and absorptive capacity
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11
Q

what releases CCK

A

I cells

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12
Q

what are the two stimuli for I cells

A
  • monitor peptide released by the pancreas
  • CCK-RP stimulated by protein and amino acids in the lumen
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13
Q

what inhibits CCK release and how

A

trypsin by inhibiting CCK-RP and monitor peptides

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14
Q

what are the two stimuli for ductal cell secretion of H2O and HCO3-

A

-secretin
- Ach (M3 receptor) through vasovagal reflex

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15
Q

what is the mechanism of ductal cell secretion and where is the negative feedback occurring

A
  • increased acid from stomach -> increased secretin secretion -> increased plasma secretin -> increased bicarbonate secretin from ductal cells in pancreas
    -> increased flow of bicarbonate into small intestine -> neutralization of intestinal acid
  • negative feedback on secretin secretion
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16
Q

what does secretin directly result in

A
  • increased cAMP
  • phosphorylation of CFTR
  • Cl- conductance
  • HCO3- secretion
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17
Q

what is the mechanism in the pancreatic duct cell for secretion of bicarbonate

A
  • H+ is returned to the blood and Na+ is pumped into the cell via the H+ Na+ active antiporter
  • HCO3- is moved into the cell actively through the Na+ HCO3- symporter
  • HCO3- is moved across the apical membrane in exchange for Cl-
  • Cl- diffuses out the apical membrane into the lumen
  • Na+ and water follows
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18
Q

when is secretin released

A

when pH is less than 4.5

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19
Q

when is secretin release maximal and what does further release depend on

A

below ph of 3. further release depends on area of small intestine affected

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20
Q

what is the maximal bicarbonate response

A

30 mEq/hour

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21
Q

during a meal pH is rarely below ____

A

3.5 or 4

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22
Q

what is the relationship between secretin release and HCO3 release

A

secretin release shows HCO3- release

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23
Q

what are the 3 phases of pancreatic secretion and what percentage accounts for secretion in each phase

A
  • cephalic - 20%
  • gastric- 5-10%
    -intestinal - 70-80%
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24
Q

what are the cephalic and gastric phases of pancreatic secretion mediated by

A

vagovagal reflex - low volume, high enzyme secretion such as Ach and GRP

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25
Q

what is secreted in the intestinal phase of pancreatic secretion in response to acid? fat/protein?

A

-acid: secretin -> HCO3- and water
- fat/protein -> CCK -> enzymes

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26
Q

what is secretion rate proportional to

A

[secretin], [Ach], and [CCK]

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27
Q

what are the levels of bicarbonate and chloride at low secretion rates

A

-bicarbonate: low
- chloride: high

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28
Q

what are the levels of bicarbonate and chloride at high secretion rates

A
  • bicarbonate: high
  • chloride: low
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29
Q

what are the levels of sodium and potassium concentrations in response to varying secretion rates

A

they remain the same as the plasma

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30
Q

pancreatic juice is always ____

A

isotonic

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31
Q

describe what happens in cystic fibrosis

A
  • abnormal sweat composition
  • decreased pulmonary and pancreatic secretion
  • mendelian autosomal recessive occurrence - single AA substitution
  • defective CTFR: sweat Cl- reabsorption, pancreatic duct cell function, pulmonary mucus clearance
32
Q

what are the types of pancreatitis and what happens

A

-acute and chronic
- trypsin activation causes pain and inflammation
- chronic disease destroys acini
- consequences reflect decreased digestive enzyme production

33
Q

what can cause pancreatic duct obstruction

A

gallstones and tumors

34
Q

what is the effects on absorption without pancreatic enzymes

A
  • 60% of fat not absorbed- steatorrhea
  • 30-40% protein and carbohydrates not absorbed
35
Q

what is the functional unit of the liver

A

the liver lobule

36
Q

what is the function of the liver

A
  • cleansing and storage of blood
  • metabolism of nutrients
    -synthesis of proteins
  • metabolism of hormones, chemicals
  • storage of energy, vitamins, iron
  • excretion of lipid soluble waste products
  • large capacity for cell regeneration
  • secretion of bile
37
Q

what proteins does the liver make

A

coagulation factors, plasma proteins, angiotensinogen

38
Q

how much bile is secreted by the liver per day

A

600-1000 ml/day

39
Q

what is the total blood input into the liver and what is percentage of resting CO

A

1,350mL/min
-27% of resting CO

40
Q

describe resistance of blood flow in liver

A

very low

41
Q

what increases resistance in the liver

A

cirrhosis and causes portal hypertension

42
Q

what percentage of lymph production does the liver account for

A

50%

43
Q

what does increased vascular resistance cause

A

ascites

44
Q

what are the 2 roles of bile

A

-bile salts (acids) and lecithin required for digestion (emulsification) and absorption (micelles) of dietary fat
- excretion of lipophilic metabolites (bilirubin), excess cholesterol, other waste products, drugs and toxins

45
Q

what do the body cholesterol pools come from and how much

A

dietary cholesterol (0.2 g/day) and hepatic and extrahepatic synthesis (0.8-1 g/day)

46
Q

what is cholesterol excreted as from the liver and how much

A

bile acids (0.2-0.4 .day)

47
Q

what do hepatocytes do

A

secrete bile salts, cholesterol, lecithin, bilirubin and many other lipophilic substances

48
Q

what do duct epithelial cells do

A

modify primary secretion and add HCO3-

49
Q

where is bile stored and concentrated

A

gallbladder

50
Q

where is some bile reabsorbed

A

in the ileum of the small intestine

51
Q

where do hepatocytes secrete organic components of bile

A

into bile ducts

52
Q

what are bile salts produced from

A

cholesteol

53
Q

what do bile duct cells secrete

A

water, Na+ and HCO3-

54
Q

where is bile transported

A

-small intestine for fat digestion
- gall bladder for storage

55
Q

what is the max volume of the gall bladder

A

30-60 mL

56
Q

where are electrolytes and water reabsorbed from bile

A

while in the gall bladder

57
Q

what substances are reabsorbed from bile

A

water, Na+, Cl-, and HCO3-

58
Q

describe what happens in a cholecystectomy

A
  • no problems with fat digestion
  • bile flow directly into duodenum
59
Q

what is the mechanism of bile flow into the duodenum

A
  • fatty acids in the duodenum causes CCK secretion -> increased plasma CCK ->
  • gallbladder contraction -> increased bile flow into common bile duct -> increased bile flow into duodenum
  • AND relaxation of the sphincter of Oddi -> increased bile flow into duodenum
60
Q

where is the sphincter of oddi located

A
  • controls opening of pancreas into the small intestine
61
Q

how does enterohepatic circulation conserve bile salts

A

-substance secreted into bile by hepatocytes
-delivered to lumen of ileum then reabsorbed
- transported to hepatocytes via sinusoids
- 94% of bile salts recirculated
-bile salts circulate 17x before lost in feces

62
Q

which is greater in the liver about bile salts: secretion or synthesis

A

secretion&raquo_space; synthesis

63
Q

what transporter actively absorbs bile salts and where

A

-apical sodium dependent bile salt transporter (ASBT) in the ileum and in the renal PT

64
Q

what are BARI and what does it stand for

A
  • bile acid reabsorption inhibitors
  • drugs that inhibit bile recycling
  • used to lower LDL levels in the blood
  • hepatocyte production of bile increases 6-10x if bile salt recycling reduced
  • LDL taken up from blood via hepatocytes as source of cholesterol for bile salts
65
Q

what are the types of BARI and what doe they do

A
  • bile acid sequestrants: bind to bile salts in intestinal lumen and block transport
  • ABST inhibitors: prevents bile salts from recirculating
66
Q

what are the benefits of BARI

A

drugs work in intestinal lumen so they dont need to be reabsorbed which reduced harmful side effects

67
Q

what is low ASBT activity associated with

A

-chrons disease
-congenital primary bile acid malabsorption
- idiopathic chronic diarrhea
- IBS

68
Q

what are the disorders of biliary secretion

A
  • hepatocyte dysfunction impairs bilirubin, bile salt secretion
  • duct obstruction
  • intestinal mucosal defects impair bile salt reabsorption
69
Q

what causes hepatocyte dysfunction to impair bilirubin and bile salt secretion

A

-drugs (acetominophen), viral hepatitis, toxins
- fibrosis, cirrhosis

70
Q

what stimulates and inhibits gastrin and what is its function

A
  • stimulates: amino acids and peptides and distention
  • inhibits: H+
  • function: increased histamine release (ECL cell), increased H+ secretion (parietal cell), increased gastric emptying, trophic affects on mucosa
71
Q

what stimulates and inhibits ghrelin and what is its function

A

stimulates: absence of nutrients
inhibits: stretch
-function: increases hunger

72
Q

what stimulates secretin and what is its function

A

-H+
- increases pancreatic and biliary HCO3- secretion
- trophic affects on exocrine pancreas
- decreased gastric acid secretion
- decreased gastric emptying

73
Q

what stimulates CCK and what is its function

A
  • amino acids and peptides
    -fatty acids
  • indirectly via secretion of CCK-RP and monitor peptide
  • increases pancreatic enzyme secretion
  • increased gall bladder contraction
  • trophic effects on exocrine pancreas
  • decreased gastric emptying
  • decreased gastric acid secretion
  • relaxation of sphincter of oddi
  • gastric receptive relaxation
74
Q

what stimulates GIP and GLP-1 and what is its function

A

glucose
- increased insulin response to glucose
- decreased gastric acid secretion
- decreased gastric emptying

75
Q

what stimulates motilin and what is its function

A
  • unknown might be alkaline pH in duodenum
  • increases gastric motility (MMC/fasting)
  • increases intestinal motility (MMC/fasting)

Physiology (41 decks)

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