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MONOGASTRIC GI > 5.3 – Secretory Functions of the Pancreas and Liver > Flashcards

5.3 – Secretory Functions of the Pancreas and Liver Flashcards

1
Q

How are pancreatic acini arranged?

A

-anastomosing tubular network that eventually form ‘classic’ acini

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2
Q

What are acini surrounded by?

A

-myoepithelial cells that contract to expel contents of the acini into the duct

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3
Q

What are most exocrine secretions stimulated by?

A

-CCK

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4
Q

How do human pancreas acinar cells stain with H&E?

A

-blue at base due to higher concentrations of RNA and nuclei
-pink at apex due to zymogen particles

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5
Q

What do centroacinar and proximal ducts produce?

A

-ions: HCO3, Cl-, Na, K
-water
*most likely driven by CCK

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6
Q

What coms ‘after’ the centroacinar/proximal duct cells?

A

-intercalated duct cells
>minimal secretory function

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7
Q

What do interlobular ducts secret?

A

-HCO3
-Cl-
-Na
-K
-water

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8
Q

What happens at the main pancreatic collecting duct?

A

-HCO3 is exchanged for chloride

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9
Q

What is pH typically in the pancreas?

A

-7.8
-if pH in duodenum is low=secretin released=increased Cl removal=pH rises to 8.2

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10
Q

What is the function of pancreatic exocrine secretion?

A

-secretion of HCO3
-secretion of enzymes

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11
Q

Secretion of HCO3 from pancreas role:

A

-neutralize gastric contents entering the duodenum from the stomach
*stimulated by secretion (low pH) in ductal system
*CCK in acini

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12
Q

Secretion of enzymes from pancreas role:

A

-most are zymogens (proenzymes)
-luminal digestion of CHO, fat and protein
*under control of CCK which is released in response to fat and protein

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13
Q

What can also enhance the effect of secretion on the pancreas?

A

-cholinergic stimulation

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14
Q

What controls the pancreatic secretions during the cephalic and gastric phases?

A

-nerves
>both enzymes and electrolytes can be stimulated by cholinergic stimulation (species dependent)

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15
Q

What happens to pancreatic flow as HCO3 increases?

A

-increase
*mediated by secretin

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16
Q

What are some proteases secreted by pancreatic acinar cells?

A

-trypsinogen
-chymotrypsinogen
-proelastase
*secreted in an inactive form
>monitor protein ‘feedbacks’

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17
Q

What is a amylotic enzyme secreted by pancreatic acinar cells?

A

-amylase

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18
Q

What are some lipases secreted by pancreatic acinar cells?

A

-lipase
-nonspecific esterase
-phospholipase A2

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19
Q

What are some nucleases secreted by pancreatic acinar cells?

A

-deoxyribonuclease
-ribonuclease

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20
Q

What are other secretory products secreted by pancreatic acinar cells?

A

-procolipase
-trypsin inhibitors
-monitor peptide

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21
Q

What are the % of pancreatic secretion during the 3 phases?

A

-cephalic: 20-25% (high volume, low protein)
-gastric: 10% (low volume, high protein)
-intestinal: 60-70%

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22
Q

CCK:

A

-potential stimulator of acinar secretion

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23
Q

What does CCK act via?

A

-monitor peptide
>produced from pancreatic acinar cells

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24
Q

Where is CCK synthesized and stored?

A

-predominantly endocrine cells in the duodenum
>released in response to digesta
*there are 2 luminally active CCK releasing factors which are small peptides (ex. CCK-RP)

25
Q

CCK-RP:

A

-derived from cells in duodenum
-released in response to FA and hydrophobic AA

26
Q

Secretin is responsible for:

A

-postprandial secretion of bicarbonate

27
Q

When is secretin released from S cells?

A

when they sense decreased pH
>bind to receptors on pancreatic ducts

28
Q

What inhibits secretin?

A

-rise in pH

29
Q

What is the function of biliary secretion?

A

-source of bile acids
- excretory role for certain metabolites and drugs
-buffer secreted into duodenum

30
Q

What is the structure of liver lobule?

A

-cords of hepatocytes arranged around a central vein
-sinusoids between cords
-portal triad at periphery of lobe

31
Q

Sinusoids:

A

-endothelium-lined spaces
-analogous to capillaries in other organs

32
Q

Portal triad consists of:

A

-portal vein
-hepatic artery
-bile duct

33
Q

Where does blood form the hepatic artery and portal vein flow?

A

-into sinusoids

34
Q

Where does bile exit the hepatocytes?

A

-on other side into ductules
>goes into finally into bile duct of the triad

35
Q

Kupffer cells:

A

-sinusoidal epithelium macrophages
-important in RBC removal

36
Q

What is the importance of the large pores in the sinusoidal epithelium?

A

-permits the unrestricted passage of albumin into extravascular space
>hepatocytes then filter/metabolize it

37
Q

What are bile acids?

A

-steroid acid (derived from cholesterol)
-comprises 80% of organic compounds in bile

38
Q

What are bile acids necessary for?

A

-fat and oil digestion and absorption
>micelle-forming surfactants to encapsulate nutrients and facilitate absorption

39
Q

What are bile salts created from:

A

-cholesterol via:
>hydroxylations
>oxidations
>isomerization
>saturations
>reductions

40
Q

What is the rate limiting step of bile salt synthesis?

A

-7alpha-hydroxylase
>drugs can act upon this step

41
Q

What are the primary bile acids?

A

-cholic acid
-chenodeoxycholic acid
*both become conjugated to taurine and glycine=bile salts

42
Q

Why are cholic and chenodeoxycholic acid conjugated to taurine and glycine?

A

-reduces pKa
>6.0 to 4.0 for glycine
>6.0 to 2.0 for taurine

43
Q

What happens when pKa is reduced with become a bile salt?

A

-increases solubility
-more impermeable to cell membrane
*high concentrations can persist in bile and intestinal contents

44
Q

What happened to cats fed a semi-purified diet containing casein as the sole source of protein?

A

-developed taurine deficiency
*cats conjugate bile almost exclusively with taurine
>conversion to glycine conjugation did NOT occur (can usually convert to taurine)
-supplementation with precursors of taurine were ineffective
*cats need animal proteins in their diet(for taurine)

45
Q

How are secondary bile salts formed?

A

-arise from deconjugation and dehyroxylation of bile acids by gut microbes

46
Q

What are secondary bile salts?

A

-deoxycholic and lithocholic acids
*at increased pH, they become insoluble=excreted in feces

47
Q

Where does active absorption of bile salts occur?

A

-intestine
>90% in ileum
>5% excreted in feces

48
Q

Under normal conditions hepatic synthesis of bile salts equals:

A

-fecal loss
*this amount of bile salts is not enough for fat digestion
>animal recycles the bile salts to increase amount in GI for digestion (via portal venous return)
»if impaired=fat and fat soluble vitamin malabsorption will occur

49
Q

How many times can bile salts turn over in some species in 24hrs?

A

-6 to 8 times

50
Q

What is the value of blood bile acids fasting?

A

-0-10umol/L

51
Q

What is the value of blood bile acids postprandial?

A

-0-20umol/L

52
Q

What does the extrahepatic tract consist of?

A

-bile duct
-common bile duct
-gall bladder
-sphincter of Oddi
*helps store bile

53
Q

Ruminant and pig extrahepatic biliary tract:

A

-almost continuous secretion of bile into intestine
-poorly defined Oddi sphincter

54
Q

Horse extrahepatic biliary tract:

A

-continuous flow
-does not have a gall bladder

55
Q

Humans, moose, giraffe, camel, elephant, pigeon, dove, rat, elk, deer extrahepatic biliary tract:

A

-intermittent flow
>due to eating patterns?
-Oddi sphincter can close when not eating and gall bladder is relaxed
*when CCK is released=sphincter relaxes and bladder contractions

56
Q

What are some excretory functions of hepatocytes?

A

-detoxification
Ex. bilirubin

57
Q

Bilirubin:

A

-end-product of Hg
-very water insoluble
-bound to albumin in blood

58
Q

What do hepatocytes do to bilirubin?

A

-conjugated with glucuronic acid=bilirubin diglucuronide
>more soluble and can be excreted into canaliculi
»what gives bile a greenish colour

MONOGASTRIC GI (24 decks)

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