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+ CAPS 301: Respiratory, Renal, GI, Endocrinology, Reproduction > Pancreas and Biliary System > Flashcards

Pancreas and Biliary System Flashcards

1
Q

Does the small intestine secrete digestive enzymes?

A

no

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2
Q

The small intestine requires secretions (ie. digestive enzymes) from…

A

pancreas and liver

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3
Q

What does the pancreas supply? (2)

A
  • enzymes that breakdown proteins, carbohydrates, and fats

- alkaline fluid to neutralize acidic gastric chyme

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4
Q

What does the liver supply?

A

bile (which emulsifies fats)

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5
Q

Where is the pancreas?

A

immediately below the stomach

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6
Q

What are parts of (or parts connected to) the pancreas? (4)

A
  • pancreatic duct
  • common bile duct
  • bile duct ampulla (ampulla of Vater)
  • sphincter of hepatopancreatic ampulla (sphincter of Oddi)
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7
Q

What are pancreatic exocrine secretions produced by?

A

cells in the pancreatic acini – acinar cells and duct cells

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8
Q

What are acinar cells?

A

cells that line the terminal end of the pancreatic acinus, and secrete pancreatic digestive enzymes

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9
Q

What are dust cells?

A

cells that line the neck of the pancreatic acinus, and secrete pancreatic aqueous alkaline fluid

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10
Q

What do pancreatic proteolytic enzymes do?

A

hydrolyze peptide bonds:

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11
Q

What are the three different pancreatic proteolytic enzymes?

A

trypsinogen (active form = trypsin)
chymotrypsinogen (active form = chymotrypsin)
procarboxypeptidase (active form = carboxypeptidase)

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12
Q

Do pancreatic proteolytic enzymes have potential for autodigestion?

A

yes – enzymes are stored inactivated in zymogen granules

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13
Q

What type of inhibitor does the pancreas produce?

A

trypsin inhibitor

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14
Q

How are pancreatic proteolytic enzymes activated?

A

two-step process:

  1. inactive trypsinogen is cleaved to active form trypsin by enterokinase
  2. trypsin activates other enzymes

all three activated enzymes act to digest ingested proteins in lumen

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15
Q

What is pancreatic amylase similar to?

A

salivary amylase

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16
Q

Does pancreatic amylase threaten pancreatic tissue?

A

no – therefore secreted in active form

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17
Q

What is pancreatic lipase?

A

the only enzyme that can digest fat

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18
Q

What happens without pancreatic lipase?

A

ingested fats remain too large and cannot be absorbed

clinically, ~60-70% of ingested fats are excreted in feces – steatorrhea

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19
Q

What type of pH environment do pancreatic enzymes require?

A

neutral pH

duodenum is not equipped to deal with acid injury

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20
Q

What is the largest component of pancreatic secretions?

A

pancreatic aqueous alkaline secretion

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21
Q

What controls the release of pancreatic secretions?

A

both autonomic and hormonal control

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22
Q

Does autonomic or hormonal control of pancreatic secretions dominate?

A

hormonal influences dominate

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23
Q

Control of Pancreatic Secretions

Describe what sympathetic and parasympathetic input of autonomic control does.

A
  • sympathetic input decreases all secretions

- parasympathetic input increases all secretions

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24
Q

Control of Pancreatic Secretions

What two hormones control secretions?

A
  • secretin

- CCK

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25
Q

What is secretin secreted by?

A

duodenal mucosal cells

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26
Q

What does secretin do?

A

increases NaHCO3 production and release

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27
Q

When does secretin get released?

A

in presence of acidic chyme in duodenum

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28
Q

What is CCK produced by?

A

duodenal mucosal cells

29
Q

What does CCK do?

A

stimulates production and release of lipase and proteolytic enzymes from pancreatic acinar cells

30
Q

When does CCK get released?

A

in presence of fat in duodenum

31
Q

Control of Pancreatic Secretions

Secretin

A
  1. acid in duodenal lumen
  2. increased secretin release from duodenal mucosa
  3. pancreatic duct cells “activated”
  4. increased secretion of aqueous NaHCO3 solution into duodenal lumen – neutralized acid
32
Q

Control of Pancreatic Secretions

CCK

A
  1. fat and protein products in duodenal lumen
  2. increased CCK release from duodenal mucosa
  3. pancreatic acinar cells “activated”
  4. increased secretion of pancreatic digestive enzymes into duodenal lumen – digests fat and protein products
33
Q

What is the liver?

A

large visceral organ that performs a variety of functions

34
Q

In the GI system, what do hepatocytes in the liver do?

A

produce bile salts – secreted into duodenum via common bile duct

35
Q

What are the two distinct blood sources that the liver receives?

A
  • venous blood from GI tract

- arterial blood via hepatic artery

36
Q

What are liver sinusoids?

A

capillary network in the liver that receives both venousand arterial blood

37
Q

What does the hepatic portal system do?

A

allows liver to process and detoxify substances absorbed from GI tract

38
Q

What is the first-pass effect?

A

the phenomenon which occurs whenever a drug is administered orally, enters the liver, and suffers extensive biotransformation to such an extent that the bioavailability is drastically reduced, thus showing subtherapeutic action

39
Q

What is the liver organized into?

A

lobules – in hexagonal arrangements around a central vein

40
Q

What are the three vessels in each of the 6 ‘corners’ of the hexagonal lobule arrangement of the liver?

A
  • branch of hepatic artery
  • branch of hepatic vein
  • bile duct
41
Q

How are hepatocytes arranged in hepatic lobules?

A
  • arranged such that each hepatocyte borders a sinusoid

- thin bile passage (bile canaliculus) also runs between each layer of hepatocytes

42
Q

What do hepatocytes continually secrete, and to where?

A

secrete bile into canaliculus

43
Q

What is the common bile duct formed by?

A

bile ducts from different lobules converge to form common bile duct

44
Q

Enterohepatic Circulation

Where is bile delivered?

A

to duodenum via sphincter of Oddi

45
Q

Enterohepatic Circulation

When does the sphincter of Oddi close?

A

in absence of duodenal chyme

46
Q

Enterohepatic Circulation

Where does bile go if the sphincter of Oddi is closed?

A

bile is diverted into gall bladder for storage

47
Q

What is the gall bladder?

A

muscular sac that stores and concentrates bile, and contracts to expel bile into duodenum

48
Q

Enterohepatic Circulation

Where is the majority of bile salts reabsorbed?

A

in terminal ileum

49
Q

Enterohepatic circulation provides a method of ____ regulation.

A

cholesterol

50
Q

Enterohepatic Circulation

% Bile Salts

A
  1. secreted bile salts consist of 95% old, recycled bile salts and 5% newly synthesized bile salts
  2. 95% of bile salts are reabsorbed by terminal ileum
  3. reabsorbed bile salts are recycled by enterohepatic circulation
  4. 5% of bile salts are lost in feces
51
Q

What are the components of bile? (4)

A
  • alkaline solution (duct cells)
  • bile salts (hepatocytes)
  • bilirubin (hepatocytes)
  • lecithin – phosphatidylcholine (hepatocytes)
52
Q

What is lecithin?

A

component of cell membranes

53
Q

What is bilirubin?

A

yellowish pigment resulting from RBC degradation

associated with jaundice

54
Q

What is bilirubin derived from?

A

derived from iron-containing haemoglobin

55
Q

What are bile salts?

A

deprotonated molecules (negatively charged)

56
Q

What are bile salts derived from?

A

derived from cholesterol, but with a negatively charged hydrophilic tail

57
Q

Where can water-soluble lipase act?

A

only on surface of fat aggregates

58
Q

What is the role of bile?

A

bile salts act as detergent and emulsify large fat aggregates into smaller pieces

  • cholesterol portion of bile salts dissolves in fat
  • its hydrophilic tail portion exposed to aqueous chyme
  • negatively-charged tail portions of one ‘droplet’ repel other droplets
59
Q

What does colipase do?

A

anchors lipase to bile salts at surface of fat droplet

60
Q

What does bile help form?

A

help form microdroplets of monoglycerides (micelles) following lipase digestion

61
Q

What are micelles composed of?

A

bile salts, cholesterol, and lecithin molecules – which form hydrophobic core with hydrophilic tail ‘shell’

62
Q

What do micelles do?

A

shuttle digested fat molecules to epithelial surface

63
Q

Structure and Function of Bile Salts

A
  • negatively charged H2O-soluble portion (polar groups – all located on one side of the molecule)
  • lipid-soluble portion (derived from hydrophobic non-polar cholesterol)
64
Q

Are small lipid droplets polar or nonpolar?

A

nonpolar – with bile salt molecules adsrobed on its surface

65
Q

Control of Bile Secretion

How is the release of bile regulated?

A

hormonal and autonomic inputs

  • CCK triggers contraction of gall bladder, and relaxation of sphincter of Oddi
  • vagal efferents augment this response
66
Q

Control of Bile Secretion

How is the production and secretion of bile regulated?

A

neuronal – vagal input increases bile production

hormonal – secretin stimulates production and secretion of NaHCO3 component of bile

67
Q

Control of Bile Secretion

How does bile salt regulate bile production and release?

A

bile salts in the blood (from reabsorption of bile salts via enterohepatic circulation) is the most potent stimulator of further bile production and release

68
Q

Control of Bile Secretion

How is the inhibition of bile regulated?

A
  1. when fats have left duodenum:
    - CCK levels drop
    - sphincter of Oddi closes
    - bile cannot enter duodenum
  2. hepatocytes continue to manufacture bile until circulating bile salt concentration in enterohepatic circulation declines – this removes the strong activation on hepatocytes, and bile production slows

+ CAPS 301: Respiratory, Renal, GI, Endocrinology, Reproduction (32 decks)

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