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

Pancreas and Biliary System Flashcards

(68 cards)

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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
What is secretin secreted by?
duodenal mucosal cells
26
What does secretin do?
increases NaHCO3 production and release
27
When does secretin get released?
in presence of acidic chyme in duodenum
28
What is CCK produced by?
duodenal mucosal cells
29
What does CCK do?
stimulates production and release of lipase and proteolytic enzymes from pancreatic acinar cells
30
When does CCK get released?
in presence of fat in duodenum
31
Control of Pancreatic Secretions Secretin
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
Control of Pancreatic Secretions CCK
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
What is the liver?
large visceral organ that performs a variety of functions
34
In the GI system, what do hepatocytes in the liver do?
produce bile salts – secreted into duodenum via common bile duct
35
What are the two distinct blood sources that the liver receives?
- venous blood from GI tract | - arterial blood via hepatic artery
36
What are liver sinusoids?
capillary network in the liver that receives both venousand arterial blood
37
What does the hepatic portal system do?
allows liver to process and detoxify substances absorbed from GI tract
38
What is the first-pass effect?
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
What is the liver organized into?
lobules – in hexagonal arrangements around a central vein
40
What are the three vessels in each of the 6 'corners' of the hexagonal lobule arrangement of the liver?
- branch of hepatic artery - branch of hepatic vein - bile duct
41
How are hepatocytes arranged in hepatic lobules?
- arranged such that each hepatocyte borders a sinusoid | - thin bile passage (bile canaliculus) also runs between each layer of hepatocytes
42
What do hepatocytes continually secrete, and to where?
secrete bile into canaliculus
43
What is the common bile duct formed by?
bile ducts from different lobules converge to form common bile duct
44
Enterohepatic Circulation Where is bile delivered?
to duodenum via sphincter of Oddi
45
Enterohepatic Circulation When does the sphincter of Oddi close?
in absence of duodenal chyme
46
Enterohepatic Circulation Where does bile go if the sphincter of Oddi is closed?
bile is diverted into gall bladder for storage
47
What is the gall bladder?
muscular sac that stores and concentrates bile, and contracts to expel bile into duodenum
48
Enterohepatic Circulation Where is the majority of bile salts reabsorbed?
in terminal ileum
49
Enterohepatic circulation provides a method of ____ regulation.
cholesterol
50
Enterohepatic Circulation % Bile Salts
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
What are the components of bile? (4)
- alkaline solution (duct cells) - bile salts (hepatocytes) - bilirubin (hepatocytes) - lecithin – phosphatidylcholine (hepatocytes)
52
What is lecithin?
component of cell membranes
53
What is bilirubin?
yellowish pigment resulting from RBC degradation associated with jaundice
54
What is bilirubin derived from?
derived from iron-containing haemoglobin
55
What are bile salts?
deprotonated molecules (negatively charged)
56
What are bile salts derived from?
derived from cholesterol, but with a negatively charged hydrophilic tail
57
Where can water-soluble lipase act?
only on surface of fat aggregates
58
What is the role of bile?
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
What does colipase do?
anchors lipase to bile salts at surface of fat droplet
60
What does bile help form?
help form microdroplets of monoglycerides (micelles) following lipase digestion
61
What are micelles composed of?
bile salts, cholesterol, and lecithin molecules – which form hydrophobic core with hydrophilic tail ‘shell’
62
What do micelles do?
shuttle digested fat molecules to epithelial surface
63
Structure and Function of Bile Salts
- 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
Are small lipid droplets polar or nonpolar?
nonpolar – with bile salt molecules adsrobed on its surface
65
Control of Bile Secretion How is the release of bile regulated?
hormonal and autonomic inputs - CCK triggers contraction of gall bladder, and relaxation of sphincter of Oddi - vagal efferents augment this response
66
Control of Bile Secretion How is the production and secretion of bile regulated?
neuronal – vagal input increases bile production hormonal – secretin stimulates production and secretion of NaHCO3 component of bile
67
Control of Bile Secretion How does bile salt regulate bile production and release?
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
Control of Bile Secretion How is the inhibition of bile regulated?
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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