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DIG > Functions and Secretions of the Pancreas > Flashcards

Functions and Secretions of the Pancreas Flashcards

1
Q

What are the 3 overall functions of the pancreas?

A

1 - Important in digestion of fats and proteins.

2 - Providing the appropriate environment for enzymatic digestion in the small bowel.

3 - Important in regulating the fed and fasted states (insulin, glucagon etc.).

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2
Q

What is the ampulla of Vater?

A

A swelling in the duodenal wall where the main pancreatic duct merges with the common bile duct.

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3
Q

Where is the sphincter of Oddi?

A

At the ampulla of Vater.

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4
Q

Where are secretions from the pancreas emptied?

A

Into the descending part of the duodenum.

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5
Q

Which structures compose the secretory units of the pancreas?

A

An acinus and a small intercalated duct.

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6
Q

What is the function of the acinus?

A
  • Contains acinar cells that synthesise and secrete proteins into the lumen of the epithelia.
  • Secretions include zymogens, digestive enzymes and an isotonic fluid that accompanies the secretions.
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7
Q

List the pancreatic cell types.

A

1 - Acinar cells.

2 - Ductal cells.

3 - Centroacinar cells.

4 - Goblet cells.

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8
Q

Describe the cellular architecture of acinar cells.

A
  • Many RER.
  • Many secretory granules and golgi bodies.
  • Exocytosis at apical poles.
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9
Q

What is the function of ductal cells?

A

To facilitate the transport of electrolytes by hydrating and alkalinising the secretions of the acinar cells.

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10
Q

What are centroacinar cells?

A
  • Function unknown.

- Exist at the junction of the acinar cells and the ductal cells.

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11
Q

What is the importance of mucus secretion in the digestive tract?

A

1 - Lubrication.

2 - Hydration.

3 - Mechanical protection of epithelia.

4 - Immunological role (binding of pathogens and interactin with immune cells).

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12
Q

What mediates stimulation of pancreatic acinar cells to secrete proteins?

A
  • In an unstimulated state, constantly secrete low levels of proteins via a constitutive pathway.
  • CCK receptors and AChRs on the basolateral membrane regulate secretion through the Gq pathway.
  • VIP and secretin receptors regulate secretion through the Gs pathway.
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13
Q

How do acinar cells secrete the isotonic, NaCl rich fluid?

A

1 - Na-K pump on the basolateral membrane pumps 3 Na+ out and 2 K+ in.

2 - Na / K / Cl cotransporter pumps on the basolateral membrane 3 Na+, 3K+ and 6Cl- in.

3 - K+ leaves the basolateral membrane via K+ channels4

4 - High intracellular Cl- establishes the electrochemical gradient for apical Cl- secretion.

5 - Secretion increases as Cl- in the lumen makes the transepithelial voltage more lumen-negative, driving Na+ into the tight junctions between acinar cells, where they can pass into the lumen.

  • Same triggers as protein secretion.
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14
Q

How do pancreatic ductal cells hydrate and alkalinise the secretions of the acinar cells?

A

1 - The Na+ / HCO3- cotransporter (basolateral) pumps Na+ and HCO3 - in the ductal cell.

2 - The cystic fibrosis transmembrane regulator (CFTR, apical) is cAMP activated and pumps Cl- out of the ductal cell.

3 - The Cl- / HCO3- exchanger (apical) pumps Cl- back into the cell and HCO3- out (Cl- recycling).

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15
Q

What is the function of secretin?

A

To stimulate HCO3- and fluid secretion by the ductal cells, predominantly in response to duodenal acidification.

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16
Q

Where is secretin secreted from?

A

From S cells in the small bowel mucosa.

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17
Q

What stimulates ductal cells to hydrate and alkalinise the secretions of the acinar cells?

A
  • Secretin stimulates the CFTR and Na+ / HCO3- cotransporter.
  • Muscarinic AChRs cause increased intracellular Ca2+, and activation of Ca2+-dependent kinases (e.g. PKC).
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18
Q

List 5 zymogens found in pancreatic juice.

A

1 - Trypsinogen.

2 - Chymotrypsinogen.

3 - Proelastase.

4 - Procarboxypeptidase A.

5 - Procarboxypeptidase B.

19
Q

List 3 active digestive enzymes found in pancreatic juice.

A

1 - Amylase.

2 - Lipase.

3 - Co-lipase.

20
Q

Where is CCK secreted from?

A

Duodenal I cells.

21
Q

What is the function of CCK?

A

To stimulate pancreatic acinar cells to increase protein secretion.

22
Q

How does CCK stimulate its effector cells?

A
  • Directly, by binding to CCKa receptors.

- Indirectly, through the parasympathetic nervous system.

23
Q

What triggers the release of CCK and how are CCK levels maintained?

A
  • CCK-releasing factors, e.g. luminal CCK releasing factor (LCRF) stimulate CCK release.
  • In the fasting state, LCRFs are degraded by digestive enzymes. During a meal, the digestive enzymes act on the chyme rather than the LCRFs, allowing LCRFs to stimulate I cells.
24
Q

What is the function of somatostatin?

A

To inhibit the release of CCK and secretin.

25
Q

Where is somatostatin secreted from?

A

D cells of the islets of Langerhans.

26
Q

What is octreotide and what is its function?

A

An analogue of somatostatin used clinically to inhibit pancreatic secretions.

27
Q

What are the phases of pancreatic secretion?

A

1 - Cephalic phase (25%).

2 - Gastric phase (10-20%).

3 - Intestinal phase (50-80%).

28
Q

What triggers the cephalic phase of pancreatic secretion?

A
  • Sight.
  • Taste.
  • Smell.
29
Q

How are the effects of the cephalic phase of pancreatic secretion brought about?

A

By stimulation of ACh receptors on the acinar cells and ductal cells.

30
Q

How are the effects of the gastric phase of pancreatic secretion phase brought about?

A
  • By the release of hormones such as gastrin.
  • By stimulating neural pathways (gastric distension stimulates pancreatic secretion through a vagovagal gastropancreatic reflex).
31
Q

What is the function of gastrin?

A

To act as a weak CCK agonist by binding to CCK receptors on acinar cells.

32
Q

Where is gastrin secreted from?

A

G cells of the antrum.

33
Q

List the mechanisms by which pancreatic secretion is stimulated during the intestinal phase.

A

1 - Gastric acid stimulates duodenal S cells to release secretin, stimulating duct cells to secrete HCO3 and fluid.

2 - Lipids stimulate duodenal I cells to release CCK, stimulating acinar cells to release digestive enzymes.

3 - Lipids also activate a vagovagal enteropancreatic reflex that stimulates acinar cells.

34
Q

How does the pancreas prevent autodigestion?

A

By preventing enzymatic activity:

1 - Digestive proteins are stored in secretory granules as inactive precursors (zymogens). Trypsinogen is only activated once it reaches enterokinase.

2 - The secretory granules are impermeable to proteins.

3 - Enzyme inhibitors such as SPINK1 are co-packaged in the secretory granule.

4 - The low pH and ionic conditions in the secretory granules inhibit enzyme activity.

35
Q

What is the function of enterokinase?

A
  • To convert trypsinogen intor trypsin (active).

- Helps prevent autodigestion of the pancreas as enzymes are only activated once at the small bowel.

36
Q

Where is it found?

A

In the brush border of the small bowel.

37
Q

Which condition may result from the failure of measures to prevent autodigestion of the pancreas?

A

Acute pancreatitis.

38
Q

List 3 possible causes of pancreatitis.

A

1 - Gallstones.

2 - Alcohol.

3 - Trauma.

39
Q

List 5 features that are a sign of acute pancreatitis.

A

1 - Abdominal pain in the epigastrium radiating to the back.

2 - Nausea.

3 - Vomiting.

4 - Serum amylase and / or lipase >= 3x upper limit.

5 - Findings of acute pancreatitis on CT scan.

40
Q

List the phases of acute pancreatitis.

A

1 - Premature activation of trypsin in acinar cells.

2 - Intra-pancreatic inflammation via activation of inflammatory and endothelial cells.

3 - Extra-pancreatic inflammation, including systemic sepsis and multi-organ failure.

41
Q

List 4 treatments of acute pancreatitis.

A

Normally mild, so supportive therapy:

1 - Intravenous fluids to combat dehydration.

2 - Pain relief

If severe:

3 - Intensive care and multi-organ support (to combat sepsis).

4 - Therapeutic endoscopic retrograde cholangiopancreatography (ERCP), e.g. for gallstone removal.

42
Q

List 5 causes of chronic pancreatitis.

A

1 - Alcohol abuse.

2 - hereditary disroders.

3 - Cystic fibrosis.

4 - Hypercalcaemia.

5 - Hyperlipidaemia.

43
Q

List 6 treatments of chronic pancreatitis.

A

1 - Pain relief.

2 - Intravenous fluids to combat dehydration.

3 - Nutritional support (low fat, small and frequent meals).

4 - Synthetic pancreatic enzyme supplementation.

5 - ERCP.

44
Q

Give an example of a complication of pancreatitis.

A

Diabetes.

DIG (20 decks)

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