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Digestive MBChB 2 > Lecture 19; Control of pancreatic and biliary secretions > Flashcards

Lecture 19; Control of pancreatic and biliary secretions Flashcards

1
Q

What is the role of the duodenum?

A
  • Inhibition of gastric emptying
  • Inhibition of acid secretion
  • Stimulation of pancreatic and biliary secretion
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2
Q

How does the duodenum detect its contents?

A

Vagal afferents

Specialised cells

  • I cells
  • S cells
  • Enterochromaffin cells
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3
Q

What do I, S and enterochromaffin cells do?

A

I cells

  • Sample luminal contents FA/AA
  • CCK

S cells

  • Senses pH
  • Releases Secretin

Enterochromaffin cell
- Serotonin cells

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4
Q

What do CCK and Secretin both inhibit?

A

Inhibit;

  • Gastric emptying
  • Acid secretion
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5
Q

What does serotonin secretion from enterochromaffin cells do?

A
  • Stimulates gut motility

- High levels in blood can activate vomiting via medulla

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6
Q

Whats the role of exocrine pancreas?

A
  • Ductal cells secrete HCO3

- Acinar cells release digestive enzymes for fat and protein digestion

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7
Q

Describe the ductal cells of the pancreas;

A
  • Intercalated ducts and centeroacinar cells (Duct cells) release HCO3 via pancreatic duct.
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8
Q

What are the 3 mechanisms of pancreatic bicarb secretion;

A

1) Secretin release causes increased cAMP in ductal cells, CFTR insertion and HCO3 release
2) Direct vagal stimulation via increased iCa2
3) Duodenum secretes Bicarb also

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9
Q

Describe the release from pancreatic enzymes;

A
  • Acinar cells
  • Stored as zymogen granules, pro-enzymes that are activated in SI
  • CCK controls release in response to FA/AA
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10
Q

How does CCK act?

A

Acts directly on acinar cells or causes vagal stimulation of acinar cells and enzyme release.

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11
Q

Where does pancreatic enzyme activation take place?

A
  • Activation takes place in the duodenal lumen at the brush border.
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12
Q

Describe the action of trypsin;

A

Trypsinogen is converted to trypsin by enterokinase.

Trysin in turn cleaves;

  • Trypsinogen
  • Chymotrypsinogen
  • Other pro-enzymes.
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13
Q

What are some other pancreatic enzymes;

A

Pancreatic lipase

Amylase

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14
Q

Describe how CCK and Secretin act on the pancreas;

A
  • FA/AA in duodenum stimulates I cells to release CCK.
  • CCK causes acinar cells to release pancreatic enzymes via 2 pathways
  • HCl in the duodenum stimulates S cells to release secretin.
  • Secretin stimulates pancreatic ductal cells to release secretions rich in HCO3 for acid neutralisation.
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15
Q

What other factors can stimulate pancreatic exocrine release?

A
  • Gastrin, also stimulates acinar cells to release digestive enzymes
  • Vagal stimulation can to a low degree cause release of digestive enzyme and HCO3 release.
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16
Q

Whats the other action of CCK?

A

Stimulates bile production in liver, gallbladder contraction, and sphincter of oddi relaxation to deliver more bile into the duodenum

17
Q

Whats the other action of secretin?

A

Causes the release of HCO3 from bile duct

18
Q

What can cause inhibition of pancreatic secretions?

A
  • Glucagon, somatostatin, peptide YY and pancreatic polypeptide

Pancreatic polypeptide via vagal inhibition

19
Q

What happens to the pancreas in CF?

A
  • Pancreatic insufficiency

Defective CFTR;

  • Cl accumulates in ductal cells
  • Draws Na and water into lumen
  • Pancreatic secretions become hyperviscous ( too thick)
20
Q

What happens to the pancreas when the secretions become hyperviscous?

A
  • Pancreatic ducts become blocked
  • Insufficient pancreatic enzymes released
  • (autodigestion -> pancreatitis -> Fibrosis) (Cystic fibrosis)
21
Q

What are the causes of pancreatitis?

A

Alcohol

Gallstones

22
Q

Whats the difference between acute and chronic pancreatitis?

A

Acute
- Acute inflammation, elevated enzymes in serum, self limiting

Chronic
- Chronic inflammation, progressive loss of pancreatic endocrine and exocrine function (alcohol)

23
Q

Describe pancreatic insufficiency at an endocrine and exocrine level;

A

Endocrine insufficiency

  • Impaired insulin production
  • Diabetes

Exocrine insufficiency

  • Impaired digestive enzymes production
  • Fat malabsorption
24
Q

How does exocrine pancreatic insufficiency present?

A
  • 90% loss of exocrine function
  • Loss of lipase (most critical)
  • Fat malabsorption -> weight loss, steatorrhoea.
  • Pancreatic enzyme supplements can be taken but issues with gastric degradation.
25
Q

Whats evident with chronic pancreatitis on a pancreatogram?

A

Dilated main branches with irregular side branches

26
Q

Whats in bile?

A
  • Bile acids
  • Cholesterol
  • Phospholipids
  • Bilirubin

= Detergent (Is irritant outside the biliary system)

27
Q

Whats the function of bile?

A

Carries bile acids
- Critical for digestion and absorption of fats and fat-soluble vitamins (A,D,E,K)

Elimination of waste products including bilirubin

28
Q

Describe bile flow through the biliary tree;

A

Hepatocytes secrete bile (large quantities of bile acids, cholesterol, etc)

  • BIle enteres canaliculi and flows into the larger bile ducts. As it flows through watery secretions rich in bicarbonate is added to the bile by ducted epithelial cells
  • Bile leaves the liver , flowing down common hepatic duct and enters cystic duct into the gallbladder
29
Q

Describe the mechanisms that drive bile flow;

A

Bile flow into canaliculi

Bile acid dependent

  • Active transport (draws water, osmotic effect)
  • Bilirubin is carried along

Bile acid independant
- Transport of other solutes and electrolytes help drive the flow of bile

( As the bile ducts become larger, more water and electrolytes is removed from the secretion)

30
Q

What are the two sources of bile acids?

A
  • 5% synthesised
  • 95% reabsorbed from terminal ilium i.e enterohepatic circulation via portal vein

Bile lost in faeces = amount synthesised per day , note failure to reabsorb bile salts causes diarrhoea

31
Q

What happens to bile in the gallbladder?

A

20x concentrations

32
Q

What is cholestasis?

A
  • Increased pressure in biliary tree and liver
  • Leads to rupture of tight junctions and leakage of bile
  • Bile contents spill back into circulation causing jaundice (hyperbillrubinaemia)
33
Q

What are malignant causes of biliary obstruction?

A

Pancreatic cancer, cancer in the head of the pancreas can cause narrowing of common bile duct, obstructing bile flow

34
Q

Whats the effect of prolonged bile duct obstruction?

A
  • Jaundice
  • Hyperbilirubinaemia (yellow skin, mucous membranes)
  • Itching
  • Nausea
  • Effects on renal perfusion
  • Malabsorption of fat and fat-soluble vitamins

Digestive MBChB 2 (31 decks)

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