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Gastrointestinal > Pancreatic Exocrine Secretions and It's Control > Flashcards

Pancreatic Exocrine Secretions and It's Control Flashcards

1
Q

Outline the flow of acini secretions

A

Acini form sacs → connect to ductal tree → enter duodenum at main common bile duct

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2
Q

What is the route taken by secretions through the ductal tree?

A

Intercalated ducts→Intralobular ducts→Extralobular ducts →interlobular ducts → common bile duct →duodenum

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3
Q

What are the Islets of Langerhans?

A

Clusters of endocrine cells in the pancreas

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4
Q

Where are islets of Langerhans located?

A

Found throughout the pancreas, mainly in the tail of the pancreas

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5
Q

What is the role of islets of Langerhans?

A

Secrete the following -
Insulin : 65% ꞵ cells
Glucagon : 20% ꭤ cells
Somatostatin : 10% δ cells

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6
Q

What are acinar cells?

A

Berry-like secretory portion consisting of pyramidal epithelial cells that secrete digestive enzymes into the Pancreatic duct

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7
Q

Where are microvilli located in acini?

A

Microvilli extend for the apical surface of epithelial cells into the acini lumen

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8
Q

Describe the structure of Intercalated ducts

A

Squamous epithelium
Begin with acini
Smallest pancreatic duct members
Drain into Intralobular ducts

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9
Q

Describe the structural features of Intralobular ducts

A

Lined with cuboidal or low columnar epithelium

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10
Q

Describe the structure of interlobular ducts

A

Larger columnar epithelium

Goblet cells in a fibrocollagenous connective tissue

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11
Q

How does the pancreatic duct accommodate pancreatic secretions?

A

Pancreatic duct wall composed of smooth muscle; as size of duct increases, the surrounding connective tissue also gets more dense

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12
Q

Outline the flow of secretions through the exocrine pancreas

A

acini→microvilli→Intercalated→Intralobular→interlobular→Pancreatic duct

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13
Q

How much fluid is secreted by the exocrine pancreas?

A

secretes 1.5 L per day

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14
Q

What does the pancreatic juice consist of?

A

Na+ and HCO₃⁻-rich juice, albumin, globulin an digestive enzymes

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15
Q

What is the role of acinar cells?

A

Acinar cells secrete digestive enzymes to hydrolyse carbohydrates, proteins, fats and nucleic acids

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16
Q

How is auto-digestion of the pancreas prevented?

A

Enzymes are secreted in their inactive form to prevent auto-digestion (proenzymes)

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17
Q

Where are the inactive enzymes activated?

A

In the duodenum

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18
Q

Describe the concentration of solution secreted by the pancreas

A

is a HCO₃⁻-rich hypertonic juice

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19
Q

What is the purpose of the alkaline pancreatic secretions?

A

HCO₃⁻-rich juice and secretions from gallbladder neutralise gastric acid (↑pH to 6 or 7)

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20
Q

How is the fluid concentration regulated?

A

Composition of the fluid is modified as it travels through the ducts

21
Q

How is the fluid composition altered?

A
  • Cl- actively exchanged for HCO₃⁻- by epithelial cells
  • H+ actively eliminated; more CO₂ and HCO₃⁻ produced
    in blood
  • H+ exchanged for K+ and Na+
    –> H+ neutralises HCO₃⁻ (forming H₂CO₃)
22
Q

How does a low secretion rate effect where its secreted from?

A

Low secretion rate = Most fluid secreted via Intralobular ducts

23
Q

What causes a high secretion rate?

A

Secretin

most additional fluid produced by Extralobular ducts

24
Q

What are the effects of Secretin on pancreatic juice?

A

composition and volume affected

reciprocal change in [Cl-] and [HCO₃⁻] after the infusion of Secretin
HCO₃⁻ increases, Cl- decreases

25
Q

What causes the decrease in amylase after Secretin infusion?

A

The fall in [amylase] probably reflects dilution effect as volume of pancreatic juice increases

26
Q

What are the 3 major types of enzymes secreted by the pancreas?

A

Proteolytic enzymes

  • trypsin
  • chymotrypsin
  • carboxypeptidases

Amylase
- starch→maltose

Lipase

27
Q

What other enzymes are secreted by the pancreas?

A

Deoxyribonuclease

ribonuclease

28
Q

How can pancreatic juice be used to diagnose acute pancreatitis?

A

Level of pancreatic amylase is increased => good diagnostic test

29
Q

What is the role of proteolytic enzymes?

A

Cause digestion of proteins

=> pancreas is at risk of auto digestion

30
Q

Explain the dual effects of Chymotrypsin C (Caldecrin)

A

At high [Ca2+] - enables activation of trypsinogen

At low [Ca2+] - facilitates trypsin degradation

31
Q

How long do the enzymes last within the duodenum?

A

Digestive enzymes survive different lengths of time in the small intestine

32
Q

What Percentage of enzymes reach the small intestine?

A

Amylase ; 75%
Trypsin ; 20%
Lipase ; 1%

33
Q

What evidence supports the fact there is bidirectional permeability at the basolateral membrane for digestive enzymes?

A

Chymotrypsinogen and amylase cross the basolateral membrane of the pancreas

34
Q

What controls the Pancreatic secretions?

A
  • Neuroendocrine signals
  • Vagal (parasympathetic stimulation
  • Sympathetic stimulation
  • Secretin and CCK
35
Q

Explain how vagal innervation affects pancreatic secretions

A

Enhances secretion rate of enzymes and aqueous components of pancreatic juice

36
Q

What is the effect of sympathetic stimulation on the exocrine pancreas?

A

Inhibits secretion via decreased blood flow

37
Q

Explain the effects of CCK and Secretin

A

Stimulate the secretion of pancreatic juice

38
Q

What occurs during the cephalic phase of digestion?

A

Vagal (Ach and VIP) stimulation of gastrin release from antrum → some protein-rich pancreatic juice

39
Q

Explain the events of the Gastric digestion phase

A

Distension (vagal reflex on fundus or antrum), amino acid- and peptide- (in antrum)-stimulated gastrin secretion → release of enzyme-rich pancreatic juice

40
Q

What effect does a vagotomy have on the Gastric phase?

A

Vagotomy → 50%↓ in response to chyme

41
Q

What happens in the Intestinal phase?

A

Chyme in duodenum and jejunum induces secretion of pancreatic juice via CCK and Secretin

42
Q

Outline the effects of CCK

A
  • released from duodenum & jejunum in response to FA
  • stimulates acinar cells to release pancreatic juice
  • stimulates secretion of conc. bile for fat absorption
  • contracts gallbladder
  • relaxes sphincter of Oddi
  • Potentiates effects of Secretin (weak acinar cell agonist)
43
Q

What are the effects of Secretin?

A
  • released from duodenum and jejunum
  • induces pancreatic duct cells to secrete HCO₃⁻ rich
    pancreatic juice
  • decreased enzyme content
  • stimulates bile production
44
Q

How does CF affect the pancreatic ducts?

A

Abnormal mucus blocks pancreatic ducts affecting pancreatic secretions;
carbohydrate, protein and lipid digestion will be affected

45
Q

What is the effect of obstructed pancreatic duct in CF patients?

A

Obstruction of the pancreatic duct by thick mucus contributes to GI symptoms in patients with cystic fibrosis (CF)

46
Q

What are the major GI symptoms of CF?

A
  • Due to dysfunction of exocrine glands, sweat glands
    secrete excessive sodium and chloride
  • Pancreatic ducts become blocked with thickened mucus
    and this leads to pancreatic insufficiency
  • Lungs also produce thickened mucus
47
Q

What are the consequences of the GI symptoms in CF patients?

A
  • Severe malabsorption
  • Steatorrhoea
  • Recurrent chest infections
  • Sterility in 98% of males
48
Q

How does CF cause sterility in males?

A

Sterility in 98% of males due to congenital bilateral aplasia of the vas deferens (CBAVD) – vas deferens fails to develop properly. Recall that normally the vas deferens carries the newly made sperm to the back of the prostate gland where it joins the outlets of the seminal vesicles. The sperm can then be released into the semen during intercourse

Gastrointestinal (18 decks)

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