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Alimentary system > Pancreas > Flashcards

Pancreas Flashcards

1
Q

The development of the pancreas

A
  • The dorsal and ventral buds arise from the foregut-midgut junction with the ventral bud being part of the hepatobiliary bud (or gall bladder bud)
  • The duodenum rotates into a c-shape and the ventral bud swings round adjacent to the dorsal bud and buds fuse
  • The ventral bud duct then becomes the main pancreatic duct
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2
Q

What is the structure of the pancreas?

A
  • The pancreas is split into: uncinate, head, neck, body, tail
  • The order from the tail is T, B, N, H, Un
  • Tail then extends to hilum of spleen
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3
Q

Where is the islet tissue most abundant?

A

In the tail

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4
Q

What is endocrine and give examples?

A
  • Secretion into blood stream, distant effect
  • Insulin, glucagon, somatostatin
  • 2%
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5
Q

What is exocrine and give examples?

A
  • Secretion into a duct, local effect

- pancreatic juices for digestion

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6
Q

Can pancreatic diseases affect both endocrine and exocrine functions?

A

Yes

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7
Q

How do pancreatic juices reach the duodenum?

A

Pancreatic juices reach the duodenum via the main and accessory pancreatic ducts

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8
Q

Which arteries supply the pancreas?

A

The coeliac and superior mesenteric arteries

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9
Q

Exocrine cells

A
  • Arranged in ducts
  • Acini are grape-like clusters of secretory units.
  • Acinar cells secrete pro-enzymes into the ducts
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10
Q

Endocrine cells

A
  • Derived from the duct system
  • The braches then become islets
  • Differentiate into alpha, beta and delta cells
  • More prevalent at the tail-end
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11
Q

Pancreatic juices - 2 main components

A
  • low volume, viscous, enzyme rich (from acinar cells)

- high volume, watery and bicarbonate rich (ducts and centroacinar cells)c

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12
Q

What is the composition of the islets?

A 
Alpha = glucagon, (15-20%)
Beta = insulin, (60-70%)
Delta = somatostatin, (5-10%)
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13
Q

What is the location of the pancreas?

A

Lies mainly on posterior abdominal wall extending from C-shaped duodenum to hilum of spleen

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14
Q

What are centroacinar cells?

A

They are an extension of the intercalated duct cells into the pancreatic acinus

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15
Q

The pancreatic juice functions and pH

A
  • Secretions rich in bicarbonate (pH ~ 7.5-8.0)

Functions to:

  • Neutralise acidic chyme from stomach
  • Prevent damage to duodenal mucosa
  • Raise pH so pancreatic enzymes can function
  • Wash low volume enzyme secretion out of pancreas
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16
Q

Effect of duodeunal pH on bicarbonate secretion rate

A

Duodenal pH <3 = not much more increase in bicarbonate secretion

Duodenal pH < 5 = significant linear increase in pancreatic bicarbonate secretion

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17
Q

Why does bicarbonate production stop when pH is still acidic?

A
  • Bile contains bicarbonate and helps neutralise the acid chyme
  • Brunner’s glands secrete alkaline fluid
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18
Q

Mechanism of bicarbonate secretion

A
  1. Catalysed by carbonic anhydrase which produces HCO3- and H+. Sodium moves down gradient via paracellular tight junctions and H20 follows
  2. Cl/HCO3- exchanged at the lumen (antiporter) and Na/H+ exchanged (antiporter) at basolateral membrane into blood
    High Na+ in blood compared to inside duct cell and high Cl- in lumen compared to in duct cell
  3. Sodium gradient into cells from blood maintained by the Na+/K+ pump using ATP
  4. K+ returns to blood via K+ channel and Cl- returns to lumen via Cl- channel
    This enables bicarbonate pumping to continue

SAME REACTION TO SECRETE HCL BY PARIETAL CELLS BUT REVERSED

19
Q

What is the chloride ion also known as?

A

CFTR channel

20
Q

What is different between gastric venous blood and pancreatic venous blood and why/

A

In the stomach, H+ goes into the gastric juice, HCO3- into the blood. Gastric venous blood is alkaline

In the pancreas, HCO3- secreted into the juice and H+ into the blood. Pancreatic venous blood is acidic

21
Q

What are structures are near the posterior of the pancreas?

A

IVC
Abdominal aorta
Left kidney

22
Q

What does stomatostatin do?

A

Suppress glucagon and insulin release

23
Q

What type of epithelium lines the pancreatic ducts?

A

Columnar epithelium lines the pancreatic ducts

24
Q

Acinar cells - features

A

They are large with apical secretion granules

25
Q

Duct cells - features

A

Small and pale

26
Q

Acinar enzyme secretion

A

Enzymes for digestion of fat, protein and carbohydrates are synthesised and stored in zymogen granules

27
Q

How do the cells avoid digesting themselves?

A

Proteases are released as inactive pro-enzymes which protects acini and ducts from auto-digestion.
Pancreas also contains a trypsin inhibitor to prevent trypsin activation.
Enzymes become activated only in duodenum e.g. trypsin to trypsinogen by enterokinase is duodeunum

28
Q

What happens if the pancreatic duct gets blocked and autodigestion occurs due to it?

A

acute pancreatitis

29
Q

What does trypsin do?

A

It converts other proteolytic and lipolytic enzymes

30
Q

Are lipases secreted in active form?

A

Yes but they require co lipase which is made as a precursor

31
Q

Can the pancreas alter its function and if so when?

A

Pancreatic secretions adapt to diet e.g. high protein, low carbs, increases proportion of proteases, decreases proportion of amylases

32
Q

What happens if pancreatic enzymes and bile are not present?

What does orlistat do?

A

Pancreatic enzymes (+ bile) are essential for normal digestion of a meal. Lack of these can lead to malnutrition even if the dietary input is okay

It inhibits pancreatic lipases

33
Q

What is the most important phase in pancreatic secretion?

A

Intestinal phase

Hormonally mediated when gastric chyme enters intestine - both components enter (enzymes and HC03- juice)

34
Q

What happens to pancreatic secretion during the cephalic and gastric phase?

A

cephalic - reflex (vagal nerve) and low amount of enzymes made not HC03- yet

Gastric - stimulation (reflex) and more enzymes made but still no HC03- juice

35
Q

How are the two components of pancreatic juice controlled?

A

Seperately - bicarbonate is controlled by hormone called secretin (cAMP) and enzymes are controlled by vagus nerve reflex and hormone called cholecystokinin (Ca2+/PLC)

36
Q

What else does CCK do?

A

stimulates bile secretion

37
Q

Which division of the nervous system is involved in digestion?

A

Parasympathetic nervous system stimulates digestion

Vagus nerve main one (cholinergic) - send infromation to and from gut and brain

38
Q

How is secretin production regulated?

A

Enteroendocrine cells in the duodenum detect more protons coming from the stomach and they produce secretin which travels in the blood to the duct cells in the pancreas, affect cAMP in them and more secretion of juice (HCO3-). A pH in lumen increases the secretin production is switched off.

39
Q

How is the production of CCK stimulated and what does it do?

A

Food enters small intestine and it contains peptides and fats - receptors detect them and cells produce CCK which goes in circulation to acinar cells (they can also be stimulated by vagus nerve during cephalic phase for example) and this causes intracellular Ca2+ cascade and proenzymes released and trypsin inhibitor. In duodenum they enzymes are activated.

40
Q

How is CCK switched off?

A

Cephalic phase ends when meals are eaten

Absorption of fats and peptides removes the local luminal stimulus for CCK release. Other mechanisms may be involved

41
Q

CCK and secretin interaction

A
  • CCK alone has no effect on bicarbonate secretion
  • Secretin alone causes small increase in bicarbonate secretion
  • CCK and secretin combined lead to increased bicarbonate secretion

Secretin has no effect on enzyme secretion, CCK does it alone

42
Q

How does vagus nerve stimulation affect secretin?

A

Vagal nerve stimulation has same effect on cells as CCK (amplifies secretin effect)

43
Q

Why may both CCK and secretin be needed for bicarbonate release?

A

Most of the duodenum doesn’t have a low pH

Alimentary system (14 decks)

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