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BRS GASTROENTEROLOGY > The Pancreas > Flashcards

The Pancreas Flashcards

1
Q

Describe the embryology of the pancreas.

A
  1. abdominal accessory organs arise as foregut outgrowth
  2. Proximal duodenum rotates clockwise
  3. Ventral and dorsal pancreatic buds and ducts fuse;
    bile and pancreatic ducts join to drain together at major papilla
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2
Q

What is the positioning of the liver, gallbladder and pancreas?

A
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3
Q

Label this diagram.

A
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4
Q

Label this diagram.

A
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5
Q

What type of imaging is this?

A

CT scan

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6
Q

What type of imaging is this?

A

MRI

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7
Q

Label this diagram.

A
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8
Q

What type of scan is this?

A

MRCP

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9
Q

What is an MRCP (google)?

A

Magnetic resonance cholangiopancreatography

used to to visualize the biliary and pancreatic ducts non-invasively

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10
Q

Label this diagram.

A
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11
Q

What is an x-ray to check blood vessels?

A

angiography§

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12
Q

What can you use angiography on in the pancreas?

A

coeliac axis
superior mesenteric artery
common hepatic artery
embolisation of gastroduodenal artery

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13
Q

Name the parts of the small intestine?

A

D
J
I

duodenum
jejunum
ileum

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14
Q

How do you carry out an agiography?

A

a very thin flexible tube (catheter) is inserted into the artery. the catheter is carefully guided to the area that’s being examined (such as the heart) a contrast agent (dye) is injected into the catheter. a series of X-rays are taken as contrast agent flows through your blood vessels.

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15
Q

How do you define endocrine vs exocrine?

A

Endocrine: Secretion into the bloodstream to have effect on distant target organ (Autocrine/Paracrine) - Ductless Glands

Exocrine: Secretion into a duct to have direct local effect

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16
Q

What are the main endocrine secretion of the pancreas and their actions?

A

Insulin: anabolic hormone
- promotes glucose transport into cells & storage as glycogen
- ↓ blood glucose
- promotes protein synthesis & lipogenesis

Glucagon: ↑s gluconeogenesis & glycogenolysis (↑s blood glucose)

Somatostatin: “Endocrine cyanide”

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17
Q

How much of the pancreas is endocrine and what part is?

A

Endocrine - 2% of gland
- Islets of Langerhans
- Secrete hormones into blood - Insulin & Glucagon (also Somatostatin and Pancreatic Polypeptide)
- Regulation of blood glucose, metabolism & growth effects - (Endocrine course)

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18
Q

How much fo the pancreas is exocrine and what part is?

A

Exocrine - 98% of gland

  • Secretes pancreatic juice into duodenum via MPD (major pancreatic duct)/sphincter of Oddi/ampulla
  • Digestive function
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19
Q

How ar acini and islets formed?

A

Formation of acini & islets from ducts in various stages of development

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20
Q

What are acini in the pancreas?

A
  • Ducts
  • Acini are grape-like clusters of secretory units
  • Acinar cells secrete pro-enzymes into ducts
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21
Q

What are islets in the pancreas?

A
  • Derived from the branching duct system
  • Lose contact with ducts – become islets
  • Differentiate into α- and β-cells secreting into blood
  • Tail > head
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22
Q

Label this diagram.

A
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23
Q

What is the composition of islets in the pancreas?

A

α-cells (A) form about 15-20% of islet tissue and secrete glucagon

β-cells (B) form about 60-70% of islet tissue and secrete insulin

δ-cells (D) form about 5-10% of islet tissue and secrete somatostatin

Acini (2)
- The islets are highly vascular, ensuring that all endocrine cells have close access to a site for secretion

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24
Q

what are the exocrine pancreatic units?

A

acini

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25
Q

What is the composition of the acini?

A

Secretory acinar cells
- Large with apical secretion granules

Duct cells
- Small & pale

26
Q

What are the components of pancreatic juice?

A

↓ vol, viscous, enzyme-rich - Acinar cells

↑ vol, watery, HCO3- rich - Duct & Centroacinar cells

27
Q

What produces the bicarbonate secretions for the pancreatic juice?

A

duct & centroacinar cells

28
Q

How would you describe pancreatic juice in terms of bicarbonate secretion?

A

Pancreatic Juice = ↑ bicarbonate
- ~ 120 mM (mmol/L) - (plasma ~25 mM)
- pH 7.5-8.0

29
Q

What does the (bicarbonate secretions in the) pancreatic juice do?

A

Neutralises acid chyme from stomach
- prevents damage to duodenal mucosa
- Raises pH to optimum range for pancreatic enzymes to work

Washes low volume enzyme secretion out of pancreas into duodenum

30
Q

What effect does duodenal pH have on HCO3- secretion rate?

A

Duodenal pH < 5 → linear ↑ in pancreatic HCO3- secretion
Duodenal pH <3 → not much more ↑ in HCO3- secretion

31
Q

Why does HCO3- secretion stop when pH is still acid?

A

Bile also contains HCO3- and helps neutralise acid chyme

Brunner’s glands secrete alkaline fluid

32
Q

What is the mechanism for HCO3-?

A
  1. Pancreatic HCO3- Secretion
    - Catalysed by carbonic anhydrase
    - Separation of H+ & HCO3-
    - Na+ moves down gradient via paracellular (“tight”) junctions
    - H2O follows
  2. Pancreatic HCO3- Secretion
    - Cl-/HCO3- exchange at lumen (anion exchanger [AE]) (Cl- enters cell and HCO3- leaves the cell)
    - Na+/H+ exchange at basolateral membrane into bloodstream (sodium-hydrogen exchanger (antiporter) type 1 [NHE-1])
  3. Pancreatic HCO3- Secretion
    - Na+ gradient into cell from blood maintained by Na+/K+ exchange pump (Na+ leave the cell, K+ enters)
    - Uses ATP - Primary active transport
  4. Pancreatic HCO3- Secretion
    - K+ returns to blood via K+- channel
    - Cl- returns to lumen via Cl- channel (cystic fibrosis transmembrane conductance regulator [CFTR])

this all happens at the pancreatic duct cell

33
Q

What drives the exchange in this step of the HCO3- mechanism…

  1. Pancreatic HCO3- Secretion
    - Cl-/HCO3- exchange at lumen (anion exchanger [AE]) (Cl- enters cell and HCO3- leaves the cell)
    - Na+/H+ exchange at basolateral membrane into bloodstream (sodium-hydrogen exchanger (antiporter) type 1 [NHE-1])
A

Electrochemical gradients
High EC (blood) Na+ compared to IC (duct cell)
High Cl- in lumen compared to IC (duct cell)

34
Q

What is the reaction that makes bicarbonate for the pancreatic juice and what cells does it occur in?

A
35
Q

What channel doesn’t work well in cystic fibrosis?

A

CFTR
- cystic fibrosis transmembrane conductance

36
Q

What is the H+ and HCO3- used for/ goes to in the stomach?

A

H+ → gastric juice
HCO3- → blood
Gastric venous blood is alkaline

37
Q

What is the H+ and HCO3- used for/ goes to in the pancrea?

A

HCO3- secreted → juice
H+ → blood
Pancreatic venous blood is acidic

38
Q

What are the enzymes that acinar cells secrete into the pancreatic juice?

A

fat (lipases)
protein (proteases)
carbohydrates (amylase)

39
Q

Where are the enzymes from the acinar cells stored and synthesised?

A

zymogen granules
zymogen= pro-enzymes

40
Q

What might be the problem for an organ making a cocktail of digestive enzymes?

A

auto-digestion

41
Q

What does auto-digestion lead to?

A

acute pancreatitis

42
Q

How can auto-digestion occur?

A

Proteases are released as inactive pro- enzymes
- protects acini & ducts from auto- digestion

Pancreas also contains a trypsin inhibitor to prevent trypsin activation
- Enzymes only activated in duodenum

Blockage of MPD (major pancreatic duct) may overload protection
- leading to auto-digestion

43
Q

What enzyme does the duodenal mucosa secrete and what is its role?

A

Enterokinase (enteropeptidase)
- converts trypsinogen → trypsin

44
Q

What does trypsin do?

A

Trypsin then converts all other proteolytic & some lipolytic enzymes

45
Q

How is lipase secrete and activated?

A

Lipase secreted in active form but requires colipase (i.e. secreted as precursor)

Lipases require presence of bile salts for effective action

46
Q

What do pancreatic secretions adapt to?

A

to diet
e.g.

↑ protein, ↓ carbs → ↑s proportion of proteases & ↓ proportion of amylases

47
Q

What are pancreatic enzymes essential for?

A

Pancreatic enzymes (+ bile) essential for normal digestion of a meal:
- Lack of these can → malnutrition even if dietary input is OK.
- (unlike salivary, gastric enzymes)

48
Q

Anti-obesity drug Orlistat inhibits pancreatic lipases – what side effects might you expect?

A

↑ faecal fat (fatty stool)
- occurs when pancreatic lipase secretion ↓
- e.g. cystic fibrosis, chronic pancreatitis, Orlistat (↓s intestinal fat absorption)

49
Q

What is the control of pancreatic juice secretion during the cephalic phase of gastric secretion?

A

Cephalic phase
- Reflex response to sight/smell/taste of food
- Enzyme-rich component only.
- Low volume - “mobilises” enzymes

50
Q

What is the control of pancreatic juice secretion during the gastric phase of gastric secretion?

A
  • Stimulation of pancreatic secretion originating from food arriving in the stomach
  • Same mechanisms involved as for cephalic phase
51
Q

What is the control of pancreatic juice secretion during the intestinal phase of secretion?

A

Intestinal phase (= 70-80% of pancreatic secretion)

  • Hormonally mediated when gastric chyme enters duodenum.
  • BOTH components of pancreatic juice stimulated
  • enzymes & HCO3- juice flows into duodenum
52
Q

How is pancreatic juice enzyme secretion controlled in acini?

A
  1. Vagus nerve –
    - Cholinergic
    - Vagal stimulation of enzyme secretin (& communicates information from gut to brain)
  2. Cholecystokinin (CCK) (Ca2+/PLC)
53
Q

How is pancreatic juice bicarbonate secretion controlled in duct and centroacinar cells?

A

Secretin (cAMP)

54
Q

How does the agus nerve control enzyme secretion in acini?

A

acetylcholine ACh

55
Q

What secretes CCK (cholecystokinin)?

A

Duodenal I cells

56
Q

What is the mechanism for controlling the release of cholecystokinin?

A

Released from duodenal I cells

Trypsin ahs an inhibitory effect on cholecystokinin secretion

Amino acids and fatty acids stimulate secretion

Gastrin releasing peptide (GRP) and ACh act on pancreas which then acts on trypsin or straight onto I cells to inhibit secretion

57
Q

Describe acinar fluid compared to plasma. And what is it primarily stimulated by?

A

Acinar fluid is isotonic
- resembles plasma in its concentrations of Na+, K+, Cl− & HCO3−

Secretion of acinar fluid & proteins it contains is stimulated primarily by CCK

58
Q

What does secretin stimulate?

A

Secretin stimulates secretion of H2O & HCO3- from cells lining extralobular ducts.

Secretin-stimulated secretion is richer in HCO3− cf acinar secretion because of Cl−/HCO3− exchange

59
Q

Describe the control of HCo3- secretions in ducts.

A

Secretin and HCO3− secretion
- Classic negative-feedback loop
- Responds to ↓in luminal pH in duodenum.

60
Q

Describe stimulus interaction differences.

A

CCK alone - no effect on HCO3− secretion

CCK can markedly ↑ HCO3− secretion that has been stimulated by secretin

Vagus nerve has similar effect to CCK

Secretin NO EFFECT on enzyme secretion

61
Q

Give the summary of a meal and what happens.

A
  1. Food mixed, digested in stomach, pH 2
  2. Chyme squirted into duodenum
  3. H+ ions in duodenum → ↑secretin → ↑pancreatic juice
    - + bile & Brunner’s gland secretions
    = ↑s pH to neutral/alkaline.
  4. Peptides & fat in duodenum cause sharp ↑ in CCK & vagal nerve stimulation
    → stimulates pancreatic enzyme release
    Peaks by 30 mins, continues until stomach empty.
  5. CCK potentiates effects of secretin on aqueous component
    - Necessary as most of duodenum not at ↓pH

BRS GASTROENTEROLOGY (25 decks)

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