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GI lectures > pancreatic exocrine function > Flashcards

pancreatic exocrine function Flashcards

1
Q

where is the pancreas

A

deep in the retroperitoneum

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2
Q

function of pancreas

A
  1. endocrine secretion
  2. exocrine secretion
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3
Q

describe exocrine gland of pancreas

A

contains the acinar and duct tissue,

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4
Q

describe endocrine gland of pancreas

A

contains the islets of Langerhans.

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5
Q

what is majority of pancreas made up of

A

the exocrine portion (85% by mass)

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6
Q

what does the exocrine portion do

A

secretes digestive enzymes, water and bicarbonate to assist in digestion.

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7
Q

what does bicarbonate do ( 2 roles)

A
  1. helps in neutralising stomach acid -

important because the small intestine is not specialised to withstand the strong acids from the stomach

this is because the small intestine, unlike the stomach, lacks a thick protective mucous layer

  1. the digestive enzymes secreted by the pancreas reach their optimum function at a basic pH

this is achieved by the bicarbonate secretions of the pancreas.

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8
Q

what is the functional unit of the exocrine pancreas

A

includes the acinus and its duct system

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9
Q

what are acinar cells specialised in

A

enzyme synthesis, storage and secretion.

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10
Q

what does the duct system do

A

modifies the aqueous secretions.

this mechanism is stimulated by the parasympathetic system and inhibited by the sympathetic system.

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11
Q

describe digestive enzyme secretion

A
  1. acinar cells produce digestive enzymes on the ReR
  2. they are then moved to the to the Golgi complex where they form condensing vacuoles.
  3. These condensing vacuoles are then concentrated into inactive zymogen granules in pancreatic acinar cells and stored for secretion.
  4. They are secreted into the main pancreatic duct, which merges with the bile duct at the head of the pancreas and forms the Ampulla of Vater.
  5. From here it enters the duodenum.
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12
Q

which digestive enzymes are secreted

A
  1. proteases
  2. pancreatic lipase
  3. amylase
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13
Q

describe proteases

A

Chymotrypsinogen and Trypsinogen

Digest proteins and peptides to single amino acids

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14
Q

describe pancreatic lipases

A

Digests triglycerides, monoglyceride and free fatty acids

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15
Q

describe amylase

A

Starch and maltose (disaccharides)

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16
Q

how is carbonic acid formed (H2CO3).

A

when water and carbon dioxide combine

catalysed by the enzyme carbonic anhydrase

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17
Q

what does carbonic acid disassociate into

A

hydrogen ions (H+) and bicarbonate ions (HCO3–)

H2CO3 -> H+ + HCO3–

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18
Q

what happens to H+ ions

A

they are transported out of the pancreatic ductal cells into the blood in exchange for Na+ ions by an H+/Na+ antiporter.

The Na+ ions that enter the cell are then removed by the Na+/H+/ATPase.

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19
Q

what happens to the HCO3– produced from the dissociation of carbonic acid

A

it is transported into the intercalated ducts of the pancreas in exchange for Cl–.

An intracellular build up of Cl– is avoided by a chloride channel which allows chloride ions to return to the lumen of the intercalated ducts.

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20
Q

what happens to the bicarbonate ions, Na+ ions and wate

A

they move through the intercalated ducts and end up at the main pancreatic duct ready for secretion into the duodenum upon an appropriate stimulus.

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21
Q

how much bicarbonate secretion

A

total 1 litre/24 hours

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22
Q

how much bicarbonate secretion

A

total 1 litre/24 hours

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23
Q

what stimulates the pancreas to secrete enzymes

A

vagal innervation to the pancreas

this occurs when we see, smell or taste food
or
when the stomach wall is stretched.

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24
Q

what stimulates the pancreas to secrete enzymes

A

vagal innervation to the pancreas

this occurs when we see, smell or taste food
or
when the stomach wall is stretched.

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25
Q

what does acidic chyme entering the duodenum stimulate

A

stimulates S cells to release secretin

  • a hormone that causes the pancreatic cells to secrete the alkaline parts of the pancreatic juices.
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26
Q

what do the fatty acids and protein present in the chyme, combined with the acidic pH stimulate

A

trigger I cells in the duodenum to release the hormone cholecystokinin (CCK).

this hormone also leads to secretion of digestive enzymes in the pancreatic juices.

also CCK stimulates bile secretion via gallbladder contraction.

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27
Q

where is the main pancreatic duct anatomically

A

it merges with the bile duct, which leads to the Ampulla of Vater.

It is here that these secretions pour into the duodenum and help neutralise and digest chyme.

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28
Q

how does the digestion of fats and proteins affect pancreatic secretion

A

as proteins and fats are digested and absorbed

pH rises

stimuli for CCK and secretin disappear

pancreatic secretion reduces.

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29
Q

role of gastrin and CCK

A

stimulate enzyme secretion and neutralise gastric acid entering small intestines

30
Q

symptoms of pancreatic exocrine insufficiency

A

maldigestion
diarrhoea
steatorrhoea
weight loss

31
Q

consequences of pancreatic exocrine insufficiency

A

malnutrition
oesteoporosis
increased cardiovascular morbidity
symptom burden

32
Q

treatment of pancreatic exocrine insufficiency

A
  • pancreatic enzyme replacement therapy
  • STOP smoking
  • bone health assessment
  • treat the underlying cause
33
Q

what initiates protein digestion

A

pepsin in the stomach

34
Q

where does majority of protein digestion occur

A

in the small intestine

35
Q

how are pancreatic proteases stored

A

as proenzymes

(trypsinogen and chymotrypsinogen)

36
Q

what activates trypsinogen

A

enterokinase

37
Q

what does trypsin activate

A

chymotrypsinogen and additional trypsinogen

38
Q

what do lipases do

A

hydrolyse triglycerides to monoglyceridees and free fatty acids

39
Q

what do bile salts do

A

aid triglyceride digestion and absoprtion of monoglycerides and free fatty acids

40
Q

what is fat digestion dependent on

A

pancreatic and hepatic secretion

41
Q

where is cholecystokinin produced

A

I cells of duodenum & jejunum

42
Q

what stimulates cholecystokinin

A

HCL
proteins ans fats entering duodenum

43
Q

what does cholecystokinin do

A

causes pancreatic enzyme and HCO3- secretion

gallbladder contraction

inhibition of gastric acid secretion

delays gastric emptying

44
Q

where is secretin produced

A

upper small intestine

45
Q

what stimulates secretin

A

low duodenal pH

46
Q

what does secretin do

A

causes pancreatic water and bicarbonate secretion

47
Q

where is gastrin produced

A

G cells in stomach

48
Q

what stimulates gastrin

A

gastric distension and irritation

49
Q

what does gastrin do

A

HCl secretion - parietal cells

enzyme release - acinar cells

50
Q

which cells secrete HCO3- (bicarbonate)

A

duct cells - epithelial cells lining the ducts

51
Q

which cells secrete digestive enzymes

A

gland cells at the pancreatic end of the duct system

the enzymes secreted are either active or precursors

52
Q

give 2 active enzymes

A

alpha amylase
lipase

53
Q

what does alpha amylase do

A

converts starch to maltose

54
Q

what does lipase do

A

Converts triglycerides to monoglyceride & fatty acids

55
Q

what does zymogen do

A

protects pancreatic cells from
autodigestion

56
Q

what is enterokinase

A

is a proteolytic enzyme that splits off a peptide from pancreatic trypsinogen forming the active enzyme TRYPSIN

57
Q

what is trypsin

A

a proteolytic enzyme which in turn goes on to active other pancreatic zymogens once activated by splitting off peptide fragments

58
Q

what do trypsin & chymotrypsin do

A

chymotrypsin are enzymes used to break peptide bonds in
proteins to form peptide fragments i.e. they digest ingested proteins

59
Q

what inhibits pancreatic exocrine
secretion

A

somatostatin produced by the D cells in the pancreatic islets/ islets of Langerhans

60
Q

how does somatostatin inhibit exocrine secretion

A

through the inhibition of cholecystokinin-stimulated enzyme secretion and secretin-stimulated bicarbonate secretion

61
Q

what are the 4 cell types in the islets of langerhans

A
  • Alpha cells - produce glucagon
  • Beta cells - produce insulin & amylin
  • Delta/D cells - produce somatostatin
  • PP cells - produce pancreatic polypeptide
62
Q

what does autoimmune destruction of the islets of langerhans cause

A

diabetes mellitus

63
Q

what are the 3 phases of pancreatic secretion

A
  • cephalic
  • gastric
  • intestinal
64
Q

what initiates the cephalic phase

A

the sensory experience of seeing & eating food

65
Q

what happens in cephalic phase

A

involves parasympathetic vagus nerve stimulation of acinar cells to produce
digestive enzymes

66
Q

what initiates gastric phase

A

the presence of food within the stomach

67
Q

what happens in gastric phase

A

also involves parasympathetic vagus nerve stimulation of acinar cells to produce digestive enzymes

68
Q

what happens by the end of the cephalic & gastric phases

A

the pancreatic ducts are filled
with inactive digestive zymogens ready for release into the intestinal lumen
along with bicarbonate via the sphincter of Oddi

69
Q

what happens when amino acids + fatty acids are present in the duodenum

A

then CCK is released and the gallbladder contracts inducing enzyme secretion

70
Q

what initiates the intestinal phase

A

the emptying of stomach contents into the small Intestine

71
Q

what happens in the intestinal phase

A

involves release of both secretin and cholecystokinin which stimulate pancreatic ductal cells to synthesize aqueous sodium bicarbonate solution

GI lectures (9 decks)

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