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pancreatic exocrine function Flashcards

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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
what does acidic chyme entering the duodenum stimulate
stimulates S cells to release secretin - a hormone that causes the pancreatic cells to secrete the alkaline parts of the pancreatic juices.
26
what do the fatty acids and protein present in the chyme, combined with the acidic pH stimulate
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.
27
where is the main pancreatic duct anatomically
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.
28
how does the digestion of fats and proteins affect pancreatic secretion
as proteins and fats are digested and absorbed pH rises stimuli for CCK and secretin disappear pancreatic secretion reduces.
29
role of gastrin and CCK
stimulate enzyme secretion and neutralise gastric acid entering small intestines
30
symptoms of pancreatic exocrine insufficiency
maldigestion diarrhoea steatorrhoea weight loss
31
consequences of pancreatic exocrine insufficiency
malnutrition oesteoporosis increased cardiovascular morbidity symptom burden
32
treatment of pancreatic exocrine insufficiency
- pancreatic enzyme replacement therapy - STOP smoking - bone health assessment - treat the underlying cause
33
what initiates protein digestion
pepsin in the stomach
34
where does majority of protein digestion occur
in the small intestine
35
how are pancreatic proteases stored
as proenzymes (trypsinogen and chymotrypsinogen)
36
what activates trypsinogen
enterokinase
37
what does trypsin activate
chymotrypsinogen and additional trypsinogen
38
what do lipases do
hydrolyse triglycerides to monoglyceridees and free fatty acids
39
what do bile salts do
aid triglyceride digestion and absoprtion of monoglycerides and free fatty acids
40
what is fat digestion dependent on
pancreatic and hepatic secretion
41
where is cholecystokinin produced
I cells of duodenum & jejunum
42
what stimulates cholecystokinin
HCL proteins ans fats entering duodenum
43
what does cholecystokinin do
causes pancreatic enzyme and HCO3- secretion gallbladder contraction inhibition of gastric acid secretion delays gastric emptying
44
where is secretin produced
upper small intestine
45
what stimulates secretin
low duodenal pH
46
what does secretin do
causes pancreatic water and bicarbonate secretion
47
where is gastrin produced
G cells in stomach
48
what stimulates gastrin
gastric distension and irritation
49
what does gastrin do
HCl secretion - parietal cells enzyme release - acinar cells
50
which cells secrete HCO3- (bicarbonate)
duct cells - epithelial cells lining the ducts
51
which cells secrete digestive enzymes
gland cells at the pancreatic end of the duct system the enzymes secreted are either active or precursors
52
give 2 active enzymes
alpha amylase lipase
53
what does alpha amylase do
converts starch to maltose
54
what does lipase do
Converts triglycerides to monoglyceride & fatty acids
55
what does zymogen do
protects pancreatic cells from autodigestion
56
what is enterokinase
is a proteolytic enzyme that splits off a peptide from pancreatic trypsinogen forming the active enzyme TRYPSIN
57
what is trypsin
a proteolytic enzyme which in turn goes on to active other pancreatic zymogens once activated by splitting off peptide fragments
58
what do trypsin & chymotrypsin do
chymotrypsin are enzymes used to break peptide bonds in proteins to form peptide fragments i.e. they digest ingested proteins
59
what inhibits pancreatic exocrine secretion
somatostatin produced by the D cells in the pancreatic islets/ islets of Langerhans
60
how does somatostatin inhibit exocrine secretion
through the inhibition of cholecystokinin-stimulated enzyme secretion and secretin-stimulated bicarbonate secretion
61
what are the 4 cell types in the islets of langerhans
* Alpha cells - produce glucagon * Beta cells - produce insulin & amylin * Delta/D cells - produce somatostatin * PP cells - produce pancreatic polypeptide
62
what does autoimmune destruction of the islets of langerhans cause
diabetes mellitus
63
what are the 3 phases of pancreatic secretion
- cephalic - gastric - intestinal
64
what initiates the cephalic phase
the sensory experience of seeing & eating food
65
what happens in cephalic phase
involves parasympathetic vagus nerve stimulation of acinar cells to produce digestive enzymes
66
what initiates gastric phase
the presence of food within the stomach
67
what happens in gastric phase
also involves parasympathetic vagus nerve stimulation of acinar cells to produce digestive enzymes
68
what happens by the end of the cephalic & gastric phases
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
what happens when amino acids + fatty acids are present in the duodenum
then CCK is released and the gallbladder contracts inducing enzyme secretion
70
what initiates the intestinal phase
the emptying of stomach contents into the small Intestine
71
what happens in the intestinal phase
involves release of both secretin and cholecystokinin which stimulate pancreatic ductal cells to synthesize aqueous sodium bicarbonate solution
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