pancreatic exocrine function Flashcards
where is the pancreas
deep in the retroperitoneum
function of pancreas
- endocrine secretion
- exocrine secretion
describe exocrine gland of pancreas
contains the acinar and duct tissue,
describe endocrine gland of pancreas
contains the islets of Langerhans.
what is majority of pancreas made up of
the exocrine portion (85% by mass)
what does the exocrine portion do
secretes digestive enzymes, water and bicarbonate to assist in digestion.
what does bicarbonate do ( 2 roles)
- 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
- 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.
what is the functional unit of the exocrine pancreas
includes the acinus and its duct system
what are acinar cells specialised in
enzyme synthesis, storage and secretion.
what does the duct system do
modifies the aqueous secretions.
this mechanism is stimulated by the parasympathetic system and inhibited by the sympathetic system.
describe digestive enzyme secretion
- acinar cells produce digestive enzymes on the ReR
- they are then moved to the to the Golgi complex where they form condensing vacuoles.
- These condensing vacuoles are then concentrated into inactive zymogen granules in pancreatic acinar cells and stored for secretion.
- 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.
- From here it enters the duodenum.
which digestive enzymes are secreted
- proteases
- pancreatic lipase
- amylase
describe proteases
Chymotrypsinogen and Trypsinogen
Digest proteins and peptides to single amino acids
describe pancreatic lipases
Digests triglycerides, monoglyceride and free fatty acids
describe amylase
Starch and maltose (disaccharides)
how is carbonic acid formed (H2CO3).
when water and carbon dioxide combine
catalysed by the enzyme carbonic anhydrase
what does carbonic acid disassociate into
hydrogen ions (H+) and bicarbonate ions (HCO3–)
H2CO3 -> H+ + HCO3–
what happens to H+ ions
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.
what happens to the HCO3– produced from the dissociation of carbonic acid
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.
what happens to the bicarbonate ions, Na+ ions and wate
they move through the intercalated ducts and end up at the main pancreatic duct ready for secretion into the duodenum upon an appropriate stimulus.
how much bicarbonate secretion
total 1 litre/24 hours
how much bicarbonate secretion
total 1 litre/24 hours
what stimulates the pancreas to secrete enzymes
vagal innervation to the pancreas
this occurs when we see, smell or taste food
or
when the stomach wall is stretched.
what stimulates the pancreas to secrete enzymes
vagal innervation to the pancreas
this occurs when we see, smell or taste food
or
when the stomach wall is stretched.
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.
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.
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.
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.
role of gastrin and CCK
stimulate enzyme secretion and neutralise gastric acid entering small intestines
symptoms of pancreatic exocrine insufficiency
maldigestion
diarrhoea
steatorrhoea
weight loss
consequences of pancreatic exocrine insufficiency
malnutrition
oesteoporosis
increased cardiovascular morbidity
symptom burden
treatment of pancreatic exocrine insufficiency
- pancreatic enzyme replacement therapy
- STOP smoking
- bone health assessment
- treat the underlying cause
what initiates protein digestion
pepsin in the stomach
where does majority of protein digestion occur
in the small intestine
how are pancreatic proteases stored
as proenzymes
(trypsinogen and chymotrypsinogen)
what activates trypsinogen
enterokinase
what does trypsin activate
chymotrypsinogen and additional trypsinogen
what do lipases do
hydrolyse triglycerides to monoglyceridees and free fatty acids
what do bile salts do
aid triglyceride digestion and absoprtion of monoglycerides and free fatty acids
what is fat digestion dependent on
pancreatic and hepatic secretion
where is cholecystokinin produced
I cells of duodenum & jejunum
what stimulates cholecystokinin
HCL
proteins ans fats entering duodenum
what does cholecystokinin do
causes pancreatic enzyme and HCO3- secretion
gallbladder contraction
inhibition of gastric acid secretion
delays gastric emptying
where is secretin produced
upper small intestine
what stimulates secretin
low duodenal pH
what does secretin do
causes pancreatic water and bicarbonate secretion
where is gastrin produced
G cells in stomach
what stimulates gastrin
gastric distension and irritation
what does gastrin do
HCl secretion - parietal cells
enzyme release - acinar cells
which cells secrete HCO3- (bicarbonate)
duct cells - epithelial cells lining the ducts
which cells secrete digestive enzymes
gland cells at the pancreatic end of the duct system
the enzymes secreted are either active or precursors
give 2 active enzymes
alpha amylase
lipase
what does alpha amylase do
converts starch to maltose
what does lipase do
Converts triglycerides to monoglyceride & fatty acids
what does zymogen do
protects pancreatic cells from
autodigestion
what is enterokinase
is a proteolytic enzyme that splits off a peptide from pancreatic trypsinogen forming the active enzyme TRYPSIN
what is trypsin
a proteolytic enzyme which in turn goes on to active other pancreatic zymogens once activated by splitting off peptide fragments
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
what inhibits pancreatic exocrine
secretion
somatostatin produced by the D cells in the pancreatic islets/ islets of Langerhans
how does somatostatin inhibit exocrine secretion
through the inhibition of cholecystokinin-stimulated enzyme secretion and secretin-stimulated bicarbonate secretion
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
what does autoimmune destruction of the islets of langerhans cause
diabetes mellitus
what are the 3 phases of pancreatic secretion
- cephalic
- gastric
- intestinal
what initiates the cephalic phase
the sensory experience of seeing & eating food
what happens in cephalic phase
involves parasympathetic vagus nerve stimulation of acinar cells to produce
digestive enzymes
what initiates gastric phase
the presence of food within the stomach
what happens in gastric phase
also involves parasympathetic vagus nerve stimulation of acinar cells to produce digestive enzymes
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
what happens when amino acids + fatty acids are present in the duodenum
then CCK is released and the gallbladder contracts inducing enzyme secretion
what initiates the intestinal phase
the emptying of stomach contents into the small Intestine
what happens in the intestinal phase
involves release of both secretin and cholecystokinin which stimulate pancreatic ductal cells to synthesize aqueous sodium bicarbonate solution
