Pancreatic and biliary activity Flashcards
where do accessory organs lie?
These exocrine organs lie outside the digestive tract
and empty their secretions through ducts into the
digestive tract lumen.
what makes up the billary system?
- Liver
- Gall bladder
what are the accessory digestive organs?
- Salivary glands
- Billiary system (liver, gall bladder)
- Exocrine pancreas
When chyme is released into duodenum, it is mixed with
secretions from the small intestine, liver, and exocrine pancreas within the duodenal lumen
what is the pancreas?
Elongated gland that lies behind and below the stomach and above the first loop of the duodenum – contains both exocrine and endocrine tissue.
what are acini?
grape like clusters of secretory cells that form sacks
what are islets of langerhan?
isolated endocrine tissue
what do endocrine organs secrete?
regulatory hormones
what regulatory hormones are secreted by endocrine?
insulin, C-peptide, glucagon, somatostatin,
amylin, pancreatic polypeptide
exocrine pancreas secretes fluid from two components.
What are they?
- Dust cells
- Acinar cells
what do acinar cells secrete?
Pancreatic digestive enzyme.
where are pancreatic digestive enzymes secreted?
zymogen granules
(secretory vesicles)
zymogen granules released by
exocytosis
Like pepsinogen, pancreatic enzymes are stored within…
… zymogen granules
Like pepsinogen, pancreatic enzymes are stored within zymogen granules and released by
exocytosis as needed
acinar cells secrete how many families of enzymes?
secrete 3 families of enzymes
Acinar cells secrete 3 families of enzymes:
- Proteolytic enzymes
- Pancreatic amylase
- Pancreatic lipase
what is the function of Proteolytic enzymes?
for protein digestion (proteolysis)
function of pancreatic amylase
for carbohydrate digestion
function of lipase
for fat digestion
acinar cells also scerete?
co-lipase - works with bile to increase lipase activity
why are pancreatic enzymes important?
These enzymes are important as they can almost completely digest
food in the absence of all other digestive secretions
pancreatic acini secrete what juice?
pancreatic juice
what are the 3 major classes of pancreatic proteolytic enzymes?
1) Trypsinogen
2) Chymotrypsinogen
3) Procarboxypeptidase
trypsinogen converted into
trypsin
how is trypsin activated?
Activated by enteropeptidase / enterokinase – an enzyme imbedded in the luminal membrane of the duodenal mucosa
Chymotrypsinogen is converted into
chymotrypsin
Chymotrypsinogen converted to chymotrypsin by…
… activated trypsin
Procarboxypeptidase is converted to
carboxypeptidase
Carboxypeptidases cleave
peptide bonds at the carboxyl terminus of amino
acid residues.
what is the result of Pancreatic Proteolytic Enzymes?
mixture of small peptides and amino acids.
Mucus secreted by intestinal cells prevents
against digestion of small intestine
wall
describe Pancreatic Amylase – Carbohydrate digestion
1) Dietary starches (polysaccharides, amylose, amylopectin)
2) glucose, maltose, sucrose, lactose, a limit dextrins
Amylase secreted in
active form as it does not endanger secretory cells
salivary amylase breaks down
starch + glycogen
salivary amylase breaks down starch and glycogen into
Short chain polysaccharides and disaccharides (maltose, lactose, sucrose)
pancreatic amylase breaks down
Short chain polysaccharides and disaccharides (Maltose, Lactose, Sucrose)
Pancreatic Amylase breaks down Short chain polysaccharides and disaccharides (Maltose, Lactose, Sucrose) into…
… Short chain Polysaccharides and Disaccharides (Maltose, Lactose, Sucrose, α-Limit Dextrins)
what does maltase, lactase, sucrase and a-limit dextrase break down?
… Short chain Polysaccharides and Disaccharides (Maltose, Lactose, Sucrose, α-Limit Dextrins)
Maltase, Lactase, Sucrase,
α-Limit Dextrinase breaks down Short chain Polysaccharides and Disaccharides
(Maltose, Lactose, Sucrose, α-Limit Dextrins) into…
… Monosaccharides (Glucose, fructose, Galactose).
Then absorbed via Intestinal capillaries & hepatic portal system to liver
pancreatic lipase is the main…
… eenzyme secreted by the digestive system that can digest fat.
pancreatic lipase hydrolyses…
… triglycerides into monoglycerides and free fatty acids
Lipase is also secreted in
an active form as it does not endanger the secretory cells.
what makes up a triglyceride?
- glycerol
- 3 fatty acid chains
what breaks down fats?
Lingual Lipase
Lingual Lipase breaks down fats into…
… Triglycerides to Diglyceride and 1 free FA
what does gastric lipase break down?
Triglycerides to Diglyceride and 1 free FA
gastric lipase breaks down Triglycerides to Diglyceride and 1 free FA into…
… Triglycerides to Diglyceride and 1 free FA
what do bile salts + pancreatic lipase break down?
Triglycerides to Diglyceride and 1 free FA
bile salts + pancreatic lipase break down Triglycerides to Diglyceride and 1 free FA into…
Triglycerides and Diglycerides to Monoglycerides
& free FAs (long/short chain)
Triglycerides and Diglycerides to Monoglycerides
& free FAs (long/short chain) are broken down by…
… bile salts into micelles.
digested fats are fianllly…
… absorbed via intestinal capillaries & hepatic portal system to liver
When pancreatic enzymes are deficient →
digestion is incomplete
pancreati clipase =
70 % of total lipase activity
Pancreatic enzyme deficiency causes
serious maldigestion and malabsorption
what is the clinial manifestation of Pancreatic enzyme deficiency?
steatorrhea
what is steatorrhea?
Excessive undigested fat in the
faeces
What are the symptoms of steatorrhea?
weight loss, abdominal cramps, gas
describe the stools of someone with pancreatic insufficiency?
Pale, bulky, foul-smelling, often floating stools, difficult to flush;
may leave oily residue in toilet wate
In pancreaatic insufficency, carbohydrates and protein are impaired to lesser degree because of
… salivary, gastric and small intestinal enzymes contributing to digestion
cyme entering the duodenum is
highly acidic
Chyme entering the duodenum is highly acidic and must be
neutralized quickly, to prevent enzyme denaturation and damage
to the intestinal mucosa
Pancreatic duct cells secrete
NaHCO3 (sodium bicarbonate) in duodenal lumen
Pancreatic duct cells secrete NaHCO3 (Sodium bicarbonate) in
duodenal lumen → what does this do?
neutralizes the acidic chyme
how much NaHCO3 is secreted per day?
1 - 2 L per day
NaHCO3: Largest component of
pancreatic secretion
Process of alkaline secretion involves
carbonic anhydrase
The lipid-permeable CO2 enters the cell through
the basolateral membrane
pool for the generation of H2CO3 and HCO3-
HCO3- leaves the cell via
a luminal anion exchanger.
the accumulated Cl- recycles
vial luminal Cl- channels
pancreatic secretion is regulated primarily by
hormones secretin and cholecystokinin
secretin action
1) acid in duodenum
2) increased secretin released into blood
3) pancreatic duct cells stimulated
4) increase NaHCO3 secreted into duodenal lumen
5) neutralises acid
Acid in the duodenum
stimulates
the release of secretin
secretin is carried int he blood to the
pancreas
secretin stimulate pancreatic duct cells where they are
stimulated to increase hteir NaHCO3 secretion
Increased NaHCO3 secreted into duodenal lumen maintains
the neutrality of the small intestine
Cholecystokinin (CCK) regulates….
… pancreatic enzyme secretion
Cholecystokinin (CCK) maint stimulus is…
… fat (and to a lesser extent protein) within the duodenum
CCK released from duodenal
mucosa where it
travels in the
blood to pancreatic acinar cells to
increase secretions
All three types of pancreatic digestive enzymes are…
… packaged together in zymogen granules
(amylase, lipase, protease)
the proportion of enzymes released does not
vary
the proportion of
enzymes released does not vary
even if
a fatty/protein rich meal is
consumed. Only the total number
of enzymes will vary.
CCK action
1) fat / protein in duodenum
2) Increased CCK released into blood
3) Pancreatic acinar cells
4) Increased pancreatic enzymes secreted into duodenal lumen.
what are the different functions of the liver?
- Storage: glycogen, vitamin A & K, Iron
- Synthesis (Gluconeogenesis)
- Detoxification (Phase 1 & 2)
- Hormone production (IGF-1)
- Hormone inactivation (Insulin)
- Bile Production
- Bilirubin production
- Urea production
- Cholesterol production
- Vitamin D activation
- Drug metabolism
liver in direct contact with blood from two sources which are
1) Hepatic artery
2) Hepatic portal vein
what is the portal triad made up of?
- Hepatic arteriole
- Portal venule
- One or two small bile ductules
- Lymphatic vessels
- Branch of the vagus nerve
what are liver sinusoids?
Expanded capillary spaces which run between hepatocytes
* Radiate like spokes linking up parts of the liver
what are kupffer cells?
Resident macrophages in the liver
what do kupffer cells do?
- Engulf and destroy bacteria and old red blood cells
- Only function not carried out by hepatocyte
hepatocyte constantly produces
bile which drains into the bile canaliculus
- This drains to bile duct
Hepatic stellate cells are also knonw as?
perisinusoidal cells
Pericytes* found in the
perisinusoidal space (AKA space of Disse)
what do hepatic stellate cells have in their cytoplasm?
Presence of multiple lipid droplets in their cytoplasm → store vitamin A as retinol ester
Hepatic stellate cells are a major cell type involved in…
… liver fibrosis
what is liver fibrosis
scar tissue in response to liver damage
The bile canaliculus runs between
the cells within the hepatic plate
Hepatocytes continuously
secrete
bile
Hepatocytes continuously secrete bile (even between meals) into
these thin channels which carries the bile to a bile
duct at the periphery of the lobule.
The bile ducts from the various lobules converge
to ….
… eventually form the common bile duct, which transports the bile from the liver to the duodenum.
Each hepatocyte is in contact with a ….
… sinusoid on one side and a bile canaliculus
on the other side.
what is the ampulla of vater ?
where the bile and pancreatic ducts merge
what is the ampulla of vater also knowna s?
hepatopancreatic ampulla
Opening of the bile duct into the duodenum is guarded by the
sphincter of Oddi, which prevents bile (& pancreatic secretions) from
entering the duodenum except during digestion.
The amount of bile secreted per day is between
250 ml - 1 litre depending on stimulation
When the sphincter is closed, bile is diverted into the
gallbladder where it is stored and concentrated between meals
what is the gall bladder?
- Small sac-like structure tucked beneath liver
the gall bladder is the site of…
… bile storage and concentration between meals
Concentration occurs due to
active transport of salt out of the gallbladder, with
water following osmotically → 5-10 times concentration
how much bile acids secreted per meal
- 3-15 g of bile acids can be secreted per meal
Cholecystokinin (CCK) stimulates the gall bladder to
contract and secrete bile when meal is eaten
CCK stimulates relaxation of the
sphincter of Oddi
CCK stimulates increased….
… bile secretion by the liver
what are gallstones?
precipitation occurs due to increased concentration & prolonged storage of bile salts in the gallbladder → slow progression
what is cholelithiasis?
formation of gallstones in the biliary tract, usually in the gallbladder
what is Choledocholithiasis?
presence of one or more gallstones in the common bile duct
what is Cholecystectomy?
surgical removal of
Gallbladder. Bile is stored in the common bile
duct (which becomes dilated)
Cholecystectomy results in
lifestyle changes
what is Lithotripsy?
ultrasound shock waves break stones or other calculi (plural of calculus) into particles small enough that can be excreted.
bile does not contain any
digestive enzymes
Bile does not contain any digestive enzymes, but contains several
… organic constituents that aid in the digestion and absorption of fats
Bile does not contain any digestive enzymes, but contains several
organic constituents that aid in the digestion and absorption of fats such as…
- Cholesterol
- Bile salts
- Lecithin
- Bilirubin
- Aqueous alkaline fluid
what is cholesterol?
sterol lipid
what are bile salts?
derivatives of cholesterol, actively secreted into bile
what is Lecithin?
phospholipid
what is Bilirubin ?
breakdown product of red blood cells
Aqueous alkaline fluid – it is similar to…
pancreatic NaHCO3
Most bile salts (95%) are
re-absorbed in the terminal ileum
Most bile salts (95%) are re-absorbed in the terminal ileum; with the
remaining 5 % lost in
faeces
Most bile salts (95%) are re-absorbed in the terminal ileum; with the
remaining 5 % lost in faeces. They are returned to the…
… liver which re-secrete them.
Bile salts act as
detergents (emulsification)
Bile salts act as detergents (emulsification): converting…
… large fat lobules into a lipid emulsion -> many small fat droplets suspended in aqueous chyme -> increased surface area.
fat droplets =
undigested triglycerides
fat droplets are not
water soluble
fat droplets must be made
smaller so pancreatic lipase can have access to all
triglycerides, not just those at the surface.
bile salts are described as…
… amphipathic (AKA amphiphilic)
bile salts have a
lipid soluble part - steroid derived from cholesterol
the lipid soluble part of bile salts are…
… hydrophobic (no affinity to water)
the water soluble part of bile salts are
hydrophillic (affinity to water).
bile salt hydrophillic parts are negatively…
… charged.
the two parts of bile salts?
lipid soluble and water soluble part
bile salts absorb onto the surface of
the fat glubule - lipid part dissolves into the fat droplet leaving the charged water soluble part projectin
- Intestinal movements break up….
… large fat droplets into smaller ones
- Intestinal movements break up large fat droplets into smaller ones
- These small droplets would quickly re-coalesce if it wasn’t for…
… bile salts adsorbing on the surface which prevent them from reforming
The hydrophilic parts of the bile salts
create a…
shell of negative charge that
repels other negative charges
Bile Salts Prevent…
… re-coalescence of fat globules
Bile Salts Prevent re-coalescence of fat globules
Creates a greater surface area for …
… lipase to attack the triglycerides
Lipase alone cannot
penetrate the bile salt layer
Uses Co-lipase (pancreas) which has both a
lipid-soluble and water soluble component (similar to bile salt)
Co-lipase displaces some
bile salts and lodges into the fat globule
Co-lipase binds to …
… lipase anchoring it to the site of action
what are the three mechanisms which stimulate bile secretion?
- Chemical mechanisms
- Hormonal mechanisms
- Neural mechanisms
chemical mechanisms of stimulating bile secretion?
Bile salts themselves – enterohepatic recirculation – stimulates more bile secretion
Hormonal mechanisms of stimulating bile secretion?
Secretin
Cholecystokinin
in bile, secretin stimulates?
alkaline bile secretion by liver ducts
in bile, Secretin does not
increase bile salt secretion
in bile, Cholecystokinin triggered by
presence of food, especially fat in chyme in intestines
in bile, cholecystokinin stimulates
gallbladder contraction and bile secretion
Neural mechanisms of stimulating bile secretion?
- Vagal stimulation of the liver – minor role
during cephalic phase of digestion - Increase in liver bile flow before food
reaches stomach or intestine
Bilirubin does not play a role in
digestion
bilirubin is a waste product actively excreted in
bile
what is bile salt?
Yellow bile pigment derived from worn out red blood cells, made from the haem (iron-containing) part of haemoglobin
Bilirubin is extracted from
the blood by the hepatocytes and once in the intestine is modified by bacterial enzymes to give the characteristic brown colour of faeces.
Small amounts of bilirubin are re-absorbed by
the intestine,
Small amounts of bilirubin are re-absorbed by the intestine, where it is
eventually excreted in the urine – largely responsible for the yellow
colour of urine
If bile duct is obstructed (e.g
gallstone) faeces become
grayish white
If rate of production exceeds
rate of excretion →
increasing level of bilirubin in the blood
If rate of production exceeds rate of excretion → increasing
level of bilirubin in the blood →
jaundice
Other possible causes of a blocked bile duct include…
… cysts of the common bile duct.
