Liver and pancreas Flashcards
What does the stomach release into the duodenum?
Chyme
What are the properties of chyme?
Low pH, acidic
Hypertonic
Partially digested
Why is chyme acidic?
Mixed with gastric acid in the stomach
Why is chyme hypertonic?
Digestion produces small molecules that are osmotically active
increased number of osmoles
Stomach wall is impermeable to water
so water cannot enter lumen of stomach to dilute the chyme
What protects the epithelial cells of the duodenum from the acidity of the chyme released into it?
Mucus containing bicarbonate ions
secreted by goblet cells in crypts
and brunner’s glands
What happens to the tonicity of the chyme in the duodenum?
Becomes isotonic
How does the chyme become isotonic in the duodenum?
The duodenum wall is permeable to water
water moves from extracellular fluid of duodenum into its lumen
dilutes the chyme
What happens to the pH of the chyme in the duodenum?
Increases to neutral pH
How is the chyme neutralised in the duodenum?
Pancreatic ductal cells secrete solution containing bicarbonate into duodenum
Bile ductal cells secrete alkaline solution in bile into gall bladder and then duodenum
What happens to partially digested molecules in the small intestines?
They are fully digested in the small intestines
How are partially digested molecules fully digested in the small intestines?
Pancreatic acinar cells secrete enzymes into duodenum
these contribute to completing digestion
When are pancreatic and liver secretions released into the duodenum?
When chyme is in the duodenum
What causes the pancreas and liver to release their secretions into the duodenum when chyme is in the duodenum?
When chyme is in the duodenum
the duodenum secretes secretin and cholecystokinin (CCK)
What are the functions of secretin?
Acts on the pancreatic ductal cells
to stimulate them to secrete bicarbonate solution into the duodenum
Acts on bile ductal cells
stimulates them to secrete alkaline solution in bile
Acts on parietal cells in the stomach
inhibits their secretion of hydrocloric acid
What are the functions of CCK?
Acts on the pancreatic acinar cells
to stimulate them to secrete enzymes into the duodenum
Acts on the gall bladder
stimulates the gall bladder to contract to release bile into the duodenum
Acts on the sphincter of Oddi
causes it to relax to allow passage of liver and pancreatic secretions into major duodenal papilla
What enzymes do acinar cells of the pancreas produce?
Amylases
Lipases
Proteases
How active are the amylases, lipases and proteases produced by acinar cells of the pancreas?
Amylases and lipases are active
Proteases are inactive
How are the proteases produced by the pancreatic acinar cells inactive?
They are produces as zymogens
and are contained in zymogen granules in the acinar cells, pancreatic duct
Why are protease enzymes produced by pancreatic acinar cells produced as zymogens?
To prevent them from being active in the pancreas
and from digesting the pancreas itself
What happens when protease enzymes produced by pancreatic acinar cells become active in the pancreas?
Digest the pancreas itself
causing it to become inflamed, pancreatitis
What is a common cause of pancreatitis?
Gall stones blocking the ampulla of vater
which the pancreatic duct feeds into
build up of pancreatic secretions in pancreas
zymogen proteases become active while still in the pancreas
When are the zymogen protease enzymes produced by pancreatic acinar cells activated?
When they are released into the intestinal lumen
What are the different types of protease enzymes produced by the pancreas (when they are active)?
Trypsin
Chymotripsin
Elastase
Carboxypeptidase
What else stimulates the pancreas to secrete solution containing bicarbonate and enzymes, apart from secretin and CCK?
Vagus nerve efferents
What inhibits the pancreas from secreting solution containing bicarbonate and enzymes?
Sympathetic post-ganglionic nerve fibres
What secretes bile?
Liver hepatocytes
Bile ductal cells
How often to liver hepatocytes and bile ductal cells produce bile?
Continuously
What happens to new bile produced when it is not being secreted into the duodenum?
Stored in the gall bladder
What happens to bile in the gall bladder?
It becomes concentrated
by water and ions being removed
What can over-concentration of bile in the gall bladder lead to?
Gall stones
What is bile made up of?
Bile acids
Bile pigments
Alkaline solution
What part of bile do liver hepatocytes secrete?
Bile acids
Bile pigments
What part of bile do bile ductal cells secrete?
Alkaline solution
What happens to bile acids?
They are conjugated with amino acids
to form bile salts
What are the two main bile acids?
Cholic acid
Chenodeoxycolic acid
What is the purpose of conjugating bile acids with amino acids to form bile salts?
Bile salts are more soluble at duodenal pH
compared to bile acids
hence they are more functional
What is the function of bile salts in the duodenum?
Emulsify lipids
Form micelles with digested lipids
What is meant by emulsifying lipids?
Disperse large lipid globules into smaller lipid droplets
What is the purpose of emulsifying fats?
Increase surface area of lipid
more surface area for lipases to act over
How do bile salts react to water?
They are amphipathic
have hydrophilic part, water-soluble
and hydrophobic part, insoluble in water, lipid-soluble
How are bile salts adapted to emulsifying fats?
Have both water-soluble and lipid-soluble parts
can act at interface between the two
What is the function of micelles produced from bile salts?
Transport digested lipids to the apical domain of enterocytes
What happens to micelles produced from bile salts at the apical domain of the enterocyte?
Digested lipids diffuse from micelle into cytosol of enterocyte
Bile salts remain in the lumen
What happens to bile salts remaining in the lumen of the small intestine from micelles?
Reabsorbed in the terminal ileum
travel through hepatic portal circulation
back to the liver
What is the advantage of bile salts being transported back to the liver?
Liver can re-use those bile salts
doesn’t have to produce more
