pancreas and bile Flashcards
pancreatic duct
There is a main pancreatic duct that runs the entire length of the pancreas,
- the duct has several branches.
○ there are branches called interlobular ducts which go between lobules
○ and then intra lobular branches come off and they Feed into the lobules themselves
branching of the intralobular branches once in the lobules
once inside the lobule these Branch even further into intercalated ducts
- each one of these intercalated ducts ends up in an acinar
§
what cells surround the duct
- surrounding the duct we’ve got pancreatic acinar cells which will secrete enzymes.
- But we’ve also got these Centro acinar cells ductile cells which secrete bicarbonate and water
why are ductule cells ciliated
if we look at these ductile cells, you can see that they are also ciliated and that’s important because the Cilia will move the Pancreatic juice through the ducts out towards the duodenum and the ileum,
- so these have got mitochondria to supply the energy for the movement of the Cilia.
the exocrine pancreas
pancreas secretes:
- enzymes
- bicarbonate + Na+, H20
The exocrine pancreas delivers its secretions of digestive enzymes, fluid, and bicarbonate ions to the duodenum following ingestion of food.
role of bicarbonate in pancreatic juice
important role in increasing the pH of the chyme entering the small intestine.
function of pancreatic juice - digestion of protein
the pancreas produces inactive precursors, and that’s really important because if these proteases Get activated within the pancreas then it will cause Auto digestion of the pancreas and inflammation and damage the pancreas.
○ So first of all - trypsinogen needs to be activated to trypsin and that’s by an enzyme called enterokinase which is produced by the cells of the duodenum
○ Once trypsin is produced it can then trigger the activation of chymotrypsinogen to chymotrypsin and also Pro carboxy peptidase into carboxy peptidase.
pancreatitis
autodigestion by enzymes
- inflammatory condiiton
- causes - gallstones, alcohol, toxins, hypertriglyceridaemia
function of pancreatic juice - digestion of carbs
pancreatic alpha-amylase
function of pancreatic juice - digestion of fat
pancreatic lipase (+bile salts)
function of pancreatic juice - neutralisation of gastric acid by bicarbonate
- protect mucosa
- optimum pH for enzymes (7)
how does secretin help in control of pancreatic secretion
Secretin stimulates the secretion of bicarbonate-rich pancreatic fluid.
- Secretin enters the intestinal lumen and stimulates bicarbonate secretion, ultimately neutralizing gastric H+, which plays an essential role in fat digestion by creating a more neutral (pH 6 to 8) environment.
bicarbonate release causes neutralization of the acidic environment, thus establishing a pH favorable for the action of digestive enzymes.
- Secretin increases bicarbonate secretion from duodenal Brunner’s gland as well
- negative feedback
how does cholecystokinin help in control of pancreatic secretion
- it is released in response to fatty acids and peptides
CCK stimulates pancreatic secretion by two possible mechanisms.
- First, CCK binds CCK-1 receptors on acinar cells and stimulates release of enzymes.
- second mechanism is indirect whereby CCK binds CCK-1 receptors on capsaicin-sensitive C-type vagal afferent fibers. Stimulation of vagal afferent nerves generates a signal that is sent to the medial nucleus tractus solitarius (NTS) located in the brain stem and eventually transmitted via cholinergic postganglionic vagal efferent fibers to the pancreas and other target organs. Acetylcholine released from the efferent nerve endings, binds M3 muscarinic receptors on the pancreatic acinar cells and causes release of pancreatic enzymes
- positive feedback
pancreatic insufficiency
incomplete digestion of fats and protein so get malabsorption
secretion of bicarbonate and water from the duct
secretion stimulated by secretin
- leads to increased cAMP
- Cl-/ HCO3 - channel activated by cAMP
how much bile secreted per day
- bile is secreted by the liver, and stored in the gall bladder
- 700 ml/day
composition of bile
- bile salts
- cholesterol
- lecithin
- bilirubin
- steroids
- heavy metals
- bicarbonate
what components of bile are involved in fat digestion and absorption
- bile salts
- cholesterol
- lecithin
what components of bile are involved in excretion
- bilirubin
- steroids
- heavy metals
role of bicarbonate ion in bile
neutralises acid
micelle formation
Micelles are formed by the self-assembly of amphiphilic molecules.
- The structures contain hydrophilic/polar region (head) and hydrophobic/nonpolar region (tail)
- Micelles are formed in aqueous solution whereby the polar region faces the outside surface of the micelle and the nonpolar region forms the core.
- Micelles can deliver both hydrophilic and hydrophobic agents. Such structures can deliver macromolecules because these molecules can provide sustained and controlled release of macromolecules, provide chemical and physical stability of the encapsulated molecules, improve drug pharmacokinetics and favorable tissue distribution, and improve drug bioavailability [1,97].
- Formulation of micelle is achieved at above critical micelle concentration
bile secretion - 2 stage secretion
- canalicular secretion - bile salts, organic anions, cholesterol
- ductal secretion - HCO3- and H20
enterohepatic circulation
bile salts are recycled in order to complete fat digestion
- absorbed from ileum and returned to liver = enterohepatic circulation
- 15g of bile salts needed to digest normal meal , but body only contains 3g = 5x recycling
control of bile secretion - choleretics
stimulation of bile secretion by the liver
1. secretin (H+)
2. vagus (in 3 digestive phases)
3. bile salts (enterohepatic circulation)
inhibited by SNS activity
control of bile secretion - cholagogues
stimulation of bile release from gall bladder
1. CCK (peptides and Fatty acids via blood and reflex
- contraction of gall bladder
- relaxation of sphincter of Oddi
malabsorption in biliary disease
- damage to hepatocytes (viral and alcoholic hepatitis)
- blockage of bile ducts (gall stones)
- bile not produced or delivered so malabsorption of fats, so increased fat = steatorrhoea
- bilirubin not excreted = jaundice (accumulation of bile in body
gallstones
very common in western countries
- caused by:
- excessive mobilisation of cholesterol into bile
- inc cholesterol crystallisation
- inc secretion of biliary mucin
- genetic link
- risk factors: obesity, T2D, high meat consumption
function of bile
functions to emulsify fats, neutralise acid and excrete bilirubin, steroids and heavy metals
