Pancreas and Liver Flashcards
What are 3 things added to chyme in duodenum?
- Adding water to reduce hypertonicity
- Secretions from Pancreas (HCO3, enzymes)
- Secretions from liver (HCO3, Bile)
Why is chyme hypertonic? (compared to plasma)
- Food produces many solutes that are dissolved in gastric juice
- Stomach wall is impermeable to water
(Duodenum is relatively permeable to water, and chyme is isotonic when it leaves the duodenum)
The pancreas is 90% Exocrine and 2% Endocrine.
Describe its innervation
Sympathetic;
- Inhibition
Parasympathetic;
- Vagus simulation
- Hormones
Describe the basic structure of the exocrine portion of the pancreas
- Acinus
- Centroacinar cells (Aqueous component of secretion)
- Duct (modifies aqueous secretion)
Describe the stimulation of the Acinus to produce secretions
- Stimulated by Vagus and CCK (from I cells in duodenum)
- Upon detection of small peptides/ fats/ hypertonicity in duodenum
List 3 enzymes secreted by Acinus (help with digestion and acid neutralisation)
- Amylases, in active form
- Lipases, in active form
- Proteases, in inactive form (Trypsin, Chymotrypsin, Elastase, Carboxypeptidase etc)
Describe the formation and release of Acinar secretions
- Formed on RER, moved to Golgi complex
- Condensed into zymogen granules
- ZGs released with appropriate stimulus (CCK/ Parasympathetic)
What does the Pancreatic duct join with to enter into duodenum
Pancreatic duct + Bile duct from gall bladder-> Common Bile Duct which empties into duodenum at the Ampulla of Vater
Describe the vasculature of the liver
- Blood from hepatic portal vein and hepatic artery drain into central vein
- Central veins combine to form Hepatic veins-> IVC
Describe the movement of bile in liver
- Bile made in hepatocytes, flow out of liver in Canaliculi
- Canaliculi join-> Bile ducts
- Ducts join-> Common bile duct
Compare the 2 components of bile
Bile acid dependent component;
- Secreted into Canaliculi by hepatocytes
- Contains bile acids + pigments
Bile acid independent component;
- Secreted by duct cells
- Similarly to pancreatic duct cell secretions, solution is alkaline and stimulated by secretin
What are the 2 primary bile acids?
What are bile salts?
- Choline acid
- Chenodeoxycholic acid
Bile acids that are conjugated with amino acids (such as glycine and taurine)
Why do we need bile salts sometimes as opposed to bile acids?
- Bile acids are not always soluble at duodenal pH (Salts generally are)
- Bile salts have an Amphipathic structure (Hydrophobic and Philic ends)
What is the significance of bile salts having an amphipathic structure?
- Can act at oil/ water surface
- Crucial for emulsification of dietary lipids
Describe fat digestion with reference to Bile acids
- Lipids tend to form large globules by the time they reach duodenum, reducing SA for enzymes (Lipases) to act
- Bile acids/ salts emulsify fat into smaller units to increase SA
- Bile acids then form Micelles containing products of lipid breakdown
Describe fat digestion after Micelle formation
- Lipid breakdown products diffuse into intestinal epithelial cells
- Inside enterocyte, re-esterified and packaged with apoproteins to form Chylomicrons
- Exocytosis of Chylomicrons into lymph capillaries/ Lacteals (too large to enter blood capillaries)
- Later, re enter vascular system
Describe the circulation of bile acids/ salts
- Don’t enter enterocytes with lipids, but remain in gut lumen
- Reabsorbed in terminal Ileum and return to liver in portal blood, where the liver extracts the bile salts for re-use
Bile is always being produced but where is it stored?
What else happens to bile here?
What can it lead to?
- Gallbladder
- Concentrates bile (removes water and ions)
- Gallstones
(CCK from duodenum stimulates gallbladder contraction and relaxation of Sphincter of Oddi)
What is Steatorrhea?
Explain how does this present?
This is when bile acids/ salts or pancreatic Lipases are not secreted adequately
Fat in faeces (not enough lipids absorbed);
- Pale
- Floating
- Foul smelling
What breakdown product is secreted into bile then excreted in faeces?
What can it lead to if not excreted?
Bilirubin from RBCs
Jaundice, if accumulates in blood
