Lecture 8 - Pancreas & Liver Flashcards
What are the 3 properties of chyme once they leave the stomach that need to be rectified?
How are these properties rectified?
1) It’s hypertonic
2) It’s acidic
3) It’s partially digested
Pancreas secrete enzyme and bicarbonate ions, liver secretes bicarbonate ions and bile. More solvent from ECF moves into gut lumen to decrease osmolality.
Why is chyme hypertonic leaving the stomach?
Why is chyme isotonic leaving the duodenum?
1) Food produces lots of solutes that are dissolved in gastric juice, and stomach wall largely impermeable to water.
2) Duodenum relatively permeable to water, movement of water from ECF into duodenum dilutes tonicity. Chyme release into duodenum must be controlled
What is the basic structure of the exocrine portion of the pancreas?
How is the pancreas innervated?
- Secretions from acinus released into duct which modified aqueous solution
- Sympathetic inhibits secretions by decreasing blood supply
- Parasympathetic stimulates secretions
- CCK also stimulates release of enzymes from pancreas
What are the enzymes released in pancreatic secretions?
How are these enzymes released from the pancreas?
- Activate amylases & lipases, Inactive proteases (trypsin, chymotrypsin, elastase & carboxypeptidase)
- Enzymes formed on RER, moved to golgi, concentrated in zymogen granules and released upon parasympathetic or CCK stimulus. Zymogen granules contain inactive precursors to prevent digesting pancreas.
Give a summary of what pancreatic secretions achieve
- Secrete enzymes for digestion upon vagus/CCK stimulation
- Secrete bicarbonate ions to neutralise acidic chyme upon secretin stimulation
What is the chief cell of the liver & what do they produce?
What is the dual blood supply provided to the liver?
- Hepatocytes (80% of mass), produce bile which is secreted into bile canaliculi which group together to form bile ducts.
- 80% of blood from hepatic portal vein, 20% from hepatic artery, blood supply mixes in hepatic sinusoids.
What are hepatic triads and where are they located?
Structural unit of liver is a lobule, in each corner of the lobule are hepatic triads, consisting of 1) hepatic artery 2) hepatic portal vein 3) bile duct
How are zones 1-3 formed formed in the liver?
Which zone will be more affected by toxins coming into the liver, which zone by ischaemia?
- Diamond shape where lobules comes together
- Zone 1 as it has closest proximity to blood being brought in by hepatic triad
- Zone 3 as it is further away from blood coming in
Where does bile from the liver drain into?
Bile drains into common bile duct and into duodenum upon relaxation of sphincter of oddi.
What are the 2 major components of bile?
1) Bile acid dependent - secreted into canaliculi by hepatocytes, contains bile acids & pigments
2) Bile acid independent - secreted by duct cells, similar alkaline secretion to pancreatic duct cells, stimulated by secretin
What are the 2 primary bile acids?
How are bile salts formed & what are their useful properties?
1) Cholic acid
2) Chenodoexycholic acid
- Bile salts are bile acids conjugated to AA’s (glycine & taurine).
- Generally soluble at duodenal pH’s, amphipathic structure crucial for emulsification of dietary lipids
How does bile facilitate the digestion of fats?
- Lipids form large globules as they reach duodenum, low SA for enzymes to act
- Bile acids emulsify fat into smaller units increasing SA for lipases to act
- Bile acids form micelles, amphipathic structure surrounding breakdown products for transport in aqueous environment allowing them to diffuse into brush border of epithelial cells.
What is the fate of lipids once they diffuse down their concentration gradient into the intestinal epithelial cells?
- Reformed into chylomicrons when packaged with apoproteins in cytosol
- Removed via BL membrane, enter lymphatic system via lacteals
- Re-enter vascular system via thoracic duct
What is the fate of bile acids after forming the micelle?
Bile salts don’t enter gut epithelium with lipids, remain in gut lumen, reabsorbed in terminal ileum, return to liver in portal blood. So liver doesn’t have to synthesise total bile acid requirements (re-uses them)
What is the role of the gallbladder?
What happens if bile acids are not secreted in adequate amounts?
- Stores & concentrates bile (removes water/ions), which can cause gallstones
- Released upon CCK stimulation, causes gallbladder contraction & sphincter of oddi relaxation
- Steatorrhoea (fatty stools), pale, floating & foul smelling
- Bilirubin secreted into bile, if blood can’t remove it, get jaundice
