GI: Pancreas and Liver Flashcards
What is the chyme like when it enters the duodenum from the stomach?
Its hypertonic - food produces lots of solutes that are dissolved in gastric juice and the stomach wall is impermeable to water
Its acidic so needs neutralising
Its only partially digested
What is the state of the chyme when it leaves the duodenum?
Isotonic because the duodenum is permeable to water so water moves in from ECF
What is the structure of a pancreatic duct?
The acinar cells produce enzymes, the centroacinar cells produce aqueous fluid and the terminal duct cells modifiy the fluid
What stimulates the acinus to produce enzymes?
Stimulates by vagus nerve and cholecystokinin (CCK)
What can be measured in the blood to indicate pancreatitis?
Amylase in blood is a good indicator of pancreatitis
What stimulates the duct cells to produce HCO3-?
Secretin
Higher flow rates = increased HCO3- in pancreatic secretion
What is unique about the blood supply to the liver?
It has mixed venous and arterial blood supply - 80% by the hepatic portal vein and 20% by the hepatic arteries
What is the structural unit of the liver?
The lobule
Hexagonal shape with a portal triad (bile duct, hepatic artery and portal vein) at each corner and the central vein in the centre where everything drains into.
What is the functional unit of the liver?
The acinus
Made up of a long axis that spans 2 central veins and a short axis that spans 2 portal triads.
Has 3 zones - zone 1 is more prone to toxic damage and zone 3 more prone to ischaemia because its furthest from blood supply
What is the function of the gallbladder?
Bile made in the liver
The gallbladder stores and concentrates the bile (can form crystals which leads to gallstones)
What are the 2 components of bile?
Bile acid dependent:
Stimulated by CCK, secreted into canaliculi by hepatocytes. Contains bile acids and pigments
Bile acid independeny:
Stimulated by secretin, secreted by duct cells. Similar alkaline solution to pancreatic duct cells - neutralises acidic chyme.
What are the 2 main bile acids?
Cholic acid
Chenodeoxycholic acid
What are bile salts?
Bile acids that are conjugated with AAs (glycine and taurine). The bile salts are more soluble in the duodenum - have an amphipathic structure which is essential for the emulsification of dietary lipids
Outline the digestion of fats
The bile acids form micelles with products of lipid breakdown - which diffuse to brush border of epithelial cells and enter down conc gradient.
Inside the cell the fats are re-esterfied and packaged with apoproteins on chylomicrons. They then go into small lymph vessels (lacteals) and empty into a large vein eg subclavian
How are the bile acids recycled?
Via the entero-hepatic circulation
Bile salts dont enter the gut epithelia with the lipids, they stay in the gut lumen and are reabsorbed in the terminal ilieum to return to liver in porttal blood.
