deck_1473170 Flashcards
What are the charactersictics of chyme?
AcidicHypertonicPartly digested
How are each of the characteristics corrected?
Acidity - HCO3- secretion Hypertonicity - H2O movement through duodenal wallPartly digested - enzymes and bile salts
Where is the HCO3- for acidity correction secreted from?
PancreasDuodenal mucosaLiver
Where do the factors needed for complete digestion come from?
Enzymes from pancreas and duodenal mucosaBile acids from the liver
What is bile made up of?
Bile acid dependent componentBile acid independent component
Describe the things that make up the bile acid dependent component
Made up of bile salts which are cholic acid and chenodeoxycholic acidCholesterolBile pigments
Where is the bile acid dependent component secreted from?
Hepatocytes lining the canaliculi
Why are bile salts important?
Have a major role in the digestion and absorption of fat – increase the surface area of fats to be absorbed by incorporating fats into micelles.
Describe the components of the bile acid independent components
Secretes HCO3-/alkaline juice like the pancreatic duct cells
Where is the bile acid independent component secreted from?
Duct cells lining the intra-hepatic bile ducts
What makes up the microscopic structure of the liver?
Hepatic lobules and acinii
Describe the hepatic lobule
Made up of a central vein an the surrounding liver tissue. The vein drains blood to the systemic system from the hepatic portal vein and the hepatic arteries via sinusoids.
Where is bile formed?
In canaliculi
Decribe what happens in response to gastric emptying
Duodenum secretes cholecystokiinin. Stimulate gall bladder contractionConcentrated bile acids, pancreatic enzymes and alkali from liver and pancreas are secreted into the duodenum via the ampulla of vater. They travel to the terminal ileum where they are actively reabsorbed by the epithelium to be brought back tot he liver via the hepatic portal system. Hepatocytes actively take up bile acids and re-secrete them into the canaliculi.
What is the main function of the gall bladder?
Stores bile acids
What risk is there of storing bile acids?
Risk of precipitation when concentrating the bile acids, which could lead to gall stones. (Remove water to concentrate it)
Describe the effects of gall stones
- often asymptomatic- can move into the neck or the biliary tree - causes biliary colic and/or obstruction
What are some further complications of gall stones?
Cholecystisisinfection of the gall bladder
When can pain from gall stones be worse?
After eating as CCK causes contraction of the gall bladder
What is secreted from the duct cells of the exocrine pancreas?
Proteases– trypsin, chymotrypsin, elastase, carboxypeptidaseLipasesAmylases
What are the cells that you find in the exocrine pancreas?
Acinar and duct cells
What does the exocrine pancreas do?
Acini secrete zymogen granules which contain inactive enzymes via exocytosis. Are activated in the intestine by enzymatic cleavageDuct cells secrete HCO3-/alkaline juice
How is HCO3- secreted into the duodenum?
Na gradient is set up by NaKATPase pump, which causes H+ ions to be actively secreted out of the cell. They bind to HCO3-, forming CO2 and H2O which are taken up into the cell. H+ and HCO3- are reformed inside the cellsHCO3- is exported to the duct lumen, to travel to the duodenum which the H+ is recycled and travels out into the ECF to collect more HCO3-
What is the secretion of HCO3- stimulated by?
Secretin which is released from jejunal cells due to low pH
What stimulate acinar pancreatic secretions?
CCK stimulates which is released from duodenal APUD cells in response to hypertonicity and fats
What stimulates ductal pancreatic secretions?
Secretin stimulates which is released from the jejunal cells in response to a low pH.
What is biliary secretion stimulated by?
CCK from the duodenum in response to gastric emptying. This stimulates gall bladder contraction.
Describe enterohepatic circulation
Bile acids are secreted by gall bladder with alkaline secretions which travel down tot eh duodenum via the ampulla of vater. They then travel through th duodenum to the terminal ileum where they are actively reabsorbed by the epithelium there. The bile acids are then transported to the hepatocytes via the hepatic portal system.
What is the consequence of inadequate bile/pancreatic lipase secretion?
Inadequate fat digestion and reabsorption causing steatorrhoea.
Describe the mechanism of digestion of fats
Bile acids break fats down into micelles giving a high surface area for the action of lipases which cleave fatty acids from glycerol. THe micelles carry the FAs and glycerol into the “unstirred layer” where FAs can diffuse into the epithelial cells. Once the FAs and glycerol are in the epithelial cells, they are converted into TAGs and re-expelled as chylomicrons into the blood.
Describe steatorrhoea
When inadequate amount of biles acids or pancreastic enzymes are secreted so fat appears in the faeces. – Are pale, float and are foul smelling
What is the mechanism of jaundice?
An accumulation of bilirubin in in the blood, if it cannot be excreted
What is bilirubin?
A bile pigment which is an excretory product. It if conjugated in the liver and secreted in the bile to be excreted in faeces.
