Flashcards in Week 6 - Pancreas and Liver Deck (54):
How is the chyme made isotonic?
-Water from ECF is drawn in and chyme is isotonic by the time it passes the pancreas
What two secretions are produced by the pancreas which alter chyme?
What two secretions are produced by the liver which alter chyme?
Why is chyme hypertonic as it leaves the stomach?
-Food produces lots of solutes which are dissolved in gastric juice
-Water cannot be added to dilute solute in chyme as the stomach is impermeable to water
Why does hypertonicity of chyme begin to change as soon as it enters the duodenum?
-Duodenum is permeable to water so water is drawn into the lumen
What are the basic structures of the exocrine pancreas and there respective functions?
-Acini -> secrete enzymes
-Ducts -> modify aqueous secretions
Describe the effects of the symp and parasymp on pancreas?
What proportion of the pancreas is exocrine?
What specifically stimulates pancreatic acinar?
What causes the release of CCK?
-Detection of hypertonic chyme and fats in duodenum
What are the main enzymes are produced by acinar cells?
-Proteases -> trypsin, chymotrypsin, elastase, carboxypeptidase
Which enzymes are secreted in an inactive form from the pancreas?
Briefly describe the synthesis of pancreatic enzymes
-Formed on rough ER and moved to golgi complex for modification, processing and packaging
-Condensed into vacuoles
-Concentrated in zymogen granules
-Released in response to stimulus
Why are proteases secreted in an inactive form?
-To prevent pancreatic digestion
What does amylase in the blood signify?
Describe the solution produced by pancreatic ductal cells
-Aqueous solution which is isotonic and contains Na, K, Cl and HCO3
What stimulates ductal cells to secrete HCO3?
What is the effect on HCO3 production of increased flow rate of pancreatic juice?
-Increased HCO3 secretion
What is the purpose of the aqueous solution produced by pancreatic ductal cells?
-Neutralise acidic chyme
What are the three major functions of the liver?
-Plasma protein production
What is the functional cell of the liver?
How are hepatocytes specialised for their function?
-Contain high amounts of rER and sER, golgi stacks and glycogen
What is a structural unit of the liver?
-Lobule of hepatocytes surrounded by connective tissue which has invaginated from the capsule
Describe a liver lobule
-Usually hexagonal collection of hepatocytes with a central vein and many portal triads at the corners
What makes up a portal triad?
What is the functional unit of the liver? Describe this
-Diamond shape formed between two central veins of adjacent lobules
-Separated into 3 zones from outside to in
Which zone of a functional unit of the liver is most oxygenated?
-Zone 1 (closest to hepatic artery)
Which zone of the functional acinus of liver is most susceptible to hypoxia?
Which zone of the functional acinus of liver is most susceptible to toxins?
What are bile canaliculi?
-Bile canals which flow out towards the bile ducts in the portal triad
What is the fate of central veins of liver lobules?
-Unite and form 3 hepatic veins which drain into IVC
What is the portal vein?
-The vein which drains all the blood from the gut and takes it to the liver for detoxification
What is the relationship between blood and bile in the liver?
-Blood from portal vein and hepatic arteries flows in towards the central vein
-Bile flows out along canaliculi to bile duct
-> opposite direction
What are the two components of bile?
-Bile acid dependant
-Bile acid independent
What is the bile acid dependant component of bile and from where is it secreted?
-Contains bile acid and pigments
-Secreted by hepatocytes into canaliculi
What is the bile acid independent component of bile and from where is it secreted?
-Aqueous alkaline secretion
-Secreted by ductal cells
What stimulates bile duct cells to secrete its aqueous solution?
What are the two primary bile acids?
What is a bile salt?
-Bile acids which are conjugated with the amino acids glycine or taurine
Why does conjugation of bile acids need to occur?
-At duodenal pH bile acids are not soluble but bile salts are
What makes bile salts soluble at duodenal pH?
What is the function of bile?
-Lipids form large globules by the time they enter duodenum -> bile emulsifies dietary lipids in order to increase SA for lipase
How are fats absorbed?What happens once they are absorbed?
-Products of lipid breakdown eg cholesterol, FAs form micelles with bile acids which then diffuse through aqueous solution to microvilli brush border and the products then diffuse into enterocytes
-Inside the cell the lipid products are re-esterified and packaged with apoproteins to form chylomicrons
What happens to the chylomicrons which are formed in the enterocytes?
-Exocytosed from basolateral membrane but are too large to enter capillaries so enter lacteals and travel through lymphatic system to re-enter vascular circulation through the thoracic duct into left subclavian vein
What happens to the bile salts in the intestinal lumen?
-Dont enter enterocytes instead remain in gut lumen and travel to terminal ileum
-Reabsorbed in terminal ileum and returned to the liver in portal blood
What is the function of the gall bladder?
-Stores and concentrated bile by removing water and ions
What stimulates gall bladder contraction?
-CCK released from duodenum
What effect does CCK have on sphincter of oddi?
What is steatorrhoea?
-Pale, floating and foul smelling stool due to fat in the faeces caused by bile acids or pancreatic lipase being secreted in inadequate amounts
What is bilirubin?
-An excretory bile pigment produced as a breakdown products of Hb
What happens to bilirubin once it is formed?
-Conjugated in the liver to make it soluble and then secreted into bile
-It is excreted in the faeces as stercobilin or in the urine as urobilinogen
What can result from concentration of bile in the gall bladder?
What is different about the jejunum and ileum?
-Jejunum is thick walled ileum is thin