6- Chyme, pancreas and liver Flashcards
(24 cards)
Describe the constituency of chyme as it enters the duodenum
Hypertonic
Acidic
Partially digested
How does the tonicity of chyme change in the duodenum?
Duodenum permeable to water, so hypertonic chyme draws water out from ECF
Means chyme release has to be controlled or duodenum would be overwhelmed with water influx
What does the duodenum secrete in response to chyme?
Scretin - stimulates pancreas to release HCO3
CCK - stimulates pancreas to release digestive enzymes
Causes gallbladder contraction and relaxes the sphincter of oddi
How are pancreatic secretions controlled?
Sympathetic inhibits
Parasympathetic - Vagus X - stimulates
Hormones secretin and CCK
What proteses are secreted from the pancreas?
Trypsin
Chymotrypsin
Elastase
Carboxypeptidase
Describe the storage of pancreatic proteases
Produced in inactive form in acinar cells stimulated by CCK
Concentrated and stored in zymogen granules, membrane bound secretions containing inactive precursor of enzymes
What do the duct cells secrete?
When stimulated by secretin
Aqueous component
Bicarbonate
To neutralise acidic chyme
How do pancreatic secretions reach the duodenum?
Pancreatic duct then ampulla of vater (convergence of pancreatic and common bile duct)
What effect will a gallstone at the common bile duct have?
Block gallbladder secretions
Block pancreatic secretions, active proteases will self digest the pancreas
Describe the function of bile
Emulsifies fat in duodenum so they are readily digested by lipases secreted by pancreas
Describe the structure of a liver lobule
Hexagonal arrangement
Triad at each corner: portal vein, hepatic artery and bile duct
Central vein in middle
Acinus (functional area
How does blood flow in/out of the liver?
Inwards towards the central vein by portal vein/hepatic artery, then via sinusoids (space between hepatocytes)
Outwards along canaliculi, into bile duct and into duodenum
Describe the structure of liver acini
Blood drains from periphery to centre, creating zones corresponding to proximity to arterial supply, 1 being closest, 3 furthest away
Describe damage to the liver acini due to ischaemia
As zone 3 is furthest away from blood supply, will receive least oxygen so most damaged.
Describe damage to liver acini due to toxicity
Zone 1 closest to blood supply so will be exposed to the highest concentration of toxin, sustain most damage
How and why is bile stored?
Continuously produced by the liver but only needed intermittently to deal with chyme Gallbladder stores (until CCK stimulates gallbladder contraction) and concentrates, which can produce gallstones
What pathway does bile take?
Liver Gallbladder Common bile duct Ampulla of vater Duodenum Terminal ileum Portal vein to liver
What is the consistency of bile?
Bile acids and pigments - secreted into canaliculi by hepatocytes
Alkaline solution - secreted by bile ducts that have been stimulated by secretin
What are bile salts?
Bile acids conjugated with amino acids (glycine and taurine)
Why do bile acids need to be conjugated?
Not soluble at duodenal pH, so are functionally useless
Bile salts are amphipathic so allow for emulsification of lipids
What are micelles and what is their function?
Micelles are the products of lipid breakdown surrounded by bile salts
Act as a vehicle to transport hydrophobic molecules to enterocytes
Describe the entero-hepatic circulation of bile acids
Bile salts do not enter eneterocyte in duodenum
Reabsorbed in terminal ileum
Returned to liver in portal blood, where it is recycled
What are chylomicrons and what is their function?
Lipoprotein found in enterocytes, combined with newly re-estified triglycerides, phospholipids and cholesterol
Function: Exocytose through basolateral membrane, carrying digested fats via the lymphatic system (too big to enter capillaries) to reach circulation
What is steatorrhoea?
Pale, floating, foul smelling faeces due to undigested fat in faeces
Due to insufficient bile acid or pancreatic lipase secretions
