Pancreas And Liver Flashcards
Decsribe the chyme in the duodenum
Low pH Hypertonic Partially digested
What are the glands in the duodenum
Duodenum - Brunner’s glands
(secrete alkaline mucosa, protecting cells lining duodenum from acidic chyme
Why is chyme in the duodenum hypertonic
-• Initial digestion of food in stomach creates solutes that make the chyme hypertonic
• Stomach wall largely impermeable to water
– Water cannot move into stomach to dilute chyme
Describe chyme as it exits teh duodenum
• Duodenum relatively permeable to water
– Hypertonic chyme draws movement of water from ECF/circulation into duodenum
• Chyme release must be controlled so as not to overwhelm duodenum!
What are the secretions from the pancreas and liver
PanceaS: enzymes, bicarbonate
Liver: bile, bicarbonate
Helps with low pH and proteins, fats and CHOs in chyme
What is released by the duodenum in response to presence of chyme
Secretin acts on pancreas to stimulate release an aqueous bicarbonate (HCO3-) component of the pancreatic secretion
CCK acts on pancreas to stimulate release of enzyme component of pancreatic secretion
CCK also acts on gallbladder (contracts) and relaxes sphincter of oddi ( see slide for location) - important it can open so secretions an be secreted in
cholecystokinin (= bile sack move)-released from duodenum in response to hypertonicity/small peptides/fats within chyme in duodenum
What is the major pancreatic function
• 90% pancreas is exocrine function
– vs much smaller proportion for endocrine function
• Pancreatic secretions (exocrine function) stimulated via gut hormones (secretin and CCK) but also autonomics
– Sympathetic inhibits
– Parasympathetic (vagus) stimulates
Decsribe the structure of the pancreas
See slide Acinar cells secrete enzymes. Duct cells secrete aqueous bicarbonate solution.mixed up in one solution once reached duct
What are the enzymes severe by the acini
• CCK (& vagus) stimulate acini (singular = acinus) to produce enzymes – Amylases and lipases (active- ready to go!) – Proteases (inactive) • Proteases (when activated) include. (Stored inactvely in zymogen granules) – Tr y ps i n – Chymotrypsin – Elastase – Carboxypeptidase
Why are Pancreatic Proteases Released in Inactive Forms?
So they do no act on pancreas itself and cause pancreatitis Protease enzymes (inactive) produced within acinar cells are concentrated and stored in zymogen granules Zymogen granules contain zymogen (in active proteases e.g. trypsinogen) which is converted to active proteases (e.g. trypsin) in intestinal lumen
What do duct cells secrete
• Duct cells secrete
– Aqueous component (isotonic)
– Bicarbonate • Will act to neutralise the acidic
chyme
What is bile
• Liver secretes bile (stored in gallbladder) into the duodenum
– Secretion of bile (250mL- 1000 mL/day)
• Bile consists of
– Bile acids and bile pigments
– Alkaline solution
• Bile plays a key role in emulsifying fat (lipids) in duodenum so that they can be readily digested by lipases secreted by pancreas
Describe the liver
Liver is largest single organ (many hugely important functions!)
• Hepatocytes are chief functional cell of liver
• Liver is highly metabolically active producing proteins and lipids for export
– Lots of rough/smooth ER
– Stacks of golgi membranes
• Contains lots of glycogen
• All blood from gut drains into liver
– Portal vein
• Bile drains from liver into gut
What are teh lobes of the liver
See slide - purely anatomical nto functionally
What are lobules
Hexagonal arrangement of cells, bile ducts and blood vessels Sheets of hepatocytes arranged towards a central hepatic venule At the 6 cornet - triad • Hexagonal arrangement • Triad of structures at each corner - Portal vein (branch) - Hepatic artery (branch) - Bile duct (branch) • Central vein in middle • Blood enters a lobule via hepatic artery and portal vein (branches of)
Decsribe the flow of blood and bile int a lobule
• Blood flows in towards central vein via sinusoids • Portal vein • Hepatic artery Moves towards central vein
- Bile flows out in the opposite direction
- Along canaliculi
- Bile duct
- Into duodenum
What is a hepatic acinus
• Blood draining from periphery of lobule to
centre
• Substances brought to liver from gut (& oxygen) therefore start at periphery and work towards middle (towards central vein)
• Creates a series of zones 1, 2, 3 (1 - nearest to blood supply ,2,3) corresponding to distance from arterial
blood supply
• Certain pathological processes lead to hepatocyte damage reflecting this acinar structure
- Toxic (zone 1 - closest to blood bringing in the toxins) vs ischaemic (zone 3) - see slide
Where is bile produced and stored
• Bile created by hepatocytes and duct cells in liver – Continuously produced – But only needed intermittently • Stored in the gallbladder – Concentrates bile (removes water/ions) • Can lead to gallstones – CCK released from duodenum stimulates gallbladder contraction • Emulsify fats aiding their digestion
What is the composition of bile
• Bile salts (arise from bile acids) and
pigments are secreted by the
hepatocytes • Alkaline juices secreted by cells lining
the bile ducts (stimulated by secretin)
What are bile salts
• Bile acids (e.g. cholic acid and chenodeoxycolic acid) synthesised in
liver, but then conjugated to amino acids* (in the liver)
• Bile salts have an amphipathic structure
• Hydrophilic end (water soluble)
• Hydrophobic end (lipid solube)
• Act at oil/water interface
• Bile salts allow emulsification of dietary lipids
What is the role of bile salts
• Lipids form large globules by time reached duodenum
– Small surface area for enzymes (lipases) to act
• Bile salts emulsify fat into smaller units
– Disperse droplets increasing surface area
– Allowing for lipases to act
• Bile salts then create micelles with products of lipid breakdown (Lipid products of digestion include cholesterol, monoglycerides, free fatty acids)
• Micelles act as a ‘vehicle’ for transporting hydrophobic
molecules (products of lipid digestion*) towards enterocyte
Wha happens when muscle reaches enterocyte
• Micelle transports digested lipids to luminal membrane of enterocyte
• Lipids diffuse into intestinal epithelial cell (cytosol of enterocyte) but bile salts do not
• Entero-hepatic circulation of bile salts
– Bile salts remain in gut (they do not enter enterocyte)
– But are reabsorbed in terminal ilium
– Returned to liver in portal blood
• Liver recycles the bile salts (does not have to re-synthesise large volumes)
What happens when lipids enter enterocytes
• Inside enterocyte lipid molecules are built back up again (re-estified)!
– Back to triglycerides, phospholipids and cholesterol
• Packed with apoproteins within enterocyte
– Chylomicrons
• Chylomicrons exocytosed from basolateral membrane
of enterocyte (gut)
– Too large to enter capillaries
– Enter lymphatic capillaries -> thoracic duct
What is steatorrhoea
• Certain pathologies may cause bile acids/salts or pancreatic lipases to not be secreted in adequate amounts
• Undigested fat appears in faeces
(steatorrhoea)
– Pale – Floating – Foul smelling
