Lecture 8 - Pancreas and liver Flashcards
Chyme
Low pH
Hypertonic
Partially digested food
Brunner’s glands
Secrete alkaline mucous, protecting the cells lining the duodenum from acidic chyme
Hypertonicity of chyme
Stomach is impermeable to water therefore chyme is hypertonic in stomach
Controlled release of chyme to prevent rapid water movement from the ECF and circulation to the chyme in the duodenum which would decrease blood pressure
Pancreatic secretions
Pancreatic enzymes aqueous bicarbonate solution
Liver secretions
Bicarbonate
Bile
Stimuli for pancreatic secretions
Acetylcholine (vagus PS)
CCK
Secretin
Secretin
Stimulated by acidity in the duodenum and jejunum
Stimulates pacreatic ductal epithelium to secrete aqueous bicarbonate solution
Cholecystokinin
Stimulated by proteins and fatty acids entering the small intestines
Stimulates pancreatic acinar to release enzymes
Causes gall bladder to contract and sphincter of Oddi to relax
Pancreatic exocrine function
90% exocrine - digestive enzymes
Pancreatic structure
Head located in the ‘C’ shape of the duodenum where the common bile duct and pancreatic duct enter the duodenum at the sphincter of Oddi
Contains:
Acinar - release enzymes
- Ducts - release aq bicarbonate solution which neutralises acidic chyme
Endocrine function:
- Islets of Langerhan - insulin and glucagon released into blood stream
Pancreatic enzymes
Amylase
Lipase
Proteases (inactive)
Proteases
Trypsin
Chymotrypsin
Elastase
Carboxypeptidase
Zymogen granules
Inactive proteases are stored in zymogen granules preventing the digestion of the pancreas
Pancreatitis
In pancreatitis due to blockage, pH decreases which activates proteases and causes pancreatic digestion
Ampulla of Vater
Where the common bile duct and pacreatic duct come together to enter the duodenum at the sphincter of Oddi
Bile
Made in the liver
Stored and concentrated in the gall bladder
Released in the duodenum (250 - 1000 ml/day)
What is bile made of?
Secreted by heaptocytes:
- Bile salts from bile acids
- Bile pigments
Alkaline solution - secreted by cells lining the bile ducts stimulated by secretin
Role of bile
Emulsifyes fats, increasing SA so they are readily digested by lipases
Liver components
Hepatocytes (80%) Lots of RER and SER Stacks of golgi apparatus Contains lots of glycogen Kupffer cells - macrophages in the liver
Portal vein
All blood from gut drains into the liver via the PORTAL VIEN
Sections of the liver
Left
Right
Caudate - near IVC
Quadrate - near gallbladder
Connective tissue connecting the liver to the abdominal wall
Falciform ligament
Liver lobule
Hexagonal
Central vein in middle
6 portal triads
Portal triad
Bile duct
Portal vein
Hepatic artery
Hepatic artery
Provides oxygenated blood to hepatocytes
Blood flow opposite to bile flow
Caniculi
Hepatocytes produce substances in bile and excreted into the caniculi to the bile duct
Functional area of liver lobule
Acinus
Acinus
Blood enters from the periphery of the lobule to the centre
Zone 1
Closest to periphery
More prone to toxicity as first exposure
Zone
Closest to the centre
More prone to ischaemia as furthest from the hepatic artery
Bile salts
Conjugated bile acids
More soluble at duodenal pH than bile acids
Bile acids
Cholic acid
Synthesised and conjugated to amino acids in liver to form bile salts
What do bile salts do?
Amphipathic - Emulsification of dietary lipids into smaller units to increase surface area
Create micelles to transport hydrophobic molecules (lipid digestion products) towards enterocytes of duodenum where the bile salt disperses.
Lipid products of digestion
Cholesterol
Free fatty acids
Monoglycerides
Bile salts at the enterocyte
Lipids diffuse into the enterocyte but bile salts do not
Bile salts remain in gut and are reabsorbed by the terminal ileum therefore returned to liver via the portal vein .
Liver recycles the bile salts
Chylomicrons
Lipids are re-estified in the enterocyte into triglycerides in ER
Packed with apoproteins and carried via chylomicrons (lipoprotein) where it is exocytosed from the cell.
Carried in the lymph system via lacteals to the thoracic duct
[chylomicrons too large to enter capillary]
Steatorrhoea
Undigested fat in the faeces
- pale
- floating
- foul smell
Due to: inadequate secretion of bile salts/bile acids/pancreatic lipase