Wk 20 Flashcards
The liver, bile and the biliary tree
The 5 main roles of the Liver
Metabolism= carbs, fats and proteins
Drug= metabolism, detoxification, excretion
Biosynthesis= bile, cholesterol, phospholipids
Immune function: screening of intestinal blood by Kupffer cells
Storage: Vit A, glycogen
Blood from digestive system follows what pathway before entering circulation?
Digestive system –> portal veins –> hepatic venules –> filter through hepatocytes –> drains to central vein –> hepatic vein –> inferior vena cava
Function of bile:
Components of Bile:
Emulsify fats (aids pancreatic lipase)
Water (97%)
Bile salts (0.7%)
Bilirubin (0.2%)
Fats (cholesterol) (0.51%)
Process of bilirubin:
Haem converted to bilirubin and transported to liver to be conjugated, conjugated bilirubin secreted into bile and sent to SI, bacteria in large intestine metabolise bilirubin to sterobilin (gives faeces brown colour)
Waste products excreted in bile: 3
Drugs/ drug metabolites
Calcium
Steroid hormones
How does gall bladder concentrate bile?
What stimulates contraction and secretion of bile into the SI?
Compare non-digestive period to digestive period:
epithelium specialised for water absorption
Contraction mediated by CCK
Non-Digestive period= sphincter of Oddi closed and bile flows from liver to gall bladder
Digestive period= Food triggers CCk release and secretin
- Secretin stimulates hepatic duct cells to release bicarbonate
- CCK triggers relaxation of sphincter of Oddi and contracts gall bladder
- Bile is released into duodenum
What is enterohepatic circulation?
Where is the uptake from the SI and what proteins mediate this?
What happens if this absorption doesn’t occur?
How bile salts are continuously recycled
Terminal Ilium, mediated by sodium-dependent bile salt transporter proteins
Little bit is okay ((degraded by LI bacteria and eliminated in faeces
Lot= Bile acid diarrhoea develops (bile salts draw water into the LI)- watery, osmotic diarrhoea
Explain the 2 functions of the pancreas (endocrine and exocrine)
Endocrine: Produces Insulin (B cells), glucagon (a cells), and somatostatin (released into circulation)
Exocrine: Produces zymogens (activate in duodenum- amylase, lipase, protease) which are released into duodenum through pancreatic duct (exits pancreas via duodenal papilla)
Pancreatic exocrine cells arrange into:
Eventually drains into:
Endocrine cells arrange into:
Acini
Pancreatic duct
Islets of langerhans (little lighter coloured ‘islands’ throughout a sea of darker acini- histology)
What are the major inactive pro-digestive enzymes (zymogens) that the pancreas synthesises and excretes? 6
Why are these zymogens packaged into granules?
- Trypsinogen (to trypsin) for protein digestion
- Chymotrypsinogen (to chymotrypsin) protein digestion
- Proelastase (to elastase) protein digestion
- Procarboxypeptidase (carboxypeptidase) protein digestion
- Prolipase (to lipase) fat digestion
- Active amylase
To avoid digestion of pancreas
What cells are zymogens (pancreatic exocrine digestive enzymes) produced by?
Acinar cells
How is chyme neutralised in duodenum? 2 main mechanisms:
Release of bile from gall bladder (regulated by CCK)
Release of bicarbonate fluid from pancreas
(duodenum is also protected by acidic chyme by a mucus layer)
How are pancreatic zymogens activated in the small intestine?
A brush boarder enzyme in the SI (enteropeptidase/ enterokinase) removes a peptide fragment from trypsinogen –> activated to trypsin
Trypsin then cleaves peptide fragments from the other zymogens and activates them
How is the pancreatic exocrine function regulated? …
Cephalic and gastric phases:
Intestinal phase:
Cephalic (sight, smell, taste of food) and gastric (gastrin produced in stomach) phases trigger vagal signalling –> triggers acinar cells to release zymogen granules and triggers duct epithelial cells to release bicarbonate fluid
Vagovagal reflexes stimulate release of zymogen granules from acinar cells
Stimulation of enteroendocrine cells by luminal contents release CCK and secretin
(CCK and secretin increase zymogen and fluid secretion)
Describe the catabolism of haem, including the sites in which reactions occur and the colour of the intermediates:
1) Breakdown of haem to green biliverdin (unconjugated bilirubin) occurs in macrophages of the spleen and liver (and some tissues) and is taken to liver via blood
2) Conjugated with glucuronic acid in liver and secreted into bile –> SI
3) In SI, glucuronic acid is removed by bacteria –> produces urobilinogen
- Some urobilinogen is reabsorbed from gut and enters portal blood (a portion of this stays in the enterohepatic urobilinogen cycle but the rest is transported via blood to kidney –> oxidised to yellow urobillin and excreted, giving urine its colour
- The urobilinogen that isn’t taken by portal vein stays in intestine and is oxidised by bacteria to brown stercobilin and excreted in faeces