Lecture 8- Pancreas and liver Flashcards
chyme enters the duodenum from the stomach, what sort of osmolarity does this chyme have
its hypertonic - more solute compared to solvent (compared to plasma)
why is chyme that leaves the stomach hypertonic
- When we break a molecule it gets broken down into say 5 molecules- therefore gores from osmotic pressure of 1 to 5
- Stomach wall impermeable to water- cannot dilute solute in chyme- toncity
why does this hypertonic solution become isotonic in the s.intestin
Duodenum is permeable to water
- chyme creates conc gradient for water- water secreted from ECF. ciruclation–> reduces toncity
chyme is
what happens to the partially digested, acidic chyme from the stomach
- pancreas releases enzymes into the duodenum
- bicarbonate ins secreted from pancreas and liver and bile
what causes bicarbonate secretion into the duodenum
- Controlled by secretin- released from S cells in response to low pH
exocrine and endocrine proportions of the pancreatic secretions
- Exocrine portions approx. 90% of pancreas
- 2% endocrine functionà into blood
Major pancreatic duct and common bile duct
come into the duodenum at the same point, through the sphincter of oddi (when it is relaxed).
exocrine cells of the pancreas
acinar
production of enzymes and water by exocrine ducts of pancreas stimulated by
vagus nerve and cholecystokinin (CCK)
- in response to
- Hypertonicity/ small peptides/ fats detected in duodenum
acinus of the pancreas produce
-
Acinus produces enzymes (acinar cells)
- Amylase/lipases (active)
- Proteases (inactive)- trypsin, chymotrypsin, elastase, carboxypeptidase
- water (centroacinar cells)
symapthetic innervation of pancreas exocrine function
inhibits release of enzyme
parasympathetic innervation of pancreas exocrine function
vagus nerve- stimulates (and CCK)
what controls how much HCO3- is released
At a higher flow rate of chyme, increased secretion of HCO3- due to increased pancreatic secretion
Formation of pancreatic enzymes in acinus
- Formed on RER
- Moved to golgi
- Condensing vacuoles
- Concentrated in zymogen granules
- Released with appropriate stimulus
- Parasympathetic/ CCK
zymogens are
inactive precursors e.g. trypsinogen instead of trypsin
(stop autodigestion)
detection of pancreatitis
finding amylase/lipase in the blood
the liver is the
single largest organ
liver function
- Function
- Energy metabolism
- Detoxification
- Plasma protein production
- In the gut- secretion of bile
- 250ml-1l/ day
dual blood supply of the liver
-
Hepatic artery (20%)
- Low in nutrients
-
Portal vein (80% of all blood)
- High in nutrients from intestines
bile is made up of
bile acids and alkaline juice
bile release causes
excretion of bile pigment and digestion of fat
hepatocytes are the
chief cells of the liver
hepatocytes produce
bile
- Very active producing proteins/ lipids for export
- Contain lots of RER/ SER
- Stacks of golgi membranes
- Good store of glycogen
the liver is made up of
lobules
at the corners of the lobules you find
portal triads
- Each portal triad has three components
- Hepatic artery- coming in
- Bile duct (bile produced by hepatocytes)- going out
- Portal vein- coming in
blood flow into the liver
- Blood flow comes from the portal triads and merge at the central vein the middle of the lobule
- Central veins of lobules drain into hepatic veins (x3 which drain into the inferior vena cava) – which takes blood away from the liver to be oxygenated (different from the hepatic portal vein which takes blood to the liver)
bile flow in the liver
- Along canaliculi- opp direction to blood
- Canaliculi merge to form bile ducts which deliver it to the duodenum
Functional unit of the liver- Acinus
- Region of adjoining liver lobules
- Diamond shape
- Has different zones
- 1- closes to the portal triads
- 2
- 3- nearest to the central vein
- Any toxins coming into the liver will affect zone ………. more than zone ……..- closest proximity to blood coming in
*
- Any toxins coming into the liver will affect zone 1 more than zone 3- closest proximity to blood coming in
Zone …… much more likely to be damaged by ischaemia- furthest away from the blood coming in
Zone 3 much more likely to be damaged by ischaemia- furthest away from the blood coming in
All the blood from the gut drains into the liver
From the hepatic portal vein (not as deoxygenated as a normal vein, high in nutrients)
Bile drains into the ………………… of the duodenum from the common bile duct into the sphincter of Oddi – stored in the gall bladder.
second part
most of bile is made up of
bile salts
2 primary bile acids
- (bile salts are bile acids conjugated with amino acids e.g. glycine and taurine)
- Cholic acid
- Chenodeoxycholic acid- further bile acids formed in gut
why do we need bile salts
- Why bile salts?
- Bile acids not soluble at duodenal pHs- bile salts generally are
*
- Bile acids not soluble at duodenal pHs- bile salts generally are
role bile acids play in digesting fats
- Amphipathic structure
- Hydrophilic end (water soluble)and hydrophobic lipid soluble)
- Act at oil/water interface
- Crucial for emulsification of dietary lipids
- larger SA for lipases to work on
bile is made up of …… choelsterol
10%
2 major compenents of bile
bile acids dependent
bile acids independent
- Bile acid dependent
- Secreted into canaliculi by hepatocytes
- Contains bile acids and pigments
- Bile acid independent
- Secreted by duct cells
- Similar alkaline solution to pancreatic duct cells
- Stimulated by secretin
Digestions of fats and bile acids
- Lipids tend to form large globules by the time they reach duodenum
- Low surface area for enzymes to acid
- Bile acids emulsify fats into smaller units
- Help disperse fatty droplets
- Increases surface area for lipases to acid
- Bile acids then from micelles with products of lipid breakdown
Micelles
- Vehicles to carry hydrophobic molecules through aqueous medium
- Products of lipid digestions e.g.
- Cholesterol
- Monoglycerides
- Free fatty acids
Diffuse with products to brush border of epithelial cells
Absorption of lipids
- Lipids diffuse down conc gradient into intestinal epithelial cells (in the micelle)
- Inside cell re-esterified back to:
- Triglycerides
- Phospholipids
- Cholesterol
- These reformed lipids are packed with apoproteins to form chylomicrons
- Chylomicrons exocytosis from basolateral membrane
- Too large to enter capillaries
-
Enter lymph capillaries
- Travel through lymphatic system
- Re-enter vascular circulation via the thoracic duct
Chylomicrons enter lymph capillaries and travel through lymphatic system
How do they re-enter vascular circulation
via the thoracic duct
Enterohepatic circulation of bile acids
- Don’t enter gut epithelial cells with lipids
- Remain in gut and reabsorbed in terminal ileum
- Returned to liver in portal blood
- Liver extracts bile salts –> therefore liver doesn’t have to resynthesise all bile acids
- Remain in gut and reabsorbed in terminal ileum
the gall bladder sits on the
- on inferior surface of liver, in the transpyloric plane – plane at L1
function of gall bladder
- Bile produced all the time but we only need it intermittently
- Stores bile
- Concentrates bile (removes water/ions)
- Can lead to gall stones
which hormones triggers release of bile from gall bladder
- CCK released from duodenum stimulates gall bladder contraction
- Relaxes sphincter of Oddi
- If bile acids (salts) or pancreatic lipases are not secreted in adequate amounts
Steatorrhea and bile pigments
- Pale poo
- Floating
- Foul smelling
bilirubin and bile
- Breakdown product of Hb
- Conjugated into the liverà soluble
- Secreted into bile
- Excreted in faeces
- Accumulates in blood if cannot be excreted à causing jaundice
