The Liver Flashcards
What are the types of cells in the liver?
Hepatocytes= metabolically active cells of the liver
Kupffer cells= resident macrophages
Other cell types=endothelial and stellate cells, which form a type of scar tissue in the liver
What is the hepatic lobule?
The functional unit of the liver is the hepatic lobule – a hexagonal plate of hepatocytes
Through the middle of each lobule is a hepatic vein
At all 6 corners we find branches of the portal vein, hepatic artery and bile duct
Blood enters the lobule via branches of the portal vein and hepatic artery and the flows through sinusoids, which are lined with hepatocytes
What is the function of the hepatocytes and hepatic microstructure?
The hepatocytes remove toxins (e.g. alcohol) from the blood before it leaves the lobule via the hepatic vein at the centre
The hepatic microstructure
Provides a large SA for substance exchange
It keeps blood and bile separate
Kupffer cells help to provide a protective barrier by removing colonic bacilli from portal blood before it can enter the systemic circulation
What is the billiary system?
Hepatocytes secrete bile into small channels between cells called canaliculi
The canaliculi carry the bile into small and then large bile ducts (left and right, then the common hepatic duct), which connect onto the common bile duct
Describe and explain bile
Green/yellow fluid complex made of H20, electrolytes, bile acids, cholesterol, phospholipids and bilirubin
Bile is produced in hepatocytes.
How is bile stored and secreted?
Bile produced in hepatocytes is transported via canaliculi into the left and right, then common hepatic duct, then the common bile duct.
Epithelial cells secrete water, Na+ and HCO3-, modifying the bile.
Once in the common bile duct, bile enters the duodenum at the ampulla of Vater, or travels up to the gallbladder via the cystic duct for storage
Bile stored in the gallbladder is released in response to fatty chyme in the duodenum
Describe Gallstones
Bile makes usually insoluble cholesterol soluble
Gallstones (cholelithiasis) is where the cholesterol precipitates out of the bile
The minority of gallstone cases are pigment-based
They can occur anywhere along the biliary tree
Risk factors:
High fat diet increases cholesterol synthesis
Female sex- excess oestrogen and HRT increase cholesterol levels
Describe the formation of bile acids
The conjugated form is secreted into cannaliculi where the intestinal bacteria convert it to secondary bile acids.
Describe bile acid circulation
Bile acids are secreted into the small intestine via the biliary tree. In the small intestine they exist as bile salts to emulsify fats
Most bile acids are reabsorbed in the terminal ileum,
and are carried back to the liver by the portal vein
They are then taken up by hepatocytes and recycled
What is the function of bile?
Bile is essential for the digestion/absorption of lipids – responsible for emulsification
Bile helps neutralise acidic chyme in the duodenum, preventing ulceration and keeping the pH optimum
Bile is secreted in response to CCK and secretin
It also helps to eliminate waste products from the blood such as bilirubin (excreted in the urine) and cholesterol (recycled to make bile acids)
What is bilirubin? How is Hb broken down?
Bilirubin= most important compound the liver excretes into bile
A toxic, yellow pigment produced in the breakdown of haemoglobin by macrophages primarily in the spleen
The Fe is recycled by the liver, globin chains are catabolised to form aas. Haem cannot be recycled so is eliminated as bilirubin
How is haem broken down and how is bilirubin excreted?
Haem is converted to green biliverdin which forms yellow bilirubin by biliverdin reductase
Bilirubin is released into the plasma and carried by albumin into the portal system
Hepatocytes absorb the bilirubin. It is conjugated with glucuronic acid and secreted into bile via canaliculi
The bile is metabolised by small intestine bacteria to form brown stercobilin (excreted in faeces) and yellow urobilinogen (excreted in urine)
Renal excretion of urobilin and stercobilin are elevated in hepatitis and hepatocyte damage
