7.3 The Liver Flashcards
Briefly describe the anatomy of the liver
The liver sits under the rib cage and above stomach, it is separated into lobes which are divided by the falciform ligaments. Each lobe is made up of lobules that are the functional units of the liver. Each lobule has a portal triad composed of the portal venule, portal arteriole and bile duct (which receives bile from the bile canaliculi).
The liver receives dual blood supply, the portal vein bringing in blood from the digestive system to be cleaned up by the liver and sent back to the systemic system and the hepatic artery bringing in oxygenated blood for the liver cells.
Bile is produced by hepatocytes and drained into bile canuliculi which merge into the hepatic duct, the hepatic duct leads to gall bladder and bile duct, then out into duodenum.
Give some functions of the liver
Functions of the liver include:
-Metabolism: Glycogen to glucose and vice versa, amino acids, synthesizes lipoproteins, protein metabolism
-Detoxification: alcohol dehydrogenase
-Excretion: bilirubin
-Storage: glycogen, triglycerides, vitamins & minerals
-Synthesis: bile salts used for the emulsification and absorption of fats & cholesterol, blood clotting factors, albumin, angiotensinogen and cholesterol
-Phagocytosis: Kupffer’s cells
-Heat production: many biochemical reactions are
exothermic
What is the cause of acute liver failure
Acute liver failure is due to massive liver cell death and progressive multi organ failure
What is Jaundice
Jaundice is caused by the blockage of bile flow. It prevents the liver function of excretion of bilirubin in bile. The retention of bilirubin causes yellowing of the skin and eye sclera where bilirubin collects. Jaundice is common in hepatitis, alcoholic liver disease, blockage of bile duct and toxic reaction to drugs. It is also known as hyperbilirubinaemia. The problems causing jaundice can be pre-hepatic (e.g too many RBCs being broken down), hepatic (bilirubin is not properly conjugated) or post hepatic (e.g blockage in the bile duct).
What is bile
Bile is an alkaline solution containing bile salts such as bicarbonate, bile pigments, cholesterol, phospholipids and inorganic ions. Its functions are in digestion, by the salts clumping around and emulsifying lipids, and in excretion
How is bilirubin excreted
Bilirubin is produced in the spleen, liver and bone marrow, it comes from the breakdown of RBCs and is potentially toxic. It is not soluble and is carried in the blood bound to albumin to the liver. In the liver it is conjugated with glucuronic acid making it more water soluble so it can be secreted in the bile to the small intestine. In the intestine, the conjugated bilirubin is then converted to urobilinogen by bacteria. Some urobilinogen is then further broken down to stercobilin which is excreted in stool and some is reabosrbed into the blood stream and excreted by kidneys in urine (as it is now much more soluble).
Explain why newborns often have mild jaundice
UDP glucoronyl transferase is an enzyme slowly synthesised after birth that catalyses the conjugation of bilirubin with glucoronic acid. Hence immediately after birth, newborns will be unable to excrete the bilirubin.
What is one was bile flow can be blocked
Via gall stones.
Hepatocytes actively transport solutes into the bile canaliculi and then the bile is then modified in the bile ductules (glucose and amino acids are reabsorbed, Cl is exchanged for bicarbonate and bile flow is increased in the post prandial period). Between meals, the bile is directed to the gall bladder (as the sphincter of oddi is closed), water is removed and the bile becomes concentrated, but the bile salts keep the lipids water soluble. But sometimes bile salts are insufficient when bile is too concentrated or if there is too much cholesterol, this can cause bile to clump together and form gall stones (aka cholelithiasis). These gall stones prevent the flow of bile
What is a problem other than jaundice associated with bile flow.
problems with bile flow can also cause malabsorption of dietary lipids and fat soluble vitamins
What are spider naevi
They are spider shaped bruises due to failure of sphincter in cutaneous arterioles failing to properly control blood flow into the capillary bed.
They are common in pregnancy as they are linked with high oestrogen level.
These high oestrogen levels can also be common is liver disease due to failure to metabolise hormones.
What are some symptoms other than spider naevi associated with problems with hormone metabolism
Breast enlargement in men and low levels of binding globulin
Describe what is synthesised by the liver
The liver synthesises bile salts used for the emulsification and absorption of fats and cholesterol, blood clotting factors, albumin, angiotensin and cholesterol
What are some symptoms related to liver synthesis issues
-bruising
-abdominal swelling, aka ascites which is due to the accumulation of excess fluid in the peritoneal cavity.
-Portal hypertension which is resistance to portal flow, often caused by cirrhosis
-Cirrhosis is resistance at the sinusoid level
What is hepatic encephalopathy
Hepatic encephalopathy is when toxic substances reach the nervous system as disease has reduced the liver’s ability to convert ammonia to urea. There is accumulation of ammonia and other toxins in the plasma. The toxins cross the blood brain barrier intro the astrocytes, causing an increase in glutamine synthesis. This leads to excitotoxicity.
