The Liver Flashcards
Describe the blood supply to the liver
- 75% of blood supply is from the portal vein , blood returning from the GI tract
- 25% from hepatic artery
- Central veins of liver lobules drain into hepatic vein and back to the vena cava
Describe what hepatocytes do and specifically what periportal and pericentral hepatocytes functions are
Hepatocytes - perform most metabolic functions
- Periportal hepatocytes immediately surround the portal tract and have the highest [oxygen] and most nutrients - specialise in oxidative metabolism - - pericentral hepatocytes surround the vein and have the lowest [oxygen] - Specialise in biotransformations and drug detoxification
State the three other types of cells found in the liver (include the role of the k________ cells)
- Kupffer cells - a type of macrophage - phagocytic activity - remove aged/damaged red blood cells, bacteria, viruses and immune complexes
- Liver sinusoidal endothelial cells
- Stellate cells
Describe what a hepatic lobule is an their overall function
- A functional unit - hexagonal plates of hepatocytes surround the central hepatic vein
- At each of the 6 corners is branches of portal vein, hepatic artery and bile duct
Lobules are important because they -
- Provide a massive surface area for the exchange of molecules
- Provide a sophisticated separation of blood from bile
State the functions of the liver
- Protective barrier
- Bile synthesis
- Protein synthesis
- Biotransformation
- Storage
- Metabolic function
Describe kupffer cells - where they are found, how they function and why they are needed
- Kupffer cells found in sinusoids
- Represent 80% of all fixed tissue macrophages
- They function as a mononuclear phagocyte system
- They are exposed to blood from the gut which contains pathogenic substances - the cells clear gut derived endotoxins from portal blood
What is bile?
This is a complex fluid containing water, electrolytes and a mix of organic molecules
Organic molecules are bile acids, cholesterol, bilirubin and phospholipids
Describe the 2 stages of bile secretion
- By hepatocytes - synthesise bile salts, cholesterol and other organic constituents
- By epithelial cells lining bile ducts - produce a large quantity of watery solution of Na+ and HCO3- stimulated by the hormone secretin in response to acid in the duodenum
Describe the biliary system
Bile from hepatic ducts -> common bile ducts -> duodenum or diverted via cystic duct -> gallbladder -> concentrated and stored -> released by cholecystokinin in response to fat in the duodenum
Extra detail -
Bile is secreted from hepatocytes and drains from both lobes of the liver via the canaliculi, intralobular ducts and collecting ducts from the right and left hepatic ducts
Ducts amalgamate to form the common hepatic duct that runs alongside the hepatic vein
What is movement of bile into the duodenum controlled by?
Relaxation of the sphincter of odii
Describe how bile is synthesised
- Cholesterol forms primary bile acids (cholic (3 OH groups) and chenodeoxycholic acids (2 OH groups) ) after reacting with 7 alpha hydrolase with oxygen, NADH and CytP450 cofactors
- The primary bile acids then conjugate with glycine and taurine to form bile salts
- These bile salts secreted into canaliculi and hepatic duct through to the common duct to go either to the for storage or travels to the small intestine
- Once in the small intestine the bile salts are broken down by intestinal bacteria into primary bile acids and glycine/taurine
- The primary bile acids then form secondary bile acids - these then travel from the duodenum through the jejunum, ileum (where most bile is reabsorbed - enterohepatic recirculation) and large intestine
What is the significance of bile?
- Essential for fat digestion and absorption via emulsification
- Bile + pancreatic juice neutralises gastric juice as it enters the small intestine - aids digestive enzymes
- Elimination of waste products from blood in particular bilirubin and cholesterol
Describe gallstones - why they arise, the 2 types and risk factors involved
- Abnormal conditions caused by an imbalance in the chemical makeup of bile inside the gallbladder which leads to gallstones
- Cholesterol is virtually insoluble in aqueous solution but is made soluble in bile - the cholesterol can precipitate out of the solution forming gallstones
- 2 types of stones - cholesterol (80%) and pigment (20%)
- Risk factors for cholesterol stones
- High fat diet (this increases synthesis of cholesterol)
- Inflammation of gallbladder epithelium (changes absorptive characteristics of mucosa so there is less absorption of H2O and bile salts so cholesterol is concentrated)
- More common is women than men - risk factors of obesity, excess oestrogen like in pregnancy and HRT
Describe the role of plasma proteins
Plasma proteins transport nutrients like glucose, amino acids, lipids and vitamins absorbed from the digestive tract to different parts of the body - they carry substances poorly soluble in water
State some common examples of plasma proteins made by the liver + their main function
- Albumin - acts as a general purpose carrier for fatty acids, hormones, drugs, osmotic regulator
- Globulin - also act as specialised carriers for metal ions e.g. Ca2+, Fe2+, Cu2+ and hormones released into the blood are transported to their target organs by plasma proteins
e.g. thyroxine binding globulin transports thyroxine, transferrin transports iron and fibrinogen is involved in blood coagulation
Plasma removes nitrogenous waste products produced after cellular metabolism and transports them to the kidney/lungs for excretion
