Liver and the Biliary Tract Flashcards
What is the composition of bile?
- Bile acids and bile salts
- Water (95%)
- Electrolytes
- Cholesterol
- Phospholipids
- Conjugated bilirubin
- Bile pigments
- Enzymes
- Vitamins
- Heavy metals
Where is bile formed?
The hepatocytes of the liver
What is bile and it’s pH?
A greenish-yellow alkaline that is stored and concentrated in the gallbladder.
pH7-8
What is the action of bile on fat?
- Acts as a detergent to fats - emulsifies large fat particles into smaller fat particles and form micelles to be attacked by lipase in pancreatic juice
- Aid transport of digested fat end-products to / through intestinal mucosal membrane
Why is bile a better emulsifier than bile acids?
Bile is amphipathic - both hydrophilic and hydrophobic parts
What are the functions of bile? (3)
- Aids digestion and absorption of fat (detergentation)
- Means for excretion for bilirubin (end product of haemoglobin destruction) and excess cholesterol synthesised by liver cells
- Exerts hormone-like effect to influence intestional metabolic pathways
What role does the gallbladder have in bile formation?
Stores and concentrates bile about 5 times.
What are bile acids formed from?
Cholesterol
What are the main primary bile acids
Cholic acid
Chenodeoxycholic acid
What happens to primary bile acids?
They are conjugated to bile salts by the addition of an amino acid group. They are then actively transported from the hepatocyte.
Once bile salts are formed, where do they get transported to?
Once the leave the liver, they travel through the hepatic duct and the common bile duct. Here, they either travel directly to the duodenum (where they act) or to the gallbladder via the cystic duct.
What stimulates gallbladder contraction and Sphincter of Oddi relaxation?
Vagal stimulation
CCK - Cholecytokinin
This is released from duodenal enteroendocrine cells in response to luminal fat presence.
How would you describe the contractions of the gallbladder?
Rhythmic contractions of gallbladder transmit peristaltic waves down common
What is the role of CCK in the bile system?
It promotes bile release into the duodenum. It’s released by enteroendocrine cells of the duodenum due to presence of luminal fat.
It causes gallbladder rhythmic contractions (contraction of the smooth muscle of the gallbladder) and relaxation of the Sphinter of Oddi (allowing bile into the duodenum).
What mediates relaxation of the gallbladder and closure of the sphincter of odds?
sympathetic nerves and the gut hormones Vasoactive Intestinal Polypeptide (VIP) and Somatostatin.
What % of bile acids recirculate and are recycled?
- 85%
- 90%
- 95%
- 99%
95%
Describe the enterohepatic circulation.
This is the circulation of bile substances (bile acids/bilirubin) and drugs. Bile acids are secreted from the liver in bile which enters the small intestine. They are then reabsorbed by enterocytes (mainly in the ileum) by active transport. They are then transported to the liver sinusoids via the portal vein.
The liver produces more bile acids to compensate.
What facilitates the transport of bile acids back to the liver?
Albumin. They are bound to albumin in blood.
What is the order of the biliary tree from smallest to largest?
Biliary canaliculi Interlobular ducts Septal bile ducts Intrahepatic ducts R. and L. hepatic ducts Common hepatic duct Common bile duct
Explain the path of the common bile duct (location).
It passes behind the duodenum and through the head of the pancreas. It joins the main pancreatic duct and this opens into the 2nd part of the duodenum (descending d.).
Terminology : Cholecystitis
Gallbladder inflammation
Terminology: Cholelithiasis
Gallstones within the gallbladder
Terminology: Cholecystectomy
Removal of the gallbladder
Terminology: Cholangitis
Gallstone within a bile duct
What vol. of bile can the gallbladder store?
- 25-45ml
- 30-50ml
- 35-55ml
- 40-60ml
30-50ml
Where does the gallbladder sit?
Located under the liver in the gallbladder fossa on the interior surface on the right love of the liver.
What are the risk factors for developing gallstones?
- Increasing age
- Family history
- Caucasian
- Low fibre diet
- Inflammatory bowel disease
- Prolonged fasting (bile held for long time in gallbladder and being concentrated)
5 F’s: Female, Fair, Fertile, Forty, Fat
What percentage of the population will develop gallstones?
7-15% of the population. 80% of these are asymptomatic which don’t require treatment.
What are the different types of gallstones and give a short description of each?
- Cholesterol only
- Solitary, large, oval, soft and clay-like. These sit in the gallbladder - Bile Pigment
- Associated with haem - Mixed
- Mostly cholesterol with some bile pigment
Describe gallstone pathogenesis (3 steps)
Cholesterol Supersaturation
- Cholesterol is solubilised by bile and high cholesterol levels results in supersaturation.
- Typically occurs w/ high oestrogen levels (obesity/pregnancy/liver disease) low b. acid levels (active Crohn’s)
Biliary Stasis
- Occurs during fasting / starvation
Increased bilirubin secretion
- Conjugated bilirubin soluble in bile
- Pigmented stones develop when: 1. Increased RBC breakdown (haematological conditions). 2. Failure of hepatic conjugation.
Why does liver disease cause high oestrogen levels?
The liver breaks down oestrogen therefore would cause men to be in a higher oestrogen state.
What complications could gallstones cause if in the gallbladder?
Biliary Colic
Acute Cholescystitis
Empyema
Cancer
What complications could gallstones cause if in the common bile duct?
Obstructive jaundice
Cholangitis
Pancreatitis
What complication could gallstones cause if in the small intestine?
Gallstone ileus
What is biliary colic? (Inc. pain, LFTs)
Sudden pain due to a gallstone.
The stone is usually impacted in the neck of the gallbladder. The pain is epigastrium / right upper quadrant / through back.
Pain provoked by eating and vomiting is a sign
Normal LFT
Often settles if stone moves back into fundus
What is acute Cholecystitis in relation to a gallstone? (Inc. symptoms, LFTs, treatment)
Gallstone in gallbladder leading to wall oedema / inflammation.
May cause a bacterial infection in the GB wall
Symptoms: pain, nausea, abdominal tenderness
LFT: inc. inflammatory markers
Treatment: antibiotics
What is post-hepatic obstructive jaundice?
Post-hepatic = after the liver Obstructive = bile excretion impaired by obstruction / loss of bile ducts Jaundice = Increased bilirubin in blood
What are common causes of post-hepatic obstructive jaundice?
- choledocholithiasis (gallstones in bile duct)
- pancreatic cancer (head of pancreas compresses common bile duct
What are signs and symptoms of post-hepatic obstructive jaundice?
- Scratch marks
- Features of chronic liver disease
- Pale stools
- Dark urine (conj. bilirubin excreted in urine from blood)
- yellow sclera
What is choledocholithiasis and how would a patient present?
- gallstones in the bile ducts (migrated from the gallbladder where stones usually form)
May present with: - obstructive jaundice
- cholangitis (need antibiotics)
- acute pancreatitis
Treat w/ cholecystectomy to prevent reoccurrence.
What are the endocrine and exocrine functions of the liver?
Exocrine role - Bile production Endocrine role - IGF - Angiotensinogen - Hepcidin, beta-trophic
Blood in the portal vein travels from where to where?
From the GI tract, gallbladder, pancreas and spleen to the liver
What are the functions of the liver? (9)
Metabolic
- Synthesis (e.g. clotting factors, albumin)
- Breakdown (e.g. drugs)
- Amino acid, carb and lipid metabolism
- Plasma protein and enzyme synthesis
- Bile production
- Detoxification
- Storage of proteins, glycogen, vitamins, metals
- Activates Vit. D
- immune function
- Urea, heparin and Vit. A production
What is the vasculature of the liver?
Hepatic artery
- 30-40% blood supply
- Supplies non-parenchymal structures w/ oxygen rich blood
- From coeliac trunk
Hepatic portal vein
- 60-70% blood supply
- supplies partially deoxygenated blood
- blood drained from SI (nutrients), spleen (RBC breakdown products) and pancreas
Connecting sinusoids
- large fenestrated capillaries
Hepatic vein
- central veins of hepatic lobule form collecting/sub-lobular veins which combine forming hepatic veins
- open into inf. vena cava
What supplies oxygenated blood to the liver?
Hepatic artery
What supplies nutrient rich and partially deoxygenated blood to the liver?
Hepatic portal vein
What artery allows the liver to perform gut-related functions?
Hepatic portal vein
What structures makes up the portal triad?
Hepatic artery (in), portal vein (in) and bile ducts (out)
What is the role of connecting sinusoids?
Receive and mix blood from hepatic artery (O2 rich) and portal vein (nutrient rich) and deliver this to central veins
Where is the liver situated?
Right hypochondrium and epigastric regions
What are the lobes of the liver?
Right with two accessory lobes; Caudate and Quadrate
Left
Which lobe of the liver is the largest?
Right
On what surface of the liver are the accessory lobes located on?
Visceral surface
How to differentiate between caudate and quadrate lobes?
Caudate - Upper aspect visceral surface Quadrate - Lower aspect - Next to gallbladder
What separates the caudate and quadrate lobe and what does it transport?
Porta hepatis fissure
- Transmits vessels, nerves and ducts leaving/entering liver except hepatic veins
What separates the left and right lobes of the liver?
The attachment of falciform ligament which also attaches to the abdominal wall.
What covers the liver?
A fibrous membrane - Glisson’s Capsule
What’s the micro-anatomy of the liver and their functions?
Hepatocytes (liver cells) - produce bile
Bile canaliculi - ducts collecting bile
Hepatic sinusoids - Supply liver w/ oxygenated and nutrient-rich blood
What are the surfaces of a hepatocyte?
3 surface types
Sinusoidal, Intercellular, Canalicular
What cell type is a hepatocyte?
Cubodial epithelial cells lined with microvilli
How are hepatocytes arranged?
Densely packed and segmented into hepatic laminae only one cell thick by sinusoids (vascular spaces)
Role of hepatocytes
Multi-functional
Parenchymal (functional unit of an organ)
They carry the function of the liver i.e. take up glucose, amino acids e.t.c for metabolism, detoxification of blood, synthesise bile e.t.c.
What are bile canaliculi and their function?
Tiny channels located between hepatocytes. They transport bile from hepatocytes to bile ducts
The bile in canaliculi flows in the opposite direction to blood in sinusoids.
What are hepatic sinusoids?
Capillaries with larges fenestrations (pores) located between hepatic laminae.
Where do hepatic sinusoids drain to?
They converge centrally, draining into a central vein which drains into the hepatic vein then the inferior vena cava.
What is the Space of Disse?
Perisinusoidal space - the spaces between layers of hepatocytes and sinusoidal endothelial cells.
What is the function of hepatic sinusoids?
Blood from the portal vein and hepatic artery mixes here, delivering oxygen and nutrient rich blood
Where are Kupffer cells situated?
They are macrophages and situated on walls of hepatic sinusoids
What is a hepatic lobule?
The structural unit of the liver. It is one way to explain the arrangement of hepatocytes into hexagons.
What is the structure of a hepatic lobule?
Hexagonal cylinders of hepatocytes which are drained by a central vein.
Lobules are separated by interlobular septum = CT containing lymphatics and blood vessels.
At each corner of the hexagonal lobule is a hepatic triad (6 for each lobule)
What are the parenchymal liver cells?
- Hepatocytes
- Endothelial cells
- Kupffer cells (macrophages)
- Perisinusoidal (fat storing) cells
- Liver-associated lymphocytes
What is the transportation sequence of bile?
Secreted by hepatocytes > collected by system of ducts > right and left hepatic ducts > common hepatic duct > joins with cystic duct (from gallbladder), forming common bile duct > runs to duodenum
50% bile is first stored in gallbladder before released into duodenum.
How is bile concentrated in the gallbladder?
Epithelial cells actively transport sodium through gallbladder mucosa. Water and other electrolytes are then reabsorbed through the epithelial cells.
What happens to the bile as it flows through the ducts?
Duct cells, lining bile ducts of the liver, release bicarbonate and water therefore diluting bile.
What regulates secretion of bile?
CCK and secretin. Also, nerve impulses from vagus nerve.
What is the role of secretin in bile secretion?
Secreted by endocrine cells in response to acidic chyme. It stimulates biliary duct cells in the liver to secrete more water and sodium bicarbonate (essential to neutralise stomach acid present in the duodenum). It also stimulates bile production.
