Gallbladder + Bile Flashcards
Where is bile synthesised?
Liver
Where is bile stored?
Gallbladder
What is role of bile?
- To emulsify fats
2. Serves as an excretory pathway for steroid hormones
Where does the gall bladder lie?
At the junction of the right mid-clavicular line & costal margin
What connects the liver to the gall bladder?
Cystic duct, branch of the common hepatic duct
What is the functional unit of the liver?
The hepatic lobule
What does a portal triad consist of?
Hepatic portal vein
Hepatic artery
Bile duct
Which blood vessel runs up the centre of hepatic lobules?
Central vein
Which liver blood vessel has fenestrated, discontinuous endothelium?
Hepatic sinusoid
How are hepatocytes separated from the hepatic sinusoids?
By the space of disse
Describe the blood content of hepatic sinusoids.
Contains oxygen-rich blood from the hepatic artery
Contains nutrient rich blood from the hepatic portal vein has come from small intestine where nutrients have been absorbed)
Give the liver blood supply, both arterial and venous.
Arterial supply is from:
75% = hepatic portal VEIN
25% = hepatic artery
Venous drainage is via the hepatic vein.
Name the cells which produce the extracellular matrix in the space of disse.
Stellate cells
What is found between adjacent hepatocytes?
Bile canaliculi - not true vessels, more like grooves.
They are bound together by tight junctions, gap junctions & desmosomes
Describe the pathway of bile into the GI tract.
- Bile passes through the bile ducts in the hepatic lobules into either the left or right hepatic ducts which join to form the common hepatic duct
- The cystic duct them joins the common hepatic duct to form the common bile duct. Allows bile to collect in the gall bladder
- The pancreatic duct joins the common bile duct at the ampulla of vater
- These two ducts then enter the duodenum at the major duodenal papilla
- The sphincter of Oddi surrounds the two ducts to regulate the entry of bile into the duodenum
Name the 6 components of bile.
Bile salts Lecithin (a phospholipid) HCO3 Cholesterol Bile pigments Trace metals
What is the main role of bile salts?
They emulsify fats
Why must bile salts be aggregated into micelles?
To reduce their damage on cell membranes until they are required
Why is HCO3 contained within bile?
To neutralise the acids in the duodenum
Which cells secrete bile salts, cholesterol, lecithin and bile pigments?
Hepatocytes
Which cells secrete the HCO3?
Epithelial cells lining the bile ducts
Which hormone stimulates the release of HCO3 by the bile ducts?
Secretin, in response to the acid of the duodenum
Is bile more concentrated in the liver or the gall bladder?
Gall bladder
Which hormone stimulates the gallbladder to contract and release bile?
CCK (cholecystokin). Also stimulates sphincter of Oddi to relax so bile can flow into the duodenum.
Describe the vasculature of the gallbladder.
Arterial: Supplied by cystic artery
Venous: No venous drainage, blood drains from the gallbladder directly into the liver
Describe enterohepatic circulation.
- During digestion of a fatty meal, the bile salts are absorbed via Na+ coupled transporters in the jejunum and terminal ileum
- The absorbed bile salts return via the portal vein to the liver where they are secreted into bile again
- The uptake of these bile salts into the hepatocytes is via secondary active transport coupled to Na+
- This recycling pathway is known as enterohepatic circulation. 5% of bile salts escape recycling and are lost in faces but the liver simply synthesises more bile salts from cholesterol
From which molecule is bile synthesised from?
Cholesterol
When is bile secretion at its greatest?
During and just after a meal
What does it mean for the gall bladder to undergo adaptive relaxation?
The gallbladder increases in size with bile but the pressure doesn’t increase as the bile duct is a low pressure system.
What are bile pigments formed from?
The haem portion of haemoglobin when old erythrocytes are broken down.
Name the predominant bile pigment. What colour is it?
Bilirubin - it is yellow
Where does erythrocyte break down normally occur?
In the spleen and bone marrow by macrophages. Also occurs in the Kuppffer cells of the liver.
Outline the steps of bilirubin metabolism.
- Macrophage ingests the erythrocyte and haemoglobin is split into haem and globin
- Globin is broken down to amino acids to be made into new erythrocytes in the one marrow
- Haem is broken down by hemoxygenase into biliverdin, Fe2+ and CO
- Fe2+ binds to transferrin and is used to make new erythrocytes
- Biliverdin is reduced to unconjugated bilirubin by biliverdin reductase
- Unconjugated bilirubin binds to albumin and travels to the liver. Glucoronic acid is added so it can be soluble and becomes conjugated bilirubin
- Conjugated bilirubin dissolves in bile. When it reaches the ileum, it is reduced by bacteria to form urobilinogen
- 10% of urobilinogen is reabsorbed into the blood and taken back to the liver to be oxidised to urobilin - makes urine yellow
- 90% of urobilinogen is oxidised by other bacteria to form stercobilin - makes faeces brown
What is jaundice?
Yellow discolouration of skin caused by a high serum bilirubin level
Name the 3 types of jaundice
Pre-hepatic
Hepatic
Post-hepatic
How is pre-hepatic jaundice caused? What are the symptoms?
Cause: Increased breakdown of erythrocytes, resulting in increased levels of unconjugated bilirubin. Caused by malaria, sickle cell anaemia, thalassaemia
Symptoms: Yellow skin, enlarged spleen, normal stools and urine
How is hepatic jaundice caused? What are the symptoms?
Cause: Hepatocellular swelling. Liver is damaged so cannot metabolise unconjugated bilirubin. Conjugated bilirubin cannot be secreted. Causes increase in conjugated and unconjugated bilirubin.
Caused by parenchymal liver disease, viral hepatitis, alcohol hepatitis
Symptoms: Dark urine, pale stools, enlarged spleen, yellow skin
How is post-hepatic jaundice caused? What are the symptoms?
Cause: Biliary system is damaged. Results in increased conjugated bilirubin. Caused by gallstones, pancreatic cancer, pancreatitis (is pancreas is inflamed, it can obstruct the common bile duct)
Symptoms: Dark urine, pale stools, yellow skin
How are gall stones formed?
When the concentration of cholesterol is high, it will crystallise out of solution
What are the consequences of having gall stones?
- Stone may lodge in opening of gallbladder, causing painful spasms of the smooth muscle
- Stone may lodge in common bile duct, preventing bile from entering the intestine. This causes decreased fat digestion and impaired absorption of fat soluble vitamins
- Stone may lodge so pancreatic secretions and bile cannot enter the intestine. Will result in failure to neutralise acid and failure to digest, resulting in nutritional deficiencies.
What controls the flow of bile and pancreatic enzymes into the duodenum?
Sphincter of Oddi
Which nerve supplies parasympathetic innervation to the gallbladder?
Vagus nerve
