Anatomy & Function of the Liver Flashcards
Where is the liver located ?
upper right-hand portion of the abdominal cavity
- beneath the diaphragm
- ontop of the stomach
What is the overall structure of the liver?
- 2 lobes
- each lobe is made up of 8 segments that consist of 1000 lobules
- lobules are connected to small ducts connected to larger ducts to form the common hepatic duct
What is the function of the common hepatic duct ?
- transports bile made by the liver cells to the gallbladder & duodenum
Describe why the liver is a vascular organ ?
- hepatic artery = supplies 02 rich blood from heart to liver
- portal vein = supplies nutrient rich blood from digestive tract
What is present in every liver lobule ?
- serval portal triads
What 5 structures make up a portal triad ?
- proper hepatic artery
- hepatic portal vein
- 1/2 small bile ducts
- lymphatic vessels
- branch of the vagus nerve
Describe the proper hepatic artery
- an arteriole branch of the hepatic artery that supplies oxygen
Describe the hepatic portal vein
- a venue branch of the portal vein, with blood rich in nutrients but low in oxygen
What are the functions of the liver ?
- manufactures bile
- controlling levels of fats, amino acids & glucose
- cholesterol synthesis
- clears blood of infections
- stores iron & vitamins
Where is bile produced ?
the liver
Where is bile stored ?
in the gallbladder
What is the function of bile ?
- required for digestion & fat absorption
- endogenous synthesis of bile salts
- absorption of fat soluble vitamins
- major route for loss of cholesterol
What is the composition of bile ?
- bile salts
- phospholipids
- cholesterol
- bilirubin
What synthesises bile salts ?
- hepatocytes
- bile pigments are picked up from blood sinusoids
What is the daily secretion of bile ?
500 mls
What are bile acids formed from ?
- cholesterol in the liver
- conjugated with glycine & taurine
What is the process of metabolism of bile salts in the liver ?
- biosynthesis of bile acids from cholesterol
- conjugation with amino acids
- conc. in gallbladder by removal of water
- intestinal bacteria in colon produce enzyme that can attack/alter bile salts
- most bile acids are reabsorbed from intestine, transported to liver and reverted to bile
Define enterohepatic circulation
the process by which substances are metabolised by the liver, secreted into liver and then reabsorbed into the body
Describe the metabolism of bilirubin
- 120 days RBCs are phagocytised & haemoglobin is released
- haemoglobin is broken down into Haem, globin & iron
What happens to haem in the blood ?
its converted to bilirubin
What happens to globin in the blood ?
it’s broken down into amino acids & recycled
What happens to iron in the blood ?
- bound by transferrin & returned to iron stored in the liver or bone marrow
Where is bilirubin degraded ?
-intestines
- intestinal bacteria degrade conjugated bilirubin to form urobilinogen
What happens to bilirubin at the liver ?
- unconjugated bilirubin flows into sinusoidal tissue, albumin releases it
- ligandin binds to unconjugated bilirubin presents it to glucuronic acid
- in the liver it becomes conjugated by UDP-glucuronyl transferase
What happens to 80% of urobilinogen ?
- its oxidised to stercobilin & excreted in faeces, giving stool brown colour
What happens to 20% of urobilinogen ?
- absorbed by extra hepatic circulation to be recycled through liver & re-excreted
- enters systemic circulation to be filtered by kidneys & excreted via urine
What are the main 2 functions of the liver in iron homeostasis ?
- major site of iron storage, regulates iron traffic into/around body via production of peptide hepcidin
- site of synthesis of major proteins in iron metabolism
What does hepcidin do?
- binds to ferroportin, inhibiting iron absorption/efflux
Where are coagulation factors mainly synthesised ?
- in the liver
What is the function of Liver Function Tests (LFTs) ?
- Detect presence of disease
- distinguish different types of liver disorders
- extent of liver damage
- follow response to treatment
How is the sample for an LFT taken?
- test is done on serum of patient
- random sample can be taken
- serum is stable for 3 days a 1-6 degrees
What are some precautions that should be taken with an LFT ?
- Avoid haemolytic
- for bilirubin fasting sample is preferred
- protect serum/plasma from light
What are the 2 subdivisions of LFTs?
- true tests of liver function
- tests indication liver injury or biliary tract disease
How are different LFTs classified ?
- based on major functions
1. excretion
2. serum enzymes
3. synthetic function
Describe an Excretion LFT
- serum bilirubin
- true test of liver function as it reflects livers ability to take up, process & secrete bilirubin into the bile
- conjugated = direct - excreted by kidney
- unconjugated = indirect - bound to albumin
What enzymes reflect damage to hepatocytes ?
- aspartate aminotransferase (AST)
- alanine aminotransferase (ALT)
These are sensitive indicators of liver cell injury
Where are aspartate aminotransferase found ?
liver, cardiac muscle, kidneys, brain & erythrocytes
Describe Aminotransferase
- normal = 10-40 U/L
- <300 U/L nonspecific may be found in any liver disorder
- > 1000 U/L = extensive hepatocellular injury = viral hepatitis, ischaemic liver injury or acute heart failure
Describe the pattern of aminotransferase in different diseases ?
- acute hepatocellular disorders = ALT > AST
- chronic viral hepatitis = ALT > AST
- Cirrhosis = AST > ALT
What does enzymes reflect cholestasis ?
- alkaline phosphatase
- gamma glutamyl transpeptidase
Describe Alkaline Phosphatase
- not specific for cholestasis
- < 3 fold in any type of liver disease
- > 4 fold in cholestatic liver disorders & infiltrative disease such as cancer
What are some examples of why non pathological elevation of alkaline phosphatase can occur ?
- Age over 60
- rapid bone growth
- late pregnancy
What can hypoalbuminaemia reflect ?
- common in chronic liver disorders = cirrhosis
- reflects severe liver damage & decreased albumin synthesis
- not specific for liver disease
Describe LFT measuring Prothrombin time (PT)
- prothrombin = plasma protein converted into thrombin during blood clotting
- formed in liver from inactive preprothrombin in the presence of Vit K
- Used to assess activity of extrinsic blood clotting pathway
What is the PT test expressed as ?
International Normalised Ration I(NR)
- Based on ratio of patients prothrombin time & normal mean prothrombin time
Which lobe of the liver is the largest ?
- the right lobe
Which cells in the liver are responsible for phagocytosis ?
- Kupffer cells
Which vitamin is stored in significant amounts in the liver ?
- Vitamin A
Which substances does the liver detoxify ?
- drugs, alcohol & ammonia
