Hepatobiliary system Flashcards
how many lobes are there in the liver and what are they called?
Left lobe and right lobe
What two vessels does inflow in the liver come from and what percentage comes from each?
Hepatic artery 25%
Portal vein 75%
What outflows from the liver?
Bile
Blood through 3 hepatic veins
What is a hepatic lobule?
Hexagonal structural unit of liver tissue
What is in the corners of each hepatic lobule?
A portal triad
How many adjacent lobules does each portal triad link to?
3
What is in the centre of liver lobule?
A central vein
Where does the central vein collect blood from?
Hepatic sinusoids
Hepatocytes facing sides????
What are the 3 parts of the portal triad?
Hepatic artery, portal vein, bile duct
WHat does the hepatic artery do?
Brings O2-rich blood into liver to support hepatocytes ↑ energy demands
What does the portal vein do?
Mixed venous blood from GIT (nutrients, bacteria & toxins) and spleen (waste products)
Hepatocytes process nutrients, detoxify blood & excrete waste
What does the bile duct do?
Bile produced by hepatocytes drains into bile canaliculi
Coalesce with cholangiocyte-lined bile ducts around lobule perimeter
What is a hepatic acinus?
Functional unit of liver
- Hard to define anatomically cf hepatic lobule
Consists of two adjacent 1/6th hepatic lobules
- Share 2x portal triads
- Extend into hepatic lobules as far as central vein
Describe the 3 zone model
Blood into hepatic acinus via Point A (portal triad)
Blood drains out of hepatic acinus via Point B (central vein)
Hepatocytes near outer hepatic lobule(zone 1) receive early exposure to blood contents:
Good components (O2)
Bad components (toxins)
Acinus split into 3x regions
Zone 1 – O2 ↑, Toxin risk ↑
Zone 2 – O2 →, Toxin risk →
Zone 3 – O2 ↓, Toxin risk ↓
Describe sinusoidal epithelial cells
No basement membrane
Fenestrated (discontinuous endothelium)
Allow lipids & large molecule movement to
and from hepatocytes
Describe Kupffer cells
Sinusoidal macrophage cells
Attached to endothelial cells
Phagocystosis
-Eliminate & detoxify substances arriving in -liver from portal circulation
Describe hepatic stellate cells
Exist in dormant state
Store vit A in liver cytosolic droplets
Activated (fibroblasts) in response to liver damage
Proliferate, chemotactic & deposit collagen in ECM
Describe hepatocytes
80% of liver mass
Cubical
Synthesis e.g. albumin, clotting factors & bile salts
Drug metabolism
Receive nutrients & building blocks from sinusoids
What do cholangiocytes do?
Secrete HCO3- & H2O into bile
What are the 3 functions of hepatocytes?
Metabolic & catabolic functions:synthesis & utilization of carbohydrates, lipids and proteins.
Secretory& excretory functions:synthesis &secretion of proteins, bile and waste products.
Detoxification & immunological functions:breakdown of ingested pathogens & processing of drugs
How are non-essential amino acids synthesised?
Transamination
Different keto-acids can be converted into multiple amino acids depending on the transaminase enzyme (vital for production of non-essential amino acids)
What are the 3 uses of bile?
Cholesterol homeostasis
Absorption of lipids & lipid soluble vitamins (A, D, E, & K)
Excretion of:
-xenobiotics/drugs
-cholesterol metabolites
-adrenocortical & other steroid hormones
-Alkaline phosphatase
How much bile is produced each day?
500ml
Why is bile yellow/green?
due to pigments such as bilirubin & biliverdin
What percentage of total bile do hepatocytes secrete?
60%
What percentage of total bile do cholangiocytes secrete?
40%
What is primary secretion of bile salts?
Bile secretions reflect serum concentrations
Secretion of bile salts (acids), lipids & organic ions
What is secondary modification of bile salts?
Alteration of pH (alkaline electrolyte solution)
H2O drawn into bile by osmosis via paracellular junctions
Luminal glucose & organic acids reabsorbed
HCO3- & Cl- actively secreted into bile by CFTR (Cystic Fibrosis Transmembrane Regulator)
IgA exocytosed
How are bile salts and toxins secreted?
By biliary transporters
Describe the main biliary transporters?
Basolateral membrane (importing):
Organic anion transporting peptide (OATPs) – bile salt uptake
Na+ taurocholate-cotransporting polypeptide (NTCP) - bile salt uptake
Apical surface (exporting):
Bile Salt Excretory Pump (BSEP) – active transport of BAs into bile
MDR related proteins (MRP2 & MRP3) –
-vely charged metabolites
Products of multidrug resistance genes
MDR1 → excretion of neutral & +ve xenobiotics & cytotoxins
MDR3 → phospatidylcholine.
