Hepatobiliary system

Question 1

how many lobes are there in the liver and what are they called?

Answer 1

Left lobe and right lobe

Question 2

What two vessels does inflow in the liver come from and what percentage comes from each?

Answer 2

Hepatic artery 25%
Portal vein 75%

Question 3

What outflows from the liver?

Answer 3

Bile
Blood through 3 hepatic veins

Question 4

What is a hepatic lobule?

Answer 4

Hexagonal structural unit of liver tissue

Question 5

What is in the corners of each hepatic lobule?

Answer 5

A portal triad

Question 6

How many adjacent lobules does each portal triad link to?

Answer 6

3

Question 7

What is in the centre of liver lobule?

Answer 7

A central vein

Question 8

Where does the central vein collect blood from?

Answer 8

Hepatic sinusoids

Question 9

Hepatocytes facing sides????

Question 10

What are the 3 parts of the portal triad?

Answer 10

Hepatic artery, portal vein, bile duct

Question 11

WHat does the hepatic artery do?

Answer 11

Brings O2-rich blood into liver to support hepatocytes ↑ energy demands

Question 12

What does the portal vein do?

Answer 12

Mixed venous blood from GIT (nutrients, bacteria & toxins) and spleen (waste products)
Hepatocytes process nutrients, detoxify blood & excrete waste

Question 13

What does the bile duct do?

Answer 13

Bile produced by hepatocytes drains into bile canaliculi
Coalesce with cholangiocyte-lined bile ducts around lobule perimeter

Question 14

What is a hepatic acinus?

Answer 14

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

Question 15

Describe the 3 zone model

Answer 15

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 ↓

Question 16

Describe sinusoidal epithelial cells

Answer 16

No basement membrane

Fenestrated (discontinuous endothelium)

Allow lipids & large molecule movement to
and from hepatocytes

Question 17

Describe Kupffer cells

Answer 17

Sinusoidal macrophage cells

Attached to endothelial cells

Phagocystosis
-Eliminate & detoxify substances arriving in -liver from portal circulation

Question 18

Describe hepatic stellate cells

Answer 18

Exist in dormant state

Store vit A in liver cytosolic droplets

Activated (fibroblasts) in response to liver damage

Proliferate, chemotactic & deposit collagen in ECM

Question 19

Describe hepatocytes

Answer 19

80% of liver mass
Cubical
Synthesis e.g. albumin, clotting factors & bile salts
Drug metabolism
Receive nutrients & building blocks from sinusoids

Question 20

What do cholangiocytes do?

Answer 20

Secrete HCO3- & H2O into bile

Question 21

What are the 3 functions of hepatocytes?

Answer 21

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

Question 22

How are non-essential amino acids synthesised?

Answer 22

Transamination

Different keto-acids can be converted into multiple amino acids depending on the transaminase enzyme (vital for production of non-essential amino acids)

Question 23

What are the 3 uses of bile?

Answer 23

Cholesterol homeostasis

Absorption of lipids & lipid soluble vitamins (A, D, E, & K)

Excretion of:
-xenobiotics/drugs
-cholesterol metabolites
-adrenocortical & other steroid hormones
-Alkaline phosphatase

Question 24

How much bile is produced each day?

Answer 24

500ml

Question 25

Why is bile yellow/green?

Answer 25

due to pigments such as bilirubin & biliverdin

Question 26

What percentage of total bile do hepatocytes secrete?

Answer 26

60%

Question 27

What percentage of total bile do cholangiocytes secrete?

Answer 27

40%

Question 28

What is primary secretion of bile salts?

Answer 28

Bile secretions reflect serum concentrations
Secretion of bile salts (acids), lipids & organic ions

Question 29

What is secondary modification of bile salts?

Answer 29

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

Question 30

How are bile salts and toxins secreted?

Answer 30

By biliary transporters

Question 31

Describe the main biliary transporters?

Answer 31

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.