liver anatomy and histology

Question 1

describe gross anatomy of the liver

Answer 1

• divided into several lobes
• species variations
• shape has no relevance to function
• bile ducts and afferent branches of hepatic artery and hepatic portal vein run parallel through the liver like branches from the trunk of a tree

Question 2

discuss blood supply to the liver

Answer 2

• supplied by hepatic portal vein mostly = rich in nutrients but poor in oxygen
• hepatic artery branching from coeliac artery which branches off aorta. = oxygen rich

Question 3

describe blood drainage from the liver

Answer 3

hepatic veins drain into caudal vena cava

Question 4

outline how blood courses through the liver

Answer 4

1. hepatic portal vein/hepatic artery brings blood to liver
2. blood goes into sinusoids
3. central veins
4. hepatic veins
5. caudal vena cava

Question 5

what makes the regeneration of the liver so effective and when does this ger complicated

Answer 5

• stem cells line the bile ducts
• liver responsive to loss of mass - if removed, cell division increases
• not useful where cell death is ongoing as get mixture of scar tissue and regenerating cells
• scar tissue distorts the architecture leading to damage to blood flow which starves more cells of nutrients and oxygen
• cycle of scarring/cell death/regeneration leads to cirrhosis

Question 6

what is hepatic parenchyma

Answer 6

functional part of liver made of hepatocytes which are responsible for hepatic function

Question 7

describe the conformation of the classic liver lobule

Answer 7

• hepatocytes are organized in radial cords forming polyhedral prisms with portal triads at each of the corners and a single central vein

Question 8

Describe the histology of the hepatic stroma

Answer 8

Thin fibres of connective tissue (reticulin fibres + collagen type III) forms thin layer => ‘floppy’

Question 9

list the components of the portal tract/triad in classic liver lobules

Answer 9

• at least one Branch of hepatic artery
• Branch of hepatic portal vein
• Bile duct
• Surrounded by connective tissue
• Large triads also contain lymphatic vessels and autonomic nerves
• Limiting plate: discontinuous border of hepatocytes forms outer boundary

Question 10

what is the portal canal

Answer 10

space containing the portal tract

Question 11

what is a hepatic sinusoid

Answer 11

fenestrated blood vessel running along the plates of hepatocytes
- portal and arterial heptaic blood mix here

Question 12

What is the function of the central vein in a classic liver lobule?

Answer 12

receive blood from sinusoids and return it to circulation via hepatic vein

Question 13

What are the cell types found in the liver?

Answer 13

• hepatocytes
• enothelial cells
• kupffer cells (sinusoidal macrophages)
• hepatic stellate cells (Ito cells

Question 14

describe the morphology of hepatocytes

Answer 14

polyhedral with round nucleus and prominent nucleolus

Question 15

Answer 15

Question 16

describe the morphology of kupffer cells

Answer 16

macrophage like

Question 17

describe the morphology of Ito cells

Answer 17

contain big intracytoplasmic vacuoles

Question 18

what are the functions of hepatocytes

Answer 18

• metabolise and store materials absorbed from the small intestine
• secrete bile

Question 19

what are the functions of kupffer cells

Answer 19

• defend against vascular carried pathogens
• remove debris (dead RBC)

Question 20

what are the functions of Ito cells

Answer 20

• involved in tissue fibrosis
• retinol metabolism (stores vitamin A)

Question 21

Answer 21

Question 22

why is the function of the smooth ER in hepatocytes

Answer 22

• contains main enzymes involved in detoxification (cytochrom P450)
• involved in lipid and glycogen metabolism

Question 23

what are the functions of peroxisomes in the hepatocytes

Answer 23

contains enzymes involved in catabolism

Question 24

what are the functions of rough ER in the hepatocytes

Answer 24

• binds ribosomes engaged in translating mRNA to proteins
• involved in proteins and lipid modifications

Question 25

what are the functions of the golgi apparatus in hepatocytes

Answer 25

• associated with protein secretion (important for bile secretion)
• involved in proteins and lipid modification

Question 26

what is the function of the mitochondria in a hepatocyte

Answer 26

• aerobic energy supply (ATP production)

Question 27

what is the function of lysozymes in the hepatocyte

Answer 27

digestion of macromolecules

Question 28

what is the function of glycogen in the hepatocyte

Answer 28

short term storage of glucose

Question 29

what is the function of lipid droplets in the hepatocyte

Answer 29

storage of esterified fatty acids

Question 30

What is the biliary tree?

Answer 30

• Biliary canaliculi (intercellular channels) formed between adjacent hepatocytes form a network => biliary tree
• merge and become bound together by cholangiocytes (epithelial cells which line the entire biliary system) to form canals of hering
• Canals of Hering drain into bile ducts of portal tracts

Question 31

what are the functions of the gall bladder

Answer 31

• storage of bile
• concentrating bile
• release bile

Question 32

what are the functions of bile

Answer 32

• fat digestion
• hepatic excretion of drugs and toxins

Question 33

explain bile ducts and the course of bile through the liver and associated structures

Answer 33

• hepatic ducts drain bile from the liver lobes to the common hepatic duct
• this divides to form the cystic duct which takes bile to the gall bladder and the bile duct which takes bile to the duodenum
• at the duodenum the bile duct joins with one of the pancreatic ducts and then empties into the duodenal lumen at the ampulla of Vater
• within the ampulla is the sphincter of Oddi which prevents backflow of chyme into the ducts
• when the SO is closed, bile fills up the gall bladder but when open bile flows from the liver and gall bladder into the duodenum
• SO and gall bladder are under hormonal and ANS control linked with digestion

Question 34

describe the microscopic appearance of the gall bladder

Answer 34

• fibromuscular sac lined by a simple epithelium which shows numerous folds in the non-distended state

Question 35

explain the flow of blood vs bile in the liver

Answer 35

bile and blood flow have opposite directions

Question 36

explain the difference between the concepts of liver lobules: classic lobules, portal lobules and hepatic acinus

Answer 36

Classical Liver Lobule:

Hexagonal Structure: It has a roughly hexagonal shape, Each lobule has a central vein in the middle. At the corners of the hexagon are the portal triads, which consist of a branch of the hepatic artery, a branch of the portal vein, and a bile duct, liver cells radiate out from the central vein. Sinusoidsrun between the rows of hepatocytes, allowing blood to flow from the portal triads to the central vein.

Portal Lobule: The portal lobule is conceptualized as a triangle with the Portal Triad at the Center and Central Veins at the Corners from three different classical lobules.This concept emphasizes the flow of bile from hepatocytes to the bile duct in the portal triad.
Hepatic Acinus: often visualized as a diamond or oval shape.Divided into three zones based on proximity to the blood supply:
- Zone 1: Closest to the portal triad, receives the most oxygen and nutrients.
- Zone 2: Intermediate zone.
- Zone 3: Closest to the central vein, receives the least oxygen and nutrients.

Question 37

what are the pathological considerations of the hepatic acinus concept

Answer 37

Zone 1 hepatocytes are more susceptible to direct-acting toxicants -> perilobular necrosis.
Zone 3 hepatocytes are more susceptible to hypoxic injury -> centrilobular necrosis
- poor blood flow (e.g. cardiopulmonary disease, less oxygen delivered)
- activity of cytochrome P450 system as it degrades toxic substances (uses oxygen)
- P450 can also produce cytotoxins from non-toxic substrates (eg pyrrolizidine alkaloids)