liver anatomy and histology Flashcards
describe gross anatomy of the liver
- 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
discuss blood supply to the liver
- 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
describe blood drainage from the liver
hepatic veins drain into caudal vena cava
outline how blood courses through the liver
- hepatic portal vein/hepatic artery brings blood to liver
- blood goes into sinusoids
- central veins
- hepatic veins
- caudal vena cava
what makes the regeneration of the liver so effective and when does this ger complicated
- 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
what is hepatic parenchyma
functional part of liver made of hepatocytes which are responsible for hepatic function
describe the conformation of the classic liver lobule
- hepatocytes are organized in radial cords forming polyhedral prisms with portal triads at each of the corners and a single central vein
Describe the histology of the hepatic stroma
Thin fibres of connective tissue (reticulin fibres + collagen type III) forms thin layer => ‘floppy’
list the components of the portal tract/triad in classic liver lobules
- 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
what is the portal canal
space containing the portal tract
what is a hepatic sinusoid
fenestrated blood vessel running along the plates of hepatocytes
- portal and arterial heptaic blood mix here
What is the function of the central vein in a classic liver lobule?
receive blood from sinusoids and return it to circulation via hepatic vein
What are the cell types found in the liver?
- hepatocytes
- enothelial cells
- kupffer cells (sinusoidal macrophages)
- hepatic stellate cells (Ito cells
describe the morphology of hepatocytes
polyhedral with round nucleus and prominent nucleolus
describe the morphology of kupffer cells
macrophage like
describe the morphology of Ito cells
contain big intracytoplasmic vacuoles
what are the functions of hepatocytes
- metabolise and store materials absorbed from the small intestine
- secrete bile
what are the functions of kupffer cells
- defend against vascular carried pathogens
- remove debris (dead RBC)
what are the functions of Ito cells
- involved in tissue fibrosis
- retinol metabolism (stores vitamin A)
why is the function of the smooth ER in hepatocytes
- contains main enzymes involved in detoxification (cytochrom P450)
- involved in lipid and glycogen metabolism
what are the functions of peroxisomes in the hepatocytes
contains enzymes involved in catabolism
what are the functions of rough ER in the hepatocytes
- binds ribosomes engaged in translating mRNA to proteins
- involved in proteins and lipid modifications
what are the functions of the golgi apparatus in hepatocytes
- associated with protein secretion (important for bile secretion)
- involved in proteins and lipid modification
what is the function of the mitochondria in a hepatocyte
- aerobic energy supply (ATP production)
what is the function of lysozymes in the hepatocyte
digestion of macromolecules
what is the function of glycogen in the hepatocyte
short term storage of glucose
what is the function of lipid droplets in the hepatocyte
storage of esterified fatty acids
What is the biliary tree?
- 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
what are the functions of the gall bladder
- storage of bile
- concentrating bile
- release bile
what are the functions of bile
- fat digestion
- hepatic excretion of drugs and toxins
explain bile ducts and the course of bile through the liver and associated structures
- 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
describe the microscopic appearance of the gall bladder
- fibromuscular sac lined by a simple epithelium which shows numerous folds in the non-distended state
explain the flow of blood vs bile in the liver
bile and blood flow have opposite directions
explain the difference between the concepts of liver lobules: classic lobules, portal lobules and hepatic acinus
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.
what are the pathological considerations of the hepatic acinus concept
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)
