Functional microanatomy of the liver Flashcards
deck complete
general anatomical features of the liver
large, lobulated exocrine and blood processing gland, with vessels and ducts entering and leaving at the porta
enclosed by a thin collagen tissue capsule, mostly covered by the mesothelium
collagen tissue of the branching vascular system provides gross support
parenchymal cells are supported by fien reticular fibres
what does the internal structure of the liver evolve around
several vessels entering or leaving the organ
portal vein
brings food rich blood from the gut
hepatic artery
bring arterial blood
hepatic veins
takes away processed blood into vena cava
lymphatics
take away lymph
hepatic ducts
remove bile to gallbladder and gut
liver blood supply
25% from hepatic artery - arterial
75% from portal vein - food rich from gut
nerve supply of liver
sympathetic and parasympathetic supply of perivascular structures, very little and sinusoidal level
first impression of liver microanatomy
uniform mass of large glandular cells throughout liver substance
closer examination of liver microanatomy
cells arranged in perforated plates, one cell wide
between plates are sinusoidal blood channels lined by endothelial cells
what are scattered in the glandular mass
blood vessels, both alone and accompanied by other vessels
distribution of these vessels defines or marks out classic hepatic lobules
central vein/terminal hepatic venule
very thin wall
lies in centre of lobule with sinusoids converging towards and opening into it
sublobular/intercalated vein
thicker wall
lies alone at periphery of lobule
branch of portal vein
at periphery of lobule
accompanied by one or more small hepatic arteries/arterioles, one or more bile ducts/ductules lined by cuboidal epithelium, and lymphatics
what constitutes a portal triad
portal vein, artery and bile duct - the area which they lie in is a portal area
hepatic lobular blood flow is what 3 things
1 - from branches of portal vein and hepatic artery, from periphery towards centre
2 - in the sinusoids between cell plates
3 - blood collected in central veins goes to sublobular veins, then to collecting veins, and then hepatic veins leaving the liver
what is intralobular bile flow
from the lobules centre towards the peripheral bile ducts, and runs within any one cell plate, between the liver cells in bile canaliculi
liver acinus
represents as a functional unit comprising parts of 3 or so lobules. explains the differences in exposure to the blood supply among various parts of lobules
what zones are the liver acini divided into
1 - periportal
2 - intermediate
3 - perivenous (close to the central vein)
features of the periportal zone of the liver acinus
roughly spheroid
isolated from periportal zones of adjacent acini
current concepts of hepatic microarchitecture
1 - primary lobule territory
2 - anatomical details: conical 3D configuration
what are liver sinusoids
low pressure vascular channels that receive blood from terminal branches of the hepatic artery and portal vein at the periphery of lobules and deliver it into central veins
what are sinusoids lined with
fenestrated epithelial cells which are loosely attached. they hold phagocytic Kupffer cells
how are fenestrated epithelial lining cells attached
loosely attached, rest of microvilli of underlying hepatic cells, without basal lamina intervening
what is formed by fenestrated epithelial lining cells and what does this result in
forms a sieve plate. means plasma can pass through into perisinusoidal space of Disse to interact with hepatocytes. some fluid may pass to periphery of lobule to be collected as lymph
what does Disse’s space contain
ECM material, no visible basal lamina
function and location of stellate cells
scarce, fat storing
lie outside endothelial cells
store vitamin A
respond to variety of insults by making collagen and causing cirrhosis (fibrosis)
what 3 things does the sinusoidal wall provide for
1 - blood cleansing, e.g. of gut bacterial toxins
2 - haemopoiesis in the embryo
3 - bringing plasma into intimate contact with hepatic cell for many metabolic functions of storage, transformations, syntheses, regulation of plasma concentration, detoxification, production of bile, and assisting defence by producing acute-phase proteins
what are hepatocytes
the main functional cell of the liver. 80% of liver mass
3D arrangement of hepatocytes
arranged in plates that anastomose with each other
polygonal in shape, sides in contact with either sinusoids of neighbouring hepatocytes
what forms bile canaliculi
modified portions of the lateral faces of hepatocytes. microvilli present abundantly on sinusoidal faces and project sparsely into bile canaliculi
hepatocyte nuclei
distinctly round, with one or two prominent nucleoli. majority have single nucleus but binucleate cells are common
features of hepatocytes/hepatic cells
large spheroid nucleus with membrane pores and ribosomes on outer membrane
extensive granular ER
smooth ER
mitochondria
actin and other filaments near bile canaliculi and elsewhere
cell membrane projecting microvilli into space of Disse - held firmly to adjacent cells
Golgi body and lysosomes lying near canaliculis
peroxisomes
glycogen granules stored in association with smooth ER
fat droplets occurring briefly after meals
lipofuscin or aging pigment
granular endoplasmic reticulum
protein synthesis for enzymes, plasma proteins, etc
smooth endoplasmic reticulum
steroid hormone and cholesterol metabolism, lipids taken in, processed and secreted in a way very like enterocytes, SER carries enzymes for detoxification
mitochondria
oxidative and other enzymes
system of canaliculi
between hepatic cells
leads to canals of hering/cholangioles
both have hepatocytes and bile duct cells in their walls
bile ducts
epithelium changes to columnar mucous cells and extrahepatically the ducts acquire smooth muscle as well as collagen tissue
cystic ducts
allow reflux into gallbladder when sphincter of Oddi at duodenal outlet of the common bile duct is closed
bile pathways
system of canaliculi > canals of hering/cholangioles > bile ductules > bile ducts > cystic duct
features of bile ductules and where they are found
in portal areas
small cuboidal cells
firmly held by membrane interdigitations and junctional complexes
few luminal microvilli
formation of lymph
formed by filtration of plasma into spaces of Disse as blood flows through sinusoids
lymph percolates between space of Disse and portal tracts then lymphatics form that run along portal vessels and biliary ducts
