major functions of the liver.
- Absorption and processing: carbs, proteins, lipds
- synthesis and endocrine secretion: plasma p, coagulation factors, metals, lipid transport proteins, cholesterol
- detox and degredation
- conversion, modification of hormones
- phagocytosis of antigens, old RBC by Kupffer cells
- exocrine secretion of bilirubin, bile salts
What encloses the liver?
dense irregular connective tissue and a layer of mesothelium
What is at each corner of a lobule?
portal canal …
portal “triad” = hepatic portal vein, hepatic artery, bile duct, lymphatic, nerves
describe blood flow
portal vein branches over lateral surfaces –> distributing veins –> inlet venules
hepatic artery branches over lateral surface –> distributing arteries –> inlet arterioles
blood mixes and enters central vein then sublobular vein then hepatic vein
what supports each lobule?
connective tissue…
within lobule is reticular fiber (coll III)
(also connective tissue in portal canal that supports liver)
describe the 3D structure of a lobule
six lateral faces
two basal faces
single apex
Name the cells in the sinusoids and their function
- kuppfer cells - phagocytose antigens and old RBC
- pit cell - NK innate immune system lymphocyte
- endothelial cells - fenestrations/discontinuous allows plasma to move into space between hepatocytes and sinusoids.
- lipcytes - lipid droplets that store vitA (essential but can be toxic)
Structure function of space of Disse
filled with only blood plasma (no RBC or platelets)
reticular fibers support walls of sinusoids
nutrients absorbed by microvilli at hepatocyte base
endocrine p secretions
Surfaces of hepatocyte?
two basal surfaces - microvilli for absorption, secrete endocrine products,
6 lateral surfaces - secrete endocrine products, uptake of nutrients
apical surface - 1/2 of bile canaliculus, excocrine secretion of bile
Bile flow?
bile canaliculi into bile ductules into canals of Hering…
merge and form bile ducts in the portal canals into gall bladder then into small intestine…
all this called the biliary tree
linings of canals of Hering?
simple cuboidal epithelium.
maybe stem cells for liver regeneration.
liver cells divide infrequently, but when damaged rapid mitosis occurs.
cells that line biliary tree post-canal of Hering?
cholangiocytes
cell surface of hepatocytes?
sides of bile canaliculus lines with junctional complex (tight junction, adhesion belt, spot desmosomes)…
hold apical and lateral surface together…
microvilli on apical surface
8 organells of hepatocyte?
- RER - membrane and secreted p synthesis (albumin, protein component of lipoprotein)
- SER - lipid syn of lipoproteins; detox of ammonia, alcohol, anesthetics; syn/deg of glycogen (assoc. with SER)
- mitos - energy
- Golgi - mostly near bile canaliculus for bile secretion, others by sinusoids for proessing/packaging of secreted p
- peroxisomes - H2O2 breakdown, ethanol oxidation, alcohol dehydrogenase
- lysosomes - breakdown of endocytosed substanced and organells, Fe storage
- Terminal web - apical. actin, myosin, other p. actin and mysoin interaction allows for contractions along canaliculi to move bile toward portal canal.
- lipid droplets - cholesterol and lipop storage
liver anicus layout
2 central canals and 2 portal canals (like two triangles)
3 zones of liver acinus
Zone 1 - blood rich in O2, nutrients; syn. glycogen and plasma p; last to die
Zone 2 - blood has less O2, nutrients
Zone 3 - blood very low in O2, nutrients; alcohol, drug detox; central necrosis (cell death near central canal); first to show steatosis (fat accumulation from reduced blood flow)
secretions in bile
bile salts, bile pigments, cholesterol, phospholipids, electrolytes
enterohepatic circulation?
bile substance produced by hepatocytes –> released to duodenum –> recovered in ileum (some secreted in feces) –> enters intestinal capilaries –> follows portal vein to liver
function of bile?
emulsify lipids in small intestine
keep cholesterol and phospholipids of bile in solution
RBC breakdown and bilirubin?
RBC breaksdown giving bile pigments (mainly bilirubin)
heme broken down by macrophages in spleen and Kupffer cells in liver
hepatocytes transport bilirubin into the bile and is released in feces
clinical relevance of bilirubin?
jaundice:
accumulation of bilirubin in blood and tissues
skin and sclerae appear yellow
from…overactive destruction of erythrocytes, impaired bilirubin processing, inadequate bile draining from obstruction
three layers of gall bladder and structure
- mucosa - epithelium, lamina propria
- muscularis externa - random arrangement of smooth muscle
- fibrosa or serosa contain large blood vessels, lympathics, adipose tissue
GB mucosa epithelium and lamina propria
epithelium - simple columnar epi with microvilli; apical junctional complexes, mitos; lateral interdigitations
lamina propria - loose connective tissue, fenestrated capillaries, small venules, lymphocytes, plasma cells
fibrose vs. serosa
fibrosa - where gallbladder attached to liver, no intervening peritoneum
serosa - parts where GB covered peritoneum (mesothelium)
