Histo: liver/gallbladder Flashcards
liver peritoneum?
simple squamous epithelium
portal system of liver?
systemic capillaries –> veins –> portal vein –> venules –> capillaries –> venules –> small veins –> hepatic v –> IVC
hepatic triad?
portal vein, hepatic artery, bile ductule, lymph vessel
liver lobule?
blood enters at periphery of lobule, percolates via sinusoids through the lobule and leaves via the central vein.
- bile travels counter-current and leaves at periphery of lobule
Muralium
= walls of hepatocytes, which radiate around the central vein and form the vascular sinusoidal channels where the blood drains to reach back to the central vein.
hepatocytes
- large mono/binucleated cells that are often polypoloid
- forms simple muralium
- 3 surfaces where it comes into contact
3 surfaces in contact with sinusoids
- sinusoidal: a cellular gap that is discontinuous capillary eptihelium with gaps between cells that allows trafficking b/w capillary and hepatocytes - capillaries are surrounded by “space of Disse”
- basolateral surface: where hepatocytes encounter other hepatocytes
- canalicular surcae: small channel where bile is carried to duct system b/w adjacent hepatocytes
hepatic sinusoids
A liver sinusoid is a type of blood vessel (with discontinuous basal lamina) that serves as a location for the oxygen-rich blood from the hepatic artery and the nutrient-rich blood from the portal vein
Hepatocytes are separated from the sinusoids by the space of Disse.
Kupffer cells are located inside the sinusoids and can take up and destroy foreign material such as bacteria.
Liver stroma
“scaffolding of liver cells” - supported by the vessels and reticular fibers
- stroma is altered in diseases such as hepatic fibrosis and hepatic cirrhosis - where the CT elements increase in the parenchyma
3 types of liver lobules?
classic: endocrine
portal lobule: exocrine
portal acinus: acinar lobule based on metabolic zonation
classic lobule
endocrine- secretion of hormones into bloodstream
- polygonal shape with portal canals at periphery and veins at the center
- products synthesized and secreted into blood & used elsewhere: fibrinogen, albumin, glucose
portal lobule
exocrine: secretion of products into ducts
- triangular shape with portal canal in center and central vein at peripheral apices
- synthesizes and secretes bile into a duct
Portal acinus
“acinar lobule” or “Rappaport’s lobule”
- oblong/oval shaped running fro central vein to central vein length wise, and portal triad to portal triad
- refelects gradient of metabolic activity in the liver
- useful in describing hepatic regeneration, development of cirrhosis, centro-lobular necrosis
Zones of portal acinus
zone 1 (periportal zone):receives blood with highest concentration of nutrients/oxygen. last to die and first to regenerate. more metabolism happens here.
zone 2 (mid-region):receives blood of intermediate “quality“ (from zone 1)
zone 3 (centrolobular zone): receives blood with lowest nutrient/oxygen content (from zone 2). first cells to die in centrolobular necrosis
hepatectomy
- liver holds great capacity for regeneration
- if liver lobule taken, hepatocytes of all zones will regnerate and liver will recover, due to polypoloidy nature
zonal damage
seen in pathology, such as hepatic cirrhosis: selective regeneration of damaged zones as opposed to regeneration in all zones
hepatic cirrhosis
abnormal regeneration due to CT elements not cooperating –> altered hepatic structure and compromised parenchymal function
mitochondria
many in hepatocytes
1000-2000 per cell
self-replicating by budding
function in : ox phos, urea cycle, TCA, lipid oxid.
lysosomes
function in catabolism (breaking down) of substances
- autophagy = internal structures
- heterophagy = external substances
low pH of 4-5 maintained via proton pump
- enyzmes synthesized in rER and transported to Golgi
- receptor–ligand complexes turned over in lysosome
- liver is target for numerous hormones endocrine receptors: growth hormone, prolactin, insulin, glucagon, NE.
lysosomal disease
- absence of specific lysosomal enzyme
- often affects lipid production
ex. Tay-Sachs disease, metachromatic leukodystrophy, type II glycogenesis
rER and golgi
plasma proteins (albumin, prothrombin, fibrinogen etc.) are synthesized on rough endoplasmic reticulum. Proteins pass through Golgi not stored secretion granules in liver. proteins are secreted in small clear vesicles
VLDL (very low density lipoproteins) transport
apoprotein for lipoproteins is synthesized in rER
complete formation of VLDL requires sER to converted from chylomicrons
smooth ER
synthesizes cholesterol and phospholipids
- esterification of FFA –> triglycerides
- detoxification/metabolism of drugs
glycogen
stored in rosettes around sER
- enzymes for glycogenolysis are membrane bound
peroxisomes
- degradatory membrane bound microbodies
- oxidize substrates using molecular O2 and H2O2
cytoskeletal elements of hepatocytes
Microtubules: vesicular transport
Microfilaments: important in bile flow. submembranous and pericannilicular location
Intermediate filaments: submembranous and pericannilicular location. seen in variety of hepatic diseases e.g. cirrhosis & cholestatic conditions
hepatic sinusoids
discontinuous wall with gaps b/w adjacent cells of basal lamina
- allows easy access of blood to hepatocytes
- excludes cellular elements from space of Disse
non-hepatocyte sinusoidal cells
endothelial cells (fenestrated) Kupffer cells (mono-nuclear phagocytes) fibroblasts lipocyte (Ito cell) hematopoetic cells during fetal life
endothelial cells
(48% of cells) fenestrated, and w/o diaphragms in humans no pericytes basal lamina indistinct type IV collagen and laminin detectable
fibroblasts
reticular fiber synthesis with type III collagen
Kupffer cells
fixed macrophage of sinusoids (40% of cells)
- have Fc and C’ receptors on their surface
- phagocytose immune complexes, bacteria, non-immune particulates
- bind & degrade hemoglobin to bilirubin: shared function with splenic phagocytes
- highly toxic in high (unbound) concentrations
- transported to hepatocyte for further processing
- can take over RBC degradation function of the spleen
- processes & presents antigen
Ito cells
hepatic lipocyte (fat cell) ~10% of non-hepatocyte cell
lipid droplets characteristic feature
- vitamin A rapidly taken up and stored in lipid droplet
- take up lipophylic/membranolytic molecules which damage lysosomes
bile
- necessary for solubilization/absorption of intestinal fat
- provides main pathway for excretion of cholesterol
- eliminates many toxins, including bilirubin
- constituents of bile include: electrolytes (Na+,K+,Ca2+,Mg2+,Cl-,HCO3-), bile acids, cholesterol conjugates, bilirubin-glucuronide
flow of bile
intrahepatic channels: bile canaliculus –> terminal ductules –> interlobular bile ducts –>
extrahepatic ducts: (right/left hepatic ducts –> proper hepatic duct –> cystic duct –> common bile duct)
bile canaliculus
- sealed by zonula occludens & desmosomes
- Golgi & sER oriented toward bile canaliculus
terminal ductules
transition from canaliculus to interlobular bile ducts
- basal surface attached to hepatocytes
- flattened to cuboidal epithelium
- bicarbonate-secreting pinocytotic vesicles modify bile
interlobular bile ducts
cuboidal to columnar epithelium
- surrounded by elastic and collagen connective tissue
- may modify bile by additional bicarbonate secretion
- surrounded by smooth muscle at porta hepatis
- narrowing of ducts
extrahepatic bile ducts
(right, left, proper hepatic ducts
- tall columnar cells with occasional mucous cells
- general plan similar to gut: (mucosa, submucosa, muscularis, adventia)
cystic duct
emerges from gallbladder neck
- neck twists, throwing spiral fold into mucosa
- folding persists in cystic duct
common bile duct
structure of duct is similar to hepatic ducts
-difference: circumferential smooth muscle sphincter present - known as sphincter of Boyden- located prior to junction with pancreatic duct
gallbladder
filled: surface even
empty: decussating folds/ruggae
Mucosa:
- simple columnar epithelium with microvili (suggest absorptive purpose - extracts water, inorganic salts and electrolytes)
- Rokintansky-Aschoff Crypts (invaginations increasing surface area)
- mucous glands (at neck of gallbladder)
Lamina Propria: thin layer of dense irregular CT -numerous small blood vessels -numerous small lymphatic vessels -no muscularis mucosa
NO SUBMUCOSA IN GALL BLADDER
Tunica Muscularis: smooth muscle layer with some collagen and elastic fibers
Serosa: thick layer of dense irregular CT with vv. and lymphatics
Secretin, CCK
secretory stimulus from gut enteroendocrine cell
- secretin - induces biliary bicarbonate and H20 secretion
- cholecystokinin (CCK ) - induces gall bladder contraction
