14 Liver Gall Bladder Pancreas

the Liver

Metabolic funcs: uptake, storage, metabolism & distribution of important nutrients & vitamins; degradation & conjugation of metabolites + potential toxins; iron recycling

Exocrine funcs: production & secretion of bile through bile duct → duodenum

Endocrine: maintaining blood component concentrations, aka synthesis & secretion into the blood of most plasma proteins (albumin, α- & β-globulins)

• liver is highly cellular
• hepatocytes are arranged in plates
• are polygonal & often binucleate
• there's very little CT; only seen around ducts & CT capsule that surrounds the entire organ

• functional unit of the liver, are hexagonal in shape
• corners have portal traids: contain 3 main structures, portal vein, hepatic artery, bile duct
• center of classic lobules is a central vein, which receives processed blood that drains into hepatic veins

• V = central vein
• PT = portal triad

• upper left: bile duct (stains darkest blue/purple)
• bile is produced/works its way from the center of a lobule OUT toward the bile duct (opposite flow as blood)

middle: portal vein - carries nutrient rich, O₂ poor blood to liver

lower right: hepatic artery - carries nutrient poor, O₂ rich blood to liver

all blood mixes, works its way through a sinusoid on its way to the central vein (not pictured) during which its acted on by surrounding hepatocytes

• white space in between hepatocytes: Sinusoids, through which blood flows on its way to the central vein
• endothelial cells lining the Sinusoids are DISCONTINUOUS, allowing hepatocytes access to nutrients/toxic substances present in blood

will go on to join larger veins - called Hepatic Veins - that will eventually go on to join the Inferior Vena Cava

• important space between the sinusoid endothelial cell & Hepatocyte (D in picture)
• reticular fibers are present in this space that slows blood flow so hepatocytes can act on materials in blood

• Macrophages, aka Kupffer cells
• are luminal compared to to sinusoidal endothelium (exist in the sinusoids) & scavenge whatever they need to
• stain darkly
• 

• where Vitamin A is stored in the liver
• are abundant 
• get activated with liver damage → secrete collagen
• cirrhosis is caused by collagen occlusion of sinusoids (by Ito cells)
• 

• BILE
• is made by hepatocytes & transported between then via a Bile Canaliculus 
• 
• needs to eventually collect @ peripheral portal triad area where it can get dumped into bile duct

• 1. Classic
• 2. Portal
• 3. Acinus

• center: central vein
• hexagonal corners: portal tracts
• has metabolic & endocrine functions
• 

• center: bile duct (portal tract)
• triangular corners: central veins
• has exocrine/excretory (waste removal) functions
• exocrine b/c product (bile) secreted toward a 'central' duct
• 

• metabolic unit
• center: incoming blood-signals
• edges: central vein
• by the time blood gets near the CV, it's been depleted of both nutrients & oxygen
• hepatocytes in this region (around CV) are most susceptible to ischemic injury
• 

zone 1, closest to their entry point (cells around the canal between 2 portal tracts)

• storage organ for bile made by hepatocytes
• bile is transported through hepatocytes via canaliculi until it reaches a bile duct
• L & R hepatic ducts converge to form the common hepatic duct
• if the common bile duct opening into the duodenum is closed, bile goes through the cystic duct into the gall bladder for storage

no muscularis mucosa or submucosa

it has a simple columnar epithelium (sans goblet cells*) with a lamina propria underneath & a muscularis externa (that contracts to expels bile into duodenum when signaled)

• individual to Gall Bladder that can help with identification
• really just the lumen but looks like 'glands' due to sectional cuts
• 

• lumen diverticula that penetrate into muscularis externa area
• sacs with fluid in them; a lot is associated with gall stone development
• 

compound made in the duodenum & jejunum that stimulates muscle contraction (muscularis externa) of the gallbladder

• stimulates bicarbonate secretion from bile duct cells themselves
• (helps neutralize chyme in the SI)

• the gall bladder epithelium
• when there are white space between the basolateral spaces of the epithelium, its actively concentrating the bile
• does so by pumping Na+ into spaces, causing water from lumen to enter the spaces (dilating them)
• 

• formation of concretions (calculi/stones) in gallbladder or bile ducts
• major component cholesterol
• factors: female, obesity, Western diet, family history
• are the most common cause of pancreatitis, cholesystitis (when stone blocks duct, any time there's a solution in stasis, can lead to inflammation)

• large, lobulated gland with exocrine & endocrine function
• exocrine secretions are transported through ducts
• endocrine secretions are secreted through fenestrated capillaries directly into the blood stream

• grape-like functional units whose ~45 secretory cells synthesize pancreatic enzymes
• each acinar cell has zymogens made in the basal RER, glycosylated & packaged in the Golgi, stored in the apical cytoplasm until hormones signal for their release via exocytosis into intralobular ducts

• 1. protein degrading enzymes (trypsinogen, carboxypeptidases,
• elastase)
• 2. carbohydrate degrading enzymes (amylase)
• 3. nucleic acid degrading enzymes (ribonuclease, deoxyribonuclease)
• zymogens are activated by trypsinogen, which itself is activated by enterokinase in the small intestine

• 
• LEFT = intra/intercalated: diluting the concentrated enzymes (clear in H&E); exist within lobules
• are much smaller

• RIGHT = inter ducts: transporting diluted enzymes through a system of ducts; exist embedded in CT between lobules
• interlobular ducts have simple cuboidal epithelium

• peptide hormone released from enteroendocrine cells in duodenum that:
• causes the release of zymogen granules from the acinar cells (pancreas)
• causes emptying of the gall bladder

• peptide hormone released from enteroendocrine cells in duodenum that:
• causes the intralobular ducts to secrete a bicarbonate-rich solution that dilutes released zymogens (pancreas)
• stimulates the cells of the bile duct to release an aqueous solution that dilutes the concentrated bile

compact clusters of epithelial cells richly vascularized with fenestrated capillaries (into which the cells secrete their hormones)

• 1. beta cells: most, secrete insulin (cellular uptake of glucose from blood)
• 2. alpha cells: secrete glucagon (cellular release of glucose into the blood)
• 3. delta cells: produce somatostatin (modulates secretion of insulin & glucagon)

• magenta cells = acini: zymogens secreted through ducts via exocrine mechanism
• light pink clumps = islets: hormones secreted through capillaries via endocrine mechanism

• Intralobular duct cell located in the middle of an acinus
• looks lighter than the surrounding acinus cells
• 

• in addition to transborting Cl-, CFTR also moves bicarbonate
• with a mutated channel ductal bicarbonate secretion is reduced
• the enzyme solution produced = too viscous
• this causes a backup of enzymes release from pancreas → inflammation, scarring
• ducts fill & form cysts (disease name)
• glycocalyx in SI is inefficient due to reduced enzyme adsorption -malabsorption results