Liver, Gall bladder, Pancreas
LIVER
- Control center for the digestive system
- Largest gland in the body
 Secretes bile
- Major metabolizing and detoxifying organ
- Hepatic blood flow
 Unique dual afferent blood supply
o Receives oxygenated blood via the hepatic artery
 Hepatic arterial tree
- Right and left hepatic arteries deliver highly oxygenated blood to the liver and
account for 20-25% of total afferent blood volume
o Receives nutrient-rich and relatively oxygen-poor blood from the portal vein
 Delivers ~75% of afferent blood volume to the liver
 This blood has already passed through the GI, spleen, and pancreas
 Nutrient (amino acids, glucose, lipids) and hormone (insulin, glucagon) rich
o When there is a lack of oxygen to the liver, hepatocytes around the hepatic artery remain alive,
while hepatocytes around the central vein die
 Arterial and venous blood mixes in hepatic sinusoids (equivalent of a capillary bed)
o Lined by a discontinuous (fenestrated) endothelium that facilitates transfer of large complex
molecules from the liver into the circulation
o Blood leaves the sinusoids to flow into the central vein (tributary of the hepatic vein)
- Hepatic anatomy
 Glisson’s Capsule
o Encapsulates liver
o Composed of collagen, fibroblasts, smooth muscle cells, small blood vessels and lymphatics
o Invaginates at the hilus &becomes continuous with intrahepatic portal connective tissue
o Encases branches of the hepatic artery, portal vein, bile duct and lymphatic channels of the
portal triads (portal tracts)
 Exhibits lobular unit anatomy with well-defined, hexagonal morphologic borders
o Portal tracts at the periphery
o Branches of the hepatic artery and portal vein travel in portal canals at the periphery to supply
blood to the sinusoids, which are drained by a central vein
 Periportal zone – Tissue closest to the blood supply (oxygen-richest)
 Central (centrilobular) zone – Tissue closest to the central vein (oxygen-poorest)
 Mid-zone – Tissues in between the periportal and central zones
Liver acinus
Liver lobule
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Exhibits a hepatic acinous architecture that originates from the blood flow patterns
o Composed of three poorly-defined concentric regions surrounding a central distributing artery
 Zone 1 – Oxygen-richest
 Zone 2
 Zone 3 – Outer-most layer extends as far as the central vein (oxygen poorest)
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Bile duct and canaliculi
 Transport bile out of the liver
o Hepatocytes absorb bilirubin from blood, conjugate and secrete into bile canaliculi
 Canaliculi are minute spaces between hepatocytes formed by tight junctions
o Bile flows from canaliculi to bile ductules (cholangioles)
 Ductules are lined by simple cuboidal epithelium
- Epithelial cells are called cholangiocytes
 Ductules transition into interlobular bile ducts
- Lined by simple cuboidal or columnar epithelium and
 Interlobular bile ducts flow into intrahepatic and hepatic duct
Cells of liver parenchyma
 Hepatocytes
o 80% of cell population
o Arranged in hepatic cords or plates
o Large polyhedral cells
o Round, centrally-located nuclei
 Frequently polyploidy (>1 nucleus)
o Specialized surface depending on cell orientation
 Microvillous surfaces face perisinusoidal space
 Canalicular surfaces face border bile canaliculi
 Sinusoidal endothelial cells
Hepatic sinusoids
o Line fenestrated wall of hepatic sinusoids
 Endothelial cell fenestrations prevent RBCs but
allow plasma to pass into the Space of Disse in order to contact hepatocyte microvilli
o Separated from the hepatocytes by an interstitial, perisinusoidal space (Space of Disse)
 Space is important because anything there has direct contact with hepatocytes
 Space pathology (e.g. fibrosis) will prevent normal contact of plasma with hepatocytes
Sinusoidal endothelial cells
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Space of Disse
Stellate cells
Ito cells (stellate cells)
o Located in the space of Disse
o Involved in production of extracellular matrix components found within the Space of Disse
o Secrete cytokines (inflammatory mediators) important in liver maintenance, growth, and repair
o Major function when quiescent
 Storage of Vitamin A and other lipid-soluble vitamins
Kupffer cells
o Located in hepatic sinusoids
o Resident liver macrophages responsible for phagocytosis
 Phagocytose bacteria and particulate matter
 Degrade bacterial endotoxin
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Remove damaged RBCs and other cellular molecules
 Contain iron from phagocytosed RBCs
 Contain lipofuscin and ceroid from lipid
metabolism
Secrete cytokines
Functions as antigen-presenting cells
Involved in tumor cell surveillance
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Kupffer cells
GALL BALDDER
- Concentrates bile via coupled active transport of salt and water
 Epithelial cells transport Na+, Cl-, and HC03- ions from cytoplasm into intercellular space, which
creates an osmotic gradient that encourages water to move into the intracellular space
- Microanatomy
 Tunica mucosa
o Very regular simple columnar epithelium
o No goblet cells or glands
 Deep folds of the mucosa sometimes look like "glands," but they really are parts of the
lumen that disappear on distention and have no secretory activity
 Propria submucosal
 Lamina propria (small)
 Tunica muscularis (thin and stringy)
 Tunica adventitia (dense CT)
o Continuous with Glisson’s capsule of the liver
 No muscularis mucosae or submucosa
PANCREAS
- Has both exocrine and endocrine functions
 Pancreas is mostly composed of exocrine tissue
o Synthesize the bulk of the digestive enzymes
needed by the intestines, that travel via a duct
system to the duodenum
o Impairment of this function leads to maldigestion,
malabsorption, and eventual death
 Consequently, pancreatic inflammation
and cancer are quite lethal
 Endocrine tissue
o Consists of Islets of Langerhans scattered
throughout exocrine tissue
Pancreas
o Endocrine products enter blood directly
- Anatomy of Exocrine Pancreas
 Acinar tissue
o Basic secretory unit is the acinus cell
 Acinar cells arranged into blind-ended acini (like in other glands)
 Cells have a deeply basophilic basal region
- Due to presence of large amounts of rER
 Cells have an eosinophilic apical region
- Contains distinct zymogen granules
 Precursor forms of digestive enzymes
 Granule membranes fuse with the plasma membrane and contents are
released into ducts via exocytosis
o Secretory cells are grouped around a small lumen into which secretions are released
 Secretory product is stored in vesicles (derived from the Golgi apparatus) and held in
the apical cytoplasm until a signal is received to release them
 Once the signal is received, inactive secretory products are released into ducts
 Secretory products become activated when they reach the intestine
- The release of active forms into ducts would destroy pancreatic tissue
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Ducts
o Duct system begins in the acinus (unique feature)
o First part of the duct system is lined by small centroacinar cells
o Centroacinar cells form intercalated ducts
 Lined by low columnar or cuboidal epithelium
o Intercalated ducts empty into interlobular ducts
 Lined by a columnar epithelium
o Interlobular ducts empty into the main pancreatic duct
 Lined by a tall columnar epithelium
Endocrine pancreas
o Islets of Langerhans
 Regions of lighter-staining tissue scattered throughout exocrine tissue
 Demarcated by very fine CT fibrils
 Well vascularized (as you would expect in any endocrine organ)
 Contain various cell types
- Mostly (beta) β-cells – secrete insulin
- (Alpha) α-cells – secrete glucagon
- (Delta) δ-cells – secrete somatostatin
- Other islet cells secrete hormones that include pancreatic polypeptide,
vasoactive intestinal peptide, secretin, and motilin
 All of the individual islet cells islets look the same
Endocrine pancreas
Exocrine pancreas