histology of liver gallbladder and pancreas Flashcards
The liver
subdivided into 4 lobes, right, left, quadrate, and caudate
Receives blood from the spleen, pancreas, and intestine, the first organ that recieves toxic substances and nutrients
Liver function: detox metabolic waste products, destruction of microbes that enter the body thru intestine, synthesis of plasma lipoproteins, synthesis of blood clotting factors, vitamin storage, metabolic functions, destruction of RBCs, synthesis and secretion of bile
cellular organization of the liver
4 functional groups: hepatocytes (arranged as anastomosing plates of cells)
Large vessels: including blood vessels, lymphatic vessels, nerves and bile ducts
Sinusoidal capillaries (sinusoids): line the plates of hepatocytes and are responsible for blood flow through the liver
Connective tissue
The organization of blood supply to the liver is critical for liver function
Hepatic artery carries oxygenated arterial blood into the liver
Hepatic portal vein caries venous blood into the liver
The central veins carry blood away from the liver toward the hepatic veins
Bile ducts transport bile from the liver
Lymphatic vessels carry lymph away from the liver
Hepatic portal arrives from the intestine, pancreas, and spleen. Blood from the intestine contains many nutrients and toxic substances, pancreatic blood contains endocrine secretions including insulin and glucagon, the spleen provides breakdown products of blood cells
Substances in the blood must gain access to the hepatocytes of the liver, arterial capillaries and inlet venules carry blood from the hepatic artey and portal veins int a network of sinusoids
portal triad
Hepatic artery, portal vein, and bile ducts are grouped in a portal triad
Branches of the hepatic artery and hepatic portal vein associate with bile ducts to form the portal triad
Lymphatic vessels are also associated with portal triad
Vessels are supported by CT running thru the portal triad
hepatocytes make up the livery parenchyma
the principle functional cell of the liver is the hepatocyte
Hepatocytes are arranged in anastomosing plates 1-2 cells thick separated by sinusoids
The plates of hepatocytes run from the central vein out toward the portal tirads
hepatocytes are large polygonal epithelial cells
hepatocytes are large polyhedral cells 30um wide that form an epithelium
They are described as having 6 surfaces, 2 face the perisinusoidal space, four face other hepatocytes and the bile canaliculi
Perisinusoidal surfaces represent the basal aspect of the cell, surfaces facing other hepatocytes are lateral and surfaces facing bile canaliculi are apical
Transfer of substances between sinusoids and heptocytes occurs accross the basal surface
Hepatocytes are extremely rich in organelles
have a large spherical nucleus located in the center of the cell, many cells in adults are binucleate and tetraploid, hepatocytes are extremely rich in organelles which reflects metabolic activity (RER and mitochondria, glycogen granules, lipid droplets
Sinusoids (type 3 capillaries) allow the exchange of substances between the blood and hepatocytes
Sinusoids are made of 2 cell types: endothelial cells/sinusoidal cells and sinusoidal macrophages (Kupffer cells)
Kupffer cells are derivatves of monocytes and are involved in the breakdown of senile RBCs
exchange of substances between blood and hepatocytes takes place in the peri sinusoidal space aka the space of disse
Space of disse lies between the basal surface of the hepatocyte and the sinusoid, hepatocytes extend microvili from the basal surface to increase surface area, Stellate (Ito cells/ adipose/lipocytes) cells are commonly found in the perisinusoidal space, major site of vit A storage and synthesize the reticular fibers supporting the liver parenchyma
Reticular fibers surround the hepatic parenchyma
the hepatocytes and sinusoids are surrounded by reticular fibers that are composed of collagen type 3, extending outward from the central vein and is the only CT within the lobule
The reticular network supports the hepatic parenchyma and contributes toward keeing the sinusoids open allowing normal blood flow, it originates from stellate/ITo cells in the space of disse, disrupted during lver disease
The liver acinus
The acinus is lozenge shaped with short axis between 2 adjacent portal triads and teh long axis between 2 central veins
Oxygenated nutrients/toxins rich blood perfuses the portal triad thru the distributing arteries and veins toward the central vein, producing a gradient of nutrients and substances encountered by hepatocytes
the hepatocytes within the acinus are arranged in 3 concentric zones
cells in zone 1 are closest to distributing arteries and veins and are the first to be affected by or to alter the incoming blood
cells in zone 3- ischemia and fat accumulation
the galbladder concentrates and stores bile
bile leaves the liver through the hepatic duct which joins the cystic duct from the gall bladder to form the common bile duct, the common bile duct joins with the pancreatic duct to enter the duodenum
Dilute bile from the liver is shunted into the gall bladder where it is concentrated 5-10x
The presence of lipid in the duodenum induces secretion of CCK stimulates fall bladder contraction and forces concentrated bile into the duodenum
Bile is produced by hepatocytes
hepatocytes actively secrete bile across their apical surface into the bile canaliculi, the bile canaliculi contain ATPases suggesting that bile secretion is an active process, canaliculi join together into small terminal ductules called canals of Herring
bile ducts are made of biliary epithelial cells
biliary epithelial cells form a cuboidal epithelium which forms a ductule, the bile flows in the opposite direction of the blood 9away from the central vein toward the portal triad), bile ducts leads from the portal triad to join the hepatic duct that carries the bile to the gall bladder
The human liver secretes approximately 1 liter of bile a day
Mucosal cells lining the gallbladder actively absorb water from the bile
The human gallbladder is a muscular sac that can store up to 100 mls of bile per day
An empty or distended gallbladder has numerous deep mucosal folds
the mucosa are made up of a simple columnar epithelial cells that closely resemble the absorptive cells of the intestine
They conain short apical microvilli and with basally located nucleus
the action of these cells concentrate bile by actively absorbing water into a capillary rich network in the lamina
