Functional Histology of the Liver Flashcards
Describe the classic hepatic lobule
The hepatic lobule is a hexagonal structure centered around a Central Vein with hepatic triads at each angle on its exterior surface.
How does blood flow through the liver and the lobules?
Blood enters the liver via the hepatic portal vein (75%) and the hepatic artery (25%). These branch into venules and arterioles and (with the bile ducts) form the Hepatic Triads. Blood flows into perilobular capillaries (hepatic sinusoids) within the hepatic lobules where it is filtered by hepatocytes as it progresses towards the Central Vein which leads to the IVC.
How are the hepatic triads, sheets of hepatocytes, endothelial cells, and Kupffer cells organized?
Hepatic triads are located at the angels of the lobules. Sheets of cuboidal hepatocytes radiate out from the central venuole, separated by the perilobular capillaries. The perilobular capillaries are lined with fenestrated endothelial cells with Kupffer cells intermixed alongside. The fenestrated endothelial cells and Kupffer cells are separated from the hepatocytes by the Space of Disse.
Describe the sinusoidal surface of the hepatocytes and the endothelial cells that overlay them.
The sinusoidal surface is the surface that faces the endothelial cells lining the perilobular capillaries. This surface is covered in microvilli which increase the surface area 8-10 fold. The endothelial cells are fenestrated, allowing plasma contents to exit the blood stream and interact with the hepatocytes. There is also a loose collection of reticular fibers between the endothelial cells and hepatocytes to maintain the structure without impeding plasma flow.
How is the structure of the sinusoidal surface of the hepatocytes and the endothelial cells related to their function?
The fenestrations of the endothelial cells are large enough to allow the plasma contents, including chylomicrons and plasma proteins, to pass into the Space of Disse. The plasma contents then encounter the large surface area of the hepatocyte microvilli and interact with the cells. The reticular fibers present in the Space of Disse anchor the cells in place while allowing the plasma contents to freely diffuse.
Where does bile arise from and how is it transported out of the liver?
Bile is created in the hepatocytes from raw components and from bile salts recycled in the hepatoenteric loop (right name??). Bile is then secreted out of the hepatocyte into the bile canaliculi that run between neighboring hepatocytes. These canaliculi are continuous through the sheets of hepatocytes, eventually leading to the Duct of Herring and out to the bile duct.
Name all of the cells of the liver
Hepatocytes
Sinusoidal Endothelial cells
Kupffer cells
Stellate cells
What are the functions of the hepatocytes?
80% of all liver cells.
Carry out the physiologic and metabolic functions of the liver.
Most metabolically versatile cells in the body.
Polyhedral, often bi-nucleated.
Apical pole faces bile front - bile secreted apically.
Basolateral pole faces blood sinusoids - blood components secreted basolaterally (constitutive pathways).
Numerous microvilli on surface for maximum surface area.
What are the functions of the sinusoidal endothelial cells?
Close proximity between hepatocytes and sinusoidal endothelial cells = maximum contact with plasma.
Single fenestrated cell layer, minimizes interference with plasma flow.
Phagocytic, but less active than Kupffer cells.
What are the functions of the Kupffer cells?
Resident liver macrophages.
Live in the sinusoid, intermixed with the endothelium.
Clean up bacteria and debris carried in the blood stream.
What are the functions of the Stellate cells?
Located in the Space of Disse.
Normally take up and store Vitamin A.
Stellate cells transform into fibroblast state in response to liver injury (inflammation/hepatitis??)
Produce Type I Collagen responsible for cirrhosis
Chronic liver injury leads to perpetual activation which gradually impedes the exchange of materials between the hepatocytes and the blood aka cirrhosis.
What is the specific structure of bile canaliculi and the pathway of bile out of the liver?
A large portion of hepatocyte membrane borders each bile canaliculi, and hepatocyte membranes of neighboring cells actually form the walls of the canaliculi. These canaliculi anastomose with those of other cells, carrying bile in the opposite direction of blood flow. In the vicinity of a portal triad, the canliculi meet at the bile duct system proper (Canal of Hering). Bile duct cells, a different cell type that form the boundary of the duct, modify biliary secretion by addition/subtraction of water and electrolytes.
What is the exocrine function of the liver?
Bile secretion
What are the three competing or alternate types of lobular formations?
Classic lobule - hexagonal, arranged around central vein
Portal lobule - Triangular, connecting 3 central veins
Ascinar lobule - Diamond shaped, 2 CV, 2 triads
What is the structure and organizing principle of the Portal Lobule?
Triangular shaped.
3 Central Veins, one at each apex.
Arranged with respect to the flow of bile (exocrine function)
Defines a territory of hepatocytes that drain bile into the interlobular bile duct which is located centrally in a Portal Lobule.
