SDL 2 - Histology of the Liver, Gallbladder, and Pancreas Flashcards
What is the surface of the liver covered by?
Thin connective tissue capsule = Glisson’s capsule
What is a liver lobule?
Basic functional unit of the liver
What are the 4 major components of a liver lobule? What is the architectural organization based on?
What is the pathway of blood through these?
- Portal triad***: hepatic artery, hepatic vein, and bile ductule
- Central vein*** (in center of lobule)
- Hepatic plates: made of hepatocytes (1 or 2 cells thick)
- FENESTRATED sinusoids (separating the plates)
Pathway: branches of portal vein and hepatic artery => sinusoids => central vein => sublobular veins => hepatic veins => IVC
Label liver lobule.
What is this?
Liver lobule
3 ways to classify liver lobules?
- Classic Hepatic Lobule: the point of focus is the central vein (blood flow perspective). Corners are formed by each of the portal triads
- Portal Lobule: the point of focus is the portal triad (bile/lymph flow perspective). From this perspective, the liver is divided in triangles, each with a portal triad at its center and a central vein at each of its three corners
- Hepatic Acinus of Rappaport (important concept from a pathologist’s perspective). The points of focus are the distribution of branches of blood vessels in the lobule (2 corners are CVs and 2 corners are portal triads) => changes in the oxygen, nutrient and toxin content of blood flowing through the sinusoid => follows the blood flow along sinusoids to the central veins and the bile flow from hepatocytes to the bile duct.
What are the 3 zones of hepatocyte function within a hepatocyte acinus? 2 names for each
What do these depend on?
The variable proximity of hepatocytes to the vascular backbone results in hepatocellular heterogeneity and the identification of three zones:
Zone 1 (periportal) - closest to distributing vessels; maximum availability of oxygen and nutrients; higher metabolic rate; larger glycogen and lipid stores; more susceptible to damage by blood-brone toxins; will survive insults better; will regenerate faster
Zone 2 (midzonal) - intermediate
Zone 3 (centrilobular) - furthermost from distributing vessels (i.e. closest to central vein); lowest availability of oxygen and nutrients; often the first to die
Clinical significance of zones of hepatocyte function within the hepatocyte acinus?
Many hepatic injuries, and hepatocellular function exhibit zonal distribution patterns
Describe the biliary system of the liver.
Begins at the hepatocyte parenchymal cell level => portions of the plasmalemmma of the hepatocyte indent to form small channels called bile canaliculi which are sealed via tight junctions to produce impermeable seals => these merge to form canals of Hering at the periphery of the lobules => limiting plate => enter small terminal ductules => enter larger ducts in interlobular septum => ducts follow the segmental anatomy of the vascular supply (in reverse direction) => enter bile ducts in portal triad => larger ducts to go to gallbladder
What are the intrahepatic biliary ducts of the liver biliary system lined by?
Cuboidal epithelium
Pathway of lymph in liver lobules?
Fenestrations in sinusoidal endothelium => space of Disse => direction counter to blood flow in sinusoids => enters lymphatics that accompany portal triads and at interlobular septa at the periphery of the lobules
Where are the ANS nerves found in the liver?
In connective tissue around portal triads, throughout the lobules, and apposed to hepatocytes in the space of Disse
Describe the sinusoids of the liver.
Lined with discontinuous endothelium, without a basal lamina (just reticular fiber support)
What is the space of Disse of liver lobules?
Subsinusoidal space that bathes hepatocytes with sinusoidal plasma (arterial and venous blood) and initiates lymph formation
2 cells within liver sinusoids? Describe each. 3 names for second type.
- Kupffer cells: between endothelial cells (incorporated into lining), resident macropages that are there for surveillance and response
- Lipocytes = ito cells = stellate cells: store lipids and vitamin A as retinyl esters
What is the limiting plate of the liver lobules? What penetrates it?
Located at the periphery of the lobule, the hepatic cells surround the circumference of the lobule forming a nearly continuous wall of hepatocytes against the interlobular septum. Only tiny branches of the hepatic artery, portal vein, and bile ducts penetrate
4 functions of the hepatocytes?
- Protein synthesis
- Metabolism – lipids and glucose/glycogen for storage and intermediary biochemical pathways e.g. converts ammonia to urea, conjugates bilirubin
- Bile secretion
- Detoxification including drugs, e.g. cytochrome P450
Describe the microscopic structure of hepatocytes.
- Large polyhedral parenchymal cells
- One or two nucleoli (some of the nuclei are larger with polyploid chromosome numbers)
- Eosinophilic cytoplasm with abundant mitochondria and other organelles to process materials absorbed from space of Disse
- Plasma membrane:
- the sinusoidal face has numerous microvilli extending into the space of Disse – increases surface area X6.
- between hepatocytes there are tight and gap junctions
- RER produces plasma proteins
- SER for bilirubin conjugation, bile salt synthesis, detoxification
- Golgi packages proteins for release into space of Disse.
- Peroxisomes contain oxidases & catalases
Describe the capacity of the liver to regenerate?
Almost unlimited, as hepatocytes can rapidly proliferate after injury
Describe the functional reserve of the liver.
There is enormous functional reserve of the liver such that failure may not be exhibited until 80-90% of hepatic tissue is lost.
2 key functions of bile? Describe each.
- Digestion - emulsification of dietary fats in the intestines to help absorb fatty acids, monoglycerides, cholesterol and other lipids from the intestine by detergent action
- Waste excretion: bilirubin and cholesterol
Describe bile: tonicity? pH? 6 constituents?
- Isotonic
- Alkaline pH (8.6)
- Constituents:
- Water: 82%
- Bile acids (conjugated): 12%
- Bilirubin (conjugated)
- Cholesterol
- Electrolytes
- Phospholipids
How do bile acids facilitate fat absorption?
They emulsify intestinal fats which facilitates actions of pancreatic lipases & absorption
What % of bile acids excreted into intestine is reabsorbed? Where? What is this called?
90% PER CYCLE
Ileum especially to return to portal vein to the hepatocyes = enterohepatic circulation => hepatocytes reabsorb this bile from the sinusoids and transport it back to the bile canniculi
