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
Lining epithelium of the Hering’s canals?
Simple cuboidal epithelium
Lining epithelium of the extrahepatic bile ducts?
Simple columnar epithelium
Concentration of bile in gallbladder? Explain the mechanism.
Resorption of water concentrates bile up to 5x
It does so by pumping H2O/Na+ from the bile to the blood stream via basolateral Na+ pumps (H2O follows osmotically)
Lining epithelium of gallbladder? What to note?
Simple columnar with microvilli
Note: cells contain many mitochondria associated with active resorption of water and Na+
Does the gallbladder contain goblet cells?
NOPE
How are gallbladder cells attached together?
Tight junctions
Modification of the mucosa of the gallbladder?
Plicae when contracted
Describe the mucosa of the gallbladder.
Branched and contains a lamina propria below the epithelium
Does the gallbladder have a serosa or an adventitia?
Adventitia
How does the gallbladder contract?
It has a thin layer of smooth muscle in its wall = muscularis externa
% of pancreatic cells that are exocrine? endocrine?
Exocrine: 90%
Endocrine = islets of Langerhands: 10%
What is the main pancreatic duct composed of?
Fused ducts from dorsal and ventral anlage in embryology
Lining epithelium of main pancreatic duct?
Simple columnar epithelium
Does the mucosa of the pancretic epithelium have goblet cells?
YUP
Describe the organization of the cells within the exocrine pancreas.
Lobules contain groups of acini and intralobular ducts and are separated by fine connective tissue septa which contain larger ducts
What are the pancreatic acini composed of? Describe these.
Acinar glands: pyramidal serous cells, which are highly polarized and exhibit strong basophilic staining in the base (abundant RER) and an acidophilic apex (filled with zymogen granules)
Through what mechanism do acinar cells secrete their granules?
Exocytosis: the secretory granules fuse with the apical plasmalemma
What cells are unique to the pancreas? What do these look like?
Centroacinal cells
Look like pale cells in the acini
What does the lining of the intercalated ducts of the pancreas secrete? How?
A watery, bicarbonate rich fluid secreted by ductular cells
Are the ducts in the pancreas striated like in the salivary glands?
NOPE
Pancreatic juice: tonicity? pH?
Isotonic and pH > 8 = alkaline
Where are pancreatic islets of Langerhands most numerous?
Tail
Does each islet of Langerhans release multiple hormones?
YUP
What is the main reason why the islets of Langerhans are distinguishable from the exocrine cells?
The islets cells do not have a lot of RER like the exocrine cells do
What separates islets from exocrine cells in the pancreas?
Delicate reticular capsule
Can the different cell types of the islet of Langerhans of the pancreas be distinguished using a routine H&E staining? Explain.
Are the relative quantaties of different cell types the same in all islets?
NOPE
They are identified by immunofluorescent staining procedures
NOPE
Alpha cells of islets of Langerhans:
- % of islet?
- location in islet?
- granules?
- hormone?
- 20%
- peripherally located
- dense core granules are round, uniform, and have a clear halo
- glucagon
Beta cells of islets of Langerhans:
- % of islet?
- location in islet?
- granules?
- hormone secreted?
- 70%
- centrally located throughout
- granules have irregular crysalline cores (packaged by Golgi)
- preproinsulin, proinsulin (proinsulin is cleaved into insulin and C peptide)
Delta cells of islets of Langerhans:
- % of islet?
- location in islet?
- hormone secreted?
- 5%
- peripherally located (?)
- somatostatin
Hormone secreted by F cells of pancreas? What to note?
Pancreatic polypeptide
Rare cell
Label the liver lobule.
Which zone of hepatocyte will have their energy stores depleted first during fasting? Why?
Zone 1 BECAUSE HIGHER METABOLIC RATE
What are Kuppfer cells of the liver derived from?
Derived from monocytes in the blood and are members of the mononuclear phagocyte system
What distinguishes the exocrine pancreas from the parotid gland in histological sections?
The presence of centroacinar cells together with the lack of striated ducts
How are cells arranged within islets in the pancreas? How many does each contain?
Within the islet, the cells are arranged in cords that are separated by a network of fenestrated capillaries
Several hundred cells
Are some pancreatic endocrine cells NOT included in an islet?
YUP, throughout the pancreas there are small clusters of these cells
How may the cytoplasm of hepatocytes appear? Why?
May appear foamy (due to glycogen or fat storage)
What sets the outer boundary of the classic hepatic lobule?
A limiting plate of hepatocytes
What important organelle do Kuppfer cells contain?
Lysosomes
What hepatocyte organelle is responsible for drug detoxification?
SER
