Liver Histology (digestive System) Flashcards
Anatomy pills
-The liver is the largest organ of the body.
-Its structural and functional unit is the hepatic lobule
-Intraperitoneal organ: enveloped by 2 layers of peritoneum (visceral and parietal)
-The liver is also held in place by different types of
mesenteries: lesser omentum, falciform ligament…
-The liver has capsule: Glisson’s capsule
-It’s innervated by intercostal nerves
-In case of inflammation and distension of the liver, the nerves can sense it and inform us of possible damage
Portal tract
The portal tract includes all the structures entering and leaving the liver:
1)Hepatic artery proper: responsible for providing 25% of
the blood directed to the liver
-It carries highly oxygenated blood
2)Portal vein: responsible for providing 75% of the blood that enters the liver
-It comes from the GIT and it carries blood rich in nutrients, together with toxins, bacteria drugs, alcohol
3)Hepatic plexus: provides innervation to the liver
-Made of sympathetic and parasympathetic fibers from
the celiac ganglia and the Vagus nerve, respectively
4)Lymphatic vessels: drain excess of intracellular fluid
from the liver
-The lymphatic vessels eventually drain into the celiac lymph nodes
5)Bile duct: receives all the bile produced by the liver
-The bile is important in several metabolic processes,
such as the emulsification of fats
-The bile also contains the metabolites that need to be
excreted from the body
Hepatic lobule
Structural and functional unit of the liver.
-It’s composed of hepatocytes
-it has a hexagonal shape
-At each pole: hepatic triad, which is composed by 3 different structures:
1)Hepatic arteriole: branch of the hepatic artery
2)Portal venule: tributary of the portal vein
3)Bile duct
-The hepatic triad is visible under microscope
-In reality, also lymphatic vessels are present, but they’re not visible under microscope
-The triad + lymphatic vessels: portal
tetrad
-From each pole, the hepatic artery and the portal vein both open into sinusoidal capillaries
-They are fenestrated capillaries, found in the
liver, spleen and bone marrow
-They also contain Kupffer cells
-The sinusoidal capillaries eventually drain inside
the central vein
-Found at the center of the hepatic lobule
-The blood flow is centripetal
-Many central veins from different lobules can meet
and fuse, forming interlobular veins
-Many interlobular veins together will form the hepatic veins, that eventually leave the liver and drain inside the Inferior vena cava
- Inside the lobule, there’s another cell population called stellate cells
Lobules are mostly composed of..
Hepatocytes
Between lobules aplical membrane there are…
Bile canalculi which collect bile produced by hepatocytes
Between sinusoidal capillaries and hepatocytes of lobules are…
Perisinusoidal space of Disse
Circulation inside the liver
Portal venule and hepatic arteriole
➡️sinusoidal capillaries➡️certain vein
-Hepatic arteriole: carries highly oxygenated
blood (95%)
-O2 is released from hemoglobin so it can diffuse to the hepatocytes located around the capillaries
-In exchange, the capillary blood receives the waste products of the hepatocytes: bicarbonate, protons and CO2
-Portal venule: carries blood rich in nutrients, but also containing bacteria and toxins
-They are eliminated by the Kupffer cells
Macrophages of lobules found inside…
Sinusoidal capillaries
Macrophages of lobules found inside…
Sinusoidal capillaries
Macrophages of lobules functions:
1) control immunointolerance-inhibition of CD8 cells and cytotonic cells
2) elimination of bacteria
3)eimination of paracytes
4) elimination of olderythrocytes
How do Macrophages (kupffer cells) of lobules eliminate bacteria?
-The Kupffer cells will form pseudopods to phagocyte
the bacteria
-The bacteria is contained inside phagosomes
inside the cell
-Eventually the phagosome will fuse with lysosomes → phagolysosome
-Will breakdown the bacteria through its enzyme
-Gram- bacteria produce an endotoxin called lipopolysaccharide (LPS)
-Kupffer cells have TLR-4 receptor and CD14 on their surfaces: allows them to recognize LPS and bind to it
-The binding causes the activation of a cascade inside the Kupffer cell → release of cytokines (TNF-α, IL-1, IL-6, ROS, TGF-β, NO, prostaglandins) → promote inflammatory response
How does macrophages of lobules eliminate old erythrocytes?
Average lifespan: 100-120 days
-After, the red blood cells start losing flexibility and
pliability and has to be degraded
-Kupffer cells will recognize an old red blood cell and break into its 2 components:
-Globin: proteic portion, further degraded into Amino Acids by other enzymes
-Heme group: broken down into biliverdin and then bilirubin + iron
-Bilirubin will be conjugated inside the hepatocytes, so it can enter the biliary system and form the bile
Stellate cells of lobules
-Store vitamin A + fat
-Usually quiescent
-Can become active in case of damage to the liver tissue → become myofibroblasts
-Produce collage type I
→ causes liver vessels to become very fibrotic
→ narrows the blood vessel wall
→ flow is impeded
→ blood starts to backflow
→ leads to portal
Hepatocytes contain
-Bile salts: 70% of bile, include bile salts,
conjugated bile salts and bile acids
-Phospholipids
-Bilirubin: gives pigmentation
-Cholesterol
Hepatocytes of lobules
Makes of 80% of liver parenchyma
Responsible for producing bile
Hepatocytes contain
-Bile salts: 70% of bile, include bile salts,
conjugated bile salts and bile acids
-Phospholipids
-Bilirubin: gives pigmentation
-Cholesterol
Hepatocytes contain
-Bile salts: 70% of bile, include bile salts,
conjugated bile salts and bile acids
-Phospholipids
-Bilirubin: gives pigmentation
-Cholesterol
Hepatocytes have 2 faces
Basolateral membrane: presents microvilli to increase the surface area
-In contact with capillary system
Apical membrane: where the bile canaliculi are found
Between basolateral membrane and apical membrane:
Between 2 juxtaposed cells there’s a point where the apical membranes fuse → creates a gap that forms the bile canaliculi
-Where the hepatocytes will released the
bile produced
-From the canaliculi, the bile continues in left and right bile ducts
➡️common hepatic bile duct
➡️fuses w/cyctic duct
➡️common bile duct
Structures of hepatic lobule:
-classic lobule
-portal lobule
-acinus lobule
Classic lobule
Centripetal 🩸 flow
-From the hepatic arteriole and the portal venule to central vein
Portal lobule
Considers direction of bile flow
-Considering a triangle between 3 central veins of 3 different lobules → at the center of this triangle there will be a triad, with a bile duct
-Bile flows from each pole of the triangle (central vein) towards the bile duct at the center → centrifugal direction
Acinus lobule
Considers flow of oxygen rich 🩸
-From portal triad to central vein: it creates zones
-Forms a rhomboid structure between 2 hepatocyte
-Zone 1: periportal, next to the triad
-Receives the blood richest in oxygen →most resistant to circulatory problems
-Zone 2
-Zone 3: perivenular
-Receives the blood with lowest partial pressure of O2 → will undergo necrosis and ischemia first in case of circulatory problems
Zone heterogeneity of acinus lobule
-Zone 1: ↑O2 → oxidative pathways
- Amino acid metabolism, gluconeogenesis,
cholesterol synthesis, bile salt synthesis, urea genesis, beta-oxidation…
-Zone 2: intermediate zone, perform functions in- between zone 1 and zone -Zone 3: ↓O2 → non-oxidative pathways
-Glycolysis, fatty acid synthesis, ketogenesis, glutamine synthesis, xenobiotic metabolism…
These zones also present different mRNA, since they require different enzymes to carry out their functions
