Download - Histo - Liver
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Histology of Liver
Dr Muhammad Ressam Nazir
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Intro
The liver is one of the largest and most important organs in the body.
The bulk of the liver consists ofhepatocytes, which are epithelial cells with
a unique configuration.
Essentially an exocrine gland, secreting bile into the intestine.
But, the liver is also an endocrine glandand a blood filter.
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Functions
It's functions include all of the following: formation and secretion ofbile.
storage ofglycogen, buffer for blood glucose.
synthesis ofurea.
metabolism ofcholesterol and fat.
synthesis and endocrine secretion of many plasma proteins, including clottingfactors.
detoxification of many drugs and other poisons.
cleansing of bacteria from blood.
processing of several steroid hormones and vitamin D.
volume reservoir for blood.
catabolism ofhemoglobin from worn-out red blood cells.
Much of the liver's organization is conditioned by its central role in removing unwantedmaterials from blood and otherwise maintaining the blood's normal composition.
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Dual vascular supply
The liver receives a dual vascular supply. The hepatic portal vein brings to the liver all of the blood
which has previously passed through the intestine andspleen.
The hepatic artery brings fresh, oxygenated blood from theaorta.
Portal venous blood from the intestine and spleen andarterial blood from the aorta mix together inhepatic sinusoids before leaving the liver in the hepatic
vein. The liver receives over 25% of the total resting cardiac
output and is responsible for over 20% of the body'sresting oxygen consumption.
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Organization of Liver Lobules The liver is organized into lobules (portal lobules, hepatic lobules) which
take the shape of hexagone. (6 sides) Each lobule is typically hexagonal in cross section and is centered on a
branch of the hepatic vein (called the central vein).
At the corners between adjacent lobules are the so-called portal
triad (portal canals, portal areas). These are regions of connective tissue
which include branches of the bile duct, the portal vein, and the hepaticartery.
The portal areas represent the stroma of the liver.
Along the central axis of each lobule runs a central vein, which is a branch
of the hepatic vein.
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Portal triad of liver
Portal triads have:
1) Hepatic artery
2) Portal vein, and
3) Bile duct
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How to look under a microscope?
The lobular organization of the human liver is not immediately evident
under the microscope.
Lobules do not have distinct boundaries, and they are seldom cut neatly
in cross section.
To visualize lobules, first locate several portal areas (small patches of
connective tissue each containing a duct, a large vein, and a small artery).
Mark the corners where lobules come together.
Then look for central veins (conspicuous spaces, with no associated connective
tissue, located roughly midway between portal areas.)
These central veins mark the centers of lobules.
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Hepatic Cords
The bulk of the liver consists of epithelial hepatocytes arranged into cords,
separated by vascular sinusoids. Each hepatocyte is attached to its neighbors all around and faces
the sinusoids at either end.
The sinusoids are vascular spaces lined by afenestratedendothelium (i.e.,
an endothelium that is full of holes).
This endothelium has no underlying basement membrane. Therefore, thefenestrations permit blood plasma to wash freely over the exposed
surfaces of the hepatocytes in the space of Disse.
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Space of Disse
The space between the
endothelium and the cords is
named the space of Disse.
Its location is that of connective
tissue, and it does contain a
network of reticular fibers (collagen
type III) (and fibroblasts) which
hold the hepatocytes together. Bile canaliculi, formed by apical
surfaces of adjacent hepatocytes,
form a network of tiny passages
contained within each cord.
Associated with the sinusoids are
stellate Kupffer cells -- liver
macrophages which effectively
catch and destroy bacteria which
entered the blood in the intestine.
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Stellate Ito cells, located at
intervals within the space of
Disse, store fat and vitamin A.
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Different Organization of Liver Lobules
The two-dimensional microarchitecture of the liver can be viewed from multiple
different perspectives.
Name Shape Model
Classical/hepatic
lobule
Hexagonal; divided into concentric
centrilobular, midzonal, periportal partsAnatomical
Portal lobule Triangular; centered around a portal triad Bile secretion
Liver acinus
Elliptical or diamond-shaped; divided into zone
I (periportal), zone II (transition zone), and
zone III (pericentral)
Blood flow and
metabolic
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Classical/hepatic lobule
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Portal lobule
This is based mainly on the
direction of bile flow.
It is a triangular region with a
portal triad at its center and a
central vein at each of its three
corners.
It contains portions of three
adjacent classic liver lobules all of
which drain bile into one portal
canal.
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Liver acinus
The acinus is roughly divided into zones
that correspond to distance from thearterial blood supply.
Those hepatocytes closest to the
arterioles (zone 1 below) are the best
oxygenated, while those farthest from the
arterioles have the poorest supply of
oxygen.
This arrangement also means that cells in
the center of the acinus (again, zone 1)
are the first to "see" and potentially
absorb blood-borne toxins absorbed into
portal blood from the small intestine.
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ANY QUESTIONS?
Thank You