histo - liver

7/29/2019 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

histo - liver

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