Practice SectionPractice Section

Liver tissueLiver tissue

Liver Anatomy Liver Anatomy

The liver is the largest single organ in the The liver is the largest single organ in the body.body.

The structure of the liver is homogeneous; The structure of the liver is homogeneous; and appears in polygonal aggregations of and appears in polygonal aggregations of cells arranged in radiating cords.cells arranged in radiating cords.

Viewing the liver section: Viewing the liver section:

Notice that in a typical liver section, the overall color is Notice that in a typical liver section, the overall color is pink with the H&E stain;pink with the H&E stain;No obvious planes are discernable.No obvious planes are discernable.It typically shows no stratification.It typically shows no stratification.No obvious lumen is visible.No obvious lumen is visible.Liver is a good practice tissue because it is comprised of Liver is a good practice tissue because it is comprised of at least 66% of cells of the same type. at least 66% of cells of the same type.Once under the microscope-Do not attempt to try to Once under the microscope-Do not attempt to try to memorize how liver looks under the microscope at this memorize how liver looks under the microscope at this point.point.Concentrate at first on identifying that the majority of the Concentrate at first on identifying that the majority of the cells are of the same type.cells are of the same type.

Generalized diagram: liver sectionGeneralized diagram: liver section

Notice that the Notice that the similar cells are similar cells are arranged in rows arranged in rows separated by separated by channels (blood channels (blood passages)passages)

Nuclei are Nuclei are identified as blue identified as blue objects scattered objects scattered within the rowswithin the rows

The Liver LobuleThe Liver Lobule

The liver lobule consists of 3 recognizable The liver lobule consists of 3 recognizable components:components:

1.1. Central vein; appearing as single holesCentral vein; appearing as single holes

2.2. Peripheral portal triads; appearing as the Peripheral portal triads; appearing as the angles of the polygons;angles of the polygons;

3.3. Hepatocytes (liver cells) which radiate Hepatocytes (liver cells) which radiate from the central vein along vascular from the central vein along vascular sinusoids.sinusoids.

Major Functions of Hepatocytes:Major Functions of Hepatocytes:

1.1. Form and secrete bile Form and secrete bile 2.2. Store glycogen and buffer blood glucose Store glycogen and buffer blood glucose 3.3. Synthesize urea Synthesize urea 4.4. Metabolize cholesterol and fat Metabolize cholesterol and fat 5.5. Synthesize plasma proteins Synthesize plasma proteins 6.6. Detoxify many drugs and other poisons Detoxify many drugs and other poisons 7.7. Process several steroid hormones and Process several steroid hormones and

vitamin D vitamin D

Structural Histology of HepatocytesStructural Histology of Hepatocytes

In appearance, In appearance, HepatocytesHepatocytes are boxy (cuboidal) cells with one or are boxy (cuboidal) cells with one or two large euchromatic nuclei and with abundant, grainy cytoplasm.two large euchromatic nuclei and with abundant, grainy cytoplasm.Hepatocytes stain well with both acid and basic dyes (reflecting the Hepatocytes stain well with both acid and basic dyes (reflecting the abundance of various cellular constituents).  abundance of various cellular constituents).   Hepatocytes are arranged into Hepatocytes are arranged into cords, cords, in which each Hepatocyte is in which each Hepatocyte is attached to adjacent cells in a two-dimensional sheet.  attached to adjacent cells in a two-dimensional sheet.  The cells abut the space of Disse, and each Hepatocyte can The cells abut the space of Disse, and each Hepatocyte can communicate across the space of Disse into adjacent sinusoids.communicate across the space of Disse into adjacent sinusoids.Hepatocytes are epithelial, but their epithelial nature is expressed in Hepatocytes are epithelial, but their epithelial nature is expressed in a rather peculiar way. They have 2 basal surfaces, on opposite ends a rather peculiar way. They have 2 basal surfaces, on opposite ends of the cells, where they face the sinusoid. of the cells, where they face the sinusoid. Most epithelial cells sit on their basal surface, and have an apical Most epithelial cells sit on their basal surface, and have an apical surface, exposed to an externalsurface, exposed to an external.  .  

PAS of the Liver PAS of the Liver

PAS-stained liver PAS-stained liver section section demonstrates the demonstrates the presence of presence of glycogenglycogen (red (red color) stored in color) stored in Hepatocytes.  Hepatocytes.    Note that in this Note that in this specimen, glycogen specimen, glycogen is more densely is more densely concentrated in concentrated in near the central near the central vein than near the vein than near the portal area.portal area.

Central VeinsCentral Veins

Central veins Central veins are located are located at the centers of liver of at the centers of liver of liver lobules.liver lobules.The area around a central The area around a central vein has little or no vein has little or no connective tissue.connective tissue.Unlike the portal area-Unlike the portal area-showing connective tissue.showing connective tissue.The central veins are The central veins are visible in any random visible in any random section of liver.section of liver.They vary greatly however They vary greatly however in their size –depending on in their size –depending on their distance from the their distance from the main trunk of the hepatic main trunk of the hepatic vein.vein.

Another view: Central veinsAnother view: Central veins

Liver HepatocytesLiver Hepatocytes

The cytoplasm of Hepatocytes The cytoplasm of Hepatocytes is eosinophillic.is eosinophillic.

Hepatocytes form sheets Hepatocytes form sheets called trabeculae.called trabeculae.

The trabeculae interface with a The trabeculae interface with a blood sinusoid;blood sinusoid;

The sinusoid resembles a large The sinusoid resembles a large capillarycapillary

Liver Bile DuctsLiver Bile Ducts

Bile ducts are tiny Bile ducts are tiny intercellular intercellular spaces that form spaces that form conduits around conduits around the Hepatocytesthe Hepatocytes

These bile ducts These bile ducts converge and converge and carry bile to the carry bile to the GB, and from GB, and from there to the there to the duodenumduodenum

The duct opening The duct opening is lined with is lined with columnar columnar epitheliumepithelium

Kupffer CellsKupffer Cells

Phagocytic cells located on the Phagocytic cells located on the inner wall of sinusoids.inner wall of sinusoids.

Long-term resident cells delivered Long-term resident cells delivered by circulating Monocytesby circulating Monocytes

Kupffer cells engulf and destroy Kupffer cells engulf and destroy most bacteria, worn-out RBC’s most bacteria, worn-out RBC’s and other matter.and other matter.

Liver H&E: This slide shows how the Hepatocytes and Liver H&E: This slide shows how the Hepatocytes and

Kupffer cells might appear in a low-power H & E sectionKupffer cells might appear in a low-power H & E section

Location of Kupffer CellsLocation of Kupffer Cells

Identification of Kupffer cellsIdentification of Kupffer cells

Kupffer cellsKupffer cells are closely associated with the are closely associated with the endothelial lining of the liver. endothelial lining of the liver. The Kupffer cells are not easily distinguished The Kupffer cells are not easily distinguished from the endothelial cells. from the endothelial cells. However, Kupffer cells can be recognized by However, Kupffer cells can be recognized by their oval nuclei closely associated with their oval nuclei closely associated with sinusoidal spaces.sinusoidal spaces.Endothelial cells appear similar, but with thinner Endothelial cells appear similar, but with thinner (flatter) and denser nuclei.(flatter) and denser nuclei.Endothelial cytoplasm is less visible.Endothelial cytoplasm is less visible.Nearby Hepatocytes can be distinguished by Nearby Hepatocytes can be distinguished by their rounder nuclei and more abundant their rounder nuclei and more abundant cytoplasm.cytoplasm.

Fenestrated endothelium:Fenestrated endothelium: ( (i.e., full of holes -- from i.e., full of holes -- from fenestrafenestra, window, window). ).

Only found in a few special places: Only found in a few special places: 1.1. Sinusoid of the liverSinusoid of the liver2.2. Glomeruli of the kidneyGlomeruli of the kidney3.3. Most endocrine glandsMost endocrine glands

In the liver, where there is also no basement In the liver, where there is also no basement membrane, the fenestrations permit blood membrane, the fenestrations permit blood plasma to wash freely over the exposed plasma to wash freely over the exposed surfaces of the Hepatocytes through the space surfaces of the Hepatocytes through the space of Disse. of Disse.

Hepatocyte micro-circulation: Hepatocyte micro-circulation:

The fenestrations of the endothelium permit free The fenestrations of the endothelium permit free movement of blood plasma, the "interstitial fluid" movement of blood plasma, the "interstitial fluid" of the space of Disse is blood plasma. of the space of Disse is blood plasma.   

Hence, for all practical purposes, Hepatocytes Hence, for all practical purposes, Hepatocytes reside in direct contact with bloodreside in direct contact with blood..

This space is not completely “free”, but does This space is not completely “free”, but does contain scattered reticular (collagen) fibers and contain scattered reticular (collagen) fibers and fibroblasts, providing support.fibroblasts, providing support.

Reticulin Fibers in the LiverReticulin Fibers in the Liver

Flow between blood and Flow between blood and Hepatocytes is facilitated by the Hepatocytes is facilitated by the fenestrated endothelial lining of fenestrated endothelial lining of the vascular sinusoids.the vascular sinusoids.

Lying between is the space of Lying between is the space of Disse-difficult to see in paraffin Disse-difficult to see in paraffin sections;sections;

However, within this space are However, within this space are the Hepatocyte microvilli which the Hepatocyte microvilli which contain delicate strands of type contain delicate strands of type III collagen (reticulin) that stain III collagen (reticulin) that stain black.black.

Also located here; are the Also located here; are the hepatic Stellate cells that store hepatic Stellate cells that store

vitamin A.vitamin A.

ReviewReview

With practice you will learn to identify liver tissue With practice you will learn to identify liver tissue under the microscope almost immediately. under the microscope almost immediately. However, we practiced eliminating obvious However, we practiced eliminating obvious possibilities, and learning to identify the nuclei, possibilities, and learning to identify the nuclei, cytoplasm and structural arrangements typical of cytoplasm and structural arrangements typical of liver tissue.liver tissue.We identified unique cells and features of liver We identified unique cells and features of liver tissue.tissue.By repeating this process with each section you By repeating this process with each section you encounter, you will begin to develop a habitual encounter, you will begin to develop a habitual method of identifying unique characteristics of method of identifying unique characteristics of different tissues under the microscopedifferent tissues under the microscope

Resources:Resources:

Southern Illinois University of Medicine, Histology website. Southern Illinois University of Medicine, Histology website. Http://www.siumed.edu. . 20082008

Ham, Arthur. Ham, Arthur. Histology,Histology, 6 6thth edition. J.B. Lippincott Co., 1969 edition. J.B. Lippincott Co., 1969

Kerr, Kerr, Atlas of Functional HistologyAtlas of Functional Histology, Mosby. 1999., Mosby. 1999.