Liver Intro
Objectives:
Be able to identify the organ from any of the species presented in the glass slides.
Be able to identify any of the named components that make up the supply and drainage systems of liver lobules.
Understand the structure, function, and cellular components of liver sinusoids.
Understand and distinguish the overlapping organizational schemes for liver lobules: Classic lobule, portal lobule, and liver acinus.
Slides
Canine Liver - Glass slide #2
Liver sinusoids:
The liver is a multifunctional organ. It serves as a filter for venous blood from the GI tract, it is a compound tubular exocrine gland, supplying bile to the duodenum, and it is an endocrine gland, adding important components directly to the blood. The liver receives a dual blood supply from the hepatic portal vein and the hepatic artery. Blood from both sources finds its way to the hepatic sinusoids, where they mix as they flow to the hepatic vein. Study glass slide 2 and note the relationship of the interanastomosing plates or cords of hepatocytes that give rise to the extensive blood sinusoids of the liver. As a rule, the plates are one cell thick and two sides of each hepatocyte line perisinusoidal spaces. An appreciation of the tremendous terminal vascular bed of the liver is essential to understanding its structure and function. The many small white spaces in this image/slide are sinuses that normally contain slow-moving blood. These sinuses frequently collapse during histological preparation. The larger white spaces in this image are central veins.
Topic: Liver sinusoids
Liver sinusoids have a unique wall structure that allows blood plasma (yellow), but not cells (pink), to contact the hepatocyte plasma membrane. Fenestrated endothelial cells are supported by reticular fibers to maintain the perisinusoidal space. This space slows plasma movement and permits diffusion of suspended substances (P) to the hepatocyte surface.
Liver sinusoids:
In this example the sinusoids have not collapsed. A few blood cells can be seen in the white sinusoidal spaces where whole blood is normally present. Examine the hepatocyte cords and plates and note the cells' exposure to the sinusoids. Sinusoids (S) are the extensive blood-filled vascular channels through which all the blood from the GI system is routed.
Topic: Liver sinusoids
Cords or plates of (purple-stained) hepatocytes are surrounded loosly by endothelial cells (black arrows). In several places here the perisinusoidal space between the cell and the sinus is visible. Black 'S' = hepatic sinusoids.
Central vein:
In this longitudinal view of a central vein, the convergence of many sinusoids is not so obvious as in cross sections. Appreciate that all sinusoidal blood eventually finds its way into a central vein. These low-pressure channels are extensively pierced and lead to the caudal (or inferior) vena cava.
Topic: Central vein
Blood from individual sinuses drains into central veins (CV).
Cell types:
Even at lower magnification, several of the typical cell types are evident. Stellate cells sometimes stain more lightly, as in this example. Kupffer cells are found at prominent spots along the sinusoids. In this example, hepatocytes are very acidophilic. Endothelial cells are similar to those seen throughout the circulatory system.
Topic: Cell types
Green outlines = probable Stellate cells; Blue arrows = probable Kupffer cells
Porcine Liver - Glass slide #166
Hepatic lobule:
This low-power view of pig liver shows blue-staining collagenous stroma (organ connective tissue) that divides the parenchyma (functional organ tissues) into lobules. In porcine liver the lobule edges sometimes appear hexagonal, though other polygonal shapes are common. Note that the lobules are well defined in porcine liver, though not geometrically identical. Near the centers of the geometric lobules are central veins, which collect the blood that flows from the outer margins near the stromal connective tissue. In this preparation most of the sinusoidal spaces have collapsed.
Topic: Hepatic lobule
Blue arrows = stroma surrounding one hepatic lobule; Red asterisks = central veins near the center of the lobule.
Central vein:
Note the roughly hexagonal outline of a classic (vascular drainage) lobule and study a similar area on your glass slide. At the center of a classic lobule is the central vein with openings where several sinusoids drain.
Topic: Central vein
CV = central vein. Arrows indicate sinusoids draining at the level of this section.
Portal area, or Triad:
The vertices of the collagenous polygon are marked by areas of connective tissue that contain branches of the portal vein, the bile duct, and the hepatic artery. These areas are called portal areas or triads because of the three kinds of structures they contain. In addition to bile duct, artery and vein, small lymph vessels and nerves are sometimes found in the portal areas. The liver sinusoids receive blood from both the terminal branches of the portal vein and the hepatic artery. Both of these vessles branch from the triads and extend along the periphery, surrounding the lobules. Remember the three-dimensional configuration of the classic liver lobule is a polygonal column about l.0 mm in diameter and 1.5 mm high.
Topic: Portal area, or Triad
Red arrow = hepatic artery (arteriole); Green arrows = bile ducts (upper example is a very small ductule); Yellow arrow = portal vein (venule); Blue arrows = possible lymphatic capillaries.
Bile canaliculi:
Bile canaliculi are formed from the plasma membranes of adjacent hepatocytes. They serve as the site of secretion for bile and they are the first minute channels through which bile approaches the portal areas. Bile ducts lined by cuboidal epithelium form in and near to the portal areas.
Topic: Bile canaliculi
Green outline represents a set of adjacent hepatocytes that contribute to the many bile canaliculi present. Red arrows = bile canaliculi.
Calf Liver - Glass slide #167
Glass slide 167 contains a section of liver from a calf. Note the liver lobules are not very well defined in comparison to the pig. The bovine liver, like that from most species, contains little connective tissue. On this slide, identify the structures described for pig liver - portal areas & contents, sinusoids (most collapsed), central veins, bile canaliculi.
Topic: undefined
Approximate boundaries of a single classic lobule in the calf liver. CV = central vein.
Liver Macrophages - Glass slide #168
Kupffer cells:
Review the typical location of the large liver macrophages (Kupffer cells) that occur at various places along the sinusoids. Notice that Kupffer cells can appear large and be prominent in the sinusoid or they can be smaller and cling close to the sinusoid wall. In this example they are easy to identify because they have phagocytized a red pigment that was injected into the intestinal portal system. Hepatocytes are indicated only by a basophilic dye.
Topic: Kupffer cells
Blue arrows = Kupffer cells, resident liver macrophages.
Rabbit Liver Glycogen - Glass slide #8
Portal area:
This image demonstrates the observation that the position of a hepatocyte within the liver acinus influences its metabolic activity. Identify liver acini in this slide and compare glycogen levels (red staining) in the portal areas to levels near the central veins. Less glycogen in zone 1 than zone 3 of the hepatic acinus suggests a fasting state in which sugars are being released from glycogen in zone 1 hepatocytes.
Topic: Portal area
Dashed line = region of portal vein, indicative of portal area staining; blue asterisks = central vein.
Central vein:
Many more hepatocytes in the region of the central vein exhibit glycogen staining. This area would typically be the last to release stored carbohydrates and the last to accumulate glycogen following feeding.
Topic: Central vein
Dashed line = region of portal vein, indicative of portal area staining; blue asterisks = central vein.