One such amazing organ in the human body is the LIVER. It is a multi-functional organ. This organ houses an important role in the human body. The liver primarily focuses on cleansifying the body. One interesting fact about the liver is that it is the largest organ in the body. In medical terminologies, the liver is referred to as hepatic.
Normal liver histology and its architecture
Like the nephron, which is the structural and functional unit of the kidney, the liver lobule is the structural and functional unit of the liver. The liver is divided into lobes, with each lobe surrounded by a connective tissue capsule. Each lobe is further divided into lobules. One can observe a clear distinction in the lobes but the same cannot be observed in lobules since each lobule is surrounded by connective tissue that are incomplete and poorly. This connective tissue is called interlobular septa. The lobule is like a hexagon that is surrounded by a portal triad at its corners with the center consisting of a central vein.
From the central vein, the hepatocytes (liver cells) radiate like spikes to form a hexagon. These radiating hepatocytes are called laminae and the space in between the laminae is called sinusoid. Triad blood from the portal vein and hepatic artery enter into the sinusoid and then drain into the central vein.
The bile duct receives bile from the hepatocytes. Between a pair of hepatocytes in the laminae, there is the bile canaliculi whose walls are formed adjacent to the plasma membrane of the hepatocyte, draining into the bile duct. The bile canaliculi are separated from the space of Disse by tight junctions. The bile canaliculi drain to the intralobular canals of hering, periportal bile ductules, and finally into the bile duct in the portal triad.
The liver sinusoids are lined by two types of cells, the endothelial cells with numerous fenestrations for passage of blood and related substances into hepatocytes for detoxification and the other are the kupffer cells. The kupffer cells are the tissue macrophages that form a component of the reticuloendothelial system aiding in immunity. The kupffer cells phagocyte the foreign substances (non-self) from the intestine that is carried by the portal vein to the liver and keep the blood sterile. Between the sinusoidal endothelium and the hepatocytes is the space of disse also known as perisinusoidal space, which contains numerous projections from the hepatocytes and contains a special cell called as a hepatic stellate cell.
In the case of chronic hepatitis, these stellate cells proliferate and lay down numerous collagen, leading to liver tissue scars. Around the canal of the herring, there are numerous hepatic stem cells that replace hepatocytes in case of a chronic injury but not in an acute injury. Hepatocytes have high replicative action which can replace the lost hepatocytes in acute injury, making the liver the organ with the quickest regenerative capacity. The mitotic and differentiation activity of hepatic stem cells produce duct-like structures and this is called ductular reaction.
Clinical Application
The most common liver pathology is the fatty liver which can lead to hepatitis and liver cirrhosis. Liver cirrhosis may further worsen to end-stage liver disease. A cirrhotic liver is composed of regenerating hepatic parenchyma in nodules surrounded by fibrous connective tissue disrupting the normal architecture of the liver. Fatty liver occurs most commonly due to alcohol metabolism. The second most common clinical application is viral hepatitis which can also lead to liver cirrhosis.
Normal Histology of Gall Bladder
To complete the story let’s look into the histology of the gall bladder. The common clinical application of gall stones is the presence of Rokitansky Aschoff sinus. The gall bladder is composed of Mucosa, fibromuscular layer, and serosa.
1. The Mucosa is lined by simple columnar epithelium with an ovoid nucleus that is placed basally. These cells absorb water and in due process concentrate the bile by the presence of microvilli. Lamina propria contains loose connective tissue without any glands and muscularis mucosa is absent. It consists of numerous folds and is stretchable in nature.
2. Fibromuscular layer contains smooth muscle fibers with dense elastic fibers in between these muscle fibers. Below this layer is a layer of loose connective tissue consisting of vessels and nerves. This layer below the muscular layer is called adventitia.
3. Serosa is present only on the inferior aspect of the gall bladder, the remaining region is covered by adventitia.
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