Digestive VI

Department of Anatomy &Histology Dr.Raja Ali
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Digestive System : Accessory Organs: Liver: (fig.1&2)
? The liver is the largest mass of glandular tissue in the body and the largest internal organ.
? It is unique because it receives its major blood supply from the hepatic portal vein, which carries venous blood from the small intestine, pancreas, and spleen.
? Thus the liver is directly in the pathway that conveys materials absorbed in the intestine. This gives the liver the first exposure to metabolic substrates and nutrients; it also makes the liver the first organ exposed to noxious and toxic substances absorbed from the intestine.
? One of the major roles of the liver is to degrade or conjugate toxic substances to render them harmless. It can, however, be seriously damaged by an excess of such substances.
? Each liver cell has both exocrine and endocrine functions.
? The exocrine secretion of the liver, called bile, contains conjugated and degraded waste products that are delivered back to the intestine for disposal. It also contains substances that bind to metabolites in the intestine to aid absorption.
? A series of ducts of increasing diameter and complexity, beginning with bile canaliculi between individual hepatocytes and ending with the common bile duct, deliver bile from the liver and gallbladder to the duodenum.
? The endocrine secretions of the liver are released directly into the blood that supplies the liver cells; these secretions include: albumin, nonimmune _?- and ?-globulins, prothrombin, and glycoproteins, including fibronectin. Glucose, released from stored glycogen, and triiodothyronine (T3), the more active deiodination product of thyroxine, are also released directly into the blood.
? Functional units of the liver, described as lobules or acini, are made up of irregular interconnecting sheets of hepatocytes separated from one another by the blood sinusoids.

Structural Organization of the Liver:
The liver include
• parenchyma, consisting of organized plates of hepatocytes, are separated by sinusoidal capillaries.
• connective tissue stroma that is continuous with the fibrous capsule of Glisson. Blood vessels, nerves, lymphatic vessels, and bile ducts travel within the connective tissue stroma.
• sinusoidal capillaries (sinusoids), the vascular channels between the plates of hepatocytes.
• perisinusoidal spaces (spaces of Disse), which lie between the sinusoidal endothelium and the hepatocytes.
The classic lobule is a roughly hexagonal block of tissue that has at its center the terminal hepatic venule (central vein) and at its six corners the portal canals (portal triads) containing in each a branch of the portal vein, hepatic artery, and bile duct (The bile ducts are composed of a simple cuboidal or columnar epithelium).
• The sinusoidal lining cells are of two distinct types:
? The Kupffer cells (KC):
? Are the more prominent cells.
? They exhibit a large nucleus and a substantial amount of cytoplasm.
? They protrude into the lumen.
? The surface of the Kupffer cell exhibits a very irregular or jagged contour because of the numerous processes.