The Liver A human liver normally weighs 1.44–1.66 kg (3.2–3.7 lb), and is a soft, pinkish-brown, triangular organ. It is both the largest internal organ (the skin being the largest organ overall) and the largest gland in the human body. It has a wide range of functions including detoxification, proteinsynthesis, and production of biochemicals necessary for digestion. It is located in the right upper quadrant of the abdominal cavity, resting just below the diaphragm. The liver lies to the right of the stomach and overlies the gallbladder . It is connected to two large blood vessels, the hepatic artery and the portal vein. The hepatic artery carries blood from the aorta to the liver, whereas the portal vein carries blood containing digested nutrients from the entire gastrointestinal tract and also from the spleen andpancreas to the liver. These blood vessels subdivide into capillaries, which then lead to a lobule. Traditionally, the liver is divided into four lobes: left, right, caudate, and quadrate. The lobes are further divided into lobules, the functional units of the liver. Each lobule is made up of millions of hepatic cells which are the basic metabolic cells of the liver.

A human liver normally weighs 1. 44–1. 66 kg (3. 2–3 A human liver normally weighs 1.44–1.66 kg (3.2–3.7 lb), and is a soft, pinkish-brown, triangular organ. The liver is both the largest internal organ (the skin being the largest organ overall) and the largest gland in the human body. The liver is connected to two large blood vessels: the hepatic artery and the portal vein. Traditionally, the liver is divided into four lobes: left, right, caudate, and quadrate. The lobes are further divided into lobules, the functional units of the liver. Each lobule is made up of millions of hepatic cells which are the basic metabolic cells of the liver. The gallbladder is a hollow organ that sits just beneath the liver and stores bile that is made in the liver. The gallbladder is divided into three sections: fundus, body, and neck. The neck connects to a system of ducts.

Liver • Repeating hepatic lobules (Hexagonal Unit) Liver • Repeating hepatic lobules (Hexagonal Unit). • Central Vein in the centre of each hepatic lobule. • Portal canals (Portal Traids) in periphery the surrounding connective tissue [Branches of the hepatic artery, hepatic portal vein, bile duct, and lymph vessels seen.] • Hepatic sinusoids (dilated blood channels) contains epithelial cells and macrophages called “Kupffer cells” • The hepatic sinusoids separated from the underlying hepatocytes by subendothelial perisinusoidal space of Disse. • The major exocrine functions of hepatocytes is synthesis and release about 500-1200ml of bile per day which is delivered to the gallbladder via the bile canaliculli Liver • Repeating hepatic lobules (Hexagonal Unit). • Central Vein in the centre of each hepatic lobule. • Portal canals (Portal Traids) in periphery the surrounding connective tissue [Branches of the hepatic artery, hepatic portal vein, bile duct, and lymph vessels seen.] • Hepatic sinusoids (dilated blood channels) contains epithelial cells and macrophages called “Kupffer cells” • The hepatic sinusoids separated from the underlying hepatocytes by subendothelial perisinusoidal space of Disse. • The major exocrine functions of hepatocytes is synthesis and release about 500-1200ml of bile per day which is delivered to the gallbladder via the bile canaliculli

The liver is the second largest organ (after the skin) and is an accessory digestive gland which plays a role in the body's metabolism. The liver has many functions some of which are important to digestion. The liver can detoxify variousmetabolites; synthesise proteins and produce biochemicals needed for digestion. It regulates the storage of glycogen which it can form from glucose (glycogenesis). The liver can also synthesise glucose from certain amino acids. Its digestive functions are largely involved with the breaking down of carbohydrates. It also maintains protein metabolism in its synthesis and degradation. In lipid metabolism it synthesises cholesterol. Fats are also produced in the process of lipogenesis. The liver synthesises the bulk of lipoproteins. The liver is located in the upper right quadrant of the abdomen and below the diaphragm to which it is attached at one part, This is to the right of the stomach and it overlies the gall bladder. The liver produces bile, an important alkaline compound which aids digestion.

In the hepatic parenchymal tissue, note the plates of hepatocytes (the arrangement of these cells in plates is not always clear, due to plane of section and the frequent interconnections of plates). Occasional hepatocytes are binucleate. Between the plates of hepatocytes are intervening sinusoids lined by a thin endothelium. Larger eosinophilic cells lining the sinusoids are mostly Kupffer cells Kupffer cells  (a type of macrophage, part of the mononuclear phagocyte system). Look for Kupffer cells using as these cells are not readily recognized in The space between the endothelial cells and hepatocytes is called the “space of Disse” and is somewhat artificially enlarged in conventional sections. Remember that blood flows from the portal veins and hepatic arteries (of the portal canals) through the sinusoids to the central veins. A classical liver lobule has a central vein in its center and has several portal triads at its periphery. Bile flows through the bile canaliculi (too small to see) to the canals..

Small Portal Triad  Differentiate between the portal vein, hepatic artery and bile duct that make up the portal “triad” and note the connective tissue that surrounds them. In the liver tissue around the portal area you will see plates of hepatocytes, with sinusoids between them. Bile canaliculi can be seen as small white spots between hepatocytes. The sinusoids are lined by endothelial cells and contain occasional Kupffer cells

l. Portal venules receive blood via the portal veins l. Portal venules receive blood via the portal veins. These venules empty into either liver sinusoids (located between the cell plates) or into the central vein. 2. Hepatic arterioles are also seen within the interlobular septae. These arterioles provide arterial blood to the septal tissues and may empty into the sinusoids. 3. The venous sinusoids are lined with two different cell types: endothelial cells - have large pores, allows H2O and plasma proteins to pass freely. Kupffer cells - reticuloendothelial cells capable of phagocytizing bacteria and other foreign matter in the blood The Hepatic Portal System The liver receives a dual blood supply: from the hepatic artery from the portal vein .

A portal triad is an arrangement of three structures within the liver lobule. At the corner of the hexagonally arranged lobule the following structures are seen together: branch of hepatic portal vein branch of hepatic artery bile duct 2. There are two types of cells present within the venous sinusoids. the endothelial cells and the Kupffer cells. The endothelial cells have very large pores which allow for H20 and plasma proteins to pass. The Kupffer cells on the other hand are reticulo-endothelial cells capable of phagocytizing foreign matter in blood.

Functions of the Liver Although this section focuses on the activities of the liver with respect to bile and plasma pro- teins, and the process of detoxification, it should be pointed out that the liver has other functions as well. These functions include: carbohydrate storage amino acid metabolism metabolism of steroidal hormones metabolism of fat

Bile is a complex solution secreted by the cells of the liver into the bile duct. Approximately 250-1000 ml/day are secreted. It is golden yellow in color due to the presence of bile pigments (bilirubin and biliverdin). These pigments, it should be noted, are the breakdown products of hemoglobin. Also found in bile are the bile salts which are sodium and potassium salts of bile acids. Bile, containing the substances just mentioned as well as cholesterol, phospholipids, water, Na, K, C1, Ca, and HCO, is secreted into the bile duct which eventually drains into the duodenum. During periods where the digestive processes are somewhat slowed, as in between meals, the duodenal orifice of the duct is closed, causing the bile to Òback ups and eventually enter the gall- bladder where it is stored.

Bile is formed by the liver cells (the liver cells are epithelial cells), and excreted into tiny bile canaliculi located between the cells. Bile does not enter the sinusoids. Instead, the canaliculi come together at the portal triad where the portal ductule is formed. These bile ductules coalesce as they approach the surface of the liver (near where the hepatic portal vein and the hepatic artery enter) to form the hepatic duct which emerges from the inferior surface of the liver. Furthermore, several proteins concerned with blood coagulation are produced by the liver, such as: Fibrinogen Prothrombin Factor VII Factor IX Factor X

Bile Bile produced by the liver is made up of water (97%), bile salts, mucus and pigments, 1% fats and inorganic salts Bilirubin is its major pigment. Bile acts partly as a surfactant which lowers the surface tension between either two liquids or a solid and a liquid and helps to emulsify the fats in the chyme. Food fat is dispersed by the action of bile into smaller units called micelles. The breaking down into micelles creates a much larger surface area for the pancreatic enzyme, lipase to work on. Lipase digests the triglycerides which are broken down into two fatty acidsand a monoglyceride. These are then absorbed by villi on the intestinal wall. If fats are not absorbed in this way in the small intestine problems can arise later in the large intestine which is not equipped to absorb fats. Bile also helps in the absorption of vitamin K from the diet. Bile is collected and delivered through the common hepatic duct. This duct joins with the cystic duct to connect in a common bile duct with the gallbladder. Bile is stored in the gallbladder for release when food is discharged into the duodenum and also after a few hours

Gallbladder The gallbladder is a hollow part of the biliary system that sits just beneath the liver, with the gallbladder body resting in a small depression. It is a small organ where the bile produced by the liver is stored, before being released into the small intestine. Bile flows from the liver through the bile ducts and into the gall bladder for storage. The bile is released in response tocholecystokinin (CKK) a peptide hormone released from the duodenum. The production of CKK (by endocrine cells of the duodenum) is stimulated by the presence of fat in the duodenum.

It is divided into three sections, a fundus, body and neck It is divided into three sections, a fundus, body and neck. The neck tapers and connects to the biliary tree via the cystic duct, which then joins the common hepatic duct to form the common bile duct. At this junction is a mucosal fold called Hartmann's pouch, where gallstones commonly get stuck. The muscular layer of the body is of smooth muscle tissue that helps the gallbladder contract, so that it can discharge its bile into the bile duct. The gallbladder needs to store bile in a natural, semi-liquid form at all times. Hydrogen ions secreted from the inner lining of the gallbladder keep the bile acidic enough to prevent hardening. To dilute the bile, water and electrolytes from the digestion system are added. Also, salts attach themselves to cholesterol molecules in the bile to keep them from crystallising

Extensive folds of the mucosa extend into the lumen . Extensive folds of the mucosa extend into the lumen. The mucosa consists of a tall, simple columnar epithelium and its underlying connective tissue (constituting a lamina propria). No submucosa is defined. The muscularis consists of scattered bundles of smooth muscle. Deep to the muscularis is an adventitia consisting of rather dense connective tissue that binds the gall bladder to the liver. Where the surface of the gall bladder faces the abdominal cavity there is a serosa.

Pancreas The pancreas is a large gland located just inferior and posterior to the stomach. It is about 6 inches long and shaped like short, lumpy snake with its “head” connected to the duodenum and its “tail” pointing to the left wall of the abdominal cavity. The pancreas secretes digestive enzymes into the small intestine to complete the chemical digestion of foods compound acinar gland, similar in structure to parotid gland. • Distinction between 2 glands can be made based on absence of striated ducts and presence of islets of Langerhans. • Initial portions of intercalated ducts penetrate lumens of acini. • Centroacinar cells constitude interacinar portion of intercalated duct.Pancreas • Mixed endocrine and exocrine gland • Exocrine

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