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liver The liver is the largest gland in the body, weighing about 1.4 Kg. It is located under the diaphragm, within the rib cage in the upper right quadrant of the abdomen. The liver is an accessory digestive gland .liver consist of 4 Lobes Major: Left and right and Minor: Caudate and quadrate Ducts Common hepatic Cystic From gallbladder Common bile Joins pancreatic duct at hepatopancreatic ampulla The liver is composed of liver lobules which are roughly hexagonal structures consisting of hepatocytes. The hepato-cytes radiate outward from a central vein. At each of the six corners of a lobule is a portal triad. Between the hepatocytes are the liver sinusoids. The hepatocytes produce bile which flows through canals, called bile canaliculi to a bile duct. The bile ducts eventually leave the liver via the common hepatic duct. The hepatocytes also process nutrients into macromolecules, store fat-soluble vitamins, and play an important part in detoxification. The total blood flow through the Liver is about 1450 ml / minutes. It has double blood supply from hepac ar ter y 20% and por tal vei n 80%. The por tal vei n drains the digestive tract, the spleen, pancreas and gallbladder. The liver empties into the hepatic vein and into vena cava. The venous sinusoids are lined by two types of cells; 1- Endothelial cells. 2- Large kupffer cells which are tissue macrophages capable of phagocytizing bacteria and other foreign matter in the blood. Endothelial cells have large pores, plasma substances even proteins can move freely from blood to hepatic cells. Plasma proteins can pass to interstitial spaces, therefore, the lymph draining from liver has a protein concentraon about 6 gm / dl . Permeability of liver sinusoids allow a large quantities of lymph to form, therefore, about one half of all the lymph formed in the body under resting condition in the liver Metabolic function of the liver: 1- Carbohydrate metabolism: A- Storage of glycogen; the liver is important for maintaining a normal blood glucose. The liver remove excess glucose from blood, in form glycogen and return it to the blood when blood glucose concentration fall too low. Adrenaline and glucagon mobilize this liver glycogen to blood glucose by glucose-6-phosphatase which is necessary for breakdown of glycogen and only liver has it. B- Conversion of galactose and fructose to glucose. C- Gluconeogenesis when glucose concentration begins to fall below normal. Large amount of amino acid are converted into glucos 2- Fat metabolism: A- Bile salt produced; which is essential for the digestion and absorption of fat. B- Fat-soluble vitamin are stored in the liver; such as vitamin A and D. water soluble vitamin B 12are also stored. C- Mobilization of depot fat in the form ketone bodies, which are metabolized by other tissues with production of heat and energy. D- Site of synthesis of cholesterol and phospholipids. E- Site of conversion of carbohydrate and protein to fat 3-Protein metabolism: A- Deamination of amino acids; with production of ammonia. B- Convert ammonia to urea. C- Synthesis certain amino acids; that non essential amino acids. 4-The blood: A- Formation and destruction of RBC. B- Site of formation of RBC; in fetal life. C- Store of iron and B12 ; for maturation of RBC. D- Excretion the bilirubin in the bile duct; into duodenum as a bile pigments from broken RBC in blood. E- Manufactures of plasma proteins; with exception of some globulin fraction which is mainly formed by plasma cells in lymph tissue of the blood. F- Formation of clotting factors; such as prothrombin and fibrinogen 5-Detoxification: Poisons, physiological substances as well as drugs are modified by the liver for excreted by kidneys. Bilirubin metabolism :It is a greenish-yellow pigment, it is formed as end product of Hb. It is fat soluble, very toxic, its secretion is one of important function of the liver. It combines with plasma albumin, called free or unconjugated bilirubin (indirect). This type of bilirubin can not be excreted by kidney because it is insoluble in water. In premature infant unconjucated bilirubin entering the nervous system where it deposited in basal ganglia leading to kernicterus. The unconjugated bilirubine is absorbed through the hepatic cell , released from the plasma albumin. 80% of it conjugates with glucuronic acid by enzyme glucuronyl transferase. 10% of it conjugates with sulfate to form bilirubin sulfate. 10% of it conjugates with other substances. Conjugated bilirubin is water soluble excreted in urine. It is not toxic to nervous system. Some of conjugated bilirubin return to plasma I n the intestine half of bilirubin is converted by bacterial action into urobilinogen which responsible for brown color of stool. Some of urobilinogen is reabsorbed through intestinal mucous to the blood, most of it is re-excreted by liver back into the gut but 5% is excreted by kidneys into urine. Figure (16)Bilirubinmetabolism senescent RBC BilirubinAlbumin Adduct Macrophages (spleen) heme Bilirubin (indirect) Feces (stercobilin) Urine Systemic Circulation (urobilin) BilirubinGlucuronide Portal Circ. Urobilinogen Intestinal Flora Bile Duct Hepatocyte