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25 Cards in this Set
- Front
- Back
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LIVER
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- Largest gland in body, largest internal organ
- exocrine function (secretes bile into duodenum) - endocrine function (synthesizes and releases substances into blood) - interposed between blood vessels of intestinal tract and general circulation - receives venous blood from intestine via portal vein - receives arterial blood via hepatic artery - drains into inferior vena cava via hepatic veins - the liver therefore receives (in the portal blood) the material absorbed from the intestine - the only exception is lipid which is transported in the lymphatics |
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Function of the Liver (8)
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(1) absorbed products of digestion are metabolized or transformed & returned to the blood
(2) toxic substances in the blood are degraded or detoxified (3) bile is produced for release into the intestine via the bile duct - bile salts act as a emulsifying agents that aid in the digestion and absorption of lipids - bile pigments detoxify bilirubin, the end product of hemoglobin degradation - phospholipids, metabolic substrates for other cells, are reabsorbed in the gut for recycling (4) the protein components of blood plasma (plasma proteins) are produced: Albumins and non-immune α & β globulins, lipoproteins, glycoproteins and prothrombin / fibrinogen (5) carbohydrates are stored as glycogen & released as glucose (glycogenolysis) - maintains blood glucose (6) cholesterol is synthesized and taken up from the blood - used to form bile salts (7) vitamins and iron are stored and converted (Vitamins A/ K/ D) (8) the structure and function of hormones are modified |
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Albumins and non-immune α & β globulins
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Maintain PLASMA COLLOID OSMOTIC PRESSURE
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Lipoproteins
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Transport --> TRIGLYCERIDES and CHOLESTEROL
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Glycoproteins
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IRON transport
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Prothrombin and fibrinogen
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Involved in the BLOOD CLOTTING
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Vitamin A (retinol)
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required for RHODOPSIN synthesis
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Vitamin D
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important in calcium and phosphate metabolism
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Vitamin K
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For synthesis of PROTHROMBIN
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Organization of Liver
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- Enclosed by a fibrous connective tissue capsule called "Glisson's capsule"
- Surrounded by a serosa or an adventitia where it is in apposition to other organs - Divided into lobes - Epithelial cells are arranged in radially disposed plates around terminal branches of the hepatic veins called: "central veins" - Plates of cells are exposed to blood flowing in a parallel system of vascular channels called "hepatic sinusoids" |
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Classical Liver Lobules Characteristics
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- Hexagonal areas with a portal area at each corner and a central vein at the centre
- Each portal area (portal tract) consists of: (1) a branch of the portal vein (2) a branch of the hepatic artery (3) a bile duct (4) sometimes a lymphatic vessel is also seen |
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2 Alternative organizational plans for the liver
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Portal lobules and the Liver Acinus
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Blood Supply and Bile Ducts
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- the portal vein, hepatic artery and bile duct enter at the porta hepatis (on inferior surface of liver)
- the hepatic artery carries much less blood than the portal vein - the portal vein comes from the digestive tract and abdominal organs - liver is the first organ to receive metabolic substances, nutrients and toxins from the GI tract - all three vessels branch repeatedly until they reach a portal area - they are accompanied throughout by a network of lymphatics - terminal branches of the artery, vein and bile duct leave the portal area - run along the boundaries between the lobules as distributing vessels - blood enters the sinusoids from these terminal branches of the artery and vein - sinusoids therefore receive both arterial and venous blood - blood leaves the sinusoids at the central vein (which is really a terminal hepatic venule) - the central vein passes to a sublobular vein -- to a hepatic vein -- to the vena cava - the smaller veins are highly contractile - they contro |
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Portal blood contains
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- Nutrients and toxic materials absorbed by intestine
- Blood cells and breakdown products of blood cells from spleen - Hormones from pancreas and GI tract |
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Liver Sinusoids Shape and Cell Type(s)
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Irregular shape
2 types of lining cells: Endothelial Cells and Kupffer Cells |
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Endothelial cells of Liver
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- large fenestrations in cells
- discontinuities (spaces) between cells - discontinuous basement membrane - provides little or no filtration barrier except to cells |
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Kupffer cells
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- Liver cells derived from monocytes - highly phagocytic - lysosomal activity
- situated between endothelial cells, form part of lining of sinusoid - surface folds and processes abundant - destroy bacteria & damaged erythrocytes - iron stored in hepatocytes |
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Perisinusoidal Space (Space of Disse) of Liver
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- Perivascular space between endothelial cells and hepatic parenchymal cells (hepatocytes)
- Numerous microvilli on hepatocytes project into space - increase surface area for absorption 6X - Mainly plasma with some proteins and lipoproteins in space - some reticular fibres - Forms a space comparable to a lymph capillary - Plasma in space drains to "space of Mall" in periportal ct, then to lymphatic capillary in portal area - Lymphatic capillaries drain into larger vessels which exit the liver and drain into thoracic duct - In fetus and in chronic anemia in the adult, space contains blood-forming cells - Hepatic stellate cells (Ito cells) |
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Hepatic stellate cells (Ito cells)
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- Located in perisinusoidal space
- storage site for vitamin A - important in vision - produce collagen in pathological conditions, resulting in perisinusoidal fibrosis - produce extracellular matrix during recovery from injury to liver |
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"Space of Mall"
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in Liver Periportal CT
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Hepatic Parenchymal Cells (Hepatocytes)
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- large, polygonal cells, often binucleate, normally tetraploid, highly regenerative
- rough ER and abundant smooth E.R. - contains enzymes involved in degradation of toxins & drugs - numerous lysosomes - storage sites for iron, increase in number during pathology - elaborate Golgi complexes lie adjacent to canaliculi, involved in secretion of lipoprotein precursors - abundant glycogen and lipid deposits, many mitochondria - numerous peroxisomes - play a role in detoxification (eg alcohol) and breakdown of fatty acids |
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Bile Canaliculi
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- minute canals between adjacent hepatocytes
- wall is formed from hepatocyte plasmalemma - lumen is an expansion the intercellular space - microvilli project into the lumen - tight junctions occur at each margin of a canaliculus - bile secretion into the canaliculus from the hepatocytes is an active process |
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Bile Ducts
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- near the portal canal canaliculi join to form intrahepatic ductules called "the canals of Hering"
- lining cells of canals of Hering proliferate extensively during liver necrosis - may be stem cells - canals of Hering drain into interlobular bile ducts in portal areas - interlobular ducts join main ducts which fuse to form the hepatic duct - hepatic duct receives cystic duct, continues to the duodenum as the common bile duct - extrahepatic ducts show many folds in the mucosa lined with tall columnar epithelium - they possess an incomplete smooth muscle layer - carry bile to the gallbladder and duodenum |
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GALL BLADDER
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- pear-shaped, distensible, hollow organ, attached to liver
- fundus, body, neck, continues into cystic duct - receives dilute bile from hepatic duct - functions in concentration and storage of bile - pancreozymin (cholecystokinin) from intestinal mucosa induces contraction of muscle layer and release of bile |
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- Gall bladder wall consists of
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- mucosa (simple columnar ep. with microvilli and junctional complexes) thrown into many folds
- lamina propria rich in fenestrated capillaries, devoid of lymphatics - contains folds of surface epithelium - fibromuscular layer which discharges bile - serosa |
