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13. Liver and Pancreas.pdf

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Anatomy & Cell Biology
ANAT 261
Craig Mandato

Naveen Sooknanan McGill Fall 2011 Liver: The liver is one of the glands in the digestive system. It does not contain any hormones. It has both endocrine and exocrine properties o Exocrine: secretes bile, which goes to the gall bladder and then the intestines o Endocrine: secreted into the bloodstream The liver is the largest gland in the body. It is located right under the diaphragm The liver is surrounded by a capsule CT which is very touch and rich in collagen fibers o When you take a blow to the liver, the capsule tears and the doctor must stich it back together because the liver would fall apart without it The porta hepatis is a layer of CT which divides the liver into lobes and smaller lobules o This CT is accompanied by 2 pairs of each portal veins and hepatic arteries o They come from the abdominal cavity, particularly the area that drains the spleen, and also from the digestive system Portal veins come from various areas including those mentioned above o Chylomicrons from the digestive tract come in from the portal veins to be digested o They have a functional circulation rather than a typical nutritional circulation Hepatic arteries are paired with the portal veins and just run in the opposite direction o They oxygenate the liver The hepatic vein has a typical nutritional function o It takes carbon dioxide produced in the liver back to the heart o It drains directly into the inferior vena cava The exocrine secretion of the liver consists of many bile ducts converging into one hepatic duct o This hepatic duct will continue to the gall bladder where it will place all of the livers exocrine secretions o It will eventually reach the intestines The liver has several important functions: The first is endocrine secretion into the blood stream. Secretion includes: o Albumin, a typical protein in the body o Fibrinogen and prothrombin are coagulation proteins o Transferrin binds to free-floating iron in the blood, which is toxic, and brings it wherever it needs to go o VLDL and LDL (very) low density lipoproteins Lipids combined with proteins can travel in the aqueous cytoplasm 1 Naveen Sooknanan McGill Fall 2011 Cholesterol is necessary for growth of the PM, but it can be bad when circulates in the blood for too long Exocrine secretion is mainly to the gall bladder o Bile acids o Bilirubin, which is a pigment coming from dead red blood cells o Phospholipids and cholesterol (travel with bile) Inactivation/elimination of substances: o Glucuronyl transferase combine glucuronic acid and bilirubin, but also produces barbiturates, antihistaminics, anticonvulsants, insecticides and other drugs Bilirubin is a product that can emulsify fats Barbiturates are anaesthetics o Endocytosis of hormones and LDL (cholesterol) particles They undergo receptor mediated endocytosis (RME) and then destruction Cholesterol can become oxidised in the blood, which is bas, so the liver needs to unoxidize these by RME Otherwise, they get eaten by macrophages, which deposit in artery walls and can cause a heart attack A hormone, problactin, in females, cannot be in the blood for too long and needs to be absorbed by the liver Conversion of substances: o Tetra-iodothyronine T4 (thyroxine) Tri-iodothyronine T3 (which is more potent) T4 is a thyroid hormone o The liver generally converts certain products into more potent compounds Hemopoiesis, production of blood cells: o The liver is the first organ to produce blood, but this only happens during fetal development o Mature hemopoiesis is done in the bone marrow Storage of substances: o Sugar monosaccharides are linked together in the liver and stored as glycogen o Cholesterols that are absorbed by RME can be stored as phospholipids o Lipids can also be stored in the liver o When sugar levels are high in the blood, insulin stimulates the liver to absorb sugar and turn them into glycogen The liver can slowly release sugar by breaking up glycogen as we sleep, or between meals This sugar can then be used as energy for the cells Hepatic lobules are individually wrapped by CT. Eventually; differentiation causes the disappearance of lobules Interlobular space contains hepatic arteries (red), portal veins (blue), and bile ducts (green) o Interlobular tissue in the liver is referred to a portal space 2Naveen Sooknanan McGill Fall 2011 A central vein penetrates into the middle of every hepatocyte o From this vein, sinusoids branch off and divide the lobule into septi, or trabeculae Remember what sinusoids are? Theyre a type of fenestrated capillary. They are very disorganized, unlike regular capillaries that we are used to seeing A sublobular vein runs parallel to rows of hepatocytes o All of the central veins drain into the sublobular vein which o Sub in this case does not necessarily mean below, as long as it is parallel to a row of hepatocytes The portal space, which means interlobular tissue for the liver, can be thickened at some places because of the presence of bile ducts We will now focus in onto one hepatic lobule and its components: The central vein is an important landmark when looking for a hepatic lobule in a slide o These veins have no proper wall (i.e. adventitia, etc.), only an endothelium o Sinusoids, which divide the hepatic lobule into septi, or trabeculae, converge into one central vein Portal venules and hepatic arterioles can also be seen, but they are not to be confused with the central vein o The portal venules is responsible for f
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