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Liver
DIAGRAM COMING SOON
Diagram 2.3 Liver
The liver is an accessory gland. Blood enters the liver from the digestive tract by the hepatic portal system. The portal vein of this system breaks into a capillary network, the liver sinusoids. Its functions are firstly, it carries out the metabolic processing of nutrients. Secondly, it detoxifies or degrades body wastes. It also synthesizes plasma proteins. Furthermore, it stores substances such as glycogen and fats and activates vitamin D. It too removes bacteria and worn-out erythrocytes and excretes cholesterol and bilirubin. More importantly, it produces bile.
Bile is formed from heme (part of hemoglobin) of broken down erythrocytes and secreted by hepatocytes (liver epithelial cells)and is stored in the gall bladder during the interdigestive period. Bile is then secreted into the duodenum when required, for the digestion and absorption of fats and for the excretion of water-insoluble substances such as cholesterol and bilirubin. Bile acids are “detergents” that help emulsify fat. Its compositionis as follows: 97% water; 0.7% bile salts; 0.2% bile pigments; 0.06% cholesterol; inorganic salts 0.7%; fatty acids 0.15%; lecithin 0.1%; others.
The control of bile secretion is affected by the amount of fatty acids in the duodenum. The higher the amount, the more the CCK secretion which in turn leads to higher plasma CCK levels. This cause the contraction of the gallbladder which increases bile flow and relaxes the sphincter of Oddi which also increases bile flow in the duodenum.
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