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oZone 2: have structural and functional characteristics intermediate between the cells in zones 1 and 3.oZone 3: farthest from branches of the portal triad They are the last to show the effects of bile obstruction or exposure to toxins.They are the first one to show the effects of impaired circulation, and the last ones to regenerate. They are also the first one to show evidence of fat accumulation.
The liver receives blood from two sources: hepatic artery it obtains oxygenated blood, and hepatic portal vein it receives deoxygenated blood containing newly absorbed nutrients, drugs, and possibly microbes and toxins from the GI tract. Branches of both hepatic artery and portal vein carry blood into hepatic sinusoids, where oxygen, nutrients and certain toxic substances are taken up by the hepatocytes.Products manufactured by the hepatocytes and nutrients needed by other cells are secreted back into the blood, which then drains into the central vein and eventually passes into a hepatic vein, inferior vena cava and lastly back to the right atrium of Because blood from the GI tact passes through the liver as part of the hepatic portal circulation, the liver is often a site for metastasis of cancer that originated in the GI tract.
Small intestinesoMost digestion and absorption of nutrients occur in a long tube called the small intestine.oIt begins at the pyloric sphincter of the stomach, coils through the central and inferior part of the abdominal cavity, and eventually opens into large intestine.Regions of small intestines are the duodenum, jejunum, and ileum. Circular folds increase the surface area of digestion and absorption in the small intestine.
Functions of the small intestinesoSegmentation mix chyme with digestive juices and bring food into contact with mucosa for absorption; peristalsis propels chyme through small intestineoCompletes digestionof carbohydrates, proteins, lipids; begins and completes digestion of nucleic acidsoabsorbs about 90% of nutrients and water that pass through digestive system.oFunction of specific structures of small intestinePlicae Circularis (Circular Folds): help increase the surface areaVilli & microvilli:help us enhance the absorptionSIGNIFICANT CELLS OF THE SMALL INTESTNES AND THEIR SECREATIONoPaneth cellsSecrete lysosome
oThe enteroendocrine cellsS cellsSecrete secretinin response to acidic chyme, promoting release of HCO3- rich pancreatic juice; secondarily, secretin slows down secretion of gastric juice.K cellsSecrete GIP(glucose-dependent insulinotropic peptide)slows down secretion of gastric juicestimulates insulin secretionCCK cellsSecrete cholecystokinin in response to amino acid and fatty acidCCK stimulates digestive enzyme-rich pancreatic juiceRelaxes the sphincter of OddiSlows gastric emptyingPromotes a feeling of satietyCauses contraction of the gallbladderCCK and secretin enhance each otheroBrunner’s glandSecrete alkaline rich mucus to counter acidic chymeLocated in the