O zone 2 have structural and functional

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o Zone 2 : have structural and functional characteristics intermediate between the cells in zones 1 and 3. o Zone 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 intestines o Most digestion and absorption of nutrients occur in a long tube called the small intestine. o It 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 intestines o Segmentation mix chyme with digestive juices and bring food into contact with mucosa for absorption ; peristalsis propels chyme through small intestine o Completes digestion of carbohydrates, proteins, lipids; begins and completes digestion of nucleic acids o absorbs about 90% of nutrients and water that pass through digestive system . o Function of specific structures of small intestine Plicae Circularis (Circular Folds): help increase the surface area Villi & microvilli: help us enhance the absorption SIGNIFICANT CELLS OF THE SMALL INTESTNES AND THEIR SECREATION o Paneth cells Secrete lysosome
o The enteroendocrine cells S cells Secrete secretin in response to acidic chyme, promoting release of HCO3- rich pancreatic juice; secondarily, secretin slows down secretion of gastric juice. K cells Secrete GIP (glucose-dependent insulinotropic peptide) slows down secretion of gastric juice stimulates insulin secretion CCK cells Secrete cholecystokinin in response to amino acid and fatty acid CCK stimulates digestive enzyme-rich pancreatic juice Relaxes the sphincter of Oddi Slows gastric emptying Promotes a feeling of satiety Causes contraction of the gallbladder CCK and secretin enhance each other o Brunner’s gland Secrete alkaline rich mucus to counter acidic chyme Located in the

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