APC_100_GI_part__2

APC_100_GI_part__2 - Histology of the Stomach Mammals: The...

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Histology of the Stomach Mammals : The epithelium of the stomach in most mammals is a simple columnar epithelium . However, in some animals that eat rough forage the esophagus has a stratified squamous epithelium , which may extend well into the stomach. Goblet cells are mucus-secreting cells that abundant throughout the epithelial lining of the stomach. Branched tubular glands occur in the cardiac and pyloric regions that also secrete copious mucus . Mucus functions to protect stomach tissue from auto-digestion. Simple tubular gastric glands , found in the body and fundus, secrete hydrochloric acid and pepsinogen . Pepsinogen is a proenzyme that is cleaved by acid into the active protease, pepsin . The same cells produce both acid and pepsinogen in most animals; however, in mammals parietal cells produce acid and chief cells produce pepsinogen.
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Small Intestine Mammals: The primary purpose of the small intestine is digestion of food and the absorption of nutrients, ions, and water. The small intestine (SI) in mammals consists of the duodenum, jejunum, and ileum. Most of the length of the small intestine is constituted by the jejunum (85%), duodenum (10%), and ileum (5%); this will vary somewhat with each species. The duodenum turns into the jejunum at the duodenaljejunal flexure, while the length of the antimesenteric ileal artery defines the ileum. There are not gross structural differences between the regions of the SI; they look pretty much the same. However, there are distinct functional and histological differences in the three regions. The duodenum produces more digestive enzymes and is more acidic than other regions. The jejunum pH is more alkaline and its villi are longer than either the duodenum or ileum. This suggests that the major job of the jejunum is absorption. The ileum absorbs bile acids, Vit B12, and any nutrients not absorbed proximally. The genesis of the name duodenum is from its length; it is about twelve human hand-widths long. The duodenum receives secretions from both the pancreas and the gallbladder. The exocrine pancreas secretes enzymes via the pancreatic duct into the proximal portion of the duodenum. These enzymes consist of lipases, amylases, and proteases. Some animals have a secondary pancreatic duct that empties more distally in the duodenum. In many mammals the liver has a small sac attached to it called the gallbladder. Hemoglobin is metabolized in the liver. Hemoglobin breakdown products and other metabolites are drained from the liver and stored in the gallbladder as bile. The gallbladder secretes bile, which enters the duodenum via the bile duct. Both the bile duct
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and the primary pancreatic duct open together into the duodenum via a common opening called the duodenal papillae. Bile is important in fat absorption as it emulsifies fat and aids in it digestion. In order to increase the efficiency of the
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APC_100_GI_part__2 - Histology of the Stomach Mammals: The...

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