moves gastric contents from the body of the stomach down into the antrum a process is known as propulsion. The pyloric sphincter normally remains almost but not completely closed. Because most food particles in the stomach initially are too large to pass through the narrow pyloric sphincter, they are forced back into the body of the stomach, a process referred to as retropulsion. Another round of propulsion then occurs moving the food particles back into the antrum. If the food particles are still too large to pass through the pyloric sphincter, a phenomenon known as gastric emptying. Gastric emptying is a slow process.Foods may remain in the fundus for about an hour without becoming mixed with gastric juice. During this time, digestion by salivary amylase glands continues. The churning action mixes chime with acidic gastric juice, inactivating salivary amylase and activating lingual lipase produced by the tongue which starts to digest triglycerides into fatty acids and diglycerides, HCL secretion by parietal cells of the stomach. The strongly acidic fluid of the stomach kills microbes in food. Pepsin serves certain peptide bonds between amino acids, breaking down a protein chain of many amino acids into smaller peptide fragments. Pepsin is most effective in the very acidic environment of the stomach.Within one hour after eating a meal, the stomach has emptied its contents into the duodenum. Foods richis carbohydrates spend the least time in the stomach; high protein foods remain somewhat longer and emptying is a slowest after a fat laden meal containing large amounts of triglycerides. Small IntestinesMost digestion and absorption of nutrients occurs in a long tube called small intestine. Because of this, its structure is specifically adapted for these functions. Its length alone provides a large surface area for digestion and absorption and that area is further increased by circularly folds, villi and microvilli. The small intestines begin at the pyloric sphincter of the stomach, coils through the central and inferior part of the abdominal cavity, and eventually opens into the large intestine.Even though the action of salivary amylase may continue in the stomach for a while, the acid pH of the stomach destroys salivary amylase and ends its activity. Thus, only a few starches are broken down by the time chyme leaves the stomach. Those starches not already broken down into maltose, malt triose, and dextrin are cleaved by pancreatic amylase, any enzyme in pancreatic juice that acts in the small intestine. Although pancreatic amylase acts on both glycogen and starches, it has no effect on another polysaccharide called cellulose, an indigestible plan fiber that is commonly referred to as “roughage’ as it movesthrough the digestive system. After amylase has split starch into fragments, a brush border enzymecalled dextranases acts on the resulting dextrin, clipping off one glucose unit at a time. Assignment 3 :: Biology 235: Human Anatomy and Physiology 8
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