Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Answers to Review Questions - Chapter 48 1. Imagine you have just taken a bite of steak. List in sequence the structures through which it passes in its journey through the digestive system. What happens in each structure? Assuming it is mostly protein, the steak would be chewed in the mouth (mechanical digestion), then passed to the pharynx for swallowing, then through the esophagus into the stomach where the chemical digestion of the protein begins. In particular, pepsin converts the protein to short polypeptides, which then flow into the small intestine. In the small intestine, further chemical digestion occurs. Trypsin and chymotrypsin convert the polypeptides into shorter chains, which are then converted to amino acids by carboxypeptidase, peptidases, and dipeptidases. The amino acids are then absorbed into the bloodstream and are carried to the liver. Any remaining waste products would then pass into the large intestine and eliminated through the anus. 2. What are the four layers of the digestive tract? What significant features/components are found in each? Mucosa - innermost layer consisting of epithelial tissue and underlying connective tissue Submucosa - surrounds mucosa - consists of connective tissue housing blood and lymph vessels and nerves. Muscle layer (muscularis) - two sublayers of smooth muscle surrounding the submucosa. Visceral peritoneum (a.k.a. serosa or adventitia) - outer connective tissue "coat" of the digestive tract 3. What are the predominant active enzymes found in each of the following regions of the digestive tract? What function does each enzyme perform? a) mouth Enzyme - salivary amylase; breaks down polysaccharides into disaccharides. b) Stomach Enzyme - pepsin; breaks down proteins (long polypeptides) into short polypeptides. c) small intestine Enzymes: Pancreatic amylase - breaks down polysaccharides into disaccharides Pancreatic lipase - breaks down fats into fatty acids and glycerol Trypsin, chymotrypsin - break down polypeptides into short polypeptides. Peptidases - break down short polypeptides into amino acids. Maltase, lactase, sucrase - break down disaccharides into monosaccharides. 4. What does the liver produce to aid in digestion? How does this material assist digestion? The liver produces bile, which contains bile salts. These salts function to emulsify (break up) large fat droplets into smaller fat droplets. This increases the surface area on which the enzymes may act to digest the lipids. 5. What are chylomicrons? Chylomicrons are protein-covered fat droplets that transport triacylglycerols to the lymph and then to the blood. 6. List the essential amino acids (see chapter 3). Why are they "essential"? Leucine, isoleucine, lysine, phenylalanine, tryptophan, valine, methionine, threonine, histidine (and arginine in children).