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PART 4 Regulation and Maintenance

2. Lipase digests lipid molecules to form free fatty acids and monoglycerides.3. Emulsification, the transformation of large lipid droplets into smallerdroplets, is accomplished by bile salts.4. Micelles form around lipid digestion products and move to epithelialcells of the small intestine, where the products pass into the cells bysimple diffusion.5. Within the epithelial cells, free fatty acids are combined with amonoglyceride to form triglycerides.6. Proteins coat triglycerides, phospholipids, and cholesterol to formchylomicrons.7. Chylomicrons enter lacteals within intestinal villi and are carriedthrough the lymphatic system to the bloodstream.8. Triglycerides are stored in adipose tissue, converted into other molecules,or used as energy.9. Lipoproteins include chylomicrons, VLDL, LDL, and HDL.10. LDL transports cholesterol to cells, and HDL transports it from cellsto the liver.11. LDLs are taken into cells by receptor-mediated endocytosis, which iscontrolled by a negative-feedback mechanism.

4. Amino acids, dipeptides, and tripeptides are absorbed by symportthat is powered by Na + or H + gradients or by facilitated diffusion.5. Amino acids are transported to the liver, where the amino acids canbe modified or released into the bloodstream.6. Amino acids are actively transported into cells under the stimulationof growth hormone and insulin.7. Amino acids are used as building blocks or for energy.

Water

Water moves in either direction across the wall of the small intestine,depending on the osmotic gradients across the epithelium.

Ions

1. Sodium, potassium, calcium, magnesium, and phosphate are activelytransported.2. Chloride ions move passively through the wall of the duodenum andjejunum but are actively transported from the ileum.3. Calcium ions are actively transported, but vitamin D is required fortransport, and the transport is under hormonal control.

Proteins

1. Pepsin in the stomach breaks proteins into polypeptide chains.2. Trypsin and other proteolytic enzymes from the pancreas producesmaller peptides.3. Peptidases, bound to the microvilli of the small intestine, break downpeptides.

24.15 Effects of Aging on the DigestiveSystem (p. 915)

The muco us layer, the connective tissue, the muscles, and the secretionsof the digestive tract all tend to decrease as a person ages. These changesmake an older person more open to infections and toxic agents.

1. Which layer of the digestive tract is in direct contact with the food thatis consumed?a. mucosa c. serosab. muscularis d. submucosa

2. The ENS is found ina. the submucosa layer.b. the muscularis layer.c. the serosa layer.d. Both a and b are correct.e. All of these are correct.

3. Dentina. forms the surface of the crown of the teeth.b. holds the teeth to the periodontal ligaments.c. is found in the pulp cavity.d. makes up most of the structure of the teeth.e. is harder than enamel.

4. The number of premolar deciduous teeth isa. 0. c. 4. e. 12.b. 2. d. 8.

5. Which of these glands does not secrete saliva into the oral cavity?a. submandibular gland c. sublingual glandb. pancreas d. parotid gland

6. The portion of the digestive tract in which digestion begins is thea. oral cavity. d. duodenum.b. esophagus. e. jejunum.c. stomach.

7. During swallowing,a. the movement of food results primarily from gravity.b. the swallowing center in the medulla oblongata is activated.

c. food is pushed into the oropharynx during the pharyngeal phase.d. the soft palate closes off the opening into the larynx.

8. The stomacha. has large folds in the submucosa and mucosa called rugae.b. has two layers of smooth muscle in the muscularis tunic.c. opening from the esophagus is the pyloric opening.d. has an area closest to the duodenum called the fundus.e. All of these are correct.

9. Which of these stomach cell types is not correctly matched with itsfunction?a. surface mucous cells—produce mucusb. parietal cells—produce hydrochloric acidc. chief cells—produce intrinsic factord. endocrine cells—produce regulatory hormones

10. Why doesn’t the stomach digest itself?a. The stomach wall is not composed of protein, so it is not affectedby proteolytic enzymes.b. The digestive enzymes of the stomach are not strong enough todigest the stomach wall.c. The lining of the stomach wall has a protective layer of epithelialcells.d. The stomach wall is protected by large amounts of mucus.

11. Which of these hormones stimulates stomach secretions?a. cholecystokinin c. gastrinb. insulin d. secretin

12. Which of these structures increase the mucosal surface of the smallintestine?a. circular folds d. length of the small intestineb. villi e. All of these are correct.c. microvilli