nutrition chapter 3

The body process over which people have most conscious control is a. ingestion. b. digestion. c. metabolism. d. excretion.

A People can choose the foods and fluids they ingest. Digestion, metabolism, and excretion are largely automatic processes. A persons actions may affect those processes indirectly (e.g., exercise affects metabolism, stress may affect digestion), but people have less control over them than over ingestion.

The action of salivary amylase in the mouth is an example of a. chemical digestion. b. chewing. c. mechanical digestion. d. peristalsis and segmentation.

A Salivary amylase is an enzyme that chemically digests starch in the mouth. It does not contribute to mechanical digestion. Chewing is an example of mechanical digestion. Peristalsis and segmentation help propel food along the gastrointestinal tract and mix food with intestinal secretions.

The layer of the gastrointestinal tract that contributes most to mechanical digestion of food is the a. mucosa. b. submucosa. c. muscularis. d. serosa.

C The muscularis is a layer of muscle tissue that causes churning, peristalsis, and segmentation of food, which contribute to mechanical digestion. The mucosa is the inside layer that releases enzymes and digestive juices. The submucosa is a layer of connective tissue that contains blood vessels and nerves that regulate digestion. The serosa is the outermost layer of the gastrointestinal wall and connects to the peritoneum lining.

What is the main difference between passive diffusion and active transport? a. In active transport, the villi membrane surrounds the substance. b. Active transport requires energy; passive diffusion does not. c. Passive diffusion is involuntary; active transport is voluntary. d. Active transport requires enzymes; passive diffusion does not.

B Active transport requires energy to absorb nutrients against a concentration gradient; passive diffusion does not require energy because nutrients travel with the concentration gradient. The absorptive process by which the villi membrane surrounds the substance is pinocytosis. Neither passive diffusion nor active transport is under voluntary control, and neither process involves enzymes

Chemicals that act as messengers are called a. proteins. b. hormones. c. enzymes. d. nerve impulses.

B Hormones act as messengers between organs to cause release of needed secretions. Some, but not all, hormones are proteins. Enzymes work locally on specific classes of nutrients to change them from one form to a simpler form. Nerve impulses send messages in the body but via electrical impulses rather than via chemicals.

If the large intestine did not carry out its main function, feces would be a. alkaline. b. acidic. c. liquid. d. very dry.

C A major function of the large intestine is absorption of water, and so if the large intestine were dysfunctional, feces would be liquid. Feces would not be dry if the large intestine did not remove water. The large intestine does not have a significant effect on the acidity or alkalinity of feces.

Release of digestive secretions into the small intestine is caused by _____ that are released when _____. a. enzymes; food enters the stomach b. enzymes; food enters the small intestine c. hormones; food enters the stomach d. hormones; enters the small intestine

D Hormones that are released when chyme enters the small intestine cause the release of digestive secretions into the small intestine. The causative agents are hormones, not enzymes. The digestive secretions contain enzymes; enzymes do not trigger their release. If hormones were released when food entered the stomach, digestive secretions would be released into the small intestine too early and could cause damage.

If pancreatic secretions were absent, a. there would be no bicarbonate to buffer the acid in chyme entering the duodenum. b. mechanical digestion in the stomach would be inhibited. c. the hormone secretin would not be secreted by the small intestine. d. the gallbladder would not contract to release bile into the small intestine.

A Pancreatic secretions contain bicarbonate, which is important in buffering the acidity of chyme from the stomach. Pancreatic secretions enter the small intestine, below the stomach, and so have no effect on the stomachs mechanical digestion. The hormone secretin causes release of pancreatic secretions; pancreatic secretions do not affect its release. Bile release is initiated by the hormone cholecystokinin (CCK), not by pancreatic secretions.

The best description of an enzyme is a(n) a. chemical messenger. b. acid and alkali buffer. c. emulsifier. d. organic catalyst.

D Enzymes are organic catalysts that work on specific classes of nutrients to change them from one form to a simpler form. The description chemical messenger applies to hormones. The emulsifier in the intestines is bile. The pancreas secretes alkaline bicarbonate to buffer stomach acid so that intestinal enzymes can work properly.

When someone walks by a bakery and smells the fresh bread, his or her mouth starts to water. As the person thinks about eating the fresh bread, another digestive function that starts to occur is a. peristalsis in the small intestine. b. stimulation of pancreatic secretions. c. increased blood flow to the gut and liver. d. release of the hormone gastrin in the stomach.

D Release of the hormone gastrin from the stomach may be caused by the cephalic phase of gastric secretions when someone thinks about eating food. Thinking about food does not stimulate peristalsis, pancreatic secretions, or blood flow to the gut and liver.

The part of the digestive system that is easiest to live without is the a. taste buds. b. gallbladder. c. large intestine. d. appendix.

D The least vital part of the intestine is the appendix; it does not have any known function in humans. The taste buds are important for the enjoyment of food and to stimulate food intake. The gall bladder is not essential, but it allows for storage of bile to be released as needed for optimal digestion. The large intestine is important for absorption of water and a few other nutrients; it is possible to live without it, but intake must be adapted to compensate for unabsorbed fluid, electrolytes, and other substances.

Examples of mechanical digestion include a. activity of salivary amylase in the mouth. b. churning and mixing of food in the stomach. c. action of bile breaking fats into smaller droplets. d. effects of secretin in stimulating the pancreas to release bicarbonate.

B Churning and mixing of food in the stomach is an example of mechanical digestion because it causes physical breakdown of the food. Salivary amylase is an enzyme that causes chemical breakdown of food; bile causes emulsification of fats. Secretin is a hormone that stimulates release of bicarbonate from the pancreas; this buffers stomach acid so that intestinal enzymes can work.

The most important function of the villi of the small intestine is to a. increase the secretion of enzymes for digestion. b. increase the surface area for absorption of nutrients. c. excrete waste into the intestines. d. secrete hormones in response to nutrients in the gut.=

B Villi increase the surface area of the small intestine, which makes it possible for it to absorb more nutrients. Digestion occurs in the small intestine but is not a function of the villi. Excretion does not occur in the small intestine. The villi do not secrete hormones

An example of a problem caused by a sphincter muscle not operating properly is a. constipation. b. gallbladder disease. c. heartburn. d. peptic ulcer.

C Heartburn is caused by reflux of acidic stomach contents into the esophagus when the sphincter muscle between these two parts of the digestive tract does not operate properly. Constipation is usually caused by slow peristalsis, often in relation to inadequate intake of dietary fiber and fluid. Gallbladder disease is unrelated to gastrointestinal sphincters. Peptic ulcer is usually caused by Helicobacter pylori infection

If the speed of peristalsis were to increase, the result would be a. heartburn. b. vomiting. c. diarrhea. d. constipation.

C If peristalsis were to speed up, food would move quickly through the gastrointestinal tract, and time for absorption of nutrients and water would be insufficient, which would result in diarrhea. Constipation can be related to decreased peristalsis. Heartburn is caused by reflux of stomach contents in the esophagus and is not related to peristalsis. Vomiting is caused by a reverse in the direction of peristalsis.

Most mechanical breakdown of food occurs in the a. large intestine. b. liver and pancreas. c. mouth and stomach. d. esophagus and mouth.

C Mechanical breakdown of food occurs in the mouth during chewing and in the stomach as the food is mixed by muscular action. By the time food reaches the large intestine, it is already broken down, and most of the nutrients have been absorbed. The liver and pancreas produce secretions that help with chemical but not mechanical breakdown of food. Food passes through the esophagus largely unchanged, and so the esophagus is not involved in breakdown.

The most important functions of the small intestine are a. digestion and denaturation. b. segmentation and excretion. c. digestion and absorption. d. peristalsis and mechanical digestion.

C Most digestion and absorption occurs in the small intestine. Denaturation is not part of the digestive process. Segmentation occurs in the small intestine, but excretion does not. Peristalsis occurs throughout the digestive tract, and mechanical digestion occurs in the mouth and stomach.

Peristalsis is necessary to make it possible for people to _____ food. a. chew b. digest c. swallow d. smell and taste

C Peristalsis makes swallowing possible as involuntary movements of circular and longitudinal muscles move food along the esophagus from the mouth to the stomach. Chewing is accomplished by jaw muscles and is not related to peristalsis. Peristalsis helps move food along the gastrointestinal tract to the places where digestion of each nutrient takes place, but it does not make digestion itself possible. Smell and taste are not related to peristalsis.