Gastrointestinal Function

What is a common cause of gastroesophageal reflux disease (GERD)?

> A weak gastroesophageal sphincter Having a weak gastroesophageal sphincter allows acidic secretions from the stomach to flow back into the esophagus and pool there, burning the esophageal lining and causing the familiar pain of heartburn. Chronic heartburn is referred to as gastroesophageal disease (GERD). Although consumption of certain foods and beverages, including spicy, fried, or fatty foods and alcoholic beverages, can contribute to GERD, this is not causative. The epiglottis closes off the trachea during swallowing, ensuring that food and drink enter the esophagus rather than the trachea. Improper closure of the epiglottis is not related to GERD. Dysphagia, or difficulty swallowing, can be caused by tumors, scar tissue, trauma, nerve damage, or stroke. A person with dysphagia may experience improper and rapid swallowing, but the condition is not related to GERD.

The main role(s) of the organs in the gastrointestinal (GI) tract is (are) to ___________. (break food down into its smallest components) (absorb the nutrients) (eliminate the wastes remaining from ingested food)

> All options are correct. All options are correct. The main roles of the organs of the gastrointestinal (GI) tract are to break food down into its smallest components, absorb the nutrients, and eliminate the remaining wastes.The main organs of the GI tract are the mouth, esophagus, stomach, small intestine, and large intestine.

What is the immune disorder that damages the villi of the small intestine when gluten is consumed?

> Celiac disease Celiac disease is the immune disorder that damages the villi of the small intestine when gluten, a protein in wheat, rye, and barley, is consumed. In people with celiac disease (about 1 in 141 Americans), an immune resonse to ingestion of gluten erodes the villi of the small intestine. This reduces their ability to absorb nutrients. A wheat allergy is an immune hypersensitivity to wheat, not specifically gluten, which is only one of many proteins found in wheat. Moreover, wheat allergy can cause a rash, wheezing, or many other symptoms, but is not associated with erosion of the intestinal villi. Irritable bowel syndrome (IBS) is a functional disorder that involves changes in colon rhythm. It is not mediated by the immune system, and it produces no structural damage. Gluten intolerance does not involve the immune system or damage the villi of the small intestine. Intolerances tend to produce significant discomfort, but the symptoms end when the offending food leaves the GI tract.

After food enters the gastrointestinal tract, which process uses enzymes, bile, and other compounds to break the food down into smaller units that can be absorbed by the body?

> Chemical digestion After food enters the gastrointestinal tract, enzymes, bile, and other compounds participate in chemical digestion, which breaks food down into smaller units that can be absorbed by the body. Mechanical digestion involves chewing, grinding, and swallowing food, and then moving it through the gastrointestinal (GI) tract via the rhythmic muscular contractions of peristalsis and the "sloshing" motions of segmentation.

Which one of the following may help to alleviate constipation?

> Consuming an adequate amount of fiber daily Consuming an adequate amount of fiber daily may help to alleviate constipation, a condition in which stools are difficult to pass. To alleviate constipation, many healthcare providers suggest increasing fiber in the diet. Five to nine servings of fruits and vegetables and six or more servings of whole grains is recommended daily. Restricting fluid intake and maintaining a sedentary lifestyle will not help relieve constipation, and it may in fact contribute to the slowed passage of dry, hard stools. Taking antacids will not help to alleviate constipation, either. Antacids may be helpful for other types of gastrointestinal distress, such as occasional heartburn, but relief of constipation requires a dietary change that increases the bulk and water content of the stools.

_____ is the process by which food is broken down into absorbable units.

> Digestion Digestion is the process by which food is broken down into absorbable units. Through a multistep process in the gastrointestinal tract, food is softened with moisture and heat and then broken down into smaller particles by chewing and exposure to enzymes. Digestion is the forerunner to absorption, the process by which digested nutrients move into the circulation, where they can be transported to and used by the body's cells. Circulation is the process through which absorbed nutrients are distributed in the cardiovascular and lymphatic systems. Elimination is the process by which the body eliminates the waste products of digestion.

Which intestinal disorder is characterized by the colon overresponding to normal stimuli, which can cause bouts of either constipation or diarrhea?

> Irritable bowel syndrome (IBS) Irritable bowel syndrome (IBS) is the intestinal disorder characterized by the colon overresponding to normal stimuli, which causes bouts of constipation or diarrhea. Although the exact cause of IBS is unknown, anxiety and stress may trigger episodes. It can be managed with dietary modification such as increasing soluble fiber, as well as stress management. Medications are available for treatment. Celiac disease is an immune disorder. People with the disease are unable to digest gluten, the protein in wheat, rye, and barley. Caliac disease erodes the lining of the small intestine, not the colon. Colon cancer is not characterized by the colon overresponding to normal stimuli. It is characterized by the conversion of abnormal polyps in the colon to aggressive, invasive tumors. Hemorrhoids are swelling and inflammation of the veins of the rectum and anus. They are caused by increased pressure from straining to pass stool.

In what order do the organs of the gastrointestinal tract digest food and absorb nutrients?

> Mouth, esophagus, stomach, small intestine, large intestine The organs of the gastrointestinal tract digest food and absorb nutrients in this order: mouth, esophagus, stomach, small intestine, large intestine. Digestion begins in the mouth. Once swallowed, a bolus (small mass) of food is pushed down the esophagus by peristalsis (involuntary constriction and relaxation of the muscles). The lower part of the esophagus relaxes, allowing the bolus to enter the stomach. The stomach mixes and churns the bolus with a variety of secretions into a liquid called chyme. Chyme is then released gradually into the small intestine, where most digestion and absorption occurs. Finally, the residue enters the large intestine, which absorbs water and some nutrients and eliminates waste via excretion at the rectum.

What is chyme?

> The semiliquid, partially digested food mass that leaves the stomach and enters the small intestine Chyme is the semiliquid, partially digested food mass that leaves the stomach and enters the small intestine. The complete digestion of chyme requires mechanical and chemical processes, most of which occur within the small intestine. By the time chyme reaches the large intestine, most of its nutrients have been absorbed. Gastrin is a digestive hormone produced in the lining of the stomach. The beneficial bacteria populating the large intestine are commonly known as the GI flora. They ferment some of the undigested food remnants, produce certain vitamins, and are thought to have many other helpful functions. Bile is the substance that emulsifies dietary lipid.

Which of the following is true regarding the small intestine?

> The small intestine has a vast surface area for absorption of nutrients. The small intestine has a vast surface area for absorption of nutrients. The folds, villi, and microvilli of the lining of the small intestine create a remarkable surface area (enough to cover a tennis court) that allows for a continuous, efficient absorption of virtually all digested nutrients. Nutrients are absorbed through these projections and are transported through both the blood vessels and lymphatic vessels throughout the body. The small intestine is critical to the process of digestion. It not only receives digestive enzymes from the pancreas, but it also secretes many digestive enzymes.

What is the name of the process that requires energy (adenosine triphosphate, or ATP) for digested nutrients to be absorbed through the small intestinal wall into the bloodstream or lymphatic system?

> active transport Active transport is the process that requires energy (adenosine triphosphate, or ATP) for digested nutrients to be absorbed through the small intestinal wall into the bloodstream or lymphatic system. Digested nutrients in low concentration are transported to an area of high concentration. This process requires both a carrier and energy to shuttle nutrients across the cell membrane. Passive diffusion is a simple process in which nutrients are absorbed due to a concentration gradient, from high to low. This process doesn't require energy or a special protein carrier. Facilitated diffusion is similar to passive diffusion in that nutrients are absorbed from a high to a low concentration and the process does not require energy. But facilitated diffusion does require a specialized protein to carry the nutrients across the cell membrane. Endocytosis occurs when whole molecules are engulfed by the cell membrane and absorbed intact.

The chemical that neutralizes the acidic chyme so that the lining of the small intestine is not eroded is _____.

> bicarbonate Bicarbonate is released from the pancreas into the small intestine. There, it neutralizes the acidic chyme entering from the stomach. Thus, the lining of the small intestine is not eroded. Amylase is an enzyme in saliva that begins to break down carbohydrates in the mouth. Mucus is a secretion of the lining cells of the gastrointestinal (GI) tract that helps protect the GI tract from mechanical and chemical injury. It provides a barrier against the acidic chyme, but it does not neutralize it. Gastrin is a hormone produced in the stomach that stimulates digestive activities, such as the secretion of gastric juice, and increases motility and emptying.

Salivary amylase begins the digestion of ________ in the ________.

> carbohydrate; mouth Salivary amylase begins the digestion of carbohydrate in the mouth. Carbohydrates, fats, and proteins are broken down by their own specific enzymes. The enzyme salivary amylase is secreted in saliva and starts digesting starch (carbohydrates) in the mouth. In the stomach, a protein-digesting enzyme called pepsin begins to break down protein, while fat digestion relies on a variety of lipases as well as bile. Iron, like all essential minerals, is an element and therefore cannot be digested anywhere in the body.

The compounds that help break down foods during digestion by speeding up chemical reactions are called _____.

> enzymes The compounds that help break down foods during digestion by speeding up chemical reactions are called enzymes. Enzymes such as amylases, lipases, and proteases break down carbohydrates, fats, and proteins respectively during digestion. Hormones are chemical messengers that regulate activities such as metabolism and the cells' use of nutrients. Proteins are energy-providing macronutrients. Phytochemicals are non-nutrient plant chemicals thought to benefit human health.

The protective tissue that covers the trachea during swallowing and prevents choking is the _____.

> epiglottis The protective tissue that covers the trachea during swallowing is the epiglottis. The epiglottis ensures that food and drink descend into the esophagus rather than the trachea. When the epiglottis doesn't work properly, food or fluid can enter the trachea, which can prompt severe coughing or life-threatening choking. The tongue is a muscle that pushes food to the back of the mouth and into the pharynx. The pharynx is a chamber that food passes through just before being swallowed.

One of the most common digestive conditions involving the esophagus is ________.

> heartburn One of the most common digestive conditions involving the esophagus is heartburn. Approximately 20 percent of adults have heartburn every day. Heartburn occurs when acidic gastric juice flows from the stomach back into the esophagus or even the throat. Difficulty swallowing, or dysphagia, can result from mechanical causes such as tumors, scar tissue, obstruction, cancer, trauma, or other barriers in the throat. Dysphagia can also result from nerve damage or a stroke. It is not a common condition. Gastroenteritis, sometimes referred to as the stomach flu, is an inflammation of the stomach or intestines—not the esophagus—caused by a virus or bacteria. Esophageal cancer is associated with obesity, heavy drinking, and smoking. It is not common. The most common cancer affecting the gastrointestinal tract is colorectal cancer.

What is the most common cause of peptic ulcers?

> infection with Helicobacter pylori bacteria Infection with Helicobacter pylori bacteria is the most common cause of peptic ulcers. A peptic ulcer is a sore or erosion in the stomach or intestinal lining. Smoking and drinking alcohol can exacerbate peptic ulcers. Stress has been linked to other digestive issues, including constipation, diarrhea, and irritable bowel syndrome (IBS), but is not considered a cause of peptic ulcers. Prolonged use of aspirin and other nonsteroidal anti-inflammatory drugs can cause peptic ulcers; however, this is not the most common cause. Eating spicy foods is not known to cause peptic ulcers.

Bile is made in the ________ and stored in the _________.

> liver; gallbladder Bile is made in the liver and stored in the gallbladder. The liver produces about 2 pints of bile each day to emulsify fats. Once bile is formed in the liver, it is collected, drained, and released into the gallbladder to be stored. The gallbladder is attached to the liver and stores approximately 1 to 2 ounces of concentrated bile at a time. The gallbladder releases bile into the small intestine through the bile duct. In addition to the liver and gallbladder, another accessory organ—the pancreas—is essential to digestion. The pancreas produces digestive enzymes and bicarbonate ions that are released into the small intestine via the pancreatic duct. It also produces hormones, including the two blood glucose-regulating hormones, insulin and glucagon.

Most fats and fat-soluble nutrients are absorbed and carried through the ______ system.

> lymphatic Most fats and fat-soluble nutrients are absorbed and carried through the lymphatic system. The lymphatic system is a complex network of vessels, valves, nodes, and ducts that helps maintain the internal fluid environment. The products of fat digestion must pass through the lymphatic system before they enter the bloodstream because they are too large to enter the bloodstream directly. Lymph also transports absorbed fat-soluble vitamins from the intestinal tract to the blood. Water-soluble nutrients are absorbed through the capillary walls in the intestinal villi and are transported in the bloodstream in vessels of the cardiovascular system. The urinary system includes the kidneys, ureters, bladder, and urethra. It functions to filter blood and produce and excrete urine. The mesentery is a fold of tissue that holds the intestines in place in the abdominal cavity and supplies them with blood vessels, nerves, and lymphatics.

Digestion begins in the _____.

> mouth Digestion begins in the mouth. The mechanical actions of chewing tear, shred, and mix food with saliva, forming a bolus, or small mass. Salivary amylase, an enzyme secreted by the salivary glands, begins the chemical breakdown of carbohydrate. The bolus then passes from the mouth through the esophagus to the stomach. The stomach mixes and churns the bolus with HCl, gastric enzymes, and other secretions into a liquid called chyme before it is propelled into the small intestine. Thus, some digestion has occurred before chyme enters the small intestine. The liver, which is outside the gastrointestinal tract, is one of the accessory organs of digestion; it produces bile and has several roles in the transport and storage of nutrients.

Which accessory organ makes and secretes digestive enzymes and bicarbonate into the small intestine?

> pancreas The pancreas is the accessory organ that makes and secretes digestive enzymes and bicarbonate into the small intestine. It also produces hormones, including the two blood glucose-regulating hormones, insulin and glucagon. The liver is the accessory organ that produces bile. It also detoxifies alcohol and stores some nutrients. The gallbladder is the accessory organ that stores the bile produced by the liver and secretes the bile through the bile duct into the small intestine. The stomach is the major digestive organ that holds food after it has moved down the esophagus and before it is propelled into the small intestine.

A key function of the gastric secretion hydrochloric acid (HCl) is to activate ________.

> pepsin A key function of the gastric secretion hydrochloric acid (HCl) is to activate pepsin, a protein-digesting enzyme. Mucus produced in the stomach acts as a barrier between the HCl and the stomach lining, protecting the lining from irritation or damage from this strong chemical. Other gastric secretions include intrinsic factor, which is essential to the absorption of the vitamin B12 in foods, and gastrin, a gastric hormone that stimulates digestive activities. Bile is not a gastric secretion.

The sphincter that connects the stomach to the small intestine is called the ________.

> pyloric sphincter The sphincter that connects the stomach to the small intestine is called the pyloric sphincter. The pyloric sphincter prevents chyme (the semiliquid, partially digested food mass) from exiting the stomach too soon, and it prevents intestinal contents from returning to the stomach. As the chyme accumulates near the pyloric sphincter, the muscular sphincter relaxes and the chyme gradually enters the small intestine. The ileocecal sphincter is the gateway between the end of the small intestine and the beginning of the large intestine. The gastroesophageal sphincter is a circular band of muscle between the esophagus and the stomach that opens and closes to allow food to enter the stomach. Cardiac sphincter is another term for gastroesophageal sphincter.

The sphincter that separates the stomach from the duodenum is the _____.

> pyloric sphincter The stomach is separated from the duodenum by the pyloric sphincter. The pyloric sphincter allows chyme to pass from the bottom of the stomach to the beginning of the duodenum, the first part of the small intestine. The gastroesophageal sphincter is between the mouth and the stomach. The ileocecal sphincter separates the ileum from the colon. The colon sphincter is also called the anal sphincter; it is the last part of the gastrointestinal tract.

Most of the digestion and absorption of food occurs in the ________.

> small intestine Most of the digestion and absorption of food occurs in the small intestine. In the small intestine, digestive enzymes from the pancreas and small intestine digest food into absorbable nutrients. The small intestine is the longest part of the gastrointestinal tract. Thousands of projections on the intestinal wall, villi, and microvilli increase the surface area to maximize nutrient absorption. Carbohydrate enzymes secreted by the salivary glands in the mouth begin carbohydrate breakdown, but the mouth plays only a minor role in digestion. The stomach performs both mechanical and chemical digestion but digestion and absorption within the small intestine is much more significant. By the time food enters the large intestine, it has been digested and the majority of the nutrients have been absorbed. Some remaining food residues are broken down by bacteria.

What is the purpose of the gallbladder?

> to concentrate and store bile The purpose of the gallbladder is to concentrate and store bile before it is released into the small intestine through the bile duct. Bile helps emulsify lipid molecules and prepare them for digestion. The liver makes the bile in dilute, liquid form. The gallbladder does not emulsify bile; rather, bile emulsifies lipids.