Chapter 28: Structure and Function of the Gastrointestinal System ( Questions)

What does the vagus nerve innervate? What system?

**parasympathetic** 1. stomach 2. small intestine 3. cecum 4. ascending colon 5. transverse colon

What does the sacral segment of the spinal cord innervate?

**parasympathetic** Rest of colon

What is the function of the stomach and where is it located?

-Acts as a food storage reservoir during early stages of digestion -left side of stomach

What does the mesentery contain & what is it's function?

-Blood vessels, nerves, and lymphatic vessels -holds organs in places & stores fat

What two enzymes does saliva contain to help with digestion initiation?

1. Ptyalin 2. Amylase

How does the sympathetic system affect the GI tract?

1. controls mucus secrection 2. reduces motility 3. enhances sphincter function 4. increases vascular smooth muscle tone of the blood vessels

Where is rhythmic movement found?

1. esophogus 2. antrum of stomach 3. small intestine

Where is tonic movement found?

1. lower esophagus 2. upper region of stomach 3. ileocecal valve 4. internal anal sphincter

The enteric nervous system contains what plexuses?

1. myenteric 2. submucosal

. What is the common cause of nausea?

A common cause of nausea is distention of the duodenum or upper small intestinal tract.

Nausea and vomiting can be side effects of many drugs as well as physiologic disturbances within the body. What is the common cause of nausea?

A common cause of nausea is distention of the duodenum or upper small intestinal tract.

What is the function of the pyloric sphincter?

A valve that controls the rate of stomach emptying & prevents regurgitation of intestinal contents back into the stomach.

_____ is the process of moving nutrients and other materials from the external environment of the GI tract into the internal environment.

Absorption

Absorption is a major function of the gastrointestinal tract. How is absorption accomplished in the gastrointestinal tract?

Absorption is accomplished by active transport and diffusion.

_____ represents a loss of appetite.

Anorexia

____ secrete large amounts of alkaline mucus that protect the duodenum from the acid content in the gastric chyme and from the action of the digestive enzymes.

Brunner glands

____ potentiates the action of secretin, increasing the pancreatic bicarbonate response to low circulating levels of secretin, stimulates biliary secretion of fluid and bicarbonate, and regulates gallbladder contraction and gastric emptying.

Cholecystokinin

Describe tonic movement.

Constant level of contractions w/o periods of relaxation

____ normally is initiated by the mass movements of the large intestine.

Defecation

What are the main physiologic functions of the GI system?

Digest food and absorb nutrients into the bloodstream

____ is the process of dismantling foods into their constituent parts.

Digestion

How are carbohydrates broken down to absorbable units?

Digestion of starch begins in the mouth with the action of amylase. Pancreatic secretions also contain an amylase. Amylase breaks down starch into several disaccharides, including maltose, isomaltose, and alpha-dextrins. The brush border enzymes convert the disaccharides into monosaccharides that can be absorbed.

The colon is home to between 300 and 500 different species of bacteria. What is their main metabolic function?

Fermentation of undigestible dietary residue. The major metabolic function of colonic microflora is the fermentation of undigestible dietary residue and endogenous mucus produced by the epithelial cells.

The stomach secretes two important hormones in the gastrointestinal tract. What are they?

Gastrin & Ghrelin.

____ has potent growth hormone-releasing activity and has a stimulatory effect on food intake and digestive function, while reducing energy expenditure.

Ghrelin

The stomach secretes two important hormones in the gastrointestinal tract. One is gastrin. What is the second hormone secreted by the stomach?

Ghrelin. Ghrelin is a newly discovered peptide hormone produced by endocrine cells in the mucosal layer of the fundus of the stomach. It displays potent growth hormone-releasing activity and has a stimulatory effect on food intake and digestive function, while reducing energy expenditure. The isolation of this hormone has led to new insights into the gut-brain regulation of growth hormone secretion and energy balance.

How does parasympathetic activity affect the GI system?

Increases activity/excites

Describe rhythmic movement.

Intermittent contractions that mix & move food along digestive tract

Where in the gastrointestinal tract is food digested and absorbed?

It is in the jejunum and ileum that food is digested and absorbed.

What is the function of mucus?

Lubrication and protection of inner surface of alimentary canal

____ monitor the stretch and distention of the GI tract wall, and ____ monitor the chemical composition of its contents.

Mechanoreceptors, chemoreceptors

foods that may contribute to colon cancer

NITRATES AND NITRITES hot dogs, bologna and other luncheon meats, bacon, ham, smoked fish, some imported cheeses

_____ is the conscious sensation resulting from stimulation of the medullary vomiting center that often precedes or accompanies vomiting.

Nausea

Saliva has more than one function. What are the functions of saliva?

Protection, lubrication, antibacterial, and initiate digestion of starches. Saliva has three functions. The first is protection and lubrication. Saliva is rich in mucus, which protects the oral mucosa and coats the food as it passes through the mouth, pharynx, and esophagus. The second function of saliva is its protective antimicrobial action. Third, saliva contains ptyalin and amylase, which initiate the digestion of dietary starches.

Describe protein digestion and absorption.

Protein digestion begins the stomach with the action of pepsin. Proteins are broken down further by pancreatic enzymes, such as trypsin, chymotrypsin, carboxypeptidase, and elastase. The pancreatic enzymes are secreted as precursor molecules. Trypsinogen, which lacks enzymatic activity, is activated by an enzyme located on the brush border cells of the duodenal enterocytes. Activated trypsin activates additional trypsinogen molecules and other pancreatic precursor proteolytic enzymes. The amino acids are liberated on the surface of the mucosal surface of the intestine by brush border enzymes that degrade proteins into peptides that are one, two, or three amino acids long. Similar to glucose, many amino acids are transported across the mucosal membrane in a sodium-linked process that uses ATP as an energy source. Some amino acids are absorbed by facilitated diffusion processes that do not require sodium.

Defecation is controlled by both an internal and an external sphincter. What nerve controls the external sphincter? What nervous system is it apart of?

Pudendal nerve Somatic nervous system (voluntary control)

Defecation is controlled by both an internal and an external sphincter. What nerve controls the external sphincter?

Pudendal nerve. The external sphincter is controlled by nerve fibers in the pudendal nerve, which is part of the somatic nervous system and therefore under voluntary control.

The circular layer of smooth muscle that lies between the stomach and the small intestine is called what?

Pyloric sphincter. At the end of the pyloric channel, the circular layer smooth muscle thickens to form the pyloric sphincter. This muscle serves as a valve that controls the rate of stomach emptying and prevents the regurgitation of intestinal contents back into the stomach. There is no cardiac sphincter in the GI tract. The antrum is a portion of the stomach that is the wider, upper portion of the pyloric region. The cardiac orifice is the opening between the esophagus and the stomach.

What neuromediator is thought to be involved in the nausea and vomiting that accompanies chemotherapy?

Serotonin.

Several neurotransmitters have been identified with nausea and vomiting. In this capacity they act as neuromediators. What neuromediator is thought to be involved in the nausea and vomiting that accompanies chemotherapy?

Serotonin. Serotonin is believed to be involved in the nausea and emesis associated with cancer chemotherapy and radiation therapy. Serotonin antagonists (e.g. graniestron and ondansetron) are effective in treating the nausea and vomiting associated with these stimuli.

____ fluid forms a moist and slippery surface that prevents friction between the continuously moving abdominal structures.

Serous

Some smooth muscle cells in the gastrointestinal tract serve as pacemakers. They display rhythmic and spontaneous oscillations in membrane potentials. What are these called?

Slow waves. No contraction can occur without an action potential and an action potential cannot occur unless the slow wave brings the membrane potential to threshold.

What kind of muscle makes up the esophagus and what is it's function?

Smooth muscle for peristalsis

What is the mechanism of acid secretion by parietal cells of the stomach?

The cellular metabolism for hydrochloric acid secretion by the parietal cells in the stomach involves the hydrogen/potassium adenosine triphosphatase transporter and chloride channels located in their luminal membrane. During the process of hydrochloric acid secretion, carbon dioxide produced by aerobic metabolism combines with water, catalyzed by carbonic anhydrase, to form carbonic acid, which dissociates into hydrogen and bicarbonate. The hydrogen is secreted with chloride into the stomach and the biocarbonate moves out of the cell and into blood from the basolateral membrane. At the luminal side of the membrane, hydrogen is secreted into the stomach via the hydrogen/potassium adenosine triphosphatase transporter and chloride follows hydrogen into the stomach by diffusing through chloride channels in the luminal membrane.

What factors are involved in stimulating the emptying of the stomach?

The emptying of the stomach is regulated by hormonal and neural mechanisms. The hormones cholecystokinin and glucose-dependent insulinotropic polypeptide are thought to partly control gastric emptying, which are released in response to the pH and the osmolar and fatty acid composition of the chyme. Afferent receptor fibers synapse with the neurons in the intramural plexus or trigger intrinsic reflexes by means of vagal or sympathetic pathways that participate in extrinsic reflexes.

What are the three functions of saliva?

The first function of saliva is protection and lubrication. Saliva is rich in mucus, which protects the oral mucosa and coats the food as it passes through the mouth, pharynx, and esophagus. The sublingual and buccal glands produce only mucus-type secretions. The second function of saliva is its protective antimicrobial action. The saliva cleans the mouth and contains the enzyme lysozyme, which has an antibacterial action. Third, saliva contains ptyalin and amylase, which initiate the digestion of dietary starches.

The nurse is preparing an educational event for a group of children in elementary school who are studying the gastrointestinal tract. What facts should the nurse know to include for these children?

The gastrointestinal tract is the largest endocrine gland in the body. Many nerves make the GI tract work. The stomach begins digestion by kneading and churning the food we eat. Food then progresses to the small intestine, where most of the food is digested and absorbed. Our food then goes into the large intestine, where it is compacted into the feces that we expel from our bodies.

Describe the incretin effect.

The incretin effect is the increase in insulin release after an oral glucose load. The two hormones that account for about 90% of the incretin effect are GLP-1, which is released from L cells in the distal small bowel, and GIP, which is released by K cells in the upper gut (mainly the jejunum). Because increased levels of GLP-1 and GIP can lower blood glucose levels by augmenting insulin release in a glucose-dependent manner (i.e. at low blood glucose levels no further insulin is secreted, minimizing the risk of hypoglycemia), these hormones have been targeted as possible antidiabetic drugs. Moreover, GLP-1 can exert other metabolically beneficial effects, including suppression of glucagon release, slowing of gastric emptying, augmenting of net glucose clearance, and decreasing appetite and body weight.

Describe the functional divisions of the GI tract.

The upper part - the mouth, esophagus, and the stomach - act as an intake source and receptacle through which food passes and in which initial digestive processes take place. The middle portion - the duodenum, jejunum, and ileum - the place where most digestive and absorptive processes occur. The lower segment - the cecum, colon, and rectum, serves as a storage channel for the efficient elimination of waste.

How does the sympathetic nervous system innervate the GI tract?

Through the thoracic chain of sympathetic ganglia & the celiac, superior mesenteric, & inferior mesenteric ganglia.

What is the function of serous fluid?

To form a moist and slippery surface to prevent friction between moving abdominal structures

____ is the sudden and forceful oral expulsion of the contents of the stomach.

Vomiting

Describe the two types of contractions seen in the small intestine.

With segmentation waves, slow contractions of the circular muscle layer occlude the lumen and drive the contents forward and backward. Most of the contraction that produce segmentation waves are local events involving only 1 to 4 cm of intestine at a time. They function mainly to mix the chyme with the digestive enzymes from the pancreas and to ensure adequate exposure of all parts of the chyme to the mucosal surface of the intestine, where absorption takes place. Peristaltic movements are rhythmic propulsive movements designed to propel the chyme along the small intestine toward the large intestine.

The upper esophageal sphincter, the pharyngoesophageal sphincter, consists of what kind of muscle?

a circular layer of striated muscle

diet lacking fiber

a factor in the development of diverticulosis, in which pockets form along the colon where waste material can lodge

normal well balanced diet

aids in digestion

hepatitis virus

attacks the liver, causing inflammation and damage to the tissue. HBV and HCV are implemented in liver cancer

The stomach and small intestine contain only a few species of _____, probably because of the composition of luminal contents.

bacteria

The enterocytes secrete ____ that adhere to the border of the villus structures.

brush border enzymes

massive internal hemorrhage

can be caused by liver trauma or laceration, however, the liver is resilient and will regenerate, if part of the liver remains functional and repair is performed quickly

food poisoning

can be prevented by adequate refrigeration, proper canning, freezing and food handling methods

alcohol, drugs, chemicals and other substances

can be toxic to the liver and are major factors in the development of cirrhosis of the liver

parasites

can cause cirrhosis, cysts or abscesses. enter the body when people wade or swim in contaminated water in tropical countries, or eat contaminated food

autoimmune diseases

can cause inflammation or fibrosis of organs in the GI system

obstruction of the bile and pancreatic ducts

can cause interference with the flow of digestive juices and of the enzymes needed for digestion

gallbladder stones

can cause irritation and create areas susceptible to inflammation and infection. can lodge in the common bile duct, causing obstruction to the flow of bile. liquid weight loss diets or very rapid weight loss appears to be associated with developing these. women develop these more frequently than men. incidence increases with age, obesity and having several children. diabetes mellitus and crohns disease are at higher risk for this disorder

irritation and inflammation of the GI mucosa

can lead to intestinal bleeding and to increased peristalsis, causing inadequate absorption of nutrients

damaged mucous membranes

can result in gastric or duodenal ulcers and chronic colitis

excessive stimulation of digestive acid and enzymes

causes a breakdown in the integrity of the mucous membrane lining of the digestive tract

maintaining abdominal tone

contributes to peristalsis and the ability to defecate normally

crohn's disease and ulcerative colitis

correlated with a genetic predisposition. more common among the jewish population

elderly patient

decreased mobility leads to digestive problems in this age group therefore ambulation is encouraged

heeding the need

defecating promptly aids in keeping the gastrocolic reflex functioning well and prevents constipation and hemorrhoids

stress

developing healthy coping mechanisms keeps this within normal limits and may prevent ulcers and irritability of the bowel

constipation

drinking at least 8 glasses of fluid a day prevents this by keeping the stool moist

The small intestine, which forms the middle portion of the digestive tract, consists of three subdivisions: the _____, _____, and _____.

duodenum, jejunum, ileum

The ____ nervous system consists of the myenteric and submucosal plexuses in the wall of the GI tract.

enteric

Each villus is covered with cells called _____ that contribute to the absorptive and digestive functions of the small bowel, and goblet cells that provide mucus.

enterocytes

The _____ cells carry out the secretory and absorptive functions of the GI tract and they produce the ____ that lubricates and protects the inner surface of the alimentary canal.

epithelial, mucus

liver

filters out many toxic substances and is constantly exposed to any infectious organisms circulating in the bloodstream

G cells secrete _____.

gastrin

The primary function of ____ is the stimulation of gastric acid secretion.

gastrin

The lower esophageal sphincter, the ____ sphincter, lies just above the area where the esophagus joins the stomach.

gastroesophageal

The major physiologic function of the _____ is to digest food and absorb nutrients into the bloodstream.

gastrointestinal (GI) system

psychological and emotional stress

greatly influences appetite and motility of the stomach and intestines. secretion of digestive juices in amounts sufficient for the breakdown of food is regulated in part by emotions

colon cancer

has a genetic link and a familial tendency

sufficient bulk

helps maintain a healthy colon by enhancing passage of waste

maintaining body weight

helps prevent hiatal hernia and esophageal reflux

The GI tract produces _____ that act locally, pass into the general circulation for distribution to more distant sites, and interact with the central nervous system by way of the enteric and autonomic nervous systems.

hormones

pancreatic cancer

incidence rises with age. incidence is higher if your a cigarette smoker. obesity, chronic pancreatitis, and diabetes mellitus are also risk factors.

The major metabolic function of colonic microflora is the fermentation of ____ and endogenous mucus produced by the epithelial cells.

indigestible dietary residue

How does sympathetic activity affect the GI system?

inhibits activity

Bile and pancreatic juices enter the intestine through openings for the common bile duct and the main pancreatic duct in the _____.

jejunum

Blue and pancreatic juices enter the intestine through openings for the common bile duct and the main pancreatic duct in the _____.

jejunum

esophageal and stomach cancer

linked to consumption of charred foods and nitrites. cigarette smoking is linked to stomach cancer

Triglycerides are broken down by pancreatic _____.

lipase

prevention of gallstones

maintaining a normal weight, eating a low fat, low cholesterol, high fiber, and high calcium diet, avoiding rapid weight loss diets, consuming alcohol in moderation, and maintaining an active lifestyle all prevent these

chemotherapy, radiation, and drug therapy

may cause GI problems as a side effect. some people who have undergone chemotherapy for cancer develop a mechanical form of sprue, a malabsorption problem that remains even after chemotherapy is complete

elimination diets

mechanical and chemical irritants that produce inflammation can be identified by doing this to determine which foods cause GI upsets

The ____ contains the blood vessels, nerves, and lymphatic vessels that supply the interstitial wall.

mesentery

genetic gallstone risk

native americans secrete high levels of cholesterol in bile. a majority of native american men have gallstones by age 60, and 70% of the women of the pima Indians in Arizona have gallstones by age 30. Mexican americans of both sexes and all ages also have high rates of gallstones

lactose intolerance

not uncommon in the older adult. may cause continuous diarrhea and malabsorption

Swallowing consists of three phases: an _____ phase, a _____ phase, and an _____ phase.

oral, pharyngeal, esophageal

Like the self-excitable cardiac muscle cells in the heart, some smooth muscle cells of the GI tract function as _____ cells.

pacemaker

The ____ cells secrete hydrochloric acid and intrinsic factor, which is necessary for the absorption of _____.

parietal, vitamin B12

The chief cells secrete _____, an enzyme that initiates proteolysis or breakdown of proteins.

pepsinogen

The upper esophageal sphincter, the ____ sphincter, consists of a circular layer of striated muscle.

pharyngoesophageal

What are the upper and lower esophageal sphincters?

pharyngoesophageal & gastroesophageal sphinctors

good hygiene and sanitation

prevents many infectious GI upsets; wash hands before eating and clean cooking utensils properly

The ____ is the major site for the digestion and absorption of food.

small intestine

The ____ lies in the left side of the abdomen and serves as a food storage reservoir during the early stages of digestion.

stomach

hemorrhoid formation

straining at stool increases intra-abdominal pressure which causes the vessels to engorge

Numerous ____ reflexes influence motility and secretions of the digestive tract.

vagovagal

How does the parasympathetic system innervate the GI system?

vagus nerve & sacral segments of the spinal cord