28. The Gastrointestinal System



The Gastrointestinal System


Objectives


Theory



Clinical Practice



Key Terms


absorption (ăb-sŏrp-shŭn, p. 623)


adhesions (ăd-HĒ-shŭnz, p. 623)


anabolism (ă-NĂB-ŏ-lĭzm, p. 623)


anorexia (ăn-ŏ-RĔK-sē-ă, p. 633)


ascites (ă-SĪ-tēz, p. 631)


catabolism (kă-TĂB-ō-lĭzm, p. 623)


chyme (KĪM, p. 621)


flatus (FLĀ-tŭs, p. 635)


mastication (măs-tĭ-KĀ-shŭn, p. 620)


metabolism (mĕ-TĂ-bō-lĭzm, p. 623)


pancreatitis (păn-krē-Ă-TĪ-tĭs, p. 624)


peristalsis (pĕr-ēs-TĂL-sĭs, p. 623)


imagehttp://evolve.elsevier.com/deWit/medsurg


Overview of Anatomy and Physiology of the Gastrointestinal System


What are the Organs and Structures of the Gastrointestinal System?



• Organs of the gastrointestinal (GI) system are the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus (Figure 28-1).


• The accessory organs are the liver, gallbladder, and pancreas (Figure 28-2).


• The gastroesophageal sphincter (cardiac sphincter) controls the opening from the esophagus into the stomach; it prevents reflux from the stomach into the esophagus.


• The stomach lies in the upper left portion of the abdominal cavity (see Figure 28-1).


• The pyloric sphincter controls release of food substances into the small intestine (Figure 28-3).


• The small intestine is divided into the duodenum, jejunum, and ileum and is about 6 m long.


• The ileocecal valve controls the progress of substances into the large intestine.


• The large intestine is divided into the cecum, colon, rectum, and anal canal; the colon is about 1.5 m long.


• The colon has four portions: the ascending, transverse, descending, and sigmoid colon.


• The appendix is attached to the cecum and has no known function in the digestive process.


• The walls of the digestive tract have four layers: mucosa, submucosa, muscular layer, and a serous layer called serosa.


• The peritoneum is a serous sac that lines the abdominal cavity and encloses the intestines, stomach, liver, and spleen and partially encloses the uterus and uterine tubes.





What are the Functions of the Gastrointestinal System?



• The teeth and tongue are instrumental in the chewing (mastication) process, and they help break down food into smaller pieces that can be acted on by various enzymes.


• Food moves from the mouth through the pharynx down the esophagus to the stomach, where mixing movements occur.


• Mucus, hydrochloric acid (HCl), intrinsic factor, pepsinogen, and gastrin are secreted into the stomach from cells within its walls and are mixed into the food to break down further the particles for absorption. The mixture produced is called chyme.


• The small intestine receives the chyme from the stomach, adds more digestive enzymes and fluids, receives bile and pancreatic enzymes from the common duct, and further digests the chyme into a more liquid state.


• Substances are moved along the intestinal tract by the peristaltic action of the intestinal smooth muscle.


• Digested food particles are absorbed into the bloodstream from the villi on the walls of the small intestine.


• The large intestine reabsorbs water and electrolytes, formulates some vitamin K, and eliminates waste products (Figure 28-4).


• The large intestine is populated with bacteria that aid in the breakdown of waste products.


• The rectum stores fecal material until it is eliminated through the anus.


• The internal anal sphincter at the top of the anal canal is under involuntary control; the external anal sphincter at the end of the anal canal is under voluntary control.


• The gastrocolic reflex initiates elimination; it is stimulated by the ingestion of food. By tightening the voluntary anal sphincter, the reflex emptying of the rectum can be stopped.



What Effects does Aging have on the Gastrointestinal System?



• Dentures or partial plates and bridges are common in those over 65. Ill-fitting dentures cause eating problems and can lead to nutritional deficits.


• With advanced age, muscles used for swallowing may become weaker and less coordinated and food particles are retained in the cheek pouches or pharynx.


• The esophageal sphincter becomes less efficient at opening and closing and risk for aspiration increases.


• Taste buds atrophy, causing inability to distinguish between flavors, particularly between salty and sweet.


• After age 70, the parietal cells in the stomach decrease their secretion of hydrochloric acid; enzyme and intrinsic factor secretion also decrease. The lack of intrinsic factor may cause pernicious anemia.


• The mucosa of the small intestine becomes less absorptive, and the large intestine may develop diminished motility.


What are the Structures and Locations of the Accessory Organs?



What are the Functions of the Gallbladder, Liver, and Pancreas?



• The gallbladder stores bile produced in the liver and delivers it as needed to the small intestine; the gallbladder can store up to 50 mL of bile.


• The liver manufactures and secretes bile and bile salts necessary to digest fat.


• The liver synthesizes albumin, fibrinogen, globulins, and clotting factors.


• The liver is a storage area for glucose (in the form of glycogen); vitamins A, D, E, K, and B12; and iron.


• The liver receives blood directly from the digestive tract via the hepatic portal vein. All nutrients and oral medications pass through the liver before being distributed to other parts of the body.


• The liver is responsible for how drugs are metabolized.


• The liver detoxifies and breaks down many compounds and drugs, preparing them for excretion; it alters ammonia, a by-product of protein metabolism, so that it does not harm the body.


• The liver helps break down and excrete hormones, drugs, cholesterol, and hemoglobin from worn-out red blood cells.


• The liver plays a major role in glucose metabolism, removing excess glucose from the blood, converting it to glycogen, and then, as glucose is needed, converting glycogen back to glucose.


• The liver plays key roles in lipid metabolism, breaking down fatty acids and synthesizing cholesterol and phospholipids, and in converting excess carbohydrates and proteins into fats.


• The liver is instrumental in protein metabolism, converting certain amino acids into different ones as needed for protein synthesis.


• The liver is a large filter containing phagocytic Kupffer cells that remove bacteria, damaged red blood cells, and other toxic materials from the blood.


• The liver may store between 200 and 400 mL of blood.


• The liver synthesizes the prothrombin needed for normal blood clotting.


• The islets of Langerhans, which are regions of endocrine tissue in the pancreas, secrete the hormones insulin and glucagon into the blood; insulin is essential to the metabolism of carbohydrates.


• The pancreatic acinar cells secrete digestive enzymes into ducts that connect with the pancreatic duct.


• The major pancreatic enzymes are amylase, protease, trypsin, and lipase; these enzymes are essential to the digestion and absorption of nutrients from the small intestine.


• Secretion of pancreatic enzymes is controlled by secretin and cholecystokinin, two substances secreted by the intestinal mucosa.


How does Aging Affect the Accessory Organs of Digestion?



The Gastrointestinal System


The intestinal tract and accessory organs of digestion perform the intake, absorption, and assimilation of food to provide nourishment for the body. The transfer of nutrients from the intestine into the blood is referred to as absorption. Food substances are moved along the intestinal tract by peristalsis (wavelike motions of involuntary muscles within the walls of the organs). Metabolism is the sum of many physical and chemical processes of the absorbed nutrients. Metabolic activities involve the synthesis of substances needed to build, maintain, and repair body tissues (anabolism). Metabolism is also responsible for the breakdown of larger molecules into smaller molecules so that energy is available (catabolism).


Gastrointestinal System Disorders


Causes


The gastrointestinal tract is subject to infection, inflammation, physical and chemical trauma, and structural defects. An intestinal tract problem may occur due to blockage of movement of food through the intestine (intestinal obstruction). Postoperative adhesions sometimes cause intestinal obstruction. Adhesions are bands of scar tissue that bind two anatomical surfaces together that are normally separate. Tumor may also cause intestinal obstruction. Obstruction of the bile or pancreatic ducts can cause interference with the flow of digestive juices and of the enzymes needed for digestion. Continued irritation and inflammation of the GI mucosa can lead to intestinal bleeding and to increased peristalsis, causing inadequate absorption of nutrients.


Psychological and emotional stresses greatly influence appetite and motility of the stomach and intestines. The secretion of digestive juices in amounts sufficient for the breakdown of food is regulated in part by the emotions. Excessive stimulation of digestive acid and enzymes can cause a breakdown in the integrity of the mucous membrane lining the digestive tract. The damage to the mucous membrane can result in gastric or duodenal ulcers and chronic colitis.


Some disorders, such as Crohn’s disease and ulcerative colitis, are correlated with a genetic predisposition. Both disorders are more common among the Jewish population. Certain forms of colon cancer have been identified as having a genetic link and there is a familial tendency for the occurrence of colon cancer. Esophageal and stomach cancer are linked to consumption of charred foods and those containing nitrites. Cigarette smoking is linked to stomach cancer.



Autoimmune diseases often affect the GI system, causing inflammation or fibrosis of organs. Treatments such as drug and radiation 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. Lactose intolerance, which is not uncommon in the older adult, may cause continuous diarrhea and malabsorption.



Causes of Gallbladder Disorders

The formation of stones within the gallbladder can cause irritation and create areas susceptible to inflammation and infection. Stones can lodge in the common duct, causing obstruction to the flow of bile. Liquid weight loss diets or very rapid weight loss appears to be associated with developing gallstones. Women develop gallstones more frequently than men. The incidence increases with age; obesity and having several children. People who have diabetes mellitus or Crohn’s disease are at higher risk for the disorder.



Causes of Liver Disorders

The liver filters out many toxic substances and is constantly exposed to any infectious organisms circulating in the bloodstream. The hepatitis virus in particular attacks the liver, causing inflammation and damage to the tissue. Hepatitis B and C are implicated in liver cancer (Clin-eguide Guideline, 2010). Healthy People 2020 objectives include not only reducing the number of hepatitis infections, but also increasing the percentage of people who are actually aware that they have a hepatitis infection.


Many drugs and chemicals are toxic to the liver, and the nurse should always be aware of the drugs a patient is taking that may cause liver damage. Alcohol and other toxic substances are major factors in image the development of cirrhosis of the liver (Box 28-1) (Mehta & Rothstein, 2009).



Liver trauma or laceration may cause massive internal hemorrhage. However, the liver is resilient and will regenerate, if part of the liver remains functional and repair is performed quickly.


Parasites may cause cirrhosis, cysts or abscesses. Most parasites that damage the liver enter the body when people wade or swim in contaminated water in tropical countries, or eat contaminated food.


Cancer in the liver may be primary, or may be secondary to metastasis from a site elsewhere in the intestinal tract.


Causes of Pancreatic Disorders

Pancreatitis (inflammation of the pancreas) is associated with alcoholism, obstructive cholelithiasis, peptic ulcer, hyperlipidemia, and trauma. Pancreatic cancer incidence rises steadily with age. Although the cause of pancreatic cancer is not known, the incidence is higher in cigarette smokers. Obesity, chronic pancreatitis, and diabetes mellitus are also risk factors for this cancer. (See Chapter 38 for information on diabetes mellitus.)


Prevention of Gastrointestinal System Disorders


Eating a normal, well-balanced diet aids digestion. Maintaining good oral health is important to the health of the rest of the body (Kullberg et al., 2009). Consuming sufficient bulk in the diet helps maintain a healthy colon by enhancing passage of waste. A diet lacking in fiber is one factor in the development of diverticulosis, in which pockets form along the colon where waste material can lodge. Drinking at least eight glasses of fluid a day prevents constipation by helping to keep the stool moist.


Heeding the need to defecate promptly aids in keeping the gastrocolic reflex functioning well and prevents constipation and hemorrhoids. Straining at stool increases intra-abdominal pressure which causes the hemorrhoidal vessels to engorge and contributes to hemorrhoid formation. Decreased mobility in the elderly patient often leads to digestive problems; therefore ambulation is encouraged



Maintaining body weight within normal limits helps prevent hiatal hernia and esophageal reflux. Developing healthy coping mechanisms and keeping stress within acceptable limits may prevent ulcers and chronic irritability of the bowel.


Mechanical and chemical irritants that produce inflammation often can be identified by elimination diets to determine the foods that cause GI upsets. Once the offending foods are identified, the patient can learn to avoid those foods and to maintain adequate nutrition.


Following general rules of good hygiene and sanitation can prevent many infectious GI upsets: wash the hands before eating and clean cooking and eating utensils properly. Food poisoning can be prevented by adequate refrigeration and by proper canning, freezing, and food-handling methods. Meats, and foods containing mayonnaise or dairy products, should be kept chilled. When not in the refrigerator, food should be kept covered.



Prevention of Gallbladder Disorders

Maintaining a normal body weight, eating a low-fat, low-cholesterol, high fiber and high calcium diet, avoiding rapid weight loss diets, consuming alcohol moderately, and maintaining an active lifestyle all help prevent gallstones (Clin-eguide, 2009). imageIf gallstones are irritating the gallbladder, prompt surgery might help to prevent cancer.


Prevention of Liver Disorders

Obtaining immunization against hepatitis A and hepatitis B helps to prevent these viral diseases. A vaccine against hepatitis C is under study at present. Using Standard Precautions (see Appendix B) when handling any body fluids, particularly blood, greatly reduces the risk of infection with hepatitis B and C, which may decrease the chance of developing liver cancer. Refraining from consuming excessive amounts of alcohol decreases the risk of developing cirrhosis of the liver. Avoiding exposure to known toxic or carcinogenic chemicals helps prevent liver damage and liver cancer.



Prevention of Pancreatic Disorders

Avoiding consumption of large quantities of alcohol may prevent pancreatitis. Removing a gallbladder that has gallstones can help prevent obstruction of the pancreatic duct with stones. Removal prevents backup of pancreatic enzymes that are thought to be a cause of pancreatitis. Compliance with therapy for a peptic ulcer helps prevent irritation of the pancreas and resultant pancreatitis. Smoking cessation decreases the risk of pancreatic cancer.


Diagnostic Tests, Procedures, and Nursing Implications


Diagnostic tests for disorders of the intestinal tract and accessory organs consist of x-rays, computed tomography (CT) scans, nuclear medicine scans, magnetic resonance imaging, ultrasound studies, endoscopy, biopsy, laboratory tests, tests of gastric secretions, and stool and urine studies (Table 28-1).



Table 28-1


Diagnostic Tests for Gastrointestinal (GI) Disorders






























Test Purpose Description Nursing Implications
Radiologic Examinations
Upper GI series (UGI) Radiographic examination with fluoroscopy to locate obstruction, ulceration, or growths in the esophagus, stomach, and duodenum Patient drinks a contrast medium and is placed in various positions on the x-ray table.
Barium enema (BE) Radiographic examination of the colon using fluoroscopy to locate tumors, obstruction, and ulceration

Computed tomography (CT)
Radiography is combined with computer techniques to provide a series of sectional pictures of the gallbladder.
Virtual colonoscopy

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Nov 17, 2016 | Posted by in NURSING | Comments Off on 28. The Gastrointestinal System

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