Amanda Egert; Kimberly Lee; and Manu Gill

Concepts Related to Gastrointestinal Elimination

This resource provides a basic introduction to the concept of gastrointestinal elimination as it relates to pharmacology. The concept of gastro-intestinal elimination is defined as “the excretion of waste products”[1] specifically through the gastrointestinal system. This chapter also discusses nausea and vomiting, which are also connected to the gastrointestinal system.

The example concept map below in figure 7.2a provides a summary of the key information necessary to understand gastrointestinal elimination informed by several resources.[2]

You are encouraged to revisit this map after you have completed the chapter.

concept map for gastrointestinal elimination
Figure 7.2a GI Elimination Concept Map [Image Description]

Overview of Gastrointestinal System and Processes

It is important to understand GI anatomy and physiology information in order to understand how GI medications work. Figure 7.2b[3] illustrates the anatomical components of the gastrointestinal system as a whole. The remainder of this section will provide a review of the digestive system, digestive system processes and regulation, the stomach, the small and large intestines, and chemical digestion and absorption. Medications related to hyperacidity, bowel disorders, and nausea and vomiting will be discussed later in the chapter, with reference to how they target pathophysiological concepts related to these organs and processes.

Illustrations showing labeled components of the GI system on a human torso
Figure 7.2b Components of GI System

Watch the videos below for a review of the gastrointestinal system and digestive system.

Gastrointestinal System Review[4]

Ted Ed Review of The Digestive System[5]

The Stomach and Digestion

The stomach contains cells that secrete different substances as part of the digestive process: parietal cells, chief cells, and surface epithelium cells. See an image of the stomach and these cells in Figure 7.2c.[7]

Illustration showing labeled parts of stomach with enlargement of the gastric gland.
Figure 7.2c An image of the stomach with surface epithelium cells in the mucosa, and an enlarged image of the gastric gland showing chief cells and parietal cells

Surface epithelium cells are found within the lining of the stomach and secrete mucus as a protective coating. Parietal cells and chief cells are found within the gastric glands. Parietal cells produce and secrete hydrochloric acid (HCl) to maintain the acidity of the environment of a pH of 1 to 4. Parietal cells also secrete a substance called intrinsic factor, which is necessary for the absorption of vitamin B12 in the small intestine. Parietal cells are the primary site of action for many drugs that treat acid-related disorders. Chief cells secrete pepsinogen that becomes pepsin, a digestive enzyme, when exposed to acid. The stomach also contains enteroendocrine cells (ECL or enterochromaffin-like cells) located in the gastric glands that secrete substances including serotonin, histamine, and somatostatin. G cells in the stomach secrete gastrin that promotes secretions of digestive substances. Although these cells play an important role in the digestive system, acid-related diseases can occur when there is an imbalance of secretions.

Elimination and Defecation

The digestive system is continually at work, but unless something goes amiss, you don’t notice your digestive system working. The final step of digestion is called defecation, when undigested materials are removed from the body as feces. During this final step, the large intestine absorbs water and changes the waste from a liquid into stool; then peristalsis helps move the stool into the rectum. Diarrhea and constipation occur when conditions occur that affect this final step of defection.

The process of defecation begins when mass movements force feces from the colon into the rectum, stretching the rectal wall and provoking the defecation reflex, which eliminates feces from the rectum. This parasympathetic reflex is mediated by the spinal cord. It contracts the sigmoid colon and rectum, relaxes the internal anal sphincter, and initially contracts the external anal sphincter. Figure 7.2d[8] reviews the anatomy of the rectum and its external and internal sphincters. The presence of feces in the anal canal sends a signal to the brain, which gives the person the choice of voluntarily opening the external anal sphincter (defecating) or keeping it temporarily closed. If defecation is delayed until a more convenient time, it takes a few seconds for the reflex contractions to stop and the rectal walls to relax. The next mass movement will trigger additional defecation reflexes until defecation occurs.[9]

The anorectum. The rectum is labelled. The final 4 centimetres of the rectum are the anal canal. The anal canal is surrounded by the internal sphincter, and the internal sphincter is surrounded by the exterior sphincter.
Figure 7.2d Anatomy of the Rectum

If defecation is delayed for an extended time, additional water is absorbed, making the feces firmer and potentially leading to constipation. Alternatively, if the waste matter moves too quickly through the intestines, not enough water is absorbed and diarrhea can result. Figure 7.2e[10] demonstrates the Bristol Stool Chart that is used to assess stool characteristics ranging from very constipated to diarrhea.

Image showing Bristol Stool Chart
Figure 7.2e Bristol Stool Chart [Image Description]

You can further review how the digestive system works at the following links:

Image Description

Figure 7.2a GI Elimination Concept Map image description: This is a concept map that shows the components of the GI elimination. It starts with the definition for GI elimination: the passage and dispelling of stool through the intestinal tract by means of intestinal smooth muscle contraction.

Variations

  • Incontinence
  • Retention

Related

  • Hyperacidity
  • Nausea
  • Vomiting

Assessment

  • GI assessment: bowel habits, quality/quantity, pain, distension, bowel sounds, nausea, vomiting lab tests, colonoscopy
  • Assess for root cause

Management

  • diet, hydration, toileting practices,
  • fecal occult blood, colonoscopy,
  • pharmacotherapy
    • anti-diarrheal
    • laxative
    • anti-emetics
    • antacid

Consequences

  • Nourishment
  • Skin breakdown, social withdrawal, changes with ADLs
  • Pain, bloating
  • Impaction
  • Dehydration
  • Bleeding

Physiological Process

  • intake (food, fluid, fibre)
  • intestinal motility (neuromuscular function, exercise)
  • output (defecation reflex)

Scope

Figure 7.2e image description: Bristol Stool Chart is used to assess stool characteristics ranging from very constipated to diarrhea.

Bristol Stool Chart
Type Descriptions Condition
Type 1 Separate hard lumps Very constipated
Type 2 Lumpy and sausage-like Slightly constipated
Type 3 A sausage shape with cracks in the surface Normal
Type 4 Like a smooth, soft sausage or snake Normal
Type 5 Soft blobs with clear-cut edges Lacking fibre
Type 6 Mushy consistency with ragged edges Inflammation
Type 7 Liquid consistency with no solid pieces Inflammation

[Return to Figure 7.2e]

 


  1. Jean Giddens, Concepts of Nursing Practice – 2nd edition (Missouri: Elsevier, 2017), page 138
  2. Jean Giddens, Concepts of Nursing Practice – 2nd edition (Missouri: Elsevier, 2017)
  3. "Components of the Digestive System" by CNX OpenStax is licensed under CC BY 4.0 Access for free at https://openstax.org/books/anatomy-and-physiology/pages/23-1-overview-of-the-digestive-system
  4. Forciea, B. ( 2015, March 18). Anatomy and Physiology of the Digestive System [Video]. YouTube. All rights reserved. Video used with permission. https://youtu.be/1ssJV-EpfiQ.
  5. Bryce, E. (2017, December 14). How Your Digestive System Works. [YouTube].  https://youtu.be/Og5xAdC8EUI.
  6. Meet the Gastrointestinal Tract! by Raja Narayan is licensed under CC BY-NC-SA 3.0
  7. "2415 Histology of StomachN.jpg" by CNX OpenStax is licensed under CC BY 3.0 Access for free at https://cnx.org/contents/FPtK1zmh@16.7:O9dvCxUQ@8/23-4-The-Stomach
  8. "Anorectum.gif" by U.S. Government National Institutes of Health is licensed under CC0
  9. This work is a derivative of Anatomy and Physiology by OpenStax licensed under CC BY 4.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction
  10. "BristolStoolChart.png" by Cabot Health, Bristol Stool Chart is licensed under CC BY-SA 3.0
  11. National Institute of Diabetes and Digestive and Kidney Diseases, National Institute of Health. (2018). Treatment for constipation.https://www.niddk.nih.gov/health-information/digestive-diseases/constipation/treatment.
  12. Digesting Food by Stanford School of Medicine and Khan Academy is licensed under CC BY-NC-SA 3.0.
  13. This work is a derivative of Anatomy and Physiology by OpenStax licensed under CC BY 4.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction
  14. This work is a derivative of Anatomy and Physiology by OpenStax licensed under CC BY 4.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction
  15. This work is a derivative of Anatomy and Physiology by OpenStax licensed under CC BY 4.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction
  16. This work is a derivative of Anatomy and Physiology by OpenStax licensed under CC BY 4.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction
  17. This work is a derivative of Anatomy and Physiology by OpenStax licensed under CC BY 4.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction
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Fundamentals of Nursing Pharmacology - Mohawk College Edition Copyright © 2023 by Amanda Egert; Kimberly Lee; and Manu Gill is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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