Gastrointestinal Elimination
7.2 Gastrointestinal Elimination Concepts
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.
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.
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]
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 wo