29.1: Introduction to the Gastrointestinal System and Oral Cavity
By the end of this section, you should be able to:
- 29.1.1 Describe the structure and function of the gastrointestinal system and oral cavity.
- 29.1.2 Discuss common conditions that affect the gastrointestinal system and oral cavity.
Gastrointestinal System
The digestive system consists of the gastrointestinal (GI) tract and accessory organs. The GI tract is also known as the alimentary canal . Together with the accessory organs, the GI tract provides nutrition and hydration to the body through the processes of ingestion , digestion , absorption , and metabolism . A healthy GI system with functional digestive processes is essential to break down and absorb nutrients from food and liquids to provide energy and growth to the human body. The ability to assimilate nutrients and hydration is crucial to cellular maintenance and repair. The final phase of digestion is to eliminate waste material not used by the body.
The average length of the adult human GI tract is about 30 feet from the mouth to the anus. Under normal conditions, nutrients are introduced into the human body through the mouth as food and fluids. As food and fluids move through the GI tract, they are transformed into useful nutrients to be assimilated into the body’s cells for survival and homeostasis. The breakdown and assimilation depend on the large surface area of the GI tract, which has traditionally been described as the size of a tennis court. However, recent literature notes that the surface area is much smaller. According to Rao and Johncy (2022), using geometric comparisons to approximate the intestinal surface area is inappropriate.
Multiple factors play a role in GI functions and health. Structural and nutritional deficiencies can alter the function of tissues and organs. Intestinal transit time, or how quickly food and fluids move through the GI tract, may also impact GI functions and health. Intestinal transit time varies based on age. Transit time is slower in newborns and gradually increases, starting at about 4 months of age. The transit time slows again in older adults due to an aging GI system with decreased GI peristalsis (muscular contractions and relaxations that propel food through the GI tract), motility, and intestinal blood flow. The aging GI system, coupled with medications that may alter absorption of food and fluids, can cause the most common GI complaints: constipation and diarrhea. Although these are some of the most frequent GI concerns in older adults, these uncomfortable conditions can affect people of any age.
Oral Cavity
The oral cavity is the beginning of the digestive tract (Figure 29.3). The oral cavity refers to the structures of the mouth: the upper and lower lips, teeth, gingiva (gums), hard and soft palate, uvula, retromolar trigone, tonsils, floor of the mouth, tongue, salivary glands, and buccal mucosa. The teeth are vital for breaking up food (mastication) for digestion and absorption. Mastication is the essential first step in digestion. The tongue is a strong muscle that facilitates mastication by mixing food and helping to form it into a bolus, which is the first step in swallowing. The tongue is also involved in the sensation of taste through taste buds. Taste buds are specialized cells that communicate the sense of taste (sweet, salty, sour, bitter, and umami) to the brain.
Salivary glands located in and around the mouth have many functions for oral health and digestion. The three types of salivary glands—sublingual, submandibular, and parotid—produce saliva to keep the oral cavity moist and lubricated to promote digestion and optimal oral health. In an adult, the salivary glands produce up to 2 L of saliva every day (Cleveland Clinic, n.d.). The presence of food increases saliva secretion. This is a parasympathetic response mediated by two cranial nerves, the facial nerve (cranial nerve VII) and the glossopharyngeal nerve (cranial nerve IX). Saliva helps protect the teeth from cavity-causing bacteria as well as maintain the pH balance in the mouth, but the most appreciated role of saliva is that of digestive aid. It helps moisten food to facilitate the swallowing of chewed food. Saliva contains an enzyme, amylase, to help break down foods, particularly complex carbohydrates (starches) into simple and more easily digested sugars. The enzymes in saliva kick-start the digestive process in addition to helping food travel through the esophagus to the stomach for further digestion.
Any disorder of the mouth or oral cavity may disrupt the digestive process. Common disorders such as “cold sores” from a herpes simplex virus (HSV), canker sores, mucositis, and candida infections may affect the oral cavity. These can be painful conditions. A thorough nursing history is essential to determine the source of any pain in order to alleviate it and ensure the client’s ability to eat. The nursing health history should include questions about oral health and dental practices, home-based treatments, and the use of both over-the-counter and prescription medications. A thorough physical examination of the oral cavity is equally important because careful inspection of the oral cavity may uncover issues that can impair biting and chewing. Nurses should teach clients that good oral hygiene is essential for this first step in digestion.