Learning Outcomes
By the end of this section, you should be able to:
- 17.1.1 Recognize the normal function of the gastrointestinal system.
- 17.1.2 Recognize cues of nutritional impact on the gastrointestinal system.
- 17.1.3 Analyze cues of nutritional impact on the gastrointestinal system.
Normal Function of the Gastrointestinal System
The gastrointestinal system comprises the organs in the upper gastrointestinal tract—the mouth, esophagus, stomach, and duodenum—and the organs in lower gastrointestinal tract—the small intestine, large intestine (or colon), rectum, and anus. The gastrointestinal system is aided by the teeth, tongue, salivary glands, and the pancreas, liver, and gallbladder, which are also known as ancillary digestive organs. The sensory system, the nervous system, the mucous membranes, and glands (digestive and adrenal) also have roles to play.
There are four main functions of the gastrointestinal system: ingestion, digestion, absorption, and metabolism. Ingestion is the swallowing and absorbing of substances into the body. This process starts with the sensory organs before food even enters the oral cavity: The smell or sight of appealing food can trigger the salivary glands to release saliva. That process, combined with hunger, can increase the desire to ingest the food. Once the food is inside the mouth, its taste, sensed through the papillae on the tongue, can either encourage or inhibit its further ingestion. Foods that register an unappetizing taste encourage expulsion from the oral cavity.
Digestion occurs when the body breaks down what is ingested into absorbable substances. This, too, starts in the oral cavity. The tongue and teeth start the digestion of food using mostly mechanical and some chemical processes known collectively as mastication. Mastication employs the use of the tongue for mechanical compression, abrasion, and distortion; secretion of mucins and lingual lipase, which assist in breaking down lipids; and manipulation to assist with movement during chewing and swallowing (Ogobuiro et al., 2023). The teeth are used strictly for mechanical processes during mastication as they cut, tear, grind, and chew food to break it down physically into smaller pieces.
Chemical digestion and lubrication in the oral cavity to aid in food movement are accomplished by the tongue and salivary glands. There are three pairs of salivary glands in the mouth: the parotid glands, which release salivary amylase to break down complex carbohydrates; sublingual glands, which release a mucus secretion that acts as a buffer and a lubricant; and the submandibular glands, which release a mixture of salivary amylase, buffers, and glycoproteins called mucins (Figure 17.2) (Ogobuiro et al., 2023).
The food is broken down and lubricated enough during mastication to be swallowed and moved to the next phase of digestion. The swallowing reflex is aided by the tongue, allowing food to travel down the esophagus via peristalsis and empty into the stomach through the lower esophageal sphincter.
Some digestion, both mechanical and chemical, occurs in the stomach, which also temporarily stores food. Food exits the stomach as chyme, a blend of gastric juices and digested food particles. The stomach also synthesizes proteins that are needed for vitamin absorption and microbial defenses, propagates the peristaltic reflex, and releases intrinsic factor from the parietal cells, which enables the small intestine to absorb vitamin B12 (Hsu et al., 2023). When chyme exits the stomach, simple carbohydrates have been digested. Larger molecules such as complex carbohydrates, fats, and proteins have not yet been broken down.
The duodenum breaks down larger molecules. In the duodenum, at the sphincter of Oddi, there is a release of digestive secretions by the ancillary organs (Ogobuiro et al., 2023), specifically from the gallbladder and the pancreas. The pancreas releases active alpha-amylase, colipase, and lipase, and the gallbladder releases bile, produced in the liver, to break down fats, proteins, and complex carbohydrates.
Absorption refers to the taking in of the broken-down substances into the cells. Very few substances are absorbed by the stomach. The small intestine handles 90% of food absorption as food travels through its three segments, the duodenum, jejunum, and ileum (Ogobuiro et al., 2023). The innermost layer of the mucosa of the small intestine is composed of absorptive cells known as enterocytes, goblet cells, and enteroendocrine cells (Fish & Burns, 2022). Enterocytes are effective at absorption because each one has around 3,000 microvilli that expand their available surface area (Figure 17.3).
The duodenum is the site for iron absorption and some vitamin B9 (folate) absorption, but the major site for vitamin B9 absorption is the jejunum (Fish & Burns, 2022). Minerals and vitamins A, D, E, and K are absorbed through the small intestine. The small intestine absorbs 90% of the water from digested food (Fish & Burns, 2022). The last segment of the small intestine, the ileum, is responsible for the absorption of bile salts and vitamin B12 (cobalamin;) (Fish and Burns, 2022). Each broken-down substance is now in a new, more usable form for use by the body's metabolic processes (Table 17.1).
| Macronutrient | Before Digestion | After Digestion |
|---|---|---|
| Carbohydrate: polysaccharides (starchy foods) | Amylose | Monosaccharides |
| Carbohydrate: disaccharides | Lactose, sucrose, maltose, trehalose | Glucose, fructose, galactose |
| Protein | Large-chain amino acids joined by peptide bonds | Separate amino acids and peptides (oligopeptides, dipeptides, tripeptides) |
| Fat | Triglycerides | Monoglycerides, fatty acids |
The last part of the absorption process takes place in the large intestine. It has three main functions in digestion: absorption of the remaining water and electrolytes, absorption and production of vitamins, and formation and movement of feces to the rectum for elimination. The first portion of the large intestine, the ascending colon, removes any remaining water and key nutrients from the indigestible material passing through it while solidifying this waste to form stool.
During this part of digestion, water osmosis causes absorption of the remaining water, sodium is absorbed via sodium channels, potassium absorption is regulated by its concentration in the lumen, and chloride and bicarbonate ions are exchanged. In addition, the large intestine houses trillions of bacteria, which produce many vitamins, including vitamin K, B vitamins, and biotin, through fermentation (Azzouz & Sharma, 2023).
Metabolism refers to the chemical processes by which the body converts absorbed substances to energy. Catabolic reactions release large amounts of protons, which are transported to mitochondria in the cells to produce adenosine triphosphate (ATP), the body’s chemical carrier of energy (Sanchez Lopez de Nava & Raja, 2022). An imbalance between energy spent and energy used, or between anabolism and catabolism, can result in obesity or cachexia (Sanchez Lopez de Nava & Raja, 2022). Obesity is clinically defined as an excessive or abnormal accumulation of fat in the body that can increase an individual’s health risks. Cachexia refers to muscle loss with or without fat mass loss.
For these processes to take place effectively and provide balanced nutrition and appropriate energy, the individual must first ingest the proper mix of the required nutrients and water.
Assessment of the Normal Gastrointestinal System
Assessment of the gastrointestinal organs and normal expected findings are explained in detail in The Digestive Process. This section will cover expected physical assessment findings in clients who demonstrate normal nutritional status. Overall normal physical assessment findings in addition to normal gastrointestinal organ–specific findings can help confirm a fully functioning gastrointestinal system (Table 17.2).
| Organ Assessed | Expected Findings |
|---|---|
| Lips |
|
| Buccal mucosa and inner lips |
|
| Gums |
|
| Tongue |
|
| Oropharynx |
|
| Teeth |
|
| Soft palate and hard palate |
|
| Abdomen: inspection |
|
| Abdomen: auscultation |
|
| Abdomen: percussion |
|
| Abdomen: palpation |
|
| Anus |
|
| Rectum |
|
In addition to assessing individual organs, the nurse should conduct a general physical assessment, being alert for specific findings that indicate adequate nutrition (Table 17.3). Such findings also help demonstrate that the gastrointestinal system is functioning correctly.
| Feature Assessed | Expected Findings |
|---|---|
| General appearance | Alert, conscious, and ambulatory within the confines of client’s ability; no general emaciation |
| Height, weight, and body mass index | Body mass index of 18.5–24.9 kg/m2; 30 and over is considered obesity, with Class 3 obesity being 40 or greater |
| Vital signs | Vital signs that fall within expected ranges can indicate good nutritional status, but many pathologies can affect vital signs without regard to nutrition. Blood pressure and pulse can indicate hydration status; low blood pressure (less than 90/60 mm Hg) and tachycardia (heart rate greater than 100 beats per minute) can indicate hypovolemia |
| Eyes | No pallor of the palpebral conjunctiva, icterus (yellowing) of the sclera, Bitot’s spots (oval or triangular patches on the conjunctiva of built-up keratin), xerosis (dryness) of the cornea, or xanthelasmas (yellow plaques on or near the eyelids) |
| Skin | No xeroderma (dry skin), petechiae, purpura, ecchymosis, jaundice, carotenoderma (yellow–orange skin discoloration), poorly healing wounds, pigmentation or rashes in sun-exposed areas (such as around the neck or on the extremities, where pigmentation might look like gloves or stockings), xanthomas (localized lipid deposits), or loss of subcutaneous adipose tissue |
| Hair | No dryness, brittleness, or unexpected discoloration; not easy to pluck; no patches of baldness or extreme thinness |
| Nails | No dryness, brittleness, discoloration, clubbing, or koilonychia (soft nails that are concave in the center and appear to be “scooped out”) |
| Extremities | No edema, weakness, paresthesia, sensation loss, bowing, ulcerations, poorly healing wounds, neuropathies, or muscle atrophy or wasting |
| Odor | No unusual odors; fruity acetone, musty, and sweet, burnt sugary odors can indicate specific nutritional issues due to pathologies |
| Function | Ability to perform functions at the client’s baseline for their age; deficits from baseline or, in infants and children, delays in development, growth, or weight can indicate poor nutritional status |
Nutritional Deficiencies Related to Abnormal Assessment Findings in the Gastrointestinal System
Abnormal findings in an assessment of the gastrointestinal system and other systems can indicate the presence of disease or nutritional deficit. To best plan nutritional strategies for the client, the nurse should know what each abnormal finding, in conjunction with laboratory results and dietary recall, could indicate. Some abnormal findings and nutritional deficiencies and toxicities related to them are shown in Table 17.4.
| Organ Assessed | Abnormal Findings | Nutritional Deficiency or Toxicity |
|---|---|---|
| Lips | Fissures, crusts, or scales on the lips or in the corners of the lips, cracked lips, angular cheilitis | Deficiency of vitamin B1 (thiamine), vitamin B12 (cobalamin), and/or iron |
| Tongue | Inflammation of the tongue | Deficiency of vitamin B2 (riboflavin) and/or B3 (niacin) |
| Loss of taste | Deficiency of zinc | |
| Halitosis | Deficiency of vitamin B12 (cobalamin) | |
| Red, painful tongue that has a burning sensation | Deficiency of iron | |
| Gums/mouth | Ulcerative gingivitis | Deficiency of vitamin B2 (riboflavin) and/or B3 (niacin) |
| Hemorrhagic gingivitis, painful mouth ulcers | Deficiency of vitamin B12 (cobalamin) | |
| Bleeding gingivitis | Deficiency of vitamin C | |
| Stomatitis (mouth inflammation) | Deficiency of vitamin B complex | |
| Salivary gland dysfunction, dysphagia | Deficiency of iron | |
| Recurrent aphthous stomatitis (canker sores) | Deficiency of zinc | |
| Salivary glands | Dry salivary glands | Dehydration or iron deficiency |
| Teeth | Pits, grooves, or missing areas in enamel of the teeth, giving teeth a translucent appearance | Deficiency of vitamin A |
| Periodontal disease | Deficiency of vitamin B6 (pyridoxine) and/or B12 (cobalamin) | |
| Abnormal bone patterns and shapes | Deficiency of vitamin D | |
| Dental caries (cavities) | Deficiency of vitamin D and/or fluoride | |
| Oropharynx | Recurrent tonsillitis | Deficiency of vitamin D |
| Pharyngitis | Deficiency of vitamin B2 (riboflavin) | |
| Inflammation of the hard and soft palates | Deficiency of iron, vitamin B2 (riboflavin), B6 (pyridoxine), B9 (folate), and/or B12 (cobalamin), D, and zinc | |
| Abdomen | Constipation (hypoactive bowel sounds, decreased frequency of bowel movements, hard stools, straining with bowel movements, increased flatus, mild abdominal distention, mild abdominal tenderness) | Deficiency of potassium, magnesium, vitamin B9 (folate), fiber, and/or fluid volume |
| Diarrhea (hyperactive bowel sounds, increased frequency of bowel movements, loose or watery stools, increased flatus, abdominal tenderness, symptoms of fluid volume deficit from losses) | Deficiency of vitamin B3 (niacin) or excessive intake of potassium | |
| Abdominal muscle pain and cramping | Deficiency of magnesium, potassium, sodium, vitamin B1 (thiamine), vitamin D, and/or calcium | |
| Anus | Hemorrhoids and fissures (caused by chronic constipation and straining to pass stools) | Deficiency of fiber and/or fluid volume |
| General appetite/ weight | Loss of appetite | Deficiency of zinc |
| Weight loss | Deficient caloric intake, protein deficiency, or impaired absorption | |
| Skin | Skin discoloration | Excessive intake of protein, carotene-containing foods, or supplements (vitamin A), causing diffuse hyperpigmentation, or excessive intake of both protein and zinc, causing carotenoderma |
| Ecchymosis | Deficiency of vitamin C, vitamin K, or zinc | |
| Muscle | Muscle pain, cramps | Deficiency of magnesium, potassium, sodium, vitamin B1 (thiamine), vitamin D, and/or calcium |
| Eyes | Pallor | Deficiency of iron, protein, or vitamin B6 (pyridoxine), B9 (folate), B12 (cobalamin), or C |
| Bitot’s spots, xerosis | Deficiency of vitamin A | |
| Xanthelasmas | Excessive caloric intake, obesity, or hypercholesterolemia | |
| Hair | Dry hair | Deficiency of vitamin A or E |
| Brittle hair | Deficiency of vitamin B7 (biotin) | |
| Discolored, easily pluckable hair; hair loss | Deficiency of protein or iron; overall severe malnutrition | |
| Nails | Dry and brittle nails | Deficiency of vitamin B7 (biotin), zinc, or protein |
| Nail discoloration | Overall poor nutritional status | |
| Koilonychia | Deficiency of iron, causing anemia | |
| Extremities | Edema | Deficiency of vitamin B1 (thiamine) or protein; excessive sodium |
| Paresthesia, muscle weakness | Deficiency of vitamin B1 (thiamine), B6 (pyridoxine), B12 (cobalamin), or E | |
| Loss of sensation | Deficiency of vitamin B12 (cobalamin) or E | |
| Muscle atrophy and wasting | Severe malnutrition | |
| Bowing of the legs (caused by rickets) | Deficiency of vitamin D |
Unfolding Case Study
Part A
Read the following clinical scenario and then answer the questions that follow. This case study will evolve throughout the chapter.
Mrs. Azan tells the nurse that she has been having muscle weakness and cramping, abdominal pain, mouth and tongue swelling, and sores in her mouth. When the nurse assesses Mrs. Azan, the nurse finds that she has angular cheilitis, multiple canker sores in her buccal areas, a red and swollen tongue, and general pallor.