What is the relevant anatomy and physiology related to gastroenteritis?

From the Guidelines

Gastroenteritis involves inflammation of the gastrointestinal tract, primarily affecting the stomach and intestines, with the digestive system's anatomy including the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus, and accessory organs like the liver, gallbladder, and pancreas [ 1 ]. The relevant anatomy includes:

• The stomach, which produces acid and enzymes that begin digestion
• The small intestine, which absorbs nutrients and water
• The large intestine, which absorbs remaining water and electrolytes and forms stool Physiologically, the stomach and intestines work together to digest food, absorb nutrients, and eliminate waste. During gastroenteritis, pathogens (viruses, bacteria, or parasites) disrupt normal function by damaging the intestinal epithelium, triggering inflammation, and activating secretory mechanisms [ 1 ]. This leads to increased intestinal motility, decreased absorption, and increased secretion of fluids and electrolytes into the intestinal lumen. The body's defense mechanisms include stomach acid, intestinal mucus, gut-associated lymphoid tissue, and normal gut microbiota. Key points to consider in the context of gastroenteritis include:
• The World Health Organization's definition of diarrhea as the passage of 3 or more loose or liquid stools per 24 hours [ 1 ]
• The different clinical presentations of infectious diarrhea, including acute watery diarrhea, acute bloody diarrhea, prolonged diarrhea, persistent diarrhea, and chronic diarrhea [ 1 ]
• The importance of fluid and electrolyte replacement in managing gastroenteritis, with oral rehydration solutions containing sodium, potassium, chloride, citrate, and glucose [ 1 ].

From the Research

Relevant Anatomy

• The stomach and intestines are the primary sites of inflammation in gastroenteritis 2
• The colon is also affected in cases of colitis, which is inflammation of the colon 2

Relevant Physiology

• The gastrointestinal tract is responsible for the digestion and absorption of nutrients, and its function is disrupted in gastroenteritis 3
• The gut-directed symptom of diarrhea is a common symptom of gastroenteritis, and is characterized by the frequent passage of unformed, liquid stools 3
• The mainstay of management of acute gastroenteritis is provision of adequate fluids to prevent and treat dehydration 3

Pathophysiology

• Viruses are the most common cause of gastroenteritis, followed by bacteria and parasites 2
• The incidence of various infections varies by age, sex, location, and vaccine availability 2
• Vaccination has reduced rotavirus infections by as much as 90% in children 2
• Postinfectious complications of gastroenteritis include irritable bowel syndrome (IBS) and lactose intolerance 2

Diagnostic Approach

• The diagnostic approach to gastroenteritis and colitis varies with symptom severity 2
• Microbial studies are not needed with mild symptoms that resolve within a week, but longer-lasting or more severe symptoms warrant microbial studies 2
• Recent antibiotic exposure should prompt testing for Clostridioides difficile 2
• Multiplex antimicrobial testing is preferred, while stool cultures and microscopic stool examinations are no longer first-line tests 2

Management

• Management of gastroenteritis depends on severity, with patients with mild or moderate symptoms treated with oral hydration if tolerated 2
• Nasogastric or intravenous hydration are used for those with more severe illness 2
• Antiemetic, antimotility, and/or antisecretory drugs can be used for symptom control 2
• Antimicrobial therapy is indicated for C difficile infections, travel-related diarrhea, other bacterial infections with severe symptoms, and parasitic infections 2, 4
• Loperamide is an effective therapy for a variety of diarrheal syndromes, including acute, nonspecific (infectious) diarrhea 5, 6