🍎Medical Nutrition Therapy I Unit 5 – GI Disorders: Lower Tract

Key Concepts and Definitions

• Lower gastrointestinal (GI) tract includes the small intestine, large intestine (colon), rectum, and anus
• Digestion involves the breakdown of food into smaller components that can be absorbed and utilized by the body
• Absorption occurs primarily in the small intestine where nutrients are transported across the intestinal wall into the bloodstream
• Motility refers to the movement of food through the GI tract via peristalsis, a series of muscular contractions
• Microbiome consists of the diverse community of microorganisms that inhabit the GI tract and play a crucial role in health and disease
  • Includes bacteria, fungi, viruses, and other microbes
  • Influences digestion, nutrient absorption, immune function, and overall health
• Inflammatory bowel disease (IBD) is a group of chronic disorders characterized by inflammation of the GI tract (Crohn's disease and ulcerative colitis)
• Irritable bowel syndrome (IBS) is a functional disorder characterized by abdominal pain, bloating, and changes in bowel habits without underlying structural abnormalities

Anatomy and Physiology Review

• Small intestine is divided into three sections: duodenum, jejunum, and ileum
  • Duodenum receives chyme from the stomach and is the site of further digestion
  • Jejunum and ileum are responsible for the majority of nutrient absorption
• Large intestine (colon) is responsible for water and electrolyte absorption, formation of feces, and storage of waste material
• Rectum is the terminal portion of the large intestine where feces are stored prior to elimination
• Anus is the opening at the end of the digestive tract through which feces are expelled
• Intestinal wall is composed of four layers: mucosa, submucosa, muscularis externa, and serosa
  • Mucosa is the innermost layer and consists of epithelial cells, which are responsible for secretion and absorption
  • Submucosa contains blood vessels, lymphatics, and nerves that support the mucosa
• Enteric nervous system (ENS) is a complex network of neurons embedded in the GI tract that regulates motility, secretion, and absorption

Common Lower GI Disorders

• Inflammatory bowel disease (IBD) includes Crohn's disease and ulcerative colitis
  • Crohn's disease can affect any part of the GI tract and is characterized by transmural inflammation and skip lesions
  • Ulcerative colitis is limited to the colon and rectum and involves continuous inflammation of the mucosa
• Irritable bowel syndrome (IBS) is characterized by abdominal pain, bloating, and changes in bowel habits (diarrhea, constipation, or alternating)
• Celiac disease is an autoimmune disorder triggered by the ingestion of gluten, leading to damage of the small intestinal mucosa
• Diverticular disease refers to the presence of diverticula (outpouchings) in the colon wall
  • Diverticulosis is the presence of diverticula without inflammation
  • Diverticulitis occurs when diverticula become inflamed or infected
• Colorectal cancer is a malignant growth in the colon or rectum, often developing from precancerous polyps
• Hemorrhoids are swollen veins in the anus and lower rectum that can cause pain, itching, and bleeding

Diagnostic Procedures and Tests

• Endoscopy involves the use of a flexible tube with a camera to visualize the inside of the GI tract
  • Colonoscopy examines the entire colon and rectum
  • Sigmoidoscopy examines the lower part of the colon and rectum
• Biopsy involves the removal of a small tissue sample for microscopic examination to diagnose conditions such as IBD and celiac disease
• Imaging studies such as X-rays, CT scans, and MRI scans can provide detailed images of the GI tract and surrounding structures
• Stool tests can detect the presence of blood, inflammation, infections, or malabsorption
  • Fecal calprotectin is a marker of intestinal inflammation used to monitor IBD activity
  • Stool culture can identify specific bacterial or parasitic infections
• Breath tests can diagnose conditions such as small intestinal bacterial overgrowth (SIBO) and lactose intolerance
• Celiac serology tests measure antibodies specific to celiac disease, such as tissue transglutaminase (tTG) and endomysial antibodies (EMA)

Nutritional Implications

• Malabsorption can occur due to damage to the intestinal mucosa, leading to deficiencies in macronutrients and micronutrients
  • Fat malabsorption can lead to deficiencies in fat-soluble vitamins (A, D, E, and K)
  • Protein malabsorption can result in hypoalbuminemia and muscle wasting
• Inflammation and ulceration can increase the risk of bleeding and anemia, particularly in IBD
• Diarrhea can lead to dehydration and electrolyte imbalances, especially in severe cases
• Strictures and adhesions can cause intestinal obstruction, limiting the passage of food and leading to malnutrition
• Nutrient deficiencies can occur due to dietary restrictions, malabsorption, or increased losses
  • Iron deficiency anemia is common in IBD and celiac disease
  • Vitamin B12 deficiency can occur in Crohn's disease affecting the terminal ileum
• Osteoporosis risk is increased in IBD and celiac disease due to malabsorption of calcium and vitamin D, as well as the use of corticosteroids

Medical and Dietary Management

• Treatment goals include reducing inflammation, promoting mucosal healing, managing symptoms, and preventing complications
• Medications used in IBD include aminosalicylates, corticosteroids, immunomodulators, and biologic therapies
  • Aminosalicylates (mesalamine) are used to induce and maintain remission in mild to moderate ulcerative colitis
  • Corticosteroids (prednisone) are used for short-term treatment of acute flares in IBD
• Dietary modifications can help manage symptoms and promote healing
  • Low-fiber diets may be recommended during acute flares of IBD to reduce irritation
  • Gluten-free diet is the primary treatment for celiac disease to allow intestinal healing
• Enteral nutrition (liquid formulas) can be used as a primary therapy in Crohn's disease, particularly in pediatric patients
• Parenteral nutrition may be necessary in severe cases of malnutrition or when the GI tract needs to rest
• Probiotics and prebiotics may help modulate the gut microbiome and reduce inflammation in certain conditions
• Surgery may be required in cases of severe disease, complications, or failure of medical management
  • Resection involves removing the diseased portion of the intestine
  • Colectomy (removal of the colon) may be necessary in severe ulcerative colitis

Case Studies and Clinical Applications

• Case 1: A 25-year-old female presents with abdominal pain, bloody diarrhea, and weight loss. Colonoscopy reveals continuous inflammation in the colon, consistent with ulcerative colitis. Treatment includes mesalamine and a low-fiber diet during the acute phase.
• Case 2: A 35-year-old male with a history of Crohn's disease presents with a small bowel obstruction. CT scan reveals a stricture in the terminal ileum. The patient is managed with bowel rest, intravenous fluids, and parenteral nutrition until the obstruction resolves.
• Case 3: A 42-year-old female with celiac disease reports persistent symptoms despite following a gluten-free diet. Duodenal biopsy shows villous atrophy, indicating ongoing intestinal damage. A thorough dietary review reveals hidden sources of gluten, and the patient is educated on strict gluten avoidance.
• Case 4: A 58-year-old male undergoes a screening colonoscopy, which reveals multiple polyps. Pathology confirms the presence of adenomatous polyps, which are precancerous lesions. The patient is advised to increase dietary fiber, limit red and processed meats, and undergo regular surveillance colonoscopies.

Key Takeaways and Review Questions

• The lower GI tract includes the small intestine, large intestine, rectum, and anus, each with specific functions in digestion and absorption
• Common lower GI disorders include inflammatory bowel disease (Crohn's disease and ulcerative colitis), irritable bowel syndrome, celiac disease, diverticular disease, colorectal cancer, and hemorrhoids
• Diagnostic procedures for lower GI disorders include endoscopy, biopsy, imaging studies, stool tests, breath tests, and celiac serology tests
• Nutritional implications of lower GI disorders include malabsorption, nutrient deficiencies, anemia, and increased risk of osteoporosis
• Medical management of lower GI disorders involves medications, dietary modifications, enteral and parenteral nutrition, and surgery in severe cases
• Dietary management plays a crucial role in symptom control and promoting intestinal healing in conditions such as IBD and celiac disease
• Review questions:
  1. What are the key differences between Crohn's disease and ulcerative colitis?
  2. How does celiac disease affect the small intestine, and what is the primary treatment?
  3. What are the potential nutritional consequences of malabsorption in lower GI disorders?
  4. Describe the role of dietary modifications in the management of inflammatory bowel disease.