07.2 Large intestine function and conditions

Large Intestine Function and Conditions

• The large intestine is responsible for the final stages of digestion, water absorption, and maintaining the microbiome.
• Inflammatory Bowel Disease (IBD) is a chronic condition, with two primary types: Crohn's Disease and Ulcerative Colitis (UC).
• Crohn's Disease is characterized by transmural inflammation that can affect any part of the gastrointestinal tract, most commonly the terminal ileum. It features "skip lesions" (discontinuous inflammation), fistula formation, and granulomas.
• Ulcerative Colitis (UC) involves inflammation confined to the mucosal layer of the colon and rectum, starting in the rectum and spreading continuously proximally.
• Symptoms of IBD can include bloody diarrhea, urgency, and tenesmus (incomplete defecation).
• Crohn's Disease can cause nutritional deficiencies due to small bowel involvement. UC can increase the risk of colorectal cancer, especially with pancolitis (inflammation throughout the entire colon).
• Complications of IBD can also include toxic megacolon.

Learning Objectives

• Describe the anatomy and function of the large intestine, including water absorption, microbiome maintenance, and stool formation.
• Explain the arterial and venous supply (superior and inferior mesenteric arteries).
• Recognize clinical presentations, diagnostic features, pathophysiological characteristics of Inflammatory Bowel Disease (IBD).
• Differentiate Crohn's Disease and Ulcerative Colitis using histological, imaging, and pathological characteristics.
• Identify current IBD pharmacological and surgical treatments, including indications, mechanisms, and complications.

Key Concepts

• Large Intestine: Cecum, ascending, transverse, descending, sigmoid colon, rectum, and anal canal. Primary functions: water absorption, electrolyte balance, stool formation, and supporting gut health via microbiota.
• Inflammatory Bowel Disease (IBD): A group of chronic idiopathic inflammatory conditions of the GI tract, including Crohn's and UC.
• Crohn's Disease: Transmural inflammation, skip lesions, fistula formation, granulomas.
• Ulcerative Colitis: Mucosal and submucosal inflammation only, continuous inflammation starting at the rectum, friable mucosa prone to bleeding and pseudo-polyp formation.

Clinical Applications

• Case Study Examples: Descriptions of Crohn's Disease and Ulcerative Colitis presentations. (details are included in the OCR text).

Pathophysiology

• IBD is an abnormal immune response in genetically susceptible individuals which leads to chronic inflammation. Crohn's is transmural, with skip lesions, while UC is mucosal and submucosal, continuous.

Pharmacology

• Treatments include Corticosteroids (prednisolone, hydrocortisone), 5-Aminosalicylic Acid (5-ASA) drugs (mesalazine, sulfasalazine), Biologics (anti-TNF agents, JAK Inhibitors) and Immunosuppressants (azathioprine, methotrexate).

Differential Diagnosis

• Differentiating IBD from Irritable Bowel Syndrome (IBS), and other conditions.

Investigations

• Endoscopy (colonoscopy), Stool Calprotectin tests, imaging (CT/MRI, barium enema), blood tests (CRP, ESR, anaemia).

Summary

• IBD consists of two major types, Crohn's and UC, differing in their location, pattern, and depth of inflammation.
• Crohn's involves patchy, transmural inflammation, while UC involves continuous mucosal inflammation limited to the colon.
• Treatment varies by severity and can include medications (corticosteroids, 5-ASAs, biologics) and surgery.