Disorders of the Lower GI System

Core Concepts

How the lower GI tract works

After the stomach, chyme enters the small intestine, where enzymes and bile finish digestion and the lining absorbs nutrients, water, and electrolytes. The colon reclaims water, forming stool; the rectum and anus control elimination.

Diarrhea and constipation

Diarrhea is loose, frequent stool. It matters because it causes dehydration and electrolyte loss — especially dangerous in older adults, infants, and people who cannot drink enough. Causes include infection, medications (including antibiotics), food intolerances, malabsorption, IBD, and IBS. Constipation is infrequent or difficult stool passage, often from low fiber and fluid, inactivity, or medications (opioids are a common culprit). Severe constipation with vomiting, distention, and inability to pass gas or stool may signal a bowel obstruction — a medical emergency, not a case for more laxatives.

Irritable bowel syndrome (IBS)

IBS is a functional disorder: the bowel looks structurally normal, but motility and sensation are disturbed, producing cramping, bloating, and bowel habit changes. There is no tissue damage; it is diagnosed after other causes are ruled out, and management focuses on symptom relief — diet changes, stress management, and prescribed treatments.

Inflammatory bowel disease (IBD): Crohn and ulcerative colitis

IBD is a group of chronic, immune-mediated inflammatory diseases:

• Crohn disease can affect any part of the GI tract, involves all bowel wall layers, often appears in "skip lesions" (diseased patches separated by healthy tissue), and can cause strictures (narrowing) and fistulas (abnormal connections to other structures).
• Ulcerative colitis is limited to the colon and rectum, involves only the inner lining, and extends continuously upward from the rectum.

Both cause diarrhea (often with blood), cramping, weight loss, and fatigue, with flares and remissions. Complications include severe bleeding, strictures, fistulas (more with Crohn), and toxic megacolon (dangerous colon dilation, more with ulcerative colitis). Long-standing ulcerative colitis raises colorectal cancer risk. Nutrition is often affected — the dietitian is a key team member — and treatment is prescribed by the provider.

Diverticular disease

Diverticulosis is the presence of small outpouchings (diverticula) in the colon wall — common with age and often symptom-free. Diverticulitis is when those pouches become inflamed or infected, causing pain (often left lower abdomen), fever, and bowel habit changes. Complications include abscess, perforation, and fistula. Older advice to avoid seeds and nuts is now seen as overly broad — fiber guidance should follow the provider's and dietitian's plan. Severe diverticulitis may require hospital care or surgery, per provider orders.

Appendicitis and bowel obstruction

Appendicitis is inflammation of the appendix. The classic story: pain starting around the navel moves to the right lower abdomen, with fever, nausea, and appetite loss — but presentations vary. Because rupture causes peritonitis (a life-threatening abdominal infection), appendicitis is treated as a surgical emergency: NPO, IV fluids per orders, and preparation for surgery. Bowel obstruction blocks the forward movement of intestinal contents — mechanically (tumor, adhesions, hernia, stricture) or functionally (ileus, when the bowel stops contracting, as after surgery). Symptoms: cramping, vomiting, distention, and failure to pass gas or stool. Management includes decompression (often an NG tube), IV fluids, and possibly surgery; signs of strangulation (fever, severe constant pain, shock) demand urgent action.

Colorectal cancer

Most colorectal cancers arise from polyps (growths on the colon lining) that slowly transform into cancer over years — which is why screening is so effective. Warning signs include change in bowel habits, blood in the stool, unexplained weight loss, and anemia — but early cancer can be silent. Screening recommendations vary by age and risk; follow current guidelines.

Nursing care across lower GI disorders

Assessment focuses on the stool (frequency, consistency, color, blood, mucus), the pain (location, quality, timing), hydration status, skin integrity (diarrhea injures perianal skin), and nutrition. Care includes protecting perineal skin, encouraging fluids within the care plan, teaching about diet and fiber, and educating about prescribed treatments. Chronic conditions like IBD need emotional support and education about living with a relapsing disease; surgical patients may need ostomy preparation (see Ostomy Care). Scope note: nurses assess, monitor, educate, and coordinate; diagnosis, treatment, and surgery are provider responsibilities, with institutional variation.

How It Works / Step-by-Step Process

1. Take the history: stool frequency and consistency, blood or mucus, pain location and character, relation to meals and stress, medications, recent travel or antibiotics, and weight changes.
2. Assess: hydration status, abdominal assessment (distention, tenderness, bowel sounds), and perianal skin.
3. Sort the pattern: acute or chronic? Diarrhea or constipation? Blood present? Localizing pain (appendix, diverticula) or cramping and diffuse (IBS, obstruction)?
4. Identify red flags: fever, vomiting, rigid abdomen, severe constant pain, no gas or stool, significant blood loss — notify the provider immediately.
5. Protect and educate: maintain hydration per the care plan, protect skin, teach diet and fiber, explain prescribed treatments and screening.
6. Coordinate: involve the provider for diagnosis, the dietitian for nutrition, and the wound/ostomy team for surgical patients.

Common Confusions