Angiodysplasiaisacommoncauseoflowergastrointestinalbleedinginolderadults.
Hemorrhoidsarecollateralvesselsthatforminresponsetovenoushypertension.
Diarrhea is defined as an increase in stool mass, frequency, or fluidity, typically to amounts greater than 200 grams per day. In severe cases, stool volume can exceed 14 L per day and, without fluid resuscitation, result in death. Worldwide, diarrheal diseases account for greater than 700,000 deaths of children under 5 years of age, making them the second leading cause of death in this age group. Painful, bloody, small-volume diarrhea is known as dysentery. Diarrhea is a common symptom of many intestinal diseases, including those due to infection, inflammation, ischemia, malabsorption, and nutritional deficiency. It can be classified into four major categories:
Secretory diarrhea is characterized by isotonic stool and persists during fasting.
Osmotic diarrhea, such as that occurring with lactase deficiency, is due to osmotic forces exerted by unabsorbed luminal solutes. The diarrheal fluid is at least 50 mOsm more concentrated than plasma, and the condition abates with fasting.
Malabsorptive diarrhea caused by inadequate nutrient absorption is associated with steatorrhea and is relieved by fasting.
Exudative diarrhea is due to inflammatory disease and characterized by purulent, bloody stools that continue during fasting.
Table 15.3 Defects in Malabsorptive and Diarrheal Disease
We begin our discussion with malabsorptive diarrhea. Other disorders associated with secretory and exudative types of diarrhea (e.g., cholera and inflammatory bowel disease, respectively) are addressed in separate sections.
Malabsorption manifests most commonly as chronic diarrhea and is characterized by defective absorption of fats, fatand water-soluble vitamins, proteins, carbohydrates, electrolytes, minerals, and water. Chronic malabsorption causes weight loss, anorexia, abdominal distention, borborygmi, and muscle wasting. A hallmark of malabsorption is steatorrhea, characterized by excessive fecal fat and bulky, frothy, greasy, yellow, or clay-colored stools.
The chronic malabsorptive disorders most commonly encountered in Western countries are pancreatic insufficiency, celiac disease, and Crohn disease. Environmental enteric dysfunction, or environmental enteropathy, which has a malabsorptive component, is pervasive in some communities within developing countries.
Malabsorption results from disturbance in at least one of the four phases of nutrient absorption:
Intraluminal digestion, in which proteins, carbohydrates, and fats are broken down into absorbable forms
Terminal digestion, which involves the hydrolysis of carbohydrates and peptides by disaccharidases and peptidases, respectively, in the brush border of the small-intestinal mucosa
Transepithelial transport, in which nutrients, fluid, and electrolytes are transported across and processed within the small-intestinal epithelium
Lymphatic transport of absorbed lipids
In many malabsorptive disorders, a defect in one of these processes predominates, but more than one usually contributes (
Table 15.3 ). As a result, malabsorption syndromes resemble each other more than they differ. Signs and symptoms include diarrhea (from nutrient
Mycobacterialinfection,Whippledisease +,Indicatesthattheprocesscanbeabnormalinthediseaseindicated.Otherprocessesarenottypicallyaffected.