Internal GI Malabsorption

Define malabsorption syndrome

A clinical condition involving defective digestion and/or absorption of nutrients in the GI tract

Difference between maldigestion and malabsorption

Maldigestion = impaired breakdown of nutrients; Malabsorption = impaired mucosal uptake/transport

Example of maldigestion

Pancreatic insufficiency → decreased lipase → fat malabsorption

Example of malabsorption

Celiac disease → villous atrophy → decreased nutrient absorption

3 phases of nutrient absorption

Luminal (digestion); Mucosal (absorption); Post-absorptive (lymphatic transport)

Most common cause of luminal phase defect

Pancreatic insufficiency

Function of villi and microvilli

Increase surface area for absorption

Length of small intestine

Approximately 6 meters

Nutrients affected in diffuse malabsorption

Carbohydrates proteins fats vitamins minerals

Hallmark symptom of malabsorption

Chronic diarrhea

Why pancreatic insufficiency causes malabsorption

Decreased digestive enzymes leads to impaired nutrient hydrolysis

Conditions causing pancreatic insufficiency

Chronic pancreatitis cystic fibrosis pancreatic cancer

Effect of Zollinger-Ellison syndrome on absorption

Acid inactivates pancreatic enzymes leading to maldigestion

Why post-gastrectomy causes malabsorption

Poor mixing of food bile and enzymes

Role of bile salts

Micelle formation required for fat absorption

Causes of bile salt deficiency

Liver disease cholestasis ileal disease

Why ileal resection causes fat malabsorption

Reduced enterohepatic recycling of bile salts

Mechanism of SIBO

Bacterial deconjugation of bile salts

Result of impaired micelle formation

Fat malabsorption leading to steatorrhea

Drugs causing bile-related malabsorption

Cholestyramine neomycin

Most important structural abnormality in mucosal disease

Villous atrophy

Diseases causing villous atrophy

Celiac Crohn lymphoma infections

Infectious causes of malabsorption

Giardia Whipple disease tuberculosis

Drug-induced mucosal injury

NSAIDs olmesartan

Definition of SIBO

Small intestinal bacterial overgrowth causing malabsorption

Cause of SIBO

Intestinal stasis such as diabetes scleroderma obstruction

Example of brush border enzyme deficiency

Lactase deficiency

Most common carbohydrate malabsorption

Lactose intolerance

Mechanism of osmotic diarrhea in lactose intolerance

Unabsorbed lactose draws water into lumen

Stool pH in carbohydrate malabsorption

Less than 6

IgA deficiency presentation

Mimics celiac disease but no response to gluten free diet

Acrodermatitis enteropathica cause

Zinc malabsorption

Result of disaccharidase deficiency

Osmotic diarrhea and bloating

Why mucosal damage causes global malabsorption

Loss of absorptive surface area

Histologic features of mucosal injury

Villous atrophy with inflammation

Function of lymphatics in absorption

Transport of chylomicrons

Result of lymphatic obstruction

Fat and protein malabsorption

Causes of lymphatic obstruction

Lymphoma tuberculosis congestive heart failure

Congenital lymphatic disease

Intestinal lymphangiectasia

Clinical result of protein loss

Edema and ascites

Types of diarrhea in malabsorption

Secretory osmotic malabsorptive exudative

Osmotic diarrhea 특징

Improves with fasting

Secretory diarrhea 특징

Persists despite fasting

Malabsorptive diarrhea 특징

Associated with steatorrhea and improves with fasting

Exudative diarrhea 특징

Bloody inflammatory persists with fasting

Define steatorrhea

Fatty bulky foul smelling stools

Why stools float in steatorrhea

High fat content

Cause of flatulence

Bacterial fermentation producing hydrogen and methane

Cause of anemia in malabsorption

Iron vitamin B12 folate deficiency

Bone disease mechanism in malabsorption

Vitamin D and calcium deficiency

Stool osmotic gap formula

290 minus 2 times sodium plus potassium

Osmotic gap greater than 100 suggests

Osmotic diarrhea

Purpose of D-xylose test

Differentiate pancreatic from small bowel disease

Low D-xylose result indicates

Small bowel disease

Normal D-xylose with malabsorption suggests

Pancreatic insufficiency

What is celiac disease

Immune mediated response to gluten gliadin

Genetic association of celiac

HLA DQ2 HLA DQ8

Histology of celiac

Villous atrophy crypt hyperplasia intraepithelial lymphocytes

Best initial test for celiac

IgA anti tissue transglutaminase and total IgA

Definitive diagnosis of celiac

Small bowel biopsy