Stool (Textbook) Flashcards
Normal Fecal Specimens
Contains:
- Bacteria
- Cellulose
- Undigested foodstuffs
- GI secretions
- Bile pigments
- Cells from the intestinal walls
- Electrolytes
- Water
Breakdown and Reabsorption Sites
Although digestion of ingested proteins, carbohydrates, and fats takes place throughout the alimentary tract
Small intestine is the primary site for the final breakdown and reabsorption of these compounds, using digestive enzymes secreted by the pancreas include trypsin, chymotrypsin, amino peptidase, and lipase. Bile salts provided by the liver aid in the digestion of fats.
Diarrhea Classification
Based on four factors:
- Illness duration
- Mechanism
- Severity
- Stool characteristics
Diarrhea lasting <4 weeks is defined as acute, and diarrhea persisting for >4 weeks is termed chronic diarrhea.
Diarrhea Mechanisms and Differentiation
The major mechanisms of diarrhea are:
- Secretory
- Osmotic
- Intestinal hypermotility
The laboratory tests used to differentiate these mechanisms are:
- Fecal electrolytes (fecal sodium, fecal potassium)
- Fecal osmolality
- Stool pH
Fecal Osmolarity and Calculation
- Total fecal osmolarity is close to the serum osmolality (290 mOsm/kg)
- Fecal sodium is 30 mmol/L
- Fecal potassium is 75 mmol/L
The fecal sodium and fecal potassium results are used to calculate the fecal osmotic gap.
Osmotic gap = 290 – [2 (fecal sodium + fecal potassium)]
Fecal Osmolarity Values
Osmotic diarrhea is >50 mOsm/kg
Secretory diarrhea is <50 mOsm/kg
Fecal pH
A fecal fluid pH of <5.6 indicates a malabsorption of sugars, causing an osmotic diarrhea.
Causes of Secretory Diarrhea
Caused by increased secretion of water.
- Bacterial
- Viral
- Protozoan infections
All produce increased secretion of water and electrolytes, which override the reabsorptive ability of the large intestine, leading to secretory diarrhea.
Other causes include: drugs, stimulant laxatives, hormones, inflammatory bowel disease (Crohn disease, ulcerative colitis, lymphocytic colitis, diverticulitis), endocrine disorders (hyperthyroidism, Zollinger-Ellison syndrome, VIPoma), neoplasms, and collagen vascular disease.
Osmotic Diarrhea Causes
Caused by poor absorption (maldigestion/malabsorbtion) that exerts osmotic pressure across the intestinal mucosa, presenting increased fecal material to the large intestine, resulting in water and electrolyte retention in the large intestine (osmotic diarrhea), which in turn results in excessive watery stool.
Causes:
- Disaccharidase deficiency (lactose intolerance)
- Malabsorption (celiac sprue)
- Poorly absorbed sugars (lactose, sorbitol, mannitol)
- Laxatives
- Magnesium-containing antacids
- Amebiasis
- Antibiotic administration
Altered Motility Diarrhea
Conditions of enhanced motility (hypermotility) or slow motility (constipation). Both can be seen in irritable bowel syndrome (IBS), a functional disorder in which the nerves and muscles of the bowel are extra sensitive
Hypermotility: excessive movement of intestinal contents through GI tract, normal absorption of intestinal contents/nutrients cannot occur. It can be caused by enteritis, the use of parasympathetic drugs, or with complications of malabsorption.
Rapid vs Slow Dumping
Rapid gastric emptying (RGE): hypermotility of the stomach and the shortened gastric emptying half-time, causing the small intestine to fill too quickly with undigested food; hallmark of early dumping syndrome (EDS). Symptoms begin 10 to 30 minutes following meal ingestion.
Late dumping: occurs 2 to 3 hours after a meal and is characterized by weakness, sweating, and dizziness.
Hypoglycemia is often a complication of dumping syndrome
Normal Excretion
Healthy people have a gastric emptying half-time range of 35 - 100 minutes, controlled by fundic tone, duodenal feedback, and GI hormones
Emptying time of <35 minutes is considered RGE.
Steatorrhea
Fecal Fat
Absence of bile salts that assist pancreatic lipase in the breakdown and subsequent reabsorption of dietary fat (primarily triglycerides) produces an increase steatorrhea that exceeds 6g per day
Cystic fibrosis, chronic pancreatitis, and carcinoma, are also associated with steatorrhea.
D-Xylose Test
Distinguishing maldigestion and malabsorption
D-Xylose is a sugar that does not need to be digested but does need to be absorbed to be present in the urine
Urobilin
Imparts brown color to feces
Conjugated bilirubin formed in the degradation of hemoglobin passes through the bile duct to the small intestine, where intestinal bacteria convert it to urobilinogen and stercobilinogen, which through intestinal oxidation is converted to urobilin.
Therefore, stools that appear pale (acholic stools) may signify a blockage of the bile duct.
