GI Disorders

• Gastrointestinal disorders


  • Vomiting
  • Diarrhea
  • Constipation
• Vomiting


  The forcible expulsion of the contents of stomach through the esophagus and out of the mouth
• Vomiting


  • It is a reflex that is coordinated by the vomiting center in the medulla oblongata
  • The vomiting center receives inputs from four sources at the periphery

  
• Neural pathways involved in vomiting

  1. Brain cortex (unpleasant smell or sight, fear, pain)

  2. Cerebellum (vestibular stimulations)

  3. Nucleus tractus solitarius (stimulation of pharynx or stomach)

  4. Area postrema chemoreceptor trigger zone (stimulations by toxins and medications present in the blood)

  
• Chemoreceptor trigger zone


  It can sense changes in the chemical composition of the blood, as the blood-brain barrier is leaky in this area of the brain

  
• Signals from the vomiting center

  1. Signals to the upper GIT organs (tongue, soft palate, pharynx, esophagus, stomach)

  2. Signals to the respiratory and abdominal muscles

  
• Vomitus


  The gastric content expelled during vomiting
• Characteristics of vomitus


  • Hematemesis (presence of blood in vomitus)
  • Yellow or green-colored vomitus (presence of bile)
• Projectile vomiting


  Vomitus is released with great force, so it is propelled over a short distance
• Treatment strategies in vomiting

  1. Cessation of vomiting (antiemetic medications)

  2. Rehydration (i.v. fluid replacement)

  3. Correcting electrolyte imbalances

  4. Restoring acid-base balance
• Diarrhea


  A medical condition associated with increased frequency of defecation and increased fluid content and volume of feces
• Classification of diarrhea


  • Large-volume diarrhea
  • Small-volume diarrhea
• Types of large-volume diarrhea

  • Osmotic
  • Secretory
  • Motility disturbances
• Osmotic diarrhea


  A nonabsorbable substance in the intestine draws water into the lumen by osmosis, which increases the volume of stool

  
• Causes of osmotic diarrhea


  • Large amounts of nonabsorbable sugars (e.g. sorbitol)
  • Large amounts of poorly absorbed ions (magnesium, sulfate, and phosphate)

  
• Lactase deficiency


  When there is no lactase, the lactose is not digested and remains in the lumen of the intestine, drawing water into the intestinal lumen by osmosis, which causes diarrhea

  
• Secretory diarrhea


  A form of large-volume diarrhea that is caused by excessive mucosal secretion of fluid in the intestine, typically caused by infection
• Causes of secretory diarrhea

  • Viral infection (norovirus in adults and rotavirus in children)
  • Bacterial infection (Salmonella, Shigella, and E.coli)
  • Parasites invasion (Cryptosporidium, Giardia, Entamoeba)
• Why secretion of water is increased during intestinal infection?

  1. Absorptive cells in intestinal crypts secrete chloride into the intestinal lumen, creating a negative charge which attracts Na+ diffusion via the paracellular pathway, and Na+ then attracts water through osmosis

  2. Conductance of the chloride channel in the luminal membrane is increased upon elevation of cAMP and Ca2+ levels in the absorptive cell, induced by enterotoxin

  
• Other causes of secretory diarrhea


  • Intestinal tumor (which may release hormones or paracrine agents that stimulate fluid secretion by enterocytes)
  • Food allergy (which results in release of histamine from the mast cells, stimulating intestinal fluid secretion)

  
• Diarrhea related to motility disturbances

  This type of diarrhea is related to excessive intestinal motility, which accelerates transit of chyme through the intestine and reduces mucosal surface contact, decreasing fluid absorption

  
• Causes of motility disturbance diarrhea

  • Resection of the small intestine
  • Irritable bowel syndrome
  • Diabetic neuropathy
  • Hyperthyroidism
• Paracrine agents


  Agents that stimulate fluid secretion by enterocytes (e.g. VIP, Ach, serotonin)

  
• Food allergy


  Results in release of histamine from mast cells, which then stimulates intestinal fluid secretion

  
• Types of large-volume diarrhea

  • Osmotic
  • Secretory
  • Motility disturbances
• Fluid absorption in large intestine

  Depends on two factors
• Diarrhea related to motility disturbances

  • Accelerates transit of chyme through the intestine, which reduces mucosal surface contact and decreases fluid absorption

  
• Causes of motility disturbance diarrhea

  • Resection of small intestine
  • Fistula formation
  • Irritable bowel syndrome
  • Diabetic neuropathy
  • Hyperthyroidism
  • Laxative abuse
• Classification of diarrhea


  • Large-volume diarrhea (osmotic, secretory, motility disturbances)
  • Small-volume diarrhea (exudative)
• Small-volume diarrhea


  Exudative diarrhea caused by exudation of mucus, blood, and protein from inflamed intestinal mucosa
• Causes of small-volume exudative diarrhea

  • Ulcerative colitis
  • Crohn's disease
  • Microscopic colitis
• Pathophysiology of diarrhea


  • Dehydration and decreased intravascular blood volume
  • Metabolic acidosis due to loss of bicarbonate
  • Hypokalemia due to high K+ concentration in diarrheal fluid

  
• About 9 liters of fluid are absorbed daily in the intestine, suggesting a huge potential for fluid loss (dehydration) in diarrhea
• Signs of dehydration


  • In adults: thirst, lack of energy, decreased urination, dizziness, loss of skin turgor
  • In children: dry mouth, decreased urination, irritability, less tears when crying, sunken eyes/cheeks/belly/fontanelle
• Prevention and treatment of diarrhea

  • Improved sanitation
  • Clean drinking water
  • Hand washing
  • Exclusive breastfeeding up to 6 months
  • Rotavirus vaccination
• Constipation


  Infrequent or difficult defecation caused by decreased intestinal motility
• Fewer than three stools per week are defined as constipation
• Fecal impaction


  A firm, immovable mass of stool obstructing the lower GI tract
• Types of primary constipation

  • Functional constipation
  • Slow transit constipation
  • Pelvic floor dysfunction
• Functional constipation


  Most common type, results from low-residue diet, low fluid intake, lack of exercise, lack of access to toilet facilities, dehydration