Patho GI

Function of GI Tract

Key Functions:

  • Motility: Movement of food through the GI tract.

    • This refers to the coordinated contractions of the smooth muscle layers in the GI tract that facilitate the movement of food from the esophagus to the rectum, ensuring that nutrients are effectively transported along the digestive pathway. Peristalsis, a wave-like muscle contraction, is essential for progressing food and mixing it with digestive juices.

  • Secretion: Release of digestive juices and enzymes.

    • The GI tract secretes various substances critical for digestion including enzymes, acids, and bile. These substances break down food components and aid in nutrient release. For example, gastric juices secreted by the stomach contain hydrochloric acid and digestive enzymes, while bile produced by the liver aids in the emulsification of fats.

  • Digestion: Breakdown of food into absorbable components.

    • This process encompasses both mechanical and chemical breakdown of food. Mechanical digestion involves physical actions such as chewing and churning in the stomach, while chemical digestion involves enzyme action that transforms complex food molecules into simpler absorbable units.

  • Absorption: Uptake of nutrients into the bloodstream.

    • Absorption occurs primarily in the small intestine, where digested nutrients pass through the intestinal walls into the bloodstream. The villi and microvilli present in the intestinal lining increase the surface area massively to enhance nutrient uptake, which is crucial for the body's energy and metabolic needs.

Nervous System Interactions in Digestive Function

  • Parasympathetic Nervous System (PNS):
      - Primarily involves the vagus nerve.
      - Effects on Digestion:
        - Triggers an increase in peristalsis (wave-like muscle contractions).
        - Stomach stretching occurs from food intake but is limited to prevent overstretching.
        - Increase in gastric pH levels.
        - Stimulated by pleasant smells and sensations of hunger.

  • Sympathetic Nervous System (SNS):
      - Effects on Digestion:
        - Conversely inhibits gastrointestinal activity.
        - Causes vasoconstriction and reduces blood flow.
        - Reduces gastric secretions and inhibits the regeneration of epithelial cells in the GI tract.

Nausea & Vomiting

  • Initiation Process:
      - Initiated by the medulla oblongata.
      - Can result from:
        - Distension or irritation in the digestive tract.
        - Visual or olfactory stimuli (sights or smells).
        - Psychological stress or pain (anxiety).
        - Inner ear imbalances (e.g., motion sickness).
        - Medication effects or exposure to noxious substances.
        - Increased intracranial pressure (IICP).

  • Significance of Vomitus:
      - Hematemesis:
        - Presence of “coffee grounds,” indicating partially digested food mixed with old blood.
        - A deeper brown color may indicate lower intestinal contents due to obstruction.
      - Recurrent Projectile Vomiting:
        - May indicate pyloric stenosis, primarily observed in children.
      - Dehydration Consequences:
        - Can lead to metabolic acidosis.

Diarrhea

  • Defined as an excessive frequency of stools.

  • Categories of Diarrhea:
      - Large Volume (Osmotic):
        - Results from short transit time, excess fluid flooding the intestine (e.g., lactose intolerance).
        - Can lead to hypovolemia and metabolic acidosis.
      - Small Volume:
        - Associated with bowel disease, may contain blood, pus, or mucous.
      - Steatorrhea:
        - Known as “fatty diarrhea,” characterized by greasy and foul-smelling stools, stemming from malabsorption syndromes.
      - Bloody Diarrhea:
        - Occult: Small, hidden amounts of blood.
        - Melena: Dark-colored (tarry) stools, indicative of upper GI bleeding.
        - Hematochezia: Presence of fresh (frank) red blood in stool.

Constipation

  • Definition: A condition that may lead to fecal impaction.

  • Causes:
      - Increased age.
      - Inadequate dietary fiber levels.
      - Insufficient fluid intake.
      - Ignoring the urge to defecate.
      - Muscle weakness and inactivity.
      - Neurological disorders (e.g., multiple sclerosis, spinal cord injuries).
      - Certain medications (e.g., opiates, drugs that block the PNS).
      - Obstruction conditions.

Upper GI Disorders

  • Mouth Disorders:
      - Cleft Lip and/or Palate: Neural tube disorder.
      - Aphthous Ulcers: Also known as canker sores or stomatitis.
      - Candidiasis: Known as thrush, a fungal infection.
      - Herpes: Primarily caused by HSV-1 (transmitted through kissing or close contact); tends to reactivate with stress.
      - Dental Issues: Varied problems affecting oral health.
      - Leukoplakia: Presence of precancerous lesions in the mouth.

  • Dysphagia:
      - Definition: Difficulty swallowing.
      - Causes Include:
        - Neurological deficits (e.g., multiple sclerosis, stroke).
        - Achalasia: Failure of the esophageal sphincter to relax.
        - Congenital atresia: Presenting as a blind pouch.
        - Fibrosis: Stenosis or stricture of the esophagus.
        - Structural compression from external sources.
        - Diverticulum formations.

  • Hiatal Hernia:
      - Definition: Protrusion of part of the stomach through the diaphragm's opening (hiatus).
      - Types Include:
        - Sliding Hiatal Hernia: Slides up and down based on body position, especially when lying down.
        - Paraesophageal Hernia: Part of the fundus of the stomach moves above the diaphragm, which can constrict blood vessels in the stomach.

  • Gastroesophageal Reflux Disease (GERD):
      - Definition: Chronic regurgitation of stomach contents into the esophagus.
      - Causes:
        - Weak esophageal sphincter.
        - Obesity as a contributing factor.
        - Presence of a hiatal hernia.

  • Esophageal Cancer:
      - Primarily squamous cell carcinoma, located mostly in the distal esophagus.
      - Causes Include:
        - Chronic irritation or injury to the esophagus (e.g., esophagitis, achalasia).
        - Risk factors include chronic alcohol abuse and smoking.
      - Prognosis: Typically poor due to late diagnosis.

Acute Gastritis

  • Definition: Inflammation of the gastric mucosa presenting as redness, edema, and ulceration, which can lead to bleeding if the mucosal barrier is compromised.

  • Causes Include:
      - Infection by pathogens.
      - Allergies to certain foods or medications.
      - Frequent ingestion of irritants (e.g., spicy foods).
      - Excessive alcohol consumption.
      - Ingestion of ulcerogenic drugs, especially on an empty stomach.
      - Exposure to radiation and chemotherapy.
      - Nature: Often self-limiting.

Chronic Gastritis

  • Definition: Characterized by chronic inflammation leading to atrophy of the mucosa with loss of gastric secretory glands.

  • Causes Include:
      - Continuation of the same causes as acute gastritis, with ongoing injury.
      - Infection from Helicobacter pylori, a bacteria often associated with peptic ulcers.

Peptic Ulcers

  • Types:
      - Gastric Ulcers: Located in the stomach.
      - Duodenal Ulcers: Most commonly found in the proximal duodenum.

  • Pathophysiology:
      - Development of small cavities in the mucosal lining that continue to erode deeper into surrounding tissues, potentially invading blood vessels leading to bleeding.
      - May perforate the stomach or intestinal wall, spilling contents into the peritoneal cavity.

  • Causes Include:
      - Helicobacter pylori infection (most common).
      - Inadequate blood supply to the gastric tissues (due to vasoconstriction from stress, smoking, and severe anemia).
      - Ulcerogenic substances like NSAIDs.
      - Atrophy of gastric mucosa as seen in chronic gastritis.
      - Increased number of acid-pepsin secretory cells (a genetic anomaly).
      - Overstimulation of acid-pepsin secretion due to factors like alcohol and caffeine.

  • Symptoms:
      - Characteristic epigastric aching and burning pain typically occurring 2-3 hours after meals or at night, often relieved by food or antacids.
      - Additional Symptoms: Heartburn, nausea, and increased symptom severity with spicy food intake.

Stress Ulcers

  • Definition: Result from severe physical trauma or stressors.

  • Examples Include:
      - Curling’s Ulcers: Associated with burns.
      - Cushing’s Ulcers: Occur following head injuries.

  • Progression: Can quickly progress to hemorrhagic conditions.

  • Prevention: Medications are typically administered to mitigate risk.

Dumping Syndrome

  • Definition: Loss of control over gastric emptying, frequently observed post-gastric resection or partial gastrectomy.

  • Mechanism:
      - Leads to improper dilution of chyme as hyperosmolar contents exit the stomach, pulling excess water into the intestine.
      - Results in distention of the intestine, stimulating the PNS and increasing peristalsis.

  • Symptoms Include: Dizziness, weakness, rapid pulse, sweating, and potential hypoglycemia.

Pyloric Stenosis

  • Definition: Narrowing and obstruction of the pyloric sphincter.

  • Presentations:
      - Seen in infants (congenital form) as hypertrophy of the sphincter leading to projectile vomiting.
      - In adults (acquired form), typically due to surgical adhesions or scarring, leading to decreased gastric emptying.

Disorders of Liver and Pancreas

  • Gallbladder Disorders:
      - Cholelithiasis: Formation of gallstones in the gallbladder.
      -     Cholecystitis: Inflammation caused by stone obstruction in bile ducts.
      - Cholangitis: Inflammation and infection of the bile ducts.
      - Choledocholithiasis: Obstruction of the biliary tract due to gallstones.

  • Gallbladder Disorder Symptoms:
      - Severe upper right quadrant pain (biliary colic) with episodes leading to referred pain.
      - Epigastric pain, nausea, and vomiting in acute phases.
      - In later stages: jaundice, fever, and leukocytosis may develop.

Hepatitis

  • Definition: Inflammation of the liver.

  • Causes:
      - Can be idiopathic (fatty liver) or viral (e.g., hepatitis A, B, C).
      - Also results from infectious mononucleosis, chemical toxicity, and chronic inflammation causing liver damage.

  • Viral Hepatitis Forms:
      - Acute Forms: Hepatitis A and E, transmitted via the oral/fecal route; typically self-limiting.
      - Chronic Forms: Hepatitis B, C, and D; transmitted through blood and body fluids, often causing long-term damage and leading to chronic infection or carrier state.

  • Clinical Manifestations (Stages):
      - Preicteric (Prodromal Stage):
        - Insidious onset characterized by fatigue, anorexia, muscle aches, fever, and mild upper right quadrant discomfort.
        - Enzymes AST and ALT begin to rise.
      - Icteric Stage:
        - Jaundice onset, increased serum bilirubin levels, light-colored stools, dark urine, severe itching (pruritus), liver tenderness, and hepatomegaly.
      - Posticteric (Recovery Stage):
        - Gradual reduction in symptoms over weeks; acute (especially Hepatitis A) typically resolves in 8-10 weeks, while prolonged recovery (especially Hepatitis B) can occur over 16 weeks.

Cirrhosis

  • Definition: Progressive destruction of liver tissue leading to liver failure.

  • Categories Include:
      - Alcoholic Liver Disease: The largest group.
      - Biliary Cirrhosis: Often due to gallstones or cystic fibrosis.
      - Postnecrotic Cirrhosis: Associated with chronic hepatitis or exposure to toxins.
      - Metabolic Cirrhosis: Storage disorders such as hemochromatosis.

  • Complications:
      - Functional losses resulting in decreased bilirubin removal and conjugation.
      - Decreased bile production and impaired nutrient digestion.
      - Loss of blood-clotting factors and plasma proteins.
      - Impairment of glucose and glycogen metabolism, insufficient storage of iron and vitamin B12, and inadequate hormone inactivation.
      - Impaired removal of toxic substances (e.g., ammonia).

  • Consequences Related to Bile Duct or Blood Flow Obstruction:
      - Reduction in bile entering the intestine causing obstructive jaundice.
      - Increased pressure in portal veins leading to portal hypertension.
      - Congestion in the spleen (Splenomegaly) due to hemolysis.
      - Impaired digestion from congestion in the intestinal walls.
      - Development of esophageal varices and ascites in the peritoneal cavity.

  • Symptoms of Cirrhosis Include:
      - Fatigue, anorexia, weight loss, anemia, diarrhea, dull aching pain in the upper right quadrant (URQ), ascites, esophageal varices, encephalopathy, edema, increased bruising, and jaundice.

Acute Pancreatitis

  • Definition: Inflammation of the pancreas resulting from the autodigestion of tissues due to premature activation of enzyme proenzymes.

  • Mechanism:
      - Early activation of trypsinogen into trypsin, leading to the conversion of other proenzymes into active forms of amylase and lipase which digest pancreatic tissue, causing inflammation and necrosis.

  • Etiology & Symptoms:
      - Commonly caused by gallstones and excessive alcohol consumption.
      - Symptoms include:
        - Severe epigastric or abdominal pain, signs of shock (low blood pressure, pallor, sweating), low-grade fever, abdominal distention, and decreased bowel sounds.
        - The presence of leukocytosis indicates infection or inflammation.

Disorders Affecting Absorption

  • Celiac Disease:
      - A malabsorption syndrome that prevents the breakdown of gluten, leading to malnutrition and intestinal inflammation.
      - Has a genetic link, often due to defects in intestinal enzymes.
      - Symptoms include steatorrhea, muscle wasting, failure to thrive, and the necessity for strict adherence to a gluten-free diet; increased risk for intestinal cancers.

  • Crohn’s Disease:
      - A chronic inflammatory bowel disease most frequently affecting the small intestine.
      - Occurs primarily in the mucosal layer, leading to shallow ulcerations and thickened walls, forming destructive masses (granulomas) and presenting with increased intestinal motility.

  • Symptoms of Crohn’s Disease:
      - Diarrhea, cramping, melena, pain and tenderness in the right lower quadrant (RLQ), anorexia, weight loss, and fatigue.

  • Ulcerative Colitis:
      - Inflammation beginning in the rectum, progressing through the colon with swollen mucosa and submucosa which becomes fragile and prone to ulcerations.
      - Granulation tissue formation occurs but is fragile, vascular, and bleeds easily, interfering with fluid and electrolyte absorption.

  • Symptoms of Ulcerative Colitis:
      - Severe abdominal cramping, tenesmus (rectal spasms), bleeding associated with diarrhea, possible medical emergencies, and potential complications leading to intestinal paralysis (toxic megacolon) and electrolyte disturbances during severe episodes.

Diverticular Disease

  • Definition: Presence of diverticula, which are herniations or outpouchings of the mucosa through the muscle layer of the colon wall, primarily seen in the sigmoid colon.

  • Diverticulosis: Asymptomatic condition usually with multiple diverticula present.

  • Diverticulitis: Inflammation of the diverticula.

  • Causes:
      - Low residue diets, irregular bowel habits, and aging.

  • Complications May Include:
      - Intestinal obstruction, perforation leading to peritonitis, and abscess formation.

  • Symptoms Include:
      - Mild lower abdominal pain, diarrhea or constipation, flatulence, and specific LLQ pain and tenderness associated with fecal stasis and subsequent inflammation.

Intestinal Obstruction

  • Functional Obstruction Causes:
      - Abdominal surgery effects, spinal cord injuries, severe inflammation with ischemia, infections in the abdominal cavity.

  • Mechanical Obstruction Causes Include:
      - Adhesions, hernias, strictures, masses, intussusception, volvulus, Hirschsprung’s disease, chronic inflammation leading to gradual obstruction.

  • Symptoms of Intestinal Obstruction:
      - Characterized by colicky pain, increased peristalsis, audible borborygmi, and attempts of the intestines to propel contents forward indicate significant disturbance in normal gastrointestinal function.