A Focus on the GI Pathologies:Intestinal and gallbladder pathologies ppt

Foregut

• The spleen is not part of the GI system, but it plays a crucial role in:
  • Early hematopoiesis
  • Mechanical filtration of aging/injured erythrocytes
  • Infection control, effective against pathogens within RBCs, like Malaria
  • Clearance of bacteria from the circulation
  • Clearance of microorganisms that the individual hasn't made a specific host antibody against

Duodenum

• The duodenum is the site of delivery for the stomach, pancreas, liver, and gallbladder
• Acidic chyme from the stomach must be neutralized in the duodenum to prevent:
  • Duodenal ulcer, most commonly occurring in the superior portion
• The duodenum is responsible for:
  • All types of digestion (protein, carbs, fats, nucleic acids)
  • A large part of digestion, while other areas focus on absorption
• Anatomic features of the duodenum:
  • Shortest segment of the small intestine
  • Starts at the pyloric sphincter and ends at the Ligament of Treitz
  • Almost completely retroperitoneal, not freely mobile in the abdominal cavity
  • The pancreatic head nestles within its "C" curve
• Segments of the duodenum:
  • Superior: releases hormonal triggers for the gallbladder and pancreas
  • Descending: pancreatic duct and common bile duct empty here
  • Horizontal: digestion occurs here; crosses the IVC and aorta
  • Ascending: continued digestion; connects to the jejunum
• Brunner's glands:
  • Unique to the proximal duodenum
  • Release bicarbonate and mucous to neutralize chyme
  • Rapidly neutralize high-pH chyme to protect the intestinal mucosa and enable intestinal enzymes to function
  • Also secrete urogastrone, which inhibits the stomach's chief cells and parietal cells

Pancreas

• The pancreas has both exocrine and endocrine functions
• It is retroperitoneal, arising from the wall of the duodenum
• Located mainly at L2, with parts including:
  • Head
  • Neck
  • Body
  • Tail
• The pancreatic ducts:
  • The main pancreatic duct runs the entire length of the pancreas
  • Empties its exocrine products at the Ampulla of Vater, where it joins the common bile duct
  • A portion of the head of the pancreas usually drains via a different duct (the accessory pancreatic duct) at the Ampulla of Santorini
• Pancreatic juice:
  • A secretion of pancreatic enzymes in a clear alkaline medium
  • Enzymes produced by the exocrine cells of the pancreas
  • Alkaline mucous liquid from the pancreatic ductal cells
  • Flows to the duodenum via the pancreatic duct system
  • Enzymes typically released in inactive form and activated by membrane-bound activators in the duodenum
• Pancreatic pain:
  • May be felt in the mid-epigastric region (foregut) and/or the back due to the retroperitoneal location
  • Can be caused by zymogens (pre-enzymes) of the pancreas activating early and causing tissue damage

Pancreatitis

• Inflammation of the pancreas
• Can occur when:
  • A duct is blocked, causing zymogens to activate early and cause tissue damage
  • Enzymes are activated prior to arriving at the duodenum
  • Secondary to infection, trauma, or pancreatic carcinoma
• Symptoms of pancreatitis:
  • Portions of the pancreas can autolyze (auto-digest)
  • Cellular damage causes pancreatic enzymes to escape into the bloodstream at higher-than-normal rates
  • Elevated amylase and lipase are markers for pancreatitis

Gallbladder

• The gallbladder's primary function is to store bile made by the liver and release it when needed
• Histology of the gallbladder:
  • Mucosa with folds to allow for enlargement
  • Simple columnar epithelium
  • Lots of mucosal folds to enable enlargement and shrinkage
  • Muscularis externa for contractions
  • Adventitia to hold the gallbladder in place
• The normal biliary tree:
  • Bile exits the liver via the left and right hepatic ducts
  • Bile can travel into the gallbladder via the cystic duct
  • Bile leaves the gallbladder via the cystic duct and enters the common bile duct
  • There is only one way into and out of the gallbladder
  • The gallbladder and pancreas share the same exit point (Sphincter of Oddi) into the duodenum

Gallbladder Problems

• Most common problems:
  • Duct blockage
  • Inflammation
  • Infection
• Symptoms after a cholecystectomy:
  • Fatty stools
  • Poor tolerance of high-fat meals
  • Dyspepsia
  • Nausea and vomiting

Cholelithiasis

• Gallstones are crystallized/packed/solidified stones of gallbladder content
• Typically made of bile salts, cholesterol, and other substances
• Pathogenesis of cholesterol gallstones:
  • More cholesterol in bile than can be dissolved
  • Bile in stasis for longer than normal
  • "Gallbladder sludge" increases the risk of gallstones
  • Decreased gallbladder motility, often caused by estrogen, increases the risk of gallstones
  • Pregnancy increases the incidence of gallstones

Inflammatory Bowel Disease

• Chronic, relapsing/recurring bowel inflammation of unknown origin
• Genetics: familial, most commonly diagnosed in those 20 to 40 years old
• Pathophysiology:
  • Alterations of epithelial barrier functions
  • Immune system reactions to intestinal flora
  • Abnormal T-cell responses
  • Presence of autoantibodies
• Two main types:
  • Ulcerative colitis
  • Crohn disease

Ulcerative Colitis

• A chronic inflammatory disease that causes ulceration of the colonic mucosa
• Sigmoid colon and rectum are most commonly affected
• Characteristic lesions:
  • Continuous with no skipped lesions
  • Limited to the mucosa
  • Not transmural
• Diarrhea (10 to 20 bowel movements per day)
• Bloody stools
• Cramps
• Increased risk for colon cancer

Crohn Disease

• Granulomatous inflammation of the GI tract
• Can affect any part of the digestive tract
• Lesions:
  • Cobblestone appearance
  • Multilayer
  • Transmural
• Abdominal pain and diarrhea are the most common signs
• More than five stools per day
• Anemia may develop due to malabsorption of vitamin B12 and folic acid

Mechanical Bowel Obstruction

• Blockage in the small or large bowel
• Small bowel contents cannot travel "downstream"
• Risk factors:
  • Prior surgery
  • Presence of carcinoma
  • Diseases causing gut inflammation/stricture (like IBD)
  • Volvulus and intussusception
• Clinical manifestations:
  • Gas/chyme builds up and the bowel distends
  • Venous flow in the GI wall slows
  • Arterial flow slows
  • Bowel wall starts to die
  • Edema and bacteria escape from the bowel into the peritoneum
  • Peritonitis and bowel perforation are common