Gastrointestinal & Nutrition Lecture Notes

Normal Structure and Function

B12 Absorption Pathway

• Pathway: Parietal cells produce intrinsic factor → B12 binds in duodenum → Absorbed in ileum.
• Pernicious Anemia Pathogenesis:
  • Caused by autoimmune attack on parietal cells.
  • Results in loss of intrinsic factor and hypochlorhydria → B12 deficiency.
• Clinical Triad of B12 Deficiency:
  • Mnemonic: B12 = Bone marrow + Brain + Belly.
  • Megaloblastic Anemia: Macrocytosis, hypersegmented neutrophils.
  • Neurologic Signs: Paresthesias, ataxia due to dorsal/lateral column demyelination.
  • GI Issues: Atrophic gastritis, possible progression to gastric carcinoma.

Gastric Anatomy and Function

• Upper Glandular Layer: Contains parietal cells.
• Deeper Glandular Layer: Contains chief cells which secrete pepsinogen.
• Muscularis: Important in understanding invasion depth in gastric cancers.
• Submucosa: Similar considerations as muscularis.

Infant GI Considerations

• Nonbilious Emesis: Indicates no obstruction distal to the duodenum.
• LES Immaturity: Leads to reflux of milk; improves by 12 months.
• GER vs GERD:
  • GER: Normal in infants, characterized by happy spitting and good weight gain.
  • GERD: Pathological with poor weight gain, respiratory issues, irritability.

Neonatal Jaundice

• Physiological Mechanisms:
  • High RBC breakdown and low UDP-glucuronosyltransferase activity.
  • Appears day 2-5, resolves in a week.
• Pathological Indicators:
  • Immediate jaundice at birth → Consider hemolysis or infection.
  • Jaundice > 2 weeks → Consider breast milk jaundice or biliary atresia.

Other Pediatric GI Conditions

• Tracheoesophageal Fistula: Coughing, choking, cyanosis during feeds.
• Increased Intracranial Pressure: Bulging fontanelle, vomiting, sunset eyes.
• Food Protein-induced Allergic Proctocolitis: Vomiting with blood/mucus in stool.
• Pyloric Stenosis: Projectile vomiting in infants 3-6 weeks old, with dehydration/weight loss.

General Anatomy

• Lesser Omentum:
  • Connects liver to stomach and proximal duodenum via ligaments.
• Germ Layers:
  • Endoderm: GI tract, lungs, thymus.
  • Mesoderm: Spleen, muscle, bone, blood, kidneys.
  • Ectoderm: Skin, nervous system.

Splenic Artery Branches

• Short Gastric Arteries: Supply stomach fundus, vulnerable due to poor collateral circulation.
• Left Gastroepiploic Artery: Supplies greater curvature, has good collateral flow.

Upper GI

• Mallory-Weiss Tears: Caused by retching, leads to hematemesis.

Liver Function and Aging

• Effects of Aging:
  • Decreased drug clearance, liver perfusion, regenerative capacity.
  • Increased toxicity risk for certain drugs.

Lymphatic Drainage

• Celiac: Drains upper GI organs.
• Left/Right Colic: Drain descending/ascending colon respectively.
• Superficial Inguinal: Drains anal canal below dentate line.

Hormonal Regulation

• Secretin: Stimulates pancreatic release of HCO₃⁻.
• CCK: Induces pancreatic enzyme release and gallbladder contraction.
• Gastrin: Stimulates gastric acid secretion.
• Somatostatin: Inhibits G cells and parietal cells.
• Glucagon and Insulin: Regulate glucose metabolism.

Gastric Acid Secretion Phases

• Cephalic Phase: Pre-meal stimulation via vagus nerve.
• Gastrin Release: Main stimulation during the gastric phase.
• Postprandial Alkaline Tide: Increase in blood HCO₃⁻ after meal.