Embryological Development of the Midgut

Introduction

• Presented by: Minas
• Focus: Development of the midgut in the Gastrointestinal Tract (GIT)
• Previous and upcoming topics: Foregut and hindgut development
• No prerequisite viewing required for this lecture

Embryological Basics

• Blastula Formation: Result of fertilization
  • Travels to the uterine canal
  • Implants into the uterine wall
• Gastrulation: Formation of three germ layers
  • Ectoderm: CNS and skin
  • Mesoderm: Divided into
    • Paraxial mesoderm (muscle and somites)
    • Intermediate mesoderm (kidneys and gonads)
    • Lateral plate mesoderm (somatic - parietal mesoderm, splanchnic - visceral mesoderm)
  • Endoderm: Focus on GIT development

Early Development

• Folding Process: Transition from a "pancake" to a more differentiated form
  • Skin starts to cover embryo
  • Neural tube develops from ectoderm
  • Endoderm forms GIT
• Mesoderm Layers
  • Parietal mesoderm becomes parietal peritoneum
  • Visceral mesoderm becomes visceral peritoneum
• Yolk Sac and Vitiline Duct: Connection with midgut
  • Development stage between weeks 3 and 4

Development by Week

• Week 6 Embryo
  • Largest focus: Entire GIT labeled
  • Blood supply differences:
    • Foregut: Celiac artery
    • Midgut: Superior mesenteric artery
    • Hindgut: Inferior mesenteric artery
• Midgut Characteristics
  • Superior mesenteric artery as axis of rotation
  • Midgut rotation:
    • 90-degree counter-clockwise rotation during herniation
    • Subsequent 180-degree rotation
  • Physiological herniation due to space constraints
  • Retracts into abdomen around the third month

Intestinal Loop Development

• Primary Intestinal Loops
  • Cephalic and caudal portions
  • Rotation Process
    • 90-degree rotation during herniation
    • Additional 180-degree rotation inside abdomen
  • Total rotation: 270 degrees counter-clockwise
• Structural Outcomes
  • Cephalic Portion: Distal duodenum, jejunum, proximal ileum
  • Caudal Portion: Distal ileum, cecum, appendix, ascending colon, proximal two-thirds of the transverse colon

Post-Rotation Development

• Differentiation and Coiling
  • Jejunum coils; colon does not
  • Cecum initially in right upper quadrant, descends to right iliac fossa
• Tinea Coli: Landmark for locating the appendix during surgery

Conclusion

• Summary of midgut embryology
• Open for questions and further assistance