Digestive System Development Notes

Parts of the Digestive System

  • Pharynx
  • Anatomical throat with 3 regions; 2 part of digestive system:
    • Oropharynx: Continuous with oral cavity anteriorly
    • Laryngopharynx: Continuous with larynx anteriorly; inferiorly transitions to esophagus

The Esophagus

  • Pathway:
  • Starts at the base of laryngopharynx
  • Passes through thorax
  • Pierces diaphragm at T10
  • Location in Thorax:
  • Anterior to vertebrae
  • Posterior to trachea
  • Medial to thoracic aorta
  • Abdominal Esophagus:
  • Short segment within abdominal cavity
  • Muscle Transition:
    • Proximal: Skeletal muscle
    • Distal: Smooth muscle

Stomach

  • Function: Mechanically and chemically breaks down food
  • Regions:
  • (C) Cardia: Surrounds esophageal opening
  • (F) Fundus: Upper left; blind end
  • (B) Body: Mid-portion, largest
  • (P) Pylorus: Contains pyloric sphincter leading into small intestine
  • Curvatures:
  • (G) Greater curvature
  • (L) Lesser curvature
  • Omenta:
  • Lesser Omentum: Between liver and lesser curvature
  • Greater Omentum: Hangs from greater curvature, anterior to intestine

Small Intestine

  • Transition from Stomach: Through pyloric sphincter
  • Subdivisions (proximal to distal):
  • Duodenum: C-shaped
  • Jejunum: Proximal 2/5th
  • Ileum: Distal 3/5th

Large Intestine

  • Characteristics: Wider but shorter than small intestine
  • Consists of:
  • Cecum
  • Colon:
    • Ascending
    • Transverse
    • Descending
    • Sigmoid
  • Rectum
  • Anal Canal
  • Anus

The Pancreas

  • Location: Between duodenum and spleen
  • Function: Enzymes travel along pancreatic ducts into small intestine at duodenal papillae
  • Anatomy:
  • Includes: Ucinate process, head, neck, body, tail

The Liver

  • Location: Under right dome of diaphragm
  • Divisions:
  • Right lobe
  • Left lobe
  • Caudate lobe (inferior surface, posterior, adjacent to inferior vena cava)
  • Quadrate lobe (inferior surface, anterior, adjacent to gallbladder)
  • Function: Bile travels along hepatic duct system to enter duodenum

The Gallbladder

  • Location: Anterior border of inferior surface of liver
  • Function: Stores and concentrates bile for future secretion; joins hepatic duct to transport bile to duodenum at major duodenal papilla.

Development of the Digestive System

  • Primitive Gut Tube Formation & Position:
  • Starts at week 4 due to transverse and longitudinal folding
  • Endoderm: Forms most gut tube epithelium and associated glands
  • Splanchnic Mesoderm: Forms muscle and connective tissues of gut wall
  • Surrounded by intra-embryonic body cavity, suspended via dorsal mesentery

Organ Classification

  • Intraperitoneal Organs:
  • Stomach
  • Portions of small intestine: jejunum, ileum, proximal duodenum
  • Portions of colon: cecum, transverse colon, sigmoid colon
  • Liver, gallbladder, spleen
  • Retroperitoneal Organs:
  • Abdominal esophagus, distal duodenum, ascending colon, descending colon, rectum, pancreas, kidneys, aorta/IVC

Mesenteries & Peritoneal Reflections

  • Mesentery: Attaches viscera to posterior abdominal wall; includes mesentery of jejunum, ileum, transverse mesocolon, mesoappendix
  • Greater Omentum: Adipose tissue-filled fold draped from greater curvature of the stomach
  • Lesser Omentum: Connects lesser curvature of stomach to liver

Developmental Anatomy

  • Foregut Derivatives:
  • Primordial pharynx, lower respiratory system, esophagus, stomach, proximal small intestine (duodenum to major duodenal papilla), liver, biliary apparatus, pancreas
  • Blood Supply: Celiac trunk

Concerning Development of Organs:

  • Esophagus: Develops from foregut tube and partitions from trachea at week 5
  • Stomach: Fusiform dilation of tubular foregut; exhibits 90-degree clockwise rotation
  • Duodenum: Forms from foregut and midgut tubes; undergoes rotation during development
  • Liver and Gallbladder: Begin as hepatic diverticulum from distal foregut in week 4
  • Midgut Derivative Development: Distal small intestine and proximal large intestine formed under inferior mesenteric artery supply

Clinical Cases

  1. Congenital Omphalocele: Midgut fails to return to abdomen; associated with chromosomal abnormalities
  2. Umbilical Hernia: Midgut returns during week 10 but later herniates; defect in umbilicus closure
  3. Congenital Ileal: Persistence of proximal part of omphaloenteric duct; malformation leading to blind pouch on ileum.