Digestive System Development

Endoderm

Epithelial lining of digestive tube

Splanchnic Mesoderm

Muscles & connective tissue surrounding digestive tube

Ectoderm

Linings of mouth and anus

Neural Crest Cells

Enteric nervous system

Primitive Gut Tube

• established by head, tail, and lateral folding

• Cranial cap: oropharyngeal membrane

• Caudal cap: cloacal membrane

Foregut

Pharynx, esophagus, stomach, duodenum, liver, gallbladder, spleen, pancreas

Midgut

Most small intestine, ascending colon, proximal 2/3 transverse colon

Hindgut

Distal 1/3 transverse colon, descending colon, rectum

Recanalization

Lumen fills with epithelium, then vacuoles form and coalesce to re-establish patent lumen; occurs thru digestive system

Errors of recanalization

Duplication: two channels

Stenosis: narrowing

Atresia: complete blockage

Organ growth and rotation

Stomach rotation: positions spleen, pancreas, liver

Midgut rotation: rapid growth outward + rotation, colon dragged across intestine (C shape), small intestine elongates and packs into abdomen, cecum moves down and right → appendix forms from cecum tip

Physiological herniation: temporary gut herniation into body stalk (6-7 weeks); intestines return by 9 weeks

Urorectal Septum Division of Cloaca

Cloaca: Caudal end of hindgut, single chamber

Urorectal Septum: divides cloaca into urogenital sinus and rectum (6 weeks)

Hirschsprung’s Disease

Cause: Defect in enteric ganglia of colon

Effect: colon contracts but doesn’t relax; inability to pass feces

Treatment: surgical removal

Esophageal Stenosis

Cause: Esophagus fails to fully recanalize

Effect: Narrowing of esophagus; excessive amniotic fluid in fetus

Treatment: Endoscopic dilation