The trilaminar embryonic disc folds to form a tube with three layers:
The inner endodermal tube is divided into three regions: foregut, midgut, and hindgut. The midgut remains connected to the yolk sac through the vitelline duct.
The endoderm forms the lining of the digestive tract and also forms glands and the parenchyma of the liver and pancreas.
Splanchnic (visceral) mesoderm gives rise to the visceral peritoneum, mesentery, muscle, blood vessels, and connective tissue. Somatic mesoderm forms the parietal peritoneum.
The dorsal mesentery of the stomach becomes the greater omentum, while the ventral mesentery becomes the lesser omentum.
Neurons in the myenteric and submucosal plexuses are derived from the neural crest.
| Structure | Derivative | Arterial supply |
|---|---|---|
| Foregut | Esophageal epithelium and glands, trachea, lungs, respiratory tract, stomach, liver, gallbladder, bile ducts, pancreas, upper duodenum | Celiac trunk |
| Midgut | Lower duodenum, jejunum, ileum, cecum, appendix, ascending colon, proximal ⅔ of the transverse colon | SMA |
| Hindgut | Distal ⅓ of transverse colon, descending colon, sigmoid colon, rectum, upper anal canal, urogenital sinus | IMA |
This gene is expressed by cells forming the anterior wall of the foregut and leads to the development of the trachea and lungs.
This gene is present in the dorsal wall of the foregut and causes differentiation of cells into the esophagus.
Noggin from the notochord, Wnt (wingless-related integration site) proteins, BMP (bone morphogenetic protein; levels should be low), and fibroblast growth factor also help in the above process. Hnf1 beta (hepatocyte nuclear factor) and retinoic acid regulate the development of the posterior foregut.
HOX genes are highly evolutionarily conserved and are important regulators of development in both prenatal and postnatal life. They are located in four clusters on chromosomes 7p, 17q, 12q, and 2q. HOX genes are ubiquitous in nature.
HOX genes control cell differentiation based on positional information and proper cranio-caudal conformation (for example, ensuring the head develops superiorly and the legs develop inferiorly). Mutations can cause malformations such as synpolydactyly, emphysema, lung cancer, pulmonary HT, leukemias, ovarian cancers, etc.
The SHH gene (Sonic Hedgehog) codes for the Sonic Hedgehog protein. It is important for normal growth, differentiation, and patterning of the developing body. It is located on chromosome 7q.
Mutations cause developmental disorders of the brain and spinal cord, eyes, limbs, and many other body parts, such as holoprosencephaly, coloboma, and microphthalmia.
This is a homeobox gene that codes for an intestine-specific transcription factor. It is also expressed in colorectal and other gastrointestinal carcinomas, AML, and Barrett’s esophagus.
TEF is a congenital malformation that causes an abnormal communication (fistula) between the trachea and esophagus and/or causes esophageal atresia.
Five types are seen: A, B, C, D, and E. Type C is the most common.
Clinically, TEF presents with poor feeding, drooling, excessive salivation, and choking while feeding. Polyhydramnios is seen in the fetal period.
Intrauterine diagnosis can be done by ultrasound. A chest X-ray after passing a nasogastric tube shows a coiled tube in the atretic esophagus.
TEF may be associated with VACTERL defects:
PDA, ASD, VSD, and imperforate anus are common anomalies associated with VACTERL defects. Pulmonary hypoplasia and congenital diaphragmatic hernia may also be seen.
Incomplete canalization of the esophagus can result in esophageal webs. They may be associated with TEF. They present with dysphagia and food impaction, sometimes years later.
HPS is a congenital disorder caused by abnormal hypertrophy and hyperplasia of the smooth muscle of the gastric pylorus, leading to gastric outlet obstruction. It has an incidence of 3 per 1000 live births per year.
It presents between the second to sixth weeks of life and is more common in whites, males (four times more common than females), and first-born children. The risk increases more than fivefold if a first-degree relative is affected.
HPS presents as projectile, non-bilious vomiting, typically with feeding. The infant is not ill-looking and has a voracious appetite. Prolonged vomiting can lead to dehydration, hypochloremic alkalosis, and unconjugated jaundice.
On clinical examination, peristaltic waves may be visible, and an “olive-like mass” can be palpated in the right costal area or epigastrium.
HPS can be identified on ultrasound as a hypertrophied and abnormally elongated pylorus greater than 14 mm long and more than 3 mm thick. This finding is also called a “cervix sign”. On the upper GI barium study, a “double track” sign is seen.
The pancreas forms by fusion of the ventral and dorsal pancreatic buds, both of which are of endodermal origin.
Following developmental malformations are seen:
Annular pancreas: In this disorder, a ring of pancreatic tissue encircles the second part of the duodenum, causing intestinal obstruction. It occurs due to errors in fusion of the two pancreatic buds. Annular pancreas is often associated with Down’s syndrome, intestinal atresia, malrotation, TEF, and cardiac defects. It presents clinically with bilious vomiting. No lump is palpated on abdominal examination. On imaging, a “double bubble” sign is seen due to a distended stomach and proximal duodenum. This sign is also seen in conditions such as duodenal atresia, midgut volvulus, and SMA syndrome.
Pancreas divisum: This is the most common developmental anomaly of the pancreas. It is caused by non-fusion or incomplete fusion of the ductal system of the ventral and dorsal pancreatic buds. As a result, the major part of the gland is drained by the smaller duct of Santorini into the minor duodenal papilla. It may cause an increased incidence of recurrent pancreatitis.
Ectopic pancreas: Ectopic pancreatic tissue may be seen in the stomach, duodenum, jejunum, or Meckel’s diverticulum.
Cysts: Multilocular pancreatic cysts are associated with VHL disease and ADPKD.
Sign up for free to take 7 quiz questions on this topic