Gastrointestinal System Case Study

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Introduction
The gastrointestinal system (digestive system) is the alimentary tract from the mouth to the anus with its associated glands and organs (Moore, 2016) It originates from two germ layers, the endoderm and mesoderm, and receives nerve supply by cells derived from the third germ layer, the ectoderm(van den Brink, 2007) (McLin et al., 2009)
The earliest stage of development is the ‘primordial gut’ which forms during the 4th week as the head, tail (caudal eminence) and lateral folds. Initially the primordial gut is closed at its cranial end by the oropharyngeal membrane and at its caudal end by the cloacal membrane.

Germ layers contributions

Endoderm mucosal epithelium, mucosal and submucosal glands.
Visceral Mesoderm lamina propria,
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The hindgut is supplied by the inferior mesenteric artery and includes: the distal 1/3 of the transverse colon, descending colon, sigmoid and anorectum.

The Foregut
Development of oesophagus

The oesophagus develops from the foregut just caudal to the pharynx.
It originates from two longitudinal ridges called the tracheoesophageal folds.
These folds will divide the tube ventrally into the trachea and dorsally into the oesophagus
It is short initially, but it elongates rapidly reaching its final relative length by the 7th week.
The endoderm gives rise to oesophageal epithelium and glands.
The epithelium continues to proliferate until it occludes the lumen.
Recanalization occurs by the end of the 8th week.
The mesenchyme gives rise to the striated muscle.

Developmental anomalies of oesophagus
Oesophageal atresia

Atresia means
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It usually affects the 3rd and/or 4th parts of the duodenum.
Presents with vomiting of the gastric contents (usually contain bile).

Duodenal atresia

It is complete occlusion of the duodenal lumen as a result of failed recanalization.
It usually affects duodenum just distal to the bile duct opening, and associates with polyhydramnios (excess of amniotic fluid).
Presents after few hours of birth by bile stained vomiting.
The diagnosis is usually predicted by seeing a ‘double-bubble sign’ on plain radiographs or ultrasound scans.
It is more common in premature babies (20%) and Down syndrome (20-30%).

Development of liver and biliary system
During the 4th week, the liver, gallbladder, and biliary apparatus arise from the ventral endoderm of the caudal part of the foregut as an outpouch called the 'hepatic diverticulum '.
The hepatic diverticulum extends into the septum transversum, splanchnic mesoderm between the developing midgut and heart, then divides into 2 parts.
The cranial part is larger and forms the primordium of the liver, whereas the caudal part becomes the

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