GIT
• The gastrointestinal development:
• The cephalocaudal and lateral folding of the embryo lead to formation of the gut tube
from the folded endoderm germ layer.
• There is a duct connecting the middle part of the gut tube with the remnant of the
yolk sac (vitelline duct).
The primitive gut tube is formed of three parts; foregut, midgut, & hindgut. The anterior
end of the foregut is closed by buccopharyngeal membrane that is ruptured to connect
the foregut tube with the amniotic cavity.
The posterior end of the hindgut is closed by the cloacal membrane that usually
ruptures to establish an opening at the junction between the endodermal and
ectodermal parts of the anal canal.
• Blood supply for the derivatives of the gut tube:
• The vitelline arteries supplying the yolk sac then become arteries of gut tube. The
derivatives of the foregut tube are supplied by the celiac trunk, the derivatives of the
midgut tube are supplied by the superior mesenteric a., and the derivatives of the
hindgut tube are supplies by the inferior mesenteric a.
• Derivatives of the foregut tube:
• esophagus;Which is formed by the division of the foregut tube into two parts by the
tracheoesophageal septum. The ventral part forms the tracheobronchial diverticulum,
the dorsal part forms the esophagus.
Anomalies:
• 1. Atresia of the esophagus (with or without tracheobronchial fistula): leads to
impaired swallowing of the amniotic fluid by the fetus so increases amniotic fluid (
polyhydramnia).
• 2.Esophageal stenosis.
• 3. Shortening of the esophagus with hiatus hernia.
• The stomach: it is formed as a dilatation of the foregut, it rotates 90 degrees clock
wise around its longitudinal axis so that its anterior surface deviates to the right side.
Also the stomach rotates around its anteroposterior axis so that its caudal end moves
upward and to the right, while its cephalic end moves downward and to the left
Anomalies:
1. Pyloric stenosis.
2. Duplication of stomach.
3. Prepyloric septation.
The upper duodenum (down to the level of the bile duct opening):
This part of the duodenum which is derived from the foregut rotates with the stomach
to the right forming C-shape, becomes retroperitoneal due to absorption of mesentery.
• The liver:
• It develops as a diverticulum from foregut, it elongates into septum transversum.
• A bud projects from liver forming gall bladder & cystic duct.
• The liver bud branches profusely around vitelline and umbilical veins forming liver
parenchyma (hepatocytes).
• Other liver cells are derived from mesoderm of septum transversum.
• Anomalies:
• 1. Atresia of gall bladder and/or bile ducts.
• 2. Double gall bladder.
• 3. Gall bladder with mesentery.
• 4. Accessory hepatic duct.
• Pancreas:
• It is derived from two buds; a dorsal and ventral buds, fused later on.
• Anomalies:
• 1. Annular pancreas.
• 2. Hetrotropic pancreatic tissues that may be found in abnormal sites.
• Derivatives of the midgut:
• 1. The lower 2/3 of duodenum below opening of bile duct.
• 2. The jejunum and ileum.
• 3. Cecum, appendix, ascending colon, & right 2/3 of transverse colon.
• The primary intestine projects out of abdomen into umbilical cord during 6th weeks
of development to form physiological umbilical hernia. This hernia returns into
abdomen during 10th week of gestation.
• primary intestine rotates 270 degrees in a counter clock wise direction around its
anteroposterior axis (which is axis of superior mesenteric artery) so that caecum,
ascending and transverse colon deviates upward and to right.
• The mesentery of duodenum, cecum and ascending colon is absorbed by zygosis.
• Anomalies:
1.Persistent vitelline duct; forming Meckel's diverticulum.
• 2.Paten tvitelline duct forming umbilical fistula wit hfecal discharge out of umbilicus.
• 3. Vitelline cyst; may be twisted causing strangulation and gangrene.
• 4. Omphalocele; physiological intestinal hernia is not returned into abdominal cavity.
5.Congenita lumbilical hernia ;by absence of skin and muscles.
• 6. Abnormal rotation of intestine; that may cause left sided colon.
• 7.Duplication of intestine.
• 8.Atresia or stenosis of intestine.
• Derivatives of the hindgut:
• 1.The left1/3of transverse colon.
• 2.Descending colon.
• 3.Sigmiod colon.
• 4.The rectum.
• 5.Upper part of anal canal.lower part of anal canal is derived from ectoderm.
• Anomalies:
• 1.Imperforated anus.
• 2. Rectal atresia.
• 3.Analstenosis.
• 4.Rectal fistula between rectum and vagina,urinary bladder, perineum, or urethra