5 Git Development

Development of the gastrointestinal tract

Early embryo In the first three weeks of intrauterine development the embryo forms a disc which undergoes eventually a folding process. This folding process takes place in the 4th week and it is a cephalo-caudal with a concomitant lateral folding

For details on early embryo development see Embryology textbooks

Primitive intestine 4th week Buccopharingeal membrane Dorsal aorta

As a result of the folding there is formation of a tube (GUT TUBE or PRIMITIVE INTESTINE) which is lined by a primitive epithelial tissue called endoderm.

Respiratory bud

PRIMITIVE INTESTINE Heart primordium

This tube is connected with two other cavities lined by the same epithelium which are largely located outside the embryo. Thes two cavities are: YOLK SAC (connected via vitelline duct) and ALLANTOIS.

Vitelline duct

allantois Cloacal membrane

Posterior wall

Primitive intestine 4th week Buccopharingeal membrane Dorsal aorta

The primitive intestine is initially intimately connected with the mesenchyme (embryonic connnective tissue) of the dorsal wall.

Respiratory bud

PRIMITIVE INTESTINE Heart primordium

The dorsal wall contains structures such as the dorsal aorta (Æ aorta) and the neural tube surrounded by mesenchyme (Æ spinal cord and vertebral column).

Vitelline duct

allantois Cloacal membrane

Posterior wall

Primitive intestine 4th week: division Dorsal aorta with the 3 branches for the GIT

Pharyngeal gut: buccal membrane Æ respiratory diverticle (mouth cavity head and neck). Foregut: up to the hepatic bud (oespohpagus – stomach – first half of duodenum – liver and pancreas).

Pharyngeal gut Respiratory bud FOREGUT

Midgut: up to the left thrid of the transverse colon (territory of superior mesenteric artery).

MIDGUT

Hindgut: up to the cloaca The pattern of arterial supply is determined early in development; therefore very rarely variable

HINDGUT

Cloacal membrane Cloaca

5th week: formation of mesentery Buccopharingeal membrane Ventral mesentery Only at terminal part of oesophagus up to the beginning of duodenum. It differentiates from septum transversum

Stomach

Dorsal aorta

Respiratory diverticle

Dorsal mesentery Differentiates dorsally and suspends the entire primitive intestine in the developing abdominal cavity forming a serosal layer.

Diaphragm Posterior wall VENTRAL MESENTERY

The entire primitive intestine is peritoneal in early stages. By the twisting and rotation processes some parts of it become secondariliy retroperitoneal.

Cloacal membrane DORSAL MESENTERY

Respiratory bud The respiratory tract Buccopharingeal membrane differentiates from the primitive intestine as a respiratory bud which later extends as a diverticle

Stomach

Dorsal aorta

RESPIRATORY DIVERTICLE

This involves ventral protrusion of part of the primitive intestinal tube and and septation of it, leaving a ventral portion (respiratory) and a dorsal portion (oesophagus). This may give rise to malformations in which pathological connections (fistulae) may remain between oesphagus and trachea if septation is incomplete or also to a blind ending oesophagus (atresia).

Diaphragm Posterior wall VENTRAL MESENTERY

Cloacal membrane DORSAL MESENTERY

Liver Buccopharingeal membrane Stomach

Liver and pancreas originate as buds from the terminal foregut. The liver bud migrates into the septum transversum which will give rise (other than to the phrenic centre) also to the ventral mesentery (ventral mesogastrium).

Dorsal aorta

DIAPHRAGM Dorsal Pancreas VENTRAL MESENTERY LIVER WITH GALL BLADDER

The liver (with gall bladder) will grow into the ventral mesogastrium which will also give rise to liver ligaments such as falciform and lesser omentum.

Ventral pancreas

Cloacal membrane DORSAL MESENTERY for details on Liver development see Embryology textbooks

Pancreas Buccopharingeal membrane Stomach

In the dorsal mesogastrium there is growth of pancreas and spleen. The pancreas originates as two buds: a ventral bud together with the liver (Æ uncinate process + caudal part of the head) and a dorsal (rest of the pancreas) in the dorsal mesogastrium. Eventually, the ventral bud grows, rotates, becomes dorsal and fuses with the rest of the pancreas.

Dorsal aorta

Diaphragm DORSAL PANCREAS VENTRAL MESENTERY Liver with gall bladder

VENTRAL PANCREAS

Cloacal membrane DORSAL MESENTERY for details on Pancreas development see Embryology textbooks

Twisting of the stomach: formation of lesser sac Buccopharingeal membrane STOMACH

In the dorsal mesogastrium there is growth of dorsal pancreas and spleen. The twisting process (11th week) brings the left sided structures frontally and the right sided structures dorsally (90°). With the twisting of the stomach, the spleen will end up to the left and the pancreas as a secondarily retroperitoneal organ. The left vagus nerve becomes anterior in the lower part of the oesophagusn (posterior mediastinum) and in the stomach, whereas the right nervus vagus becomes posterior.

Dorsal aorta

Diaphragm DORSAL PANCREAS VENTRAL MESENTERY Liver with gall bladder

Ventral pancreas

Cloacal membrane DORSAL MESENTERY

Twisting of the stomach: formation of lesser sac Liver in ventral mesogastrium

In the dorsal mesogastrium there is growth of dorsal pancreas and spleen. The twisting process (11th week) brings the left sided structures frontally and the right sided structures dorsally (90°). With the twisting of the stomach, the spleen will end up to the left and the pancreas as a secondarily retroperitoneal organ. The left vagus nerve becomes anterior in the lower part of the oesophagusn (posterior mediastinum) and in the stomach, whereas the right nervus vagus becomes posterior.

Peritoneum in green

STOMACH Spleen in dorsal mesogastrium Pancreas in dorsal mesogastrium

twisting

Liver in ventral mesogastrium

Spleen in dorsal mesogastrium

STOMACH Pancreas in dorsal mesogastrium left

right

CROSS SECTIONS THROUGH DEVELOPING ABDOMINAL CAVITIES

Twisting of the stomach: formation of lesser sac twisting

In the dorsal mesogastrium there is growth of dorsal pancreas and spleen. The twisting process (11th week) brings the left sided structures frontally and the right sided structures dorsally (90°). With the twisting of the stomach, the spleen will end up to the left and the pancreas as a secondarily retroperitoneal organ. The left vagus nerve becomes anterior in the lower part of the oesophagusn (posterior mediastinum) and in the stomach, whereas the right nervus vagus becomes posterior.

Peritoneum in green

Liver in ventral mesogastrium

Spleen in dorsal mesogastrium

Pancreas in dorsal mesogastrium STOMACH

left

right

CROSS SECTIONS THROUGH DEVELOPING ABDOMINAL CAVITIY

Twisting of the stomach: formation of lesser sac In the dorsal mesogastrium there is growth of dorsal pancreas and spleen. The twisting process (11th week) brings the left sided structures frontally and the right sided structures dorsally (90°). With the twisting of the stomach, the spleen will end up to the left and the pancreas as a secondarily retroperitoneal organ. The left vagus nerve becomes anterior in the lower part of the oesophagusn (posterior mediastinum) and in the stomach, whereas the right nervus vagus becomes posterior.

Falciform ligament

twisting Peritoneum in green

Liver

Lesser omentum Gastrosplenic ligament SPLEEN

Pancreaticolienal ligament

STOMACH

PANCREAS secondarily retroperitoneal

Dashed line: degenerating peritoneum left

LESSER SAC right

CROSS SECTIONS THROUGH DEVELOPING ABDOMINAL CAVITIY

Formation of greater omentum Diaphragm

Liver Lesser omentum

Pancreas + Duodenum

Stomach

Dorsal mesogastrium

Transverse colon

Int. loop

After that pancreas and duodenum have become secondarily retroperitoneal there is fusion of the dorsal mesentery layers (that of the transverse colon with that of the stomach) with formation of the greater omentum

Formation of greater omentum Diaphragm

Liver Liver

Pancreas + Duodenum

Lesser omentum

Pancreas + Duodenum

Stomach Lesser omentum

Stomach

Dorsal mesogastrium

GREATER OMENTUM

mesentery Transverse colon

Transverse mesocolon

mesentery Int. loop

Transverse colon

Transverse mesocolon

Int. loop

After that pancreas and duodenum have become secondarily retroperitoneal there is fusion of the dorsal mesentery layers (that of the transverse colon with that of the stomach) with formation of the greater omentum

Midgut The midgut undergoes a rotation process which brings the intestinal tube from being initially a straight tube to its final winded shape with loops and flexures.

Dorsal aorta

This follows the territory of distribution of the superior mesenteric artery. Concomitant to this process, in the 6th week, there is also rapid growh in size of the liver (haematopoiesis!). The intestinal loops grow and are „parked“ into the umbilical cord, i.e. outside the abdominal cavity (physiological herniation) which has become too narrow (due to liver growth). Failing in retraction (which begins at 10th week) will cause congenital hernias.

Celiac trunk

Sup mes art

Inf mes art

Midgut End of 5th week: formation of the vitelline loop (primary loop) which is along the superior mesenteric artery.

Dorsal aorta

Rotation begins with a couterclockwise twisting of the vitelline loop (6th week). The primitive intestine is still connected to the yolk sac via the vitelline duct at the level of the vitelline loop.

Celiac trunk VITELLINE LOOP

Lack of regression of this duct will give rise to the Diverticle of Meckel (about 70 cm prox. to the ilio-cecal valve).

Sup mes art

VITELLINE DUCT

The process is a 270° rotation with position changes of cecum and sec. retroperitoneal location of parts of the gut. Variations in position are possible and common.

Inf mes art

Midgut End of 5th week: formation of the vitelline loop (primary loop) which is along the superior mesenteric artery.

Dorsal aorta

Rotation begins with a couterclockwise twisting of the vitelline loop (6th week). The primitive intestine is still connected to the yolk sac via the vitelline duct at the level of the vitelline loop. Lack of regression of this duct will give rise to the Diverticle of Meckel (about 70 cm prox. to the ilio-cecal valve). The process is a 270° rotation with position changes of cecum and sec. retroperitoneal location of parts of the gut. Variations in position are possible and common.

Celiac trunk

VITELLINE LOOP Sup mes art

VITELLINE DUCT

Inf mes art

Midgut End of 5th week: formation of the vitelline loop (primary loop) which is along the superior mesenteric artery.

Stomach

Rotation begins with a couterclockwise twisting of the vitelline loop (6th week). The primitive intestine is still connected to the yolk sac via the vitelline duct at the level of the vitelline loop.

Pancreas

SUP MES ART

VITELLINE LOOP

Lack of regression of this duct will give rise to the Diverticle of Meckel (about 70 cm prox. to the ilio-cecal valve). The process is a 270° rotation with position changes of cecum and sec. retroperitoneal location of parts of the gut. Variations in position are possible and common.

VITELLINE DUCT

Midgut End of 5th week: formation of the vitelline loop (primary loop) which is along the superior mesenteric artery.

Stomach

Rotation begins with a couterclockwise twisting of the vitelline loop (6th week). The primitive intestine is still connected to the yolk sac via the vitelline duct at the level of the vitelline loop. Lack of regression of this duct will give rise to the Diverticle of Meckel (about 70 cm prox. to the ilio-cecal valve). The process is a 270° rotation with position changes of cecum and sec. retroperitoneal location of parts of the gut. Variations in position are possible and common.

Pancreas

Duodenum

SUP MES ART VITELLINE LOOP

Cecum

VITELLINE DUCT

Colon

Small intestine

Midgut End of 5th week: formation of the vitelline loop (primary loop) which is along the superior mesenteric artery. Rotation begins with a couterclockwise twisting of the vitelline loop (6th week). The primitive intestine is still connected to the yolk sac via the vitelline duct at the level of the vitelline loop.

Duodenum Stomach

Ascending colon

Pancreas

SUP MES ART

Cecum

Transverse colon

Lack of regression of this duct will give rise to the Diverticle of Meckel (about 70 cm prox. to the ilio-cecal valve). The process is a 270° rotation with position changes of cecum and sec. retroperitoneal location of parts of the gut. Variations in position are possible and common.

Descending colon

Small intestinal loops

Sigmoid colon

Rectum VITELLINE DUCT

Midgut End of 5th week: formation of the vitelline loop (primary loop) which is along the superior mesenteric artery. Rotation begins with a couterclockwise twisting of the vitelline loop (6th week).

Duodenum Stomach

Pancreas

Ascending colon

The primitive intestine is still connected to the yolk sac via the vitelline duct at the level of the vitelline loop.

SUP MES ART Cecum Transverse colon

Lack of regression of this duct will give rise to the Diverticle of Meckel (about 70 cm prox. to the ilio-cecal valve). The process is a 270° rotation with position changes of cecum and sec. retroperitoneal location of parts of the gut. Variations in position are possible and common.

Descending colon

Sigmoid colon

Small intestinal loops

VITELLINE DUCT

Rectum

Midgut End of 5th week: formation of the vitelline loop (primary loop) which is along the superior mesenteric artery. Rotation begins with a couterclockwise twisting of the vitelline loop (6th week). The primitive intestine is still connected to the yolk sac via the vitelline duct at the level of the vitelline loop.

Duodenum Stomach

Transverse colon

Pancreas

SUP MES ART Ascending colon

Lack of regression of this duct will give rise to the Diverticle of Meckel (about 70 cm prox. to the ilio-cecal valve).

Descending colon Cecum

The process is a 270° rotation with position changes of cecum and sec. retroperitoneal location of parts of the gut. Variations in position are possible and common.

Sigmoid colon Rectum Small intestinal loops

Hindgut From the hindgut will arise: left part of transv. colon, desc. colon, sigma, rectum and upper part of anal canal.

Dorsal aorta

The hindgut opens in the cloaca. The posterior part of the cloaca will contribute to the ano-rectal canal. The anterior part will develop into the uro-genital sinus which is the primordium of the urinary bladder. Failing in division of the cloaca and its derivatives will result in uro-rectal fistulas.

Celiac trunk

ALLANTOIS

Sup mes art

Here we have opening of the allantois which will develop in urachus and is the provisional opening of the bladder. Inf mes art

Post natal obliteration of the urachus will give rise to the medial umbilical ligament which connects the bladder with the internal abdominal wall at the umbelicus.

CLOACAL MEMBRANE

CLOACA

for details on bladder and urethral development see Embryology textbooks