Development of the foregut (esophagus and stomach
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Transcript of Development of the foregut (esophagus and stomach
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Learning the Objectives
The students should be able to; • Enlist the different parts of the foregut
• Describe the development of the Esophagus
• Describe the development of Stomach and its curvatures
• Describe the formation of Greater & Lesser omentum and the
Omental Bursa.
• Enlist the most common congenital anomalies of the Esophagus and Stomach
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Formation of the Primitive Gut • The ‘cephalocaudal’ and
‘lateral’ foldings of the embryo will lead to partial incorporation of endoderm lined cavity into the embryo to form the “primitive gut tube”.
• In the cranial & caudal ends of the embryo the primitive gut forms a blind ending tube, the ‘foregut’ & ‘Hindgut’, respectively.
• The middle part of the tube, ‘Midgut’ remains temporarily connected to the yolk sac by means of a vitelline duct/yolk stalk.
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General consideration: • As a result of embryonic folding, the
dorsal part of yolk sac is enclosed inside the embryo to form the Gut.
• The gut is endodermal in origin, which is surrounded by splanchno- pleuric mesoderm.
• The Foregut is separated from the stomodeum by the Buccopharyngeal membrane.
• The Hindgut, is separated from the proctodeum by Cloacal membrane.
• The Midgut is connected to definitive yolk sac by Vittellointestinal duct.
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Derivatives of the Foregut • Oral cavity (tongue,
tonsils, salivary glands)
• Pharynx
• Esophagus
• Stomach
• Duodenum (Proximal half )
• Liver + Biliary apparatus
• Pancreas
Extent of Foregut Foregut starts from the Oral cavity and terminates at the level of Ampulla of Vater (the point where common bile duct opens into Duodenum)
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Development of the Esophagus • During the 4th wk., a small diverticulum appears in the ventral wall of
Pharynx.
• A ‘Tracheoesophageal Septum’ gradually separates the ventral Respiratory diverticulum from the dorsal part of foregut.
• As a result, the Pharynx is divided into;
– a ventral portion the “respiratory primordium”,
– a dorsal portion, the “esophagus”.
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Growth of esophagus
• Up to the 4th week it is very short.
• Then, it elongates rapidly due to the descent of developing heart and lungs.
• By the 7th week it reaches its final position.
• Its lumen is completely or partially obliterated due to proliferation of its epithelial lining.
• Recanalization occurs by the end of embryonic period (after 8th wk).
• Its muscles developed from the surrounding mesoderm.
• It is striated in the upper 1/3, • mixed in the middle 1/3 and • smooth in the lower 1/3 (vagus)
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Congenital malformations of Esophagus
Atresia of Esophagus & Esophageal Fistula:
• Mostly is the result of a spontaneous deviation of Tracheoesophageal septum in the posterior direction
• As a result the proximal part of the esophagus ends as a blind sac, and the distal part is connected to the trachea by a narrow canal just at the point of tracheal bifurcation.
• Atresia of Esophagus prevents the normal passage of amniotic fluid into the intestinal tract leading to the accumulation of excess fluid in the amniotic sac (Polyhydroamnios)
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Development of the Stomach
• Develops as a fusiform dilatation of the caudal part of foregut in the middle of 4th wk.
• Initially oriented in the midline.
• The swelling shows an expansion.
• During the next 2 weeks, the right wall of the swelling grows more rapidly than the left wall.
• This leads to the formation of future ‘greater’ & ‘lesser’ curvatures of the adult stomach.
(The anterior/ventral border becomes lesser curvature and the posterior/dorsal border becomes greater curvature)
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Rotation of Stomach Longitudinal axis:
• As the stomach enlarges, it slowly rotates 90⁰ (clockwise) around its longitudinal axis. As a result;
• The ventral border moves to the right & the dorsal border moves to the left
• The original left side becomes ventral surface & the original right side becomes dorsal surface ( grows faster than the ventral surface)
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In Transverse/Horizontal
axis: • The rapidly growing
dorsal/posterior wall of stomach slightly rotates the stomach on the transverse plane
• As a result, the cranial (esophageal) end of stomach moves down & to the left, while, the caudal (duodenal) end moves up and to the right.
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Formation of the Lesser sac/Omental Bursa
• During its development, the stomach is suspended in the midline with the help of double-layered mesenteries (mesogastrium),
• the Dorsal mesogastrium connects it to the posterior/dorsal body wall.
• The Ventral mesogastrium attaches the gut tube to the anterior abdominal wall
• Rotation around the longitudinal axis pulls the ‘dorsal mesogastrium’ to the left.
• This move leads to the formation of ‘Omental Bursa’ (a pouch of peritoneal cavity located behind the stomach).
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Formation of Greater & Lesser Omenta • With the rotation of stomach in
transverse/horizontal axis, the greater curvature along with the attached double-layered dorsal mesogastrium also comes to lie transversely.
• This mesogastrium hanging from the greater curvature covers the coils of intestine like a curtain & is
known as ‘Greater Omentum’
• A small part of the ventral
mesogastrium which is lying between the lesser curvature of stomach & the inferior surface of
liver is known as ‘Lesser Omentum’
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Congenital Malformation of Stomach
Pyloric Stenosis: • Sometimes the circular or
longitudinal musculature of the stomach in the region of the pylorus is hypertrophied.
• One of the most common anomalies in newborns
• Treatment: Surgical excision of the thickened sphincter.
Projectile vomiting
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Development of the distal part of Foregut (Duodenum)
With the 90⁰clockwise rotation. the greater posterior wall of stomach moves to the left in abdomen & the C-shaped Duodenum moves to the right.
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Blood supply of the derivatives of Foregut:
• Celiac trunk is the branch of dorsal aorta which supplies all the derivatives of developing foregut.