Development of the foregut (esophagus and stomach

DEVELOPMENT OF THE FOREGUT (ESOPHAGUS AND STOMACH)

Dr.Sahar Hafeez [email protected]

2014

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

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.

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.

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)

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”.

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)

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)

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)

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)

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.

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).

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’

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

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.

Blood supply of the derivatives of Foregut:

• Celiac trunk is the branch of dorsal aorta which supplies all the derivatives of developing foregut.